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   7571篇
  免费   700篇
  国内免费   602篇
化学   504篇
晶体学   6篇
力学   509篇
综合类   118篇
数学   5627篇
物理学   2109篇
  2024年   8篇
  2023年   63篇
  2022年   91篇
  2021年   90篇
  2020年   153篇
  2019年   168篇
  2018年   155篇
  2017年   182篇
  2016年   207篇
  2015年   166篇
  2014年   305篇
  2013年   643篇
  2012年   349篇
  2011年   418篇
  2010年   353篇
  2009年   470篇
  2008年   507篇
  2007年   497篇
  2006年   502篇
  2005年   389篇
  2004年   348篇
  2003年   343篇
  2002年   327篇
  2001年   264篇
  2000年   254篇
  1999年   254篇
  1998年   209篇
  1997年   155篇
  1996年   151篇
  1995年   90篇
  1994年   98篇
  1993年   76篇
  1992年   59篇
  1991年   49篇
  1990年   54篇
  1989年   36篇
  1988年   48篇
  1987年   30篇
  1986年   26篇
  1985年   47篇
  1984年   42篇
  1983年   24篇
  1982年   37篇
  1981年   23篇
  1980年   20篇
  1979年   24篇
  1978年   13篇
  1977年   17篇
  1976年   11篇
  1974年   9篇
排序方式: 共有8873条查询结果,搜索用时 15 毫秒
1.
2.
This paper is dedicated to studying the following Schrödinger–Poisson system Δ u + V ( x ) u K ( x ) ϕ | u | 3 u = a ( x ) f ( u ) , x 3 , Δ ϕ = K ( x ) | u | 5 , x 3 . Under some different assumptions on functions V(x), K(x), a(x) and f(u), by using the variational approach, we establish the existence of positive ground state solutions.  相似文献   
3.
4.
5.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data.  相似文献   
6.
周晓林  刘科  陈向荣  朱俊 《中国物理》2006,15(12):3014-3018
We employ a first-principles plane wave method with the relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter (HGH) scheme in the frame of DFT to calculate the equilibrium lattice parameters and the thermodynamic properties of AlB2 compound with hcp structure. The obtained lattice parameters are in good agreement with the available experimental data and those calculated by others. Through the quasi-harmonic Debye model, obtained successfully are the dependences of the normalized lattice parameters a/a0 and c/c0 on pressure P, the normalized primitive cell volume V/V0 on pressure P, the variation of the thermal expansion α with pressure P and temperature T, as well as the Debye temperature \ThetaD and the heat capacity CV on pressure P and temperature T.  相似文献   
7.
An orthogonal system of rational functions is discussed. Some inverse inequalities, imbedding inequalities and approximation results are obtained. Two model problems are considered. The stabilities and convergences of proposed rational spectral schemes and rational pseudospectral schemes are proved. The techniques used in this paper are also applicable to other problems on the whole line. Numerical results show the efficiency of this approach.  相似文献   
8.
Formalization for problems of multicriteria decision making under uncertainty is constructed in terms of guaranteed and weak estimates. A relevant definition of the vector maximinimax value is given. Parameterization and approximation of maximum, minimax, and maximinimax values based on the inverse logical convolution are suggested. An application for multicommodity networks is considered. Received: December 13, 2000 / Accepted: August 21, 2001?Published online May 8, 2002  相似文献   
9.
10.
This paper is concerned with the implementation and testing of an algorithm for solving constrained least-squares problems. The algorithm is an adaptation to the least-squares case of sequential quadratic programming (SQP) trust-region methods for solving general constrained optimization problems. At each iteration, our local quadratic subproblem includes the use of the Gauss–Newton approximation but also encompasses a structured secant approximation along with tests of when to use this approximation. This method has been tested on a selection of standard problems. The results indicate that, for least-squares problems, the approach taken here is a viable alternative to standard general optimization methods such as the Byrd–Omojokun trust-region method and the Powell damped BFGS line search method.  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