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   638304篇
  免费   4854篇
  国内免费   1730篇
化学   309767篇
晶体学   8849篇
力学   34303篇
综合类   18篇
数学   103592篇
物理学   188359篇
  2021年   5365篇
  2020年   5815篇
  2019年   6586篇
  2018年   18633篇
  2017年   18520篇
  2016年   18016篇
  2015年   7390篇
  2014年   11419篇
  2013年   25304篇
  2012年   23090篇
  2011年   32825篇
  2010年   22674篇
  2009年   22980篇
  2008年   28003篇
  2007年   29767篇
  2006年   20085篇
  2005年   18914篇
  2004年   17887篇
  2003年   16782篇
  2002年   15787篇
  2001年   16044篇
  2000年   12424篇
  1999年   9561篇
  1998年   8395篇
  1997年   8157篇
  1996年   7633篇
  1995年   6837篇
  1994年   6784篇
  1993年   6598篇
  1992年   6934篇
  1991年   7390篇
  1990年   7077篇
  1989年   7029篇
  1988年   6773篇
  1987年   6563篇
  1986年   6318篇
  1985年   7893篇
  1984年   8358篇
  1983年   7017篇
  1982年   7327篇
  1981年   6786篇
  1980年   6459篇
  1979年   6975篇
  1978年   7289篇
  1977年   7170篇
  1976年   7083篇
  1975年   6760篇
  1974年   6622篇
  1973年   6897篇
  1972年   5059篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Mass distributions of fragments in the low-energy fission of nuclei from 187Ir to 213At have been analysed. This analysis has shown that shell effects in symmetric-mode fragment mass yields from the fission of pre-actinide nuclei could be described if one assumes the existence of two strongly deformed neutron shells in the arising fragments with neutron numbers N1 ≈ 52 and N2 ≈ 68. A new method has been proposed for quantitatively describing the mass distributions of the symmetric fission mode for pre-actinides with A ≈ 180–220.  相似文献   
102.
103.
It is shown that the exact solution of the problem of convective heat exchange in a low-Prandtl-number fluid flow (Pr ? 1) can be obtained for a two-dimensional body of arbitrary shape provided that the conformal mapping relating the body contour with a circle is known. By way of example, the Joukowsky airfoil is considered.  相似文献   
104.
A class of Hamiltonian dynamic systems integrated by the variable separation method is considered. The integration for this class is the inversion of an Abel mapping on hyperelliptic curves. We prove that the derivative of the Abel mapping is the Stäckel matrix, which determines a diagonal Riemannian metric and curvilinear orthogonal coordinate systems in a flat space. Lax representations with the spectral parameter are constructed. The corresponding classicalr-matrices are dynamic. It is shown how the class of pointwise canonical transformations can be naturally generalized using the Abel integral reduction theory.  相似文献   
105.
A model kinetic equation is constructed for the transport of a massless Bose gas. This equation is applied to solve the boundary value problem for the transport of radiation in the half-space occupied by a dispersive medium that is in local thermal equilibrium with the radiation. It is shown that the difference in temperature between the dispersive medium and the incident radiation substantially depends on the character of the scattering properties of the particles in the medium. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 111, No. 3, pp. 462–472, June, 1997.  相似文献   
106.
107.
108.
A set theory ZFI′ which does not employ the Law of the Excluded Middle φ ∀ ⊥ φ, for all φ, retians the stock of expressive capacities of the classical set theory ZF, on the one hand, and has many of the features of an effective theory on the other. In the article, a broad class of formulas σ is constructed for which ZF ⊥ σ implies ZFI′ ⊥ σ. This result provides a generalization of Friedman's theorem on AE-arithmetic formulas. Besides, we prove transfer theorems of classical logic for the case of rings; in particular, Hilbert's theorem on zeros and Artin's theorem on ordered fields are extended to the case of regular f-rings, and we bring in appropriate upper bounds for them. Supported by RFFR grant No. 93-012-1027. Translated fromAlgebra i Logika, Vol. 36, No. 3, pp. 282–303, May–June, 1997.  相似文献   
109.
We show that the modified method for finite-dimensional approximation of solutions of Fredholm integral equations of the first kind presented in this paper is more economical than traditional methods for finite-dimensional approximation. Institute of Mathematies, Ukrainian Academy of Science, Kiev. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 49, No. 2, pp. 289–295, February, 1997.  相似文献   
110.
Solutions of the dispersion equations for polariton states in finite one-dimensional crystals of arbitrary length are obtained. The appearance and evolution of the radiative and nonradiative polariton branches are traced as the length varies from two monomers to limiting values, above which the spectrum no longer undergoes significant changes. The dependences of the frequencies and radiative widths on the polariton wave vector are found for various orientations of the dipole moment of the quantum transition. The evolution of superradiance as the length of the crystal increases is traced. Some previously unknown significant features of the polariton spectrum are noted particularly the damping of the branch traditionally termed nonradiative as a consequence of emission from the end faces. Fiz. Tverd. Tela (St. Petersburg) 40, 2136–2140 (November 1998)  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