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   76188篇
  免费   1701篇
  国内免费   296篇
化学   39251篇
晶体学   499篇
力学   2214篇
综合类   36篇
数学   17815篇
物理学   18370篇
  2023年   349篇
  2022年   314篇
  2021年   514篇
  2020年   711篇
  2019年   648篇
  2018年   2102篇
  2017年   2264篇
  2016年   2438篇
  2015年   1976篇
  2014年   1866篇
  2013年   3754篇
  2012年   5803篇
  2011年   5030篇
  2010年   3540篇
  2009年   2995篇
  2008年   3046篇
  2007年   2837篇
  2006年   2602篇
  2005年   6313篇
  2004年   5538篇
  2003年   3689篇
  2002年   1843篇
  2001年   1327篇
  2000年   1191篇
  1999年   955篇
  1998年   720篇
  1997年   563篇
  1996年   680篇
  1995年   510篇
  1994年   556篇
  1993年   486篇
  1992年   671篇
  1991年   560篇
  1990年   604篇
  1989年   509篇
  1988年   494篇
  1987年   389篇
  1986年   372篇
  1985年   492篇
  1984年   450篇
  1983年   362篇
  1982年   360篇
  1981年   378篇
  1980年   308篇
  1979年   316篇
  1978年   305篇
  1977年   291篇
  1976年   358篇
  1974年   294篇
  1973年   312篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
111.
In this note we make a correction in the paper [1] by two of the authors. Specifically we modify an auxiliary localization result and prove that the applications to the saturation theory of some outstanding conservative operators remain valid. Moreover, we enrich a corollary dealing with the well-known Szász-Mirakjan operators. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
112.
The following generalization of the Hahn-Mazurkiewicz theorem is proved: Let (E,e) be a locally compact locally connected metric space. Let M be a continuum in this space and let d,e∈ M. Then there is a continuous mapping f: [0,1]→E such that f(0) = d, f(1)= e and M⊂f([0,1]). Also some corollaries of this theorem are proved.  相似文献   
113.
The crystal structure of 1-[3-(3,4-dimethoxyphenyl)-2-propenoyl]pyrrolidine (C15H19NO3) (I) has been determined by X-ray analysis. It crystallizes orthorhombic space group Pbca with a = 24.295(3), b = 15.086(3), c = 7.552(3)A, V = 2768(1)A3, Z = 8, Dcalc = 1.254 g/cm3, mu = (Mo K(alpha)) = 0.87 cm(-1). The title compound has analgesic activity of cycloaliphatic amine part. The molecule is deviated from planar configuration.  相似文献   
114.
Summary. We introduce linear semi-implicit complementary volume numerical scheme for solving level set like nonlinear degenerate diffusion equations arising in image processing and curve evolution problems. We study discretization of image selective smoothing equation of mean curvature flow type given by Alvarez, Lions and Morel ([3]). Solution of the level set equation of Osher and Sethian ([26], \[30]) is also included in the study. We prove and estimates for the proposed scheme and give existence of its (generalized) solution in every discrete time-scale step. Efficiency of the scheme is given by its linearity and stability. Preconditioned iterative solvers are used for computing arising linear systems. We present computational results related to image processing and plane curve evolution. Received April 25, 2000 / Revised version received June 11, 2001 / Published online November 15, 2001  相似文献   
115.
116.
We derive the incompressible and compressible kε model for locally homogeneous turbulence. The model is rigorously derived on formal mathematical grounds using the MPP modelling technique. This lets us calculate by either analytical or numerical means the closure constants of the model. To cite this article: T. Chacón Rebollo, D. Franco Coronil, C. R. Acad. Sci. Paris, Ser. I 337 (2003).  相似文献   
117.
We consider toy cosmological models in which a classical, homogeneous, spinor field provides a dominant or sub-dominant contribution to the energy-momentum tensor of a flat Friedmann-Robertson-Walker universe. We find that, if such a field were to exist, appropriate choices of the spinor self-interaction would generate a rich variety of behaviors, quite different from their widely studied scalar field counterparts. We first discuss solutions that incorporate a stage of cosmic inflation and estimate the primordial spectrum of density perturbations seeded during such a stage. Inflation driven by a spinor field turns out to be unappealing as it leads to a blue spectrum of perturbations and requires considerable fine-tuning of parameters. We next find that, for simple, quartic spinor self-interactions, non-singular cyclic cosmologies exist with reasonable parameter choices. These solutions might eventually be incorporated into a successful past- and future-eternal cosmological model free of singularities. In an Appendix, we discuss the classical treatment of spinors and argue that certain quantum systems might be approximated in terms of such fields.  相似文献   
118.
The multivariate model, where not only parameters of the mean value of the observation matrix, but also some other parameters occur in constraints, is considered in the paper. Some basic inference is presented under the condition that the covariance matrix is either unknown, or partially unknown, or known. Supported by the grant of the Council of Czech Republic MSM 6 198 959 214.  相似文献   
119.
We introduce and investigate the properties of Hochschild cohomology of algebras in an abelian monoidal category M. We show that the second Hochschild cohomology group of an algebra in M classifies extensions of A up to an equivalence. We characterize algebras of Hochschild dimension 0 (separable algebras), and of Hochschild dimension ≤1 (formally smooth algebras). Several particular cases and applications are included in the last section of the paper.  相似文献   
120.
We prove that directly reducible lattices and selfdual subdirectly irreducible lattices of locally finite length are determined by their sublattice-lattices. As a corollary we obtain that splitting varieties are closed under the isomorphism of sublattice-lattices iff they are selfdual. A class of selfdual non-closed varieties is given too.  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