期刊文献+
共找到28,510篇文章
< 1 2 250 >
每页显示 20 50 100
Magnetic properties and magnetic entropy change of perovskite manganites La0.9-xEuxSr0.1MnO3(x=0.000,0.075) by experimental method and numerical fitting
1
作者 Xiang Jin Jianjun Zhao +8 位作者 Hongye Wu Bao Xu Yunbin Sun Xiaodong Sun Fengze Cao Kai Wang Wenxing Wang Yutong Zhang Yi Lu 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第6期622-627,共6页
Polycrystalline samples La0.9-xEuxSr0.1MnO3(x = 0.000, 0.075) were prepared by the standard solid-state reaction method. The results show that the samples preform a characteristic of clusters spin-glass state at low t... Polycrystalline samples La0.9-xEuxSr0.1MnO3(x = 0.000, 0.075) were prepared by the standard solid-state reaction method. The results show that the samples preform a characteristic of clusters spin-glass state at low temperature. The samples show a characteristic of ferromagnetism(FM) characteristic in the temperature range of 15-125 K and 15-150 K respectively;the samples show preformed clusters in the temperature range of 125-343 K and 150-325 K, respectively, the samples show paramagnetism(PM)characteristic above 343 and 325 K, respectively. The second-order transitions are found at 118 and 135 K for undoped and doped sample, respectively. When the applied magnetic field is 7 T, the maximum magnetic entropy change |△SM| value of the samples is near the Curie temperature(Tc), and the value of|△SM| reaches 2.76 and 3.03 J/(K kg), respectively. In addition, the relative cooling power(RCP) is found to be 425.28 and 443.53 J/kg. The numerical fitting data fit well with experimental data. These results indicate that both the samples have the potential to realize magnetic refrigeration in the high temperature region(T > 77 K). 展开更多
关键词 PEROVSKITE MAGNETIC properties MAGNETIC ENTROPY change Preforming cluster phase Least SQUARE method Rare earths
Effects of rare earth elements on inclusions and impact toughness of high-carbon chromium bearing steel
2
作者 Chaoyun Yang Yikun Luan +1 位作者 Dianzhong Li Yiyi Li 《材料科学技术学报:英文版》 SCIE EI CAS CSCD 2019年第7期1298-1308,共11页
High-carbon chromium bearing steels with different rare earth (RE) contents were prepared to investigate the effects of RE on inclusions and impact toughness by different techniques. The results showed that RE additio... High-carbon chromium bearing steels with different rare earth (RE) contents were prepared to investigate the effects of RE on inclusions and impact toughness by different techniques. The results showed that RE addition could modify irregular Al2O3 and MnS into regular RE inclusions. With the increase of RE content, the reaction sequence of RE and potential inclusion forming elements should be O, S, As, P and C successively. RE inclusions containing C might precipitate in molten steel and solid state, but the precipitation tem perature was significantly higher than that of carbides in high-carbon chromium bearing steel. For experim ental bearing steels, the volume fraction of inclusions increased steadily with the increase of RE content, but smaller and more dispersed inclusions could be obtained by 0.018% RE content compared with bearing steel without RE, whereas the continuous increase of RE content led to an increasing trend for inclusion size and a gradual deterioration for inclusion distribution. RE addition could improve the transverse impact toughness and isotropy of bearing steel, and for modified highcarbon chrom ium bearing steel by RE alloying, the increase of RE content continuously increased both transverse and longitudinal im pact toughness until excessive RE addition. 展开更多
关键词 High-carbon CHROMIUM BEARING steel RARE earth INCLUSIONS Impact TOUGHNESS
Micromagnetic simulations on demagnetization processes in anisotropic Nd2Fe14B magnets
3
作者 Lei Li Shengzhi Dong +5 位作者 Rui Han Kuikui Song Dong Li Minggang Zhu Wei Li Wei Sun 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第6期628-632,共5页
Individual grains with diverse dimensional parameters were introduced to investigate the magnetization reversals in anisotropic Nd2 Fe14B magnets. The micromagnetic simulations were carried out via Object Oriented Mic... Individual grains with diverse dimensional parameters were introduced to investigate the magnetization reversals in anisotropic Nd2 Fe14B magnets. The micromagnetic simulations were carried out via Object Oriented MicroMagnetic Framework(OOMMF). With the same bottom area and height, analysis results show that the coercive fields for different bottom shapes are of similar values. Designed as a cubic grain,the coercive field presents descending tendency as grain volume ascends. Under constant grain volume,with aspect ratio increasing, the coercive field decreases in the beginning and increases soon. Based on the demagnetization field vector, the effects of bottom shape, grain volume and aspect ratio on the coercive field can be explained. The nucleation point is chosen to discuss. Its synthetic field and reversal field are calculated by parallelogram law and inverse external field equation, respectively. The synthetic field equal to the reversal field is defined as critical field, which always shows the same tendency as the coercive field for all cases of this study. It can be concluded that critical field is qualified to be a reference index to measure the magnitude of coercive field. 展开更多
