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   48350篇
  免费   3269篇
  国内免费   2577篇
化学   22548篇
晶体学   236篇
力学   4414篇
综合类   755篇
数学   16813篇
物理学   9430篇
  2024年   83篇
  2023年   452篇
  2022年   1140篇
  2021年   1197篇
  2020年   1232篇
  2019年   1199篇
  2018年   1100篇
  2017年   1388篇
  2016年   1769篇
  2015年   1309篇
  2014年   1918篇
  2013年   3475篇
  2012年   2643篇
  2011年   2497篇
  2010年   2140篇
  2009年   2744篇
  2008年   2700篇
  2007年   3086篇
  2006年   2572篇
  2005年   2327篇
  2004年   2173篇
  2003年   1874篇
  2002年   1558篇
  2001年   1318篇
  2000年   1258篇
  1999年   1125篇
  1998年   1049篇
  1997年   955篇
  1996年   820篇
  1995年   775篇
  1994年   677篇
  1993年   546篇
  1992年   499篇
  1991年   430篇
  1990年   390篇
  1989年   247篇
  1988年   248篇
  1987年   169篇
  1986年   142篇
  1985年   176篇
  1984年   149篇
  1983年   77篇
  1982年   129篇
  1981年   81篇
  1980年   73篇
  1979年   97篇
  1978年   55篇
  1977年   34篇
  1976年   34篇
  1975年   11篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.

Harmonic mappings from the Sierpinski gasket to the circle are described explicitly in terms of boundary values and topological data. In particular, all such mappings minimize energy within a given homotopy class. Explicit formulas are also given for the energy of the mapping and its normal derivatives at boundary points.

  相似文献   

32.
A consistent quantization with a clear notion of time and evolution is given for the anisotropic Kantowski–Sachs cosmological model. It is shown that a suitable coordinate choice allows to obtain a solution of the Wheeler–DeWitt equation in the form of definite energy states, and that the results can be associated to two disjoint equivalent theories, one for each sheet of the constraint surface.  相似文献   
33.
NA列加权乘积和的完全收敛性   总被引:4,自引:0,他引:4  
本文讨论了NA和几类加权部分和及加权乘积和的完全收敛性,其中部分结果要优于iid列的已知结论。  相似文献   
34.
In this paper, the author studies the Laplace operator on the quaternionic Heisenberg group, construct a fundamental solution for it and use this solution to prove the Lp-boundedness and the weak (1-1) boundedness of certain singular convolution operators on the quaternionic Heisenberg group.  相似文献   
35.
A criterion for the nonexplosion of solutions to semilinear evolution equations on Banach spaces is proved. The result is obtained by applying a modification of the Bihari type inequality to the case of a weakly singular nonlinear integral inequality.  相似文献   
36.
Algebraic methods in quantum mechanics: from molecules to polymers   总被引:2,自引:0,他引:2  
We present a brief review of algebraic techniques developed and applied in molecular spectroscopy in the last five years. We also outline perspectives for new applications of the Lie algebraic method in the first decade of the new century. Received 21 November 2001  相似文献   
37.
环保意识调查问卷的Logistic模型   总被引:1,自引:0,他引:1  
本文应用多元统计分析中的方差分析 ,logistic模型等方法对环保意识调查问卷反馈的信息进行统计分析 ,建立被调查企业对环境保护意识的logistic模型 ,进而可对企业家的环境保护意识的好坏进行判断。  相似文献   
38.
This paper develops a modified quasi-Newton method for structured unconstrained optimization with partial information on the Hessian, based on a better approximation to the Hessian in current search direction. The new approximation is decided by both function values and gradients at the last two iterations unlike the original one which only uses the gradients at the last two iterations. The modified method owns local and superlinear convergence. Numerical experiments show that the proposed method is encouraging comparing with the methods proposed in [4] for structured unconstrained optimization Presented at the 6th International Conference on Optimization: Techniques and Applications, Ballarat, Australia, December 9–11, 2004  相似文献   
39.
The conformational properties of polymers derived from isocyanodipeptides have been investigated with a combination of model calculations, X‐ray diffraction, and circular dichroism spectroscopy. Depending on the configuration of the side chains, defined arrays of hydrogen bonds along the polymeric backbone are formed. This leads to a well‐defined conformation as, for example, expressed in the formation of lyotropic liquid‐crystalline phases and increased helical stability. Upon the disruption of the hydrogen bonds by a strong acid, a less well‐defined macromolecular conformation is observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1725–1736, 2003  相似文献   
40.
By further generalizing the skew-symmetric triangular splitting iteration method studied by Krukier, Chikina and Belokon (Applied Numerical Mathematics, 41 (2002), pp. 89–105), in this paper, we present a new iteration scheme, called the modified skew-Hermitian triangular splitting iteration method, for solving the strongly non-Hermitian systems of linear equations with positive definite coefficient matrices. We discuss the convergence property and the optimal parameters of this new method in depth. Moreover, when it is applied to precondition the Krylov subspace methods like GMRES, the preconditioning property of the modified skew-Hermitian triangular splitting iteration is analyzed in detail. Numerical results show that, as both solver and preconditioner, the modified skew-Hermitian triangular splitting iteration method is very effective for solving large sparse positive definite systems of linear equations of strong skew-Hermitian parts.  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