首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   31066篇
  免费   4032篇
  国内免费   3401篇
化学   22650篇
晶体学   396篇
力学   1532篇
综合类   248篇
数学   3824篇
物理学   9849篇
  2023年   468篇
  2022年   512篇
  2021年   775篇
  2020年   998篇
  2019年   1033篇
  2018年   877篇
  2017年   819篇
  2016年   1246篇
  2015年   1294篇
  2014年   1514篇
  2013年   2127篇
  2012年   2554篇
  2011年   2767篇
  2010年   1947篇
  2009年   1921篇
  2008年   2157篇
  2007年   1942篇
  2006年   1739篇
  2005年   1547篇
  2004年   1217篇
  2003年   984篇
  2002年   896篇
  2001年   755篇
  2000年   605篇
  1999年   570篇
  1998年   513篇
  1997年   445篇
  1996年   477篇
  1995年   412篇
  1994年   396篇
  1993年   356篇
  1992年   338篇
  1991年   295篇
  1990年   244篇
  1989年   200篇
  1988年   172篇
  1987年   140篇
  1986年   146篇
  1985年   164篇
  1984年   107篇
  1983年   69篇
  1982年   76篇
  1981年   56篇
  1980年   76篇
  1979年   61篇
  1978年   59篇
  1977年   78篇
  1976年   53篇
  1974年   51篇
  1973年   50篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
41.
Fully utilizing solar energy for catalysis requires the integration of conversion mechanisms and therefore delicate design of catalyst structures and active species. Herein, a MOF crystal engineering method was developed to controllably synthesize a copper–ceria catalyst with well-dispersed photoactive Cu-[O]-Ce species. Using the preferential oxidation of CO as a model reaction, the catalyst showed remarkably efficient and stable photoactivated catalysis, which found practical application in feed gas treatment for fuel cell gas supply. The coexistence of photochemistry and thermochemistry effects contributes to the high efficiency. Our results demonstrate a catalyst design approach with atomic or molecular precision and a combinatorial photoactivation strategy for solar energy conversion.  相似文献   
42.
Jiao  Jiajia  Li  Hao  Lin  Wen  Wang  Rui  Meng  Zihan  Guo  Weibin  Zhao  Shengqiu  Li  Junsheng  Tang  Haolin 《Journal of Solid State Electrochemistry》2020,24(3):771-779
Journal of Solid State Electrochemistry - Practical application of Li-S battery is limited by the fast capacity decay and low coulombic efficiency caused by the shuttling phenomenon. Modification...  相似文献   
43.
Li  Qiang  Schultz  Paul  Lin  Wei  Kurths  Jürgen  Ji  Peng 《Nonlinear dynamics》2020,102(2):653-665
Nonlinear Dynamics - A complex system’s structural–dynamical interplay plays a profound role in determining its collective behavior. Irregular behavior in the form of macroscopic chaos,...  相似文献   
44.
Eucommia ulmoides Oliv. (E. ulmoides) is a valuable and nourishing medicinal herb in China that has been used in the treatment of hypertension. Given the fact that most traditional Chinese medicine is mainly used to treat disease, investigating the pharmacokinetics of traditional Chinese medicines in the pathological state is more useful than that in the normal state. However, the differences in the absorption kinetics of active ingredients of E. ulmoides extract between pathological and physiological conditions have not been reported. Therefore, in this study, the rat intestinal in situ circulatory perfusion model was used to investigate the differences in absorption kinetics of seven active ingredients of E. ulmoides extract in normal and spontaneously hypertensive rats, namely, genipinic acid, protocatechuic acid, neochlorogenic acid, chlorogenic acid, cryptochlorogenic acid, (+)-pinoresinol di-O-β-D -glucopyranoside and (+)-pinoresinol 4′-O-β-D -glucopyranoside. Our results indicate that the pathological state of spontaneous hypertension may change the absorption of active components of E. ulmoides extracts, and these findings may provide a reference for improving the rational use of E. ulmoides in the clinic.  相似文献   
45.
Ginkgo biloba L. leaf (GBL) is one of the most commonly used medicinal plants in the world. Phenolic acids with biological activities have a relatively high content in G. biloba leaf extracts (GBE); therefore they are of great significance for the quality control of GBL, GBE and its preparations. However, there have been few studies focused on their analysis. In this work, 12 phenolic acids, including 11 phenolic acid glycosides, were identified by liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (LC–Q-TOF/MS). Then, a method combining enzymolysis with HPLC was established for quantification of phenolic acid glycosides. It was found that the aglycones of phenolic acid glycosides mainly comprised five phenolic acids: 2,4,6-trihydroxybenzoic acid, protocatechuic acid, p-hydroxybenzoic acid, vanillic acid and p-coumaric acid. The quantitative method was validated, and the correlation coefficient (0.9993–0.9999), recovery (≥88.4%), repeatability (≤0.8%), and inter-day precision (≤5.5%) were satisfactory. Finally, the contents of glycosides of five phenolic acids in GBL, GBE and GBE injection from different sources were determined by the developed method. The method was accurate, repeatable and practicable, which could be helpful for the quantification of phenolic acid glycosides in other products containing GBL or GBE.  相似文献   
46.
Lin  Yingzi  Zhu  Yang  Li  Ang  Wu  Tianmo  Song  Yingji 《Research on Chemical Intermediates》2020,46(2):1405-1424
Research on Chemical Intermediates - In this study, biomorphic WO3-Cx nanomaterial was successfully prepared with rice hull as biological templates. The structure and morphology of the nanomaterial...  相似文献   
47.
蓝宝石的冲击消光现象是高压领域中的研究热点.低压段(86 GPa范围内)的实验研究表明蓝宝石的冲击消光与晶向相关,但在高压段(压力范围:131255 GPa)是否也具有晶向相关性目前尚不清楚.为此,利用第一性原理方法,分别计算了八个不同晶向的蓝宝石理想晶体和含氧离子空位缺陷晶体在高压段的光吸收性质,结果发现:1)蓝宝石在高压段的冲击消光表现出明显的晶向效应,且该效应还随压力增大而增强;一步的数据分析可以看出,在冲击实验采用的波段内,a晶向的消光最弱(透明性最好),c晶向的消光最强与c晶向的消光接近,g晶向的消光要弱于s晶向的消光.鉴于此,如果在高压段开展加窗冲击波实验,建议选择a晶向或m晶向的蓝宝石作为其光学窗口.本文结果不仅有助于深入地认识蓝宝石在极端条件下的光学性质,而且对未来的实验研究有重要的参考作用.  相似文献   
48.
Yang  Y.  Wan  Z.-Q.  Zhang  J.  Jiang  H.-J.  Zhang  Z.-Q.  Ju  Y.-C. 《Crystallography Reports》2020,65(1):78-83
Crystallography Reports - The {[Sm2(FDC)2](FDC) · 10H2O}n complex, where H2FDC is a 2,5-furandicarboxylic acid, has been prepared by hydrothermal reaction and structurally characterized by...  相似文献   
49.
Herein, we report a highly efficient and practical method for pyridine‐derived heterobiaryl synthesis through palladium‐catalyzed electrophilic functionalization of easily available pyridine‐derived quaternary phosphonium salts. The nice generality of this reaction was goes beyond arylation, enabling facile incorporation of diverse carbon‐based fragments, including alkenyl, alkynyl, and also allyl fragments, onto the pyridine core. Notably, the silver salt additive is revealed to be of vital importance for the success of this transformation and its pivotal role as transmetallation mediator, which guarantees a smooth transfer of pyridyl group to palladium intermediate, is also described.  相似文献   
50.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号