关键词 MICROMAGNETIC simulation DEMAGNETIZATION FIELD Coercive FIELD SYNTHETIC FIELD CRITICAL FIELD Rare earths
Corrosion mechanism of H2O on Sm2Fe17 and nitrogenation process of corroded Sm2Fe17
4
作者 Jianwei Xu Jingwu Zheng +7 位作者 Haibo Chen Liang Qiao Yao Ying Wei Cai Wangchang Li Jing Yu Min Lin Shenglei Che 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第6期638-644,共7页
Sm2 Fe17 prepared by reduction-diffusion method needs to be washed with water to remove calcium oxide. Electrochemical corrosion occurs when Sm2 Fe17 powder is in contact with liquid water. Corrosion mechanism of H2 O... Sm2 Fe17 prepared by reduction-diffusion method needs to be washed with water to remove calcium oxide. Electrochemical corrosion occurs when Sm2 Fe17 powder is in contact with liquid water. Corrosion mechanism of H2 O on Sm2 Fe17 powder and nitrogenation process of corroded Sm2 Fe17 were studied by analyzing the structure and morphology. It is indicated that the metallic hydroxide forms and deposits on the Sm2 Fe17 powder surfaces during water corrosion. At the same time, oxygen and hydrogen enter the unit cell of Sm2 Fe17, causing a slight increase in Curie temperature. In the subsequent nitriding process,the hydroxide is dehydrated and hydrogen is desorbed. The resulting oxide reacts with Sm2 Fe17Nx to form a-Fe and Sm2 O3. Thermodynamic calculations using the HSC Chemistry 6.0 software indicate that the reaction can occur spontaneously. The effect of water corrosion on the magnetic properties of the nitride can be eliminated by hydrogen reduction prior to nitriding. 展开更多
关键词 Sm2Fe17 NITROGENATION Reduction-diffusion method Water CORROSION Α-FE FORMATION RARE earths
Grain boundary segregation and its influences on ionic conduction properties of scandia doped zirconia electrolytes
5
作者 Qiannan Xue Xiaowei Huang +2 位作者 Jianxing Zhang He Zhang Zongyu Feng 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第6期645-651,共7页
Solid oxide fuel cell is a promising energy conversion system which converts chemical energy into electrical energy directly. Electrolyte is the key component and determines the working temperature. In this paper,ceri... Solid oxide fuel cell is a promising energy conversion system which converts chemical energy into electrical energy directly. Electrolyte is the key component and determines the working temperature. In this paper,ceria and scandia co-doped zirconia electrolytes sintered from 1300 to 1550 ℃ were chosen as research objects. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were performed to characterize the ceramic samples. The effects of grain size and grain boundary element segregation on the electrical conductivity were focused. Electrochemical impedance spectroscopy was used to calculate the bulk, grain boundary and specific grain boundary conductivity. Results show that the bulk and grain boundary ionic conductivity increases with the increasing grain size.However, the specific grain boundary conductivity decreases with the increasing grain size. This is explained by the fact that Sc3+ is segregated at the grain boundary, which leads to higher oxygen vacancy concentration when sintered at lower temperature. 展开更多
关键词 Electrolytes CO-DOPED ZIRCONIA Grain size DOPANT SEGREGATION IONIC CONDUCTIVITY Rare earths
Simultaneous recovery of rare earth elements and phosphorus from phosphate rock by phosphoric acid leaching and selective precipitation:Towards green process
6
作者 Shengxi Wu Longsheng Zhao +4 位作者 Liangshi Wang Xiaowei Huang Yunhan Zhang Zongyu Feng Dali Cui 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第6期652-658,共7页
Phosphate rock has been considered as one of the potential promising resources for rare earth elements(REEs). But the cost issues and the technical challenges caused by the low content of REEs in ores did hinder the f... Phosphate rock has been considered as one of the potential promising resources for rare earth elements(REEs). But the cost issues and the technical challenges caused by the low content of REEs in ores did hinder the further development of REEs recovery technologies. In order to explore a green process for the recovery of REEs from phosphate rock, this study investigates the effects of phosphoric acid concentration, liquid-to-solid ratio(L/S ratio), leaching time and temperature on the leaching efficiencies of the major components from phosphate rock. A REEs recovery of 94.3% and a phosphorus recovery of 95.3%are achieved under the optimal conditions of attacking phosphate rock using 30%P2 O5 acid with an L/S ratio of 10:1 and a stirring speed of 250 r/min at 25 ℃ for 4 h. Then,the selective precipitation of REEs with 81.3% REEs recovery is realized by heating up the leaching solution from 25 to 90 ℃ and keeping for4 h. Thereafter, more than 95% phosphoric acid is recovered by H2 SO4 and high purity gypsum, more than95% CaSO4(tested by XRF), is also produced at the same time. Ultimately, a green process that leaches phosphate rock with H3 PO4, selectively precipitates REEs from leaching solution by heating up, recovers H3 PO4 with H2 SO4 is proposed. Compared with REE recovery in traditional processes, this process owns the merits of simple operation, energy saving and minimum wastes. 展开更多
