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   471550篇
  免费   4395篇
  国内免费   2280篇
化学   241096篇
晶体学   6528篇
力学   22714篇
综合类   67篇
数学   76143篇
物理学   131677篇
  2020年   3410篇
  2019年   3778篇
  2018年   15013篇
  2017年   14855篇
  2016年   12963篇
  2015年   5225篇
  2014年   7033篇
  2013年   17015篇
  2012年   16830篇
  2011年   26088篇
  2010年   16870篇
  2009年   17011篇
  2008年   21518篇
  2007年   23709篇
  2006年   14740篇
  2005年   14465篇
  2004年   13268篇
  2003年   12455篇
  2002年   11348篇
  2001年   11501篇
  2000年   9072篇
  1999年   6616篇
  1998年   5643篇
  1997年   5642篇
  1996年   5519篇
  1995年   4667篇
  1994年   4775篇
  1993年   4676篇
  1992年   5029篇
  1991年   5126篇
  1990年   4862篇
  1989年   4780篇
  1988年   4640篇
  1987年   4572篇
  1986年   4534篇
  1985年   5881篇
  1984年   6081篇
  1983年   4968篇
  1982年   5412篇
  1981年   5125篇
  1980年   4755篇
  1979年   5126篇
  1978年   5379篇
  1977年   5413篇
  1976年   5423篇
  1975年   5032篇
  1974年   5162篇
  1973年   5321篇
  1972年   3912篇
  1967年   3233篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Cleavage near microhardness indentations on the surface of corundum is found to appear long (20–30 days) after unloading.  相似文献   
922.
In this paper, we present an explicit calculation of the heat kernel, fundamental solution and Schwartz kernel of the resolvent for the Heisenberg Laplacian using Wiener path integrals and their realizations via the Trotter product formula. This also gives another derivation of mehler’s formula.  相似文献   
923.
Water molecule mobility in ion-containing and nonionic aqueous solutions of β-cyclodextrin was studied by quasielastic neutron scattering (QENS). The total self-diffusion coefficients and their components corresponding to the contributions from collective (Lagrange type) and single-particle (jump diffusion) parts of molecular motions were determined. From the data obtained, one can conclude that the molecular mobility of free water in nonionic aqueous solutions of β-cyclodextrin with guest molecules (2-aminopyridine) proceeds by a single-particle mechanism. The addition of Pb2+ ions into the solution leads to increase in self-diffusion coefficients and growth of a bound water fraction.  相似文献   
924.
925.
Leibniz agebras are a generalization of Lie algebras, where no symmetry properties of the bracket are required. In this Letter we introduce a notion of R-matrices for this structure and the related Yang–Baxter equations, and discuss some of their basic properties.  相似文献   
926.
Nonuniform distributions of the order parameter in a film of an incommensurate ferroelectric whose free energy expansion does not contain Lifshitz invariants are considered. An equation describing the order parameter distribution over the film thickness is derived in the approximation of slowly varying amplitudes. The effect of film thickness and surface properties on the temperature of transition to the incommensurate phase is analyzed.  相似文献   
927.
An “almost diagonal” reduced density matrix (in coordinate representation) is usually a result of environment induced decherence and is considered the sign of classical behavior. We show that the proton of a ground state hydrogen atom can indeed possess such a density matrix. This example demonstrates that the “almost diagonal” structure may be derived from an interaction with a low number of degrees of freedom which play the role of the environment. We also show that decoherence effects in our example can only be observed if the interaction with the measuring device is significantly faster than the interaction with the environment (the electron). In the opposite case, when the interaction with the environment is significant during the measurement process, coherence is maintained. Finally, we propose a neutron scattering experiment on cold He atoms to observe decoherence which shows up as an additional positive contribution to the differential scattering cross section. This contribution is inversely proportional to the bombarding energy.  相似文献   
928.
929.
930.
The Beam Mode Expansion (BME) approach for corrugated conical feed horn plus meniscus lens is presented. This approach is useful for providing the radiation pattern as it propagates through an optical system. A developed theoretical model has been verified measuring near and far field of a built horn and lens. These results have been used for designing the optical system of a Cassegrain antenna at 100GHz using the fundamental Gaussian beam mode (GBM) of the new approach. Multimode analysis has been performed with the pre-designed system in order to test the fundamental GBM results.  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