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   294913篇
  免费   3285篇
  国内免费   1693篇
化学   145311篇
晶体学   3653篇
力学   15427篇
综合类   61篇
数学   55420篇
物理学   80019篇
  2020年   1755篇
  2019年   1891篇
  2018年   12621篇
  2017年   12528篇
  2016年   9540篇
  2015年   3230篇
  2014年   3810篇
  2013年   9151篇
  2012年   11283篇
  2011年   19501篇
  2010年   12058篇
  2009年   12278篇
  2008年   15101篇
  2007年   17288篇
  2006年   8567篇
  2005年   8927篇
  2004年   8322篇
  2003年   7954篇
  2002年   6943篇
  2001年   6932篇
  2000年   5344篇
  1999年   3807篇
  1998年   3213篇
  1997年   3141篇
  1996年   3208篇
  1995年   2732篇
  1994年   2791篇
  1993年   2673篇
  1992年   2880篇
  1991年   2957篇
  1990年   2754篇
  1989年   2670篇
  1988年   2615篇
  1987年   2552篇
  1986年   2520篇
  1985年   3303篇
  1984年   3355篇
  1983年   2803篇
  1982年   3046篇
  1981年   2803篇
  1980年   2621篇
  1979年   2797篇
  1978年   3008篇
  1977年   3028篇
  1976年   3044篇
  1975年   2796篇
  1974年   2899篇
  1973年   2962篇
  1972年   2317篇
  1971年   1833篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
51.
52.
53.
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   
54.
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   
55.
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   
56.
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   
57.
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   
58.
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   
59.
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   
60.
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   
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