关键词 Rare earth elements PHOSPHATE rock Monocalcium PHOSPHATE Minimum
Microstructure and mechanical properties of A356 alloy with yttrium addition processed by hot extrusion
7
作者 Zhifan Wei Yushun Lei +2 位作者 Hong Yan Xihao Xu Jiajia He 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第6期659-667,共9页
The effects of the rare earth element yttrium(Y) and hot extrusion on the microstructure and mechanical properties of A356 alloy were investigated by mechanical properties testing and microstructure observation. The r... The effects of the rare earth element yttrium(Y) and hot extrusion on the microstructure and mechanical properties of A356 alloy were investigated by mechanical properties testing and microstructure observation. The results indicate that the addition of Y improves the microstructure of the as-cast alloy. The distribution of primary α-Al is uniform and orderly. The long needle-like eutectic Si phases and β-Fe phases turn to strips and short rods. When the content of Y increases to 0.2 wt%, the mean diameter of aAl(40.3 μm) and the aspect ratio of the eutectic Si phase(2.3) reach the minimum values, which are68.9% and 86.1% lower, respectively, than that of the alloy without Y addition. Under extrusion stress, the shape of the eutectic Si phase is changed from long rod-like to near grain-like after solution treatment.The size of the eutectic Si phase is significantly reduced. The needle-like β-Fe phases are squeezed and broken. The mechanical properties of the as-extruded alloy are significantly improved compared to the as-cast alloy. When the rare earth content is 0.2 wt%, the ultimate tensile strength, hardness and elongation of the alloy reach the maximum values, which are 328.2 MPa, 110.4 HV and 21.3%, respectively, and increase by 42.01%, 37.71% and 481.91%, respectively, in comparison to the as-cast alloy without Y addition. 展开更多
关键词 A356 alloy with Y ADDITION Micro structure Mechanical properties Hot EXTRUSION RARE earths
RARE FINDS
8
作者 Yuan Yuan 《北京周报:英文版》 2019年第10期18-19,共2页
Leading up to Rare Disease Day on February 28,Wang Yiou was busy preparing for various activities for a special event.The 37-year-old with brittle bone disease has been trying to raise awareness about rare diseases in... Leading up to Rare Disease Day on February 28,Wang Yiou was busy preparing for various activities for a special event.The 37-year-old with brittle bone disease has been trying to raise awareness about rare diseases in China since 2008,when she founded an association in Beijing to support and care for such patients. 展开更多
关键词 RARE DISEASE PATIENTS
Double-shell structure of Al3(Zr,Sc) precipitate induced by thermomechanical treatment of Al-Zr-Sc alloy cable
9
作者 Jiayi Zhang Tao Hu +2 位作者 Danqing Yi Hongxuan Wang Bin Wang 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第6期668-672,共5页
A spheroidal Al3(Zr,Sc) precipitate with a double-shell structure, comprising a Sc-enriched core enveloped by a Zr-enriched inner shell and a Sc-enriched outer shell(~9 nm in thickness), appears in an Al-0.2 Zr-0.1 Sc... A spheroidal Al3(Zr,Sc) precipitate with a double-shell structure, comprising a Sc-enriched core enveloped by a Zr-enriched inner shell and a Sc-enriched outer shell(~9 nm in thickness), appears in an Al-0.2 Zr-0.1 Sc alloy cable after thermomechanical treatment. The average diameter of the spheroidal Al3(Zr,Sc) precipitate is approximately 80 nm. The double-shelled Al3(Zr,Sc) precipitate presents three different interfaces and is semi-coherent with the Al matrix. Atom probe tomography(APT) analyses further show that the outer shell of Al3(Zr,Sc) precipitate is Sc element enrichment. The electrical conductivity of Al-0.2 Zr-0.1 Sc alloy cable increases by 6.5 MS/m within the aging time from 0.2 to 100 h at 350 ℃, with double-shelled Al3(Zr,Sc)precipitate. 展开更多
关键词 Aluminum alloys DOUBLE-SHELL STRUCTURE THERMOMECHANICAL processing Electrical properties Rare earths
China's export of rare earth permanent magnet products was stable tn April 2019 预览
10
《中国稀土信息:英文版》 2019年第6期1-8,共8页
China is a global prcducec and expoCec of rcrc each perma nent mag net products. ExpoC is one of the impoCant salos channels for many large and medium-sized magnetin materinl prcductinn entercrises in China.
