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   227372篇
  免费   3252篇
  国内免费   1329篇
化学   127284篇
晶体学   3292篇
力学   9006篇
综合类   61篇
数学   25421篇
物理学   66889篇
  2020年   1926篇
  2019年   2085篇
  2018年   2657篇
  2017年   2702篇
  2016年   3938篇
  2015年   2659篇
  2014年   3779篇
  2013年   9322篇
  2012年   8202篇
  2011年   9912篇
  2010年   6950篇
  2009年   6766篇
  2008年   9242篇
  2007年   9282篇
  2006年   8737篇
  2005年   8009篇
  2004年   7144篇
  2003年   6270篇
  2002年   6167篇
  2001年   6798篇
  2000年   5169篇
  1999年   3737篇
  1998年   3091篇
  1997年   3050篇
  1996年   3084篇
  1995年   2664篇
  1994年   2765篇
  1993年   2634篇
  1992年   2885篇
  1991年   2918篇
  1990年   2733篇
  1989年   2639篇
  1988年   2569篇
  1987年   2509篇
  1986年   2537篇
  1985年   3322篇
  1984年   3379篇
  1983年   2814篇
  1982年   3061篇
  1981年   2824篇
  1980年   2619篇
  1979年   2796篇
  1978年   3003篇
  1977年   3044篇
  1976年   3068篇
  1975年   2801篇
  1974年   2912篇
  1973年   2963篇
  1972年   2324篇
  1971年   1848篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Russian Journal of General Chemistry - A method was developed for the synthesis of an organofluorine derivative of β-D-ribofuranoside. Biological tests revealed high insecticidal activity and...  相似文献   
53.
Molecular dynamics simulation was performed to study the formation of cluster structure, interfaces, and surfaces with different curvature radii in a perfect nanocrystal passed through by a nonlinear wave. It is shown that this process is a type of nanostructure self-organization in response to an external energy flux with subsequent development of a strong rotational field.  相似文献   
54.
Algebras and Representation Theory - We introduce and study the category of twisted modules over a triangular differential graded bocs. We show that in this category idempotents split, that it...  相似文献   
55.
Annals of Operations Research - The vehicle routing problem is a traditional combinatorial problem with practical relevance for a wide range of industries. In the literature, several specificities...  相似文献   
56.
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   
57.
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   
58.
Crystallography Reports - The formation of Zn-based nanotubes by electrochemical synthesis in pores of template polymer matrices is considered. It is established that the number of defects in the...  相似文献   
59.
Crystallography Reports - The specific features of the formation of concentration inhomogeneities in crystals grown by the Czochralski method (GaSb:Te, Ge:Ga) and by the Bridgman method...  相似文献   
60.
Journal of Solid State Electrochemistry - In this study, galvanostatic electrolysis, through the use of the platinum supported on Ti (Ti/Pt) and Ti/TiO2-nanotubes/PbO2 anodes, was conducted in an...  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