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   240871篇
  免费   3645篇
  国内免费   1358篇
化学   135866篇
晶体学   3357篇
力学   9288篇
综合类   61篇
数学   28035篇
物理学   69267篇
  2020年   2064篇
  2019年   2239篇
  2018年   2874篇
  2017年   2904篇
  2016年   4465篇
  2015年   3005篇
  2014年   4189篇
  2013年   10129篇
  2012年   8966篇
  2011年   10714篇
  2010年   7466篇
  2009年   7239篇
  2008年   9944篇
  2007年   10074篇
  2006年   9431篇
  2005年   8683篇
  2004年   7722篇
  2003年   6764篇
  2002年   6572篇
  2001年   7079篇
  2000年   5422篇
  1999年   3940篇
  1998年   3259篇
  1997年   3207篇
  1996年   3270篇
  1995年   2820篇
  1994年   2934篇
  1993年   2759篇
  1992年   2990篇
  1991年   3045篇
  1990年   2870篇
  1989年   2757篇
  1988年   2684篇
  1987年   2622篇
  1986年   2633篇
  1985年   3457篇
  1984年   3539篇
  1983年   2914篇
  1982年   3163篇
  1981年   2951篇
  1980年   2726篇
  1979年   2882篇
  1978年   3088篇
  1977年   3122篇
  1976年   3134篇
  1975年   2873篇
  1974年   2953篇
  1973年   3008篇
  1972年   2345篇
  1971年   1877篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
61.
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   
62.
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   
63.
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   
64.
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   
65.
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   
66.
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   
67.
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   
68.
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   
69.
Exosomes are nanovesicles secreted by most cellular types that carry important biochemical compounds throughout the body with different purposes, playing a preponderant role in cellular communication. Because of their structure, physicochemical properties and stability, recent studies are focusing in their use as nanocarriers for different therapeutic compounds for the treatment of different diseases ranging from cancer to Parkinson's disease. However, current bioseparation protocols and methodologies are selected based on the final exosome application or intended use and present both advantages and disadvantages when compared among them. In this context, this review aims to present the most important technologies available for exosome isolation while discussing their advantages and disadvantages and the possibilities of being combined with other strategies. This is critical since the development of novel exosome‐based therapeutic strategies will be constrained to the effectiveness and yield of the selected downstream purification methodologies for which a thorough understanding of the available technological resources is needed.  相似文献   
70.
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