关键词 China is the Red Cross Society of China Rare Earth PERMANENT MAGNET PRODUCTS Global SOURCING
在线阅读 下载PDF
Influence of Er2O3 content on microstructure and mechanical properties of ZTA-TiO2 composites
11
作者 Yudong Sui Li’na Han +1 位作者 Yehua Jiang Quan Shan 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第3期299-304,共6页
The influence of Er2 O3 addition on the phase evolution and mechanical properties of sintered(1600 ℃,4 h) ZTA(yttria stabilized zirconia toughened alumina)-TiO2 composites was investigated. The SEM and XRD results re... The influence of Er2 O3 addition on the phase evolution and mechanical properties of sintered(1600 ℃,4 h) ZTA(yttria stabilized zirconia toughened alumina)-TiO2 composites was investigated. The SEM and XRD results reveal the formation of a new erbium zirconium oxide,Zr3 Er4 O12,with a granulate morphology when Er2 O3 content is higher than 1 wt%. The grain sizes of both Al2 O3 and yttria-stabilized zirconia phases decrease with an increase in the Er2 O3 content. The relative density, Vickers hardness and fracture toughness of the composites are found to be strongly dependent on their grain sizes, relative densities and the formation of the Zr3 Er4 O12 secondary phases. The composite with 5 wt% Er2 O3 shows the highest relative density(99.93%), Vickers hardness(1752 HV) and fracture toughness(7.92 MPa·m1/2). 展开更多
关键词 Er2O3 Microstructure VICKERS HARDNESS FRACTURE TOUGHNESS ZTA-TiO2 ceramic composite Rare earths
Development course of separating rare earths with acid phosphorus extractants: A critical review
12
作者 Deqian Li 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第5期468-486,共19页
This paper reviews the development course of separating rare earths with acid phosphorus extractants,including extraction chemistry(thermodynamics and kinetics), separation process and industrial application, the loss... This paper reviews the development course of separating rare earths with acid phosphorus extractants,including extraction chemistry(thermodynamics and kinetics), separation process and industrial application, the loss/degradation of extractants, etc. 展开更多
关键词 Rare earths ACID PHOSPHORUS EXTRACTANTS Extraction chemistry Separation process Loss/Degradation of EXTRACTANTS
Elevated temperature wear behaviour of CeO2 modified WC-12Co coating
13
作者 Yan Liu Guiying Yang +3 位作者 Zongqiu Hang Hao Fu Naiyuan Xi Hui Chen 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第6期673-678,共6页
With the service environment becoming more and more severe, WC-Co coatings are required to apply in high temperature wear condition. In the present study, the sliding wear tests of CeO2 modified WC-12 Co coatings were... With the service environment becoming more and more severe, WC-Co coatings are required to apply in high temperature wear condition. In the present study, the sliding wear tests of CeO2 modified WC-12 Co coatings were conducted at temperature of 450, 550 and 650 ℃. The wear loss and friction coefficient were recorded. The morphologies of wear tracks were observed every 1 h to investigate the dynamic wear mechanisms. The results show that the volume wear loss decreases with temperature increasing.The lowest volume wear loss is obtained at the temperature of 650 ℃ due to oxide films generated in the process of wearing. The wear mechanism is different at the temperature of 450, 550 and 650 0 C. Micro cutting wear, abrasive wear and oxidation wear dominate the wear mechanism at 450, 550 and 650 ℃,respectively. Abrasive wear and oxidation wear are the wear mechanisms at various temperatures. 展开更多
关键词 CEO2 MODIFIED WC-12CO coating Dynamic process ELEVATED temperature WEAR mechanism Rare earths
Extraction kinetics of neodymium from chloride medium using HEH/EHP saponified with magnesium bicarbonate solution
14
作者 Hao Lv Xiaowei Huang +5 位作者 Zongyu Feng Meng Wang Xu Sun Xinlin Peng Dali Cui Yihanna Hu 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第3期305-311,共7页
