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   239212篇
  免费   6719篇
  国内免费   3879篇
化学   136001篇
晶体学   2844篇
力学   10184篇
综合类   300篇
数学   26802篇
物理学   73679篇
  2021年   2059篇
  2020年   2705篇
  2019年   2768篇
  2018年   3194篇
  2017年   3227篇
  2016年   4687篇
  2015年   3391篇
  2014年   4748篇
  2013年   10452篇
  2012年   9644篇
  2011年   11369篇
  2010年   7999篇
  2009年   7767篇
  2008年   10239篇
  2007年   10219篇
  2006年   9638篇
  2005年   8714篇
  2004年   7648篇
  2003年   6629篇
  2002年   6083篇
  2001年   6946篇
  2000年   5237篇
  1999年   3917篇
  1998年   3251篇
  1997年   3201篇
  1996年   3193篇
  1995年   2941篇
  1994年   3004篇
  1993年   2836篇
  1992年   3022篇
  1991年   3063篇
  1990年   2857篇
  1989年   2697篇
  1988年   2630篇
  1987年   2529篇
  1986年   2555篇
  1985年   3317篇
  1984年   3348篇
  1983年   2802篇
  1982年   3041篇
  1981年   2784篇
  1980年   2582篇
  1979年   2755篇
  1978年   2972篇
  1977年   3009篇
  1976年   3030篇
  1975年   2776篇
  1974年   2886篇
  1973年   2938篇
  1972年   2301篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
101.
Russian Journal of Organic Chemistry - Three-component reaction of methyl 4-aryl-2,4-dioxobutanoates with aromatic aldehyde and 2-aminoacetonitrile sulfate in glacial acetic acid in the presence of...  相似文献   
102.
Li  S. K.  Huang  L. L.  Lv  Y. D.  Feng  H. D. 《Russian Journal of Organic Chemistry》2019,55(9):1432-1438
Russian Journal of Organic Chemistry - A rapid and efficient catalytic approach has been proposed for the synthesis of dimethyl 2-[2-(aryl-amino)but-3-en-1-yl]- and...  相似文献   
103.
Tetrahydrotetrazoles are five‐membered‐ring heterocycles containing four contiguous saturated nitrogen atoms. Very few examples of such compounds have been reported in the literature. Our previous attempt at the synthesis of a member of this class of compound suggested that the N—N bonds may be more labile than expected. This finding raised the question as to whether the structures of any of the previously reported tetrahydrotetrazoles had been properly assigned. We have reproduced the synthesis of a reported tetrahydrotetrazole, namely 1,2‐di‐tert‐butyl 3‐phenyl‐1H,2H,3H,10bH‐[1,2,3,4]tetrazolo[5,1‐a]isoquinoline‐1,2‐dicarboxylate, C25H30N4O4, and have now confidently confirmed its structure via X‐ray crystallography. However, while sufficiently stable in the crystal phase, we discovered that it remains very labile in solution (having a half‐life of only 15 min at 20 °C in CDCl3). A tentative reaction pathway for its dissociation based on 1H NMR spectral evidence is provided.  相似文献   
104.
105.
106.
Russian Journal of Organic Chemistry - The structure of 6-polyfluoroalkyl-2-thiouracils and reactivity of nucleophilic centers in their molecules were analyzed by quantum chemical calculations....  相似文献   
107.
Russian Journal of Applied Chemistry - The possibility of replacing the currently widely used ammonium perchlorate as an oxidizing agent (dispersant) in the composition of solid boron-containing...  相似文献   
108.
Russian Journal of Organic Chemistry - The reaction of methyl aroylpyruvates with 2-(4-aminobenzenesulfonamido)thiazole (norsulfazole) in acetic acid-ethanol (1: 1) afforded methyl...  相似文献   
109.
Bruzy  N.  Coret  M.  Huneau  B.  Kermouche  G.  Mondon  M.  Bertrand  E.  Stainier  L. 《Experimental Mechanics》2019,59(8):1145-1157

The allotropic phase change from ferrite to austenite represents a moment of massive interplay between the microstructural and mechanical states of iron. The difference of compacity between the two phases induces a microplastic accommodation in the material at grain scale. However, mechanical heterogeneities resulting from the transformation process remain challenging to characterise due to the high temperature conditions it is associated with. We developed experimental equipment for in situ observation of α ? γ and γ ? α transformations. Images of the surface of an iron sample taken by an optical camera were used as input for a Digital Image Correlation (DIC) routine. Special care was taken to maximize image resolution to capture sub-grain phenomena. Observations show that, at the mesoscopic scale, shear strain fields exhibit strong localisations that are evidence of transformations that are occurring.

  相似文献   
110.
Wang  Zenghao  Xie  Yongshuai  Xu  Chonghe  Shi  Shuying  Wang  Lin  Zhang  Guanghui  Wang  Xinqiang  Zhu  Luyi  Xu  Dong 《Journal of Solid State Electrochemistry》2019,23(1):269-276
Journal of Solid State Electrochemistry - Lithium-ion batteries have been receiving more and more attention because of the energy crisis. As an important subassembly of lithium-ion batteries, the...  相似文献   
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