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   268864篇
  免费   2407篇
  国内免费   628篇
化学   142891篇
晶体学   4174篇
力学   11943篇
综合类   9篇
数学   29795篇
物理学   83087篇
  2019年   2315篇
  2018年   3119篇
  2017年   3120篇
  2016年   4504篇
  2015年   2671篇
  2014年   4302篇
  2013年   10706篇
  2012年   8117篇
  2011年   9936篇
  2010年   7122篇
  2009年   6918篇
  2008年   9369篇
  2007年   9562篇
  2006年   8927篇
  2005年   8121篇
  2004年   7468篇
  2003年   6768篇
  2002年   6688篇
  2001年   7349篇
  2000年   5687篇
  1999年   4379篇
  1998年   3871篇
  1997年   3862篇
  1996年   3599篇
  1995年   3345篇
  1994年   3504篇
  1993年   3203篇
  1992年   3683篇
  1991年   3681篇
  1990年   3610篇
  1989年   3465篇
  1988年   3581篇
  1987年   3478篇
  1986年   3293篇
  1985年   4379篇
  1984年   4648篇
  1983年   3882篇
  1982年   4018篇
  1981年   3940篇
  1980年   3922篇
  1979年   3886篇
  1978年   4202篇
  1977年   4115篇
  1976年   4179篇
  1975年   3861篇
  1974年   3899篇
  1973年   4060篇
  1972年   2854篇
  1971年   2381篇
  1970年   2183篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
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   
63.
Radiophysics and Quantum Electronics - Wind-related weather hazards remain difficult to recognize targets for weather radars. Methods that use estimates of the width of the reflected-signal...  相似文献   
64.
Russian Journal of General Chemistry - Highly dispersed CaO has been synthesized by heating an aqueous solution of calcium nitrate and D-glucose up to 800°C. Calcium oxide is formed with an...  相似文献   
65.
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   
66.
Journal of Analytical Chemistry - HPTLC is a widely used tool in standardization of herbs because of its ability to estimate the presence of active components in samples. HPTLC-bioautography is a...  相似文献   
67.
Journal of Applied Spectroscopy - Aqueous solutions of human hemoglobin have been studied by the multi-angle static light scattering method. The tendency of sickle-shaped erythrocytes to aggregate...  相似文献   
68.
Xu  H. J.  Zhang  Q. G.  Debenest  G. 《Transport in Porous Media》2021,140(3):625-627
Transport in Porous Media - The theme of coupling problems for adsorption, absorption and thermochemical transport in porous media is very important for engineering applications. Based on the...  相似文献   
69.
Aliev  A. B.  Shafieva  G. H. 《Differential Equations》2022,58(8):1028-1042
Differential Equations - We study a mixed problem for systems of one-dimensional semilinear hyperbolic equations with variable nonlinearity growth rate and nonlinear boundary conditions. Theorems...  相似文献   
70.
Journal of Sol-Gel Science and Technology - High temperature stable brookite rich titanium dioxide of average crystallite size 20&;nbsp;nm has been prepared by a novel aqueous sol–gel...  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