Magnesium bicarbonate solution is considered as an environmentally friendly extractant saponification agent for the solvent extraction of rare earth elements due to its advantage of minimum water pollution.In order to... Magnesium bicarbonate solution is considered as an environmentally friendly extractant saponification agent for the solvent extraction of rare earth elements due to its advantage of minimum water pollution.In order to reveal the extraction regularity, optimize production-process and guide the use of this new extraction system, the extraction of Nd(Ⅲ) in chloride medium with HEH/EHP saponified by magnesium bicarbonate solution was investigated with the self-designed constant interfacial area cell. Besides, the effects of stirring rate, temperature, specific interfacial area and concentration of Mg-HEH/EHP on the extraction rate of Nd(Ⅲ) were systematically investigated. Results show that, the rate of extraction is governed by both diffusion and chemical reaction, and the extraction reaction takes place at the interface. The apparent activation energy of the extraction reaction is 16.88 kJ/mol. The corresponding rate equation is deduced. The mechanisms and rate-determining step are speculated based on interfacial reaction models, which is consistent with the experimental results. 展开更多
关键词 Extraction KINETICS HEH/EHP SAPONIFICATION NEODYMIUM Rare earths
Leaching of rare Earth elements from an Illinois basin coal source
15
作者 X.Yang J.Werner R.Q.Honaker 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第3期312-321,共10页
The existence of rare earth elements(REEs) in coal sources at elevated concentrations has been the focus of several studies over the past decade. However, limited research has been conducted on methods to recover and ... The existence of rare earth elements(REEs) in coal sources at elevated concentrations has been the focus of several studies over the past decade. However, limited research has been conducted on methods to recover and refine the REEs. This paper reports the results of a detailed study into the potential of selectively recovering REEs in an Illinois basin coal source by leaching. Leaching characteristics are obtained for several segments obtained from a core sample as well as three different reject materials collected at a coal processing plant. Using a 1.2 mol/L sulfuric acid solution at 75 ℃,over 60% REE recovery is achieved from the direct floor and an inner parting material as well as the coal-rich core segments that are pretreated by low-temperature plasma oxidation to obtain access to the microdispersed mineral matter. In the leachable parting material, fluorapatite is detected by XRD analysis,which is one of the more soluble phosphate minerals with a documented association with REEs. For the three plant reject samples, the leaching recovery values obtained for the heavy REEs are higher than those obtained for the light REEs under the standard leaching conditions and when 0.1 mol/L(NH4)2SO4 was used to extract REEs by an ion exchange mechanism. Thermal activation by roasting or chemical activation by pretreatment using 8 mol/L NaOH solution increases the total REE recovery with significantly higher gains obtained for the light REEs. Leaching kinetics are relatively fast within the first 2 h and then slow to provide relatively low overall recovery values under the standard test conditions for the coarse and fine reject samples. However, significantly higher recovery values are realized when treating mixed-phase(middling) particles existing within the coarse reject material. 展开更多
关键词 LEACHING COAL Thermal ACTIVATION Chemical ACTIVATION RARE earth elements
La2Ce2O7 supported ruthenium as a robust catalyst for ammonia synthesis
16
作者 Wenfeng Han Zhi Li Huazhang Liu 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第5期492-499,共8页
