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   456314篇
  免费   5942篇
  国内免费   1584篇
化学   252047篇
晶体学   6844篇
力学   18978篇
综合类   11篇
数学   51623篇
物理学   134337篇
  2018年   2976篇
  2016年   5682篇
  2015年   4531篇
  2014年   6254篇
  2013年   19967篇
  2012年   14377篇
  2011年   18016篇
  2010年   11476篇
  2009年   11337篇
  2008年   16553篇
  2007年   16898篇
  2006年   16246篇
  2005年   14828篇
  2004年   13416篇
  2003年   11893篇
  2002年   11706篇
  2001年   13839篇
  2000年   10616篇
  1999年   8505篇
  1998年   6791篇
  1997年   6665篇
  1996年   6696篇
  1995年   6123篇
  1994年   5871篇
  1993年   5568篇
  1992年   6423篇
  1991年   6166篇
  1990年   5858篇
  1989年   5750篇
  1988年   5947篇
  1987年   5692篇
  1986年   5445篇
  1985年   7677篇
  1984年   7774篇
  1983年   6388篇
  1982年   6826篇
  1981年   6833篇
  1980年   6493篇
  1979年   6756篇
  1978年   6940篇
  1977年   6825篇
  1976年   6715篇
  1975年   6489篇
  1974年   6296篇
  1973年   6477篇
  1972年   3920篇
  1971年   3039篇
  1968年   3375篇
  1967年   3280篇
  1966年   2992篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Recently, the theory of sortability of partition property has been shown to be an effective tool to prove the existence of an optimal partition with that property. In this paper, we extend the theory to multi-partition where the partition is on t types of components. We apply our results to settle an optimal assignment problem whose proof was incomplete as given in the literature.  相似文献   
992.
It is shown that the construction of needle variations can be carried out for almost lower semicontinuous differential inclusions rather than for the case of ordinary single-valued continuously differentiable vector fields usually considered in the literature. The construction leads to needle variations whose flows are in general set-valued but still have good differentiability properties. The variations are constructed by using single-valued selections that are not necessarily continuous with respect to the state variable, but have instead a much weaker 'integral continuity' property, somewhat more general that the 'directional continuity' considered in previous work by A. Cambini and S. Querci, A. Pucci, and A. Bressan. The existence of many such selections is proved by slightly adapting an argument due to Bressan, extending it from the lower semicontinuous to the almost lower semicontinuous case, and strengthening it to yield not only directional continuity at all points but also full continuity at a specified point.  相似文献   
993.
A series of N-substituted 2-[(2-imidazolylsulfinyl)methyl]anilines (3) was synthesized and evaluated for its biological activity against gastric H+/K(+)-ATPase prepared from rabbit stomach and gastric acid secretions in Heidenhain pouch dogs. Monoalkyl substituents on the nitrogen atom of the aniline moiety markedly inhibited the enzyme activity to the same degree as omeprazole, a representative H+/K(+)-ATPase inhibitor. Most of these compounds, administered at 3 mg/kg i.v. inhibited histamine-stimulated gastric acid secretion. The inhibitory activity of these derivatives on the enzymes at pH 6.0 was more potent than that at pH 7.4, and was distinctly correlated to stability in aqueous solution at pH 5.0.  相似文献   
994.
This article is about a different representation of the geometry of the gravitational field, one in which the paths of test bodies play a crucial role. The primary concept is the geometry of the motion of a test body, and the relation between different such possible motions. Space-time as a Lorentzian manifold is regarded as a secondary construct, and it is shown how to construct it from the primary data. Some technical problems remain. Yang-Mills fields are defined by their holonomy in an analogous construction. I detail the development of this idea in the literature, and give a new version of the construction of a bundle and connection from holonomy data. The field equations of general relativity are discussed briefly in this context.  相似文献   
995.
A one-dimensional lattice random walk in the presence ofm equally spaced traps is considered. The step length distribution is a symmetric exponential. An explicit analytic expression is obtained for the probability that the random walk will be trapped at thejth trapping site.  相似文献   
996.
997.
A cosmological model is presented that produces He, C, O, D, Li, Be, and B in their observed abundances without a Big Bang. The elements are produced during the 1.5-Gy formation period of a galaxy, with C, O, and other heavy elements produced by stars of M>12 M3 , He by stars of 6 Ms<M<12 Ms, and D, Li, Be, and B by cosmic-ray reactions in a nearly pure H plasma halo. Thus, the model shows that the major elements used in astrophysical studies can be produced during galactic formation by exactly the same processes known to function today at much lower rates  相似文献   
998.
We show that the canonical embeddingC(K) →L Φ(μ) has Gaussian cotypep, where μ is a Radon probability measure onK, and Φ is an Orlicz function equivalent tot p(logt) p/2 for larget.  相似文献   
999.
Minimum conditions for the formation of surface craters by laser irradiation were studied experimentally and theoretically for various metals. The critical power density for crater formation within 20 ns was about 1011 W/m2. It is therefore concluded that crater formation by ion bombardment requires an ion current density on the order of 1010 A/m2  相似文献   
1000.
Applying tight-binding approximation and spin pairing of like charge carriers in a pair of excitons created in a lattice, the possibility of forming a bound exciton-exciton state is studied. It is found that, provided there exists strong exciton-lattice interaction, such a bound state may be formed and its energy may lie within the valence band deforming the material into a crystalline solid with no energy gap. Lowering of the energy is calculated in naphthalene and anthracene crystals where some experimental results are known. The excess energy released after the formation of such bound state can be adequate, depending on the material, to desorb neutral atoms or eject of electrons from surfaces.  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