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   411316篇
  免费   4304篇
  国内免费   1097篇
化学   204378篇
晶体学   5920篇
力学   19439篇
综合类   7篇
数学   59493篇
物理学   127480篇
  2020年   1983篇
  2019年   1959篇
  2018年   10974篇
  2017年   11854篇
  2016年   7908篇
  2015年   4153篇
  2014年   4550篇
  2013年   14102篇
  2012年   15029篇
  2011年   25633篇
  2010年   15522篇
  2009年   15444篇
  2008年   22729篇
  2007年   26292篇
  2006年   12389篇
  2005年   18268篇
  2004年   13575篇
  2003年   12175篇
  2002年   10052篇
  2001年   10264篇
  2000年   7983篇
  1999年   6152篇
  1998年   4938篇
  1997年   4753篇
  1996年   4915篇
  1995年   4451篇
  1994年   4192篇
  1993年   4004篇
  1992年   4492篇
  1991年   4356篇
  1990年   4071篇
  1989年   3897篇
  1988年   4199篇
  1987年   3861篇
  1986年   3736篇
  1985年   5395篇
  1984年   5486篇
  1983年   4450篇
  1982年   4824篇
  1981年   4866篇
  1980年   4621篇
  1979年   4751篇
  1978年   4763篇
  1977年   4670篇
  1976年   4651篇
  1975年   4553篇
  1974年   4399篇
  1973年   4603篇
  1972年   2594篇
  1971年   1896篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
933.
We show that Abelian gauge theories in 2+1 space-time dimensions with the introduction of a topological Chern-Simons term can be quantized with the use of the symplectic formalism. The consistency of our results are verified by the agreement with the ones from the Dirac case.  相似文献   
934.
The application of some recently proposed algebraic multilevel methods for the solution of two-dimensional finite element problems on nonuniform meshes is studied. The locally refined meshes are created by the newest vertex mesh refinement method. After the introduction of this refinement technique it is shown that, by combining levels of refinement, a preconditioner of optimal order can be constructed for the case of local refinement along a line. Its relative condition number is accurately estimated. Numerical tests demonstrating the performance of the proposed preconditioners will be reported in a forthcoming paper.  相似文献   
935.
Thermoelastic stress analysis was used to document the effect of composite damage on the stress distribution in three ceramic matrix composites. Composite damage was found to significantly alter the thermoelastic response of each material, with the greatest effect noted in SiC/CAS. Thermoelastic imaging of these materials affords a more complete picture of how the various damage mechanisms affect the stress distribution. In particular, a stress concentration factor computed from thermoelastic images, serves as an indicator of stress redistribution. The stress concentration factors were computed by comparing notch root to far field temperatures, and monitored after the introduction of various amounts of damage. In each material, the stress concentration factor diminished as the damaging load approached the ultimate stress. Reduction in the stress concentration is associated with local changes in modulus, mechanistically arising from combinations of fiber, matrix and interface fracture. Stress redistribution occurs as a consequence of modulus changes, leading to lower notch sensitivity in each of the tested composites.  相似文献   
936.
We present some classical solutions to a gauge theory based on quadratically nonlinear Lie algebras without a central term. We observe that instanton-like and meron-like solutions force the internal fields to behave like solitons.  相似文献   
937.
938.
The phase behavior of binary blends of poly(ether ether ketone) (PEEK), sulfonated PEEK, and sulfamidated PEEK with aromatic polyimides is reported. PEEK was determined to be immiscible with a poly(amide imide) (TORLON 4000T). Blends of sulfonated and sulfamidated PEEK with this poly(amide imide), however, are reported here to be miscible in all proportions. Blends of sulfonated PEEK and a poly(ether imide) (ULTEM 1000) are also reported to be miscible. Spectroscopic investigations of the intermolecular interactions suggest that formation of electron donoracceptor complexes between the sulfonated/sulfamidated phenylene rings of the PEEKs and the n-phenylene units of the polyimides are responsible for this miscibility. © 1993 John Wiley & Sons, Inc.  相似文献   
939.
940.
This paper provides a rigorous proof of the existence of an infinite number of black hole solutions to the Einstein-Yang/Mills equations with gauge groupSU(2), for any event horizon. It is also demonstrated that the ADM mass of each solutions is finite, and that the corresponding Einstein metric tends to the associated Schwarzschild metric at a rate 1/r 2, asr tends to infinity.Research supported in part by the NSF, Contract No. DMS-89-05205Research supported in part by the DE, Contract No. De-FG 02-88 EF 25065  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