La2Ce2O7 nanoparticles were prepared by citric acid complexation method followed by calcination at varied temperatures. Then, supported with 4 wt% Ru, they were evaluated as the catalysts for ammonia synthesis under c... La2Ce2O7 nanoparticles were prepared by citric acid complexation method followed by calcination at varied temperatures. Then, supported with 4 wt% Ru, they were evaluated as the catalysts for ammonia synthesis under conditions similar with industry. With La2Ce2O7 being calcinated at 700 or 800℃, the experimental results indicate that the Ru/La2Ce2O7 catalyst exhibits much higher ammonia concentration or ammonia synthesis rate than that of Ru/CeO2 and Ru/La2O3. In addition, Ru/La2Ce2O7 possesses high stability under over-heating test. In the absence of any promotor, ammonia concentration of Ru/La2Ce2O7 catalyst approaches 14% at 450℃, GHSV of 10000 h-1 and pressure of 10 MPa. The rate-determining step of ammonia synthesis, dissociation of N2 is significantly facilitated by the strong metalesupport interaction(SMSI) between Ru and La2Ce2O7. Due to the interaction, La2Ce2O7 tends to donate electrons to Ru,resulting in the high electron density over the surface of Ru active sites which is favorable for the dissociation of N2. Consequently, high activity is achieved. 展开更多
关键词 AMMONIA synthesis RUTHENIUM La2Ce2O7 ACTIVATION energy NANOPARTICLES Rare earths
孕产期少见型急腹症25例临床分析
17
作者 单龙 段丽君 +4 位作者 孙晓彤 毛燕 黄遐 杨燕 罗亚莉 《中国计划生育和妇产科》 2019年第7期71-76,89共7页
目的分析孕产期25例少见和罕见急腹症的发病原因、诊疗过程,为临床孕产期急腹症的诊断与鉴别诊断提供借鉴与帮助。方法对甘肃省人民医院2012年7月至2017年7月孕产期25例临床少见急腹症病例进行回顾性分析。结果①25例少见急腹症病因主要... 目的分析孕产期25例少见和罕见急腹症的发病原因、诊疗过程,为临床孕产期急腹症的诊断与鉴别诊断提供借鉴与帮助。方法对甘肃省人民医院2012年7月至2017年7月孕产期25例临床少见急腹症病例进行回顾性分析。结果①25例少见急腹症病因主要为:妊娠期:腹部卒中2例,子宫肌壁间妊娠1例,胃穿孔1例,子宫破裂3例,宫内妊娠合并异位妊娠破裂2例,子宫阔韧带肌瘤变性1例,子宫浆膜下肌瘤扭转2例,卵巢囊肿扭转坏死2例,妊娠期肝内胆汁郁积症合并重症肝炎和贫血1例,急性化脓性腹膜炎1例,酮症酸中毒1例,输卵管细末小动脉破裂1例。产褥期:子宫浆膜下血管破裂2例,腹肌小动脉破裂1例,腹膜动脉破裂1例,后腹膜及侧腹膜血肿1例,子宫粘连带小动脉破裂2例。②病例不典型,但均可引起恶心、呕吐、全腹压痛或反跳痛甚至体温、血象及感染指数升高等急腹症症状或体征。③难与较常见的急腹症鉴别,易于误诊,误诊率达到11.3%,相比常见急腹症误诊率更高。结论在诊断孕产期急腹症时,不仅要想到常见和多发病种,更要与少见和罕见疾病加以鉴别,减少误诊率和提高抢救成功率。 展开更多
关键词 妊娠期 产褥期 急腹症 罕见 误诊 分析
Fluorescence Properties of Eu3+ Doped in Na5Lu9F32 Single Crystals
18
作者 WANG Hui XIA Haiping +2 位作者 SHI Xudong CHENG Guanghai ZHANG Jianli 《武汉理工大学学报:材料科学英文版》 SCIE EI CAS 2019年第2期317-323,共7页
Eu3+ ion doped cubic Na5Lu9F32 single crystals with high quality were synthesized by a modified Bridgman method by using a high 70-90 ℃/cm temperature gradient for cross solid-liquid interface. The optical spectrosco... Eu3+ ion doped cubic Na5Lu9F32 single crystals with high quality were synthesized by a modified Bridgman method by using a high 70-90 ℃/cm temperature gradient for cross solid-liquid interface. The optical spectroscopic investigations of the obtained single crystal were reported for the absorption, excitation and emission. The experimental results show that a strong red emission at 609 nm attributing to the 5D0→7F2 transition of Eu3+ doped Na5Lu9F32 single crystals can be obtained under the excitation of 394 nm light and reach the maximum when the Eu3+ doping concentration is 4 mol% in present research. The local covalent is enhanced and symmetry is reduced with the increase of Eu3+ concentrations inferring from the strength parameters Ω2 and Ω4 calculated by their measured emission spectra. The CIE chromaticity coordinates of the 4 mol% Eu3+ doped Na5Lu9F32 single crystals are calculated as(x=0.626, y=0.3736), which are close to the NTSC standard values for red(x=0.67, y=0.33). The experimental results reveal that the single crystal can be used as potential red phosphors under near ultraviolet(NUV) light excitation. 展开更多
关键词 optical materials crystal growth red PHOSPHORS RARE earth
Geochronology and Geochemistry of Li(Be)-Bearing Granitic Pegmatites from the Jiajika Superlarge Li-Polymetallic Deposit in Western Sichuan, China
19
作者 Hongzhang Dai Denghong Wang +2 位作者 Lijun Liu Yang Yu Jingjing Dai 《地球科学学刊:英文版》 SCIE CAS CSCD 2019年第4期707-727,共21页
Strategic emerging minerals such as lithium,beryllium,niobium and tantalum are the most important rare metals currently,especially with the increasing demand of emerging industries on rare metals in China.The Jiajika ... Strategic emerging minerals such as lithium,beryllium,niobium and tantalum are the most important rare metals currently,especially with the increasing demand of emerging industries on rare metals in China.The Jiajika deposit with a complete Li-Be-Nb-Ta metallogenic series is the largest pegmatite type rare metal deposit in China at present.In this paper,systematic researches of geochronology and petrogeochemistry were carried out to understand the genetic relationships between mineralization and magma evolution in the Jiajika deposit,which might be helpful to further rare-element prospecting in Songpan-Garze area.Zircon LA-ICP-MS U-Pb dating yields a concordia age of 217±1.1 Ma and a weighted mean 206 Pb/238 U age of 217±0.84 Ma for the aplite from the No.308 pegmatite.Cassiterite LA-MC-ICPMS dating yields concordant ages of 211±4.6 Ma for the No.308 pegmatite vein and198±4.4 Ma for the No.133 pegmatite vein,indicating that the rare metal mineralization mainly occurred in the Late Indosinian Period,further suggesting that the granites,aplites and pegmatites in Jiajika formed during a relatively stable stage after the intense orogeny of the Indosinian cycle.The rare metal-bearing granitic rocks and pegmatites show a clear linear relationship between A/CNK and A/NK and are enriched in total alkalis and depleted in CaO,FeO,MnO,MgO,Ba and Sr.All barren rocks and mineralized rocks feature similar rare earth element and trace element geochemical patterns.Thus,these characteristics indicate that the aplites and pegmatites represent the highly differentiated products of the two-mica granite(MaG)in this area,which is the most likely parent magma.During the evolution of magma,strong alkali metasomatism occurred between the melt phase and the volatile-rich fluid phase;as a result,large-scale rare metal mineralization occurred in certain structural zones of the pegmatite veins in the Jiajika deposit. 展开更多
关键词 GRANITIC pegmmatites rare mmetals METALLOGENIC EPOCH geochemical characterizatiion Jia ajika
Recent advances in solid-state LED phosphors with thermally stable luminescence
20
作者 Jianwei Qiao Jing Zhao +1 位作者 Quanlin Liu Zhiguo Xia 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第6期565-572,共8页
Phosphor-converted white light-emitting diode(LED) lighting has gained tremendous achievements since the invention of the InGaN blue LED by Nakamura et al., who won the Nobel Physics Prize in 2014.By far, a significan... Phosphor-converted white light-emitting diode(LED) lighting has gained tremendous achievements since the invention of the InGaN blue LED by Nakamura et al., who won the Nobel Physics Prize in 2014.By far, a significant challenge comes from the thermal quenching(TQ) behavior of the present LED phosphors during the high-power LED operation or the updated laser lighting. But systematic research or review on the luminescence quenching character and/or how to realize thermally stable luminescence are lacking. Since TQ is an inherent property of phosphors, it can be diminished by different approaches.This review proceeds from the mechanism of TQ, summarizes previous researches on improving the thermal stability of LED phosphors and also discusses future research opportunities in this field. The developments of the phosphors with properties of high luminance and thermal stability, as well as the improved strategies involved,will benefit the basic researches and applications in high power lighting or high-luminance laser lighting. 展开更多
关键词 WHITE LEDS PHOSPHOR Thermal QUENCHING Rare earths
上一页 1 2 250 下一页 到第
使用帮助 返回顶部 意见反馈