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   2483篇
  免费   132篇
  国内免费   139篇
化学   294篇
晶体学   2篇
力学   55篇
综合类   33篇
数学   2053篇
物理学   317篇
  2024年   3篇
  2023年   29篇
  2022年   27篇
  2021年   30篇
  2020年   50篇
  2019年   78篇
  2018年   73篇
  2017年   68篇
  2016年   86篇
  2015年   40篇
  2014年   95篇
  2013年   262篇
  2012年   74篇
  2011年   115篇
  2010年   83篇
  2009年   157篇
  2008年   156篇
  2007年   134篇
  2006年   137篇
  2005年   123篇
  2004年   100篇
  2003年   85篇
  2002年   93篇
  2001年   74篇
  2000年   87篇
  1999年   67篇
  1998年   65篇
  1997年   59篇
  1996年   43篇
  1995年   27篇
  1994年   25篇
  1993年   29篇
  1992年   21篇
  1991年   11篇
  1990年   12篇
  1989年   9篇
  1988年   13篇
  1987年   18篇
  1986年   13篇
  1985年   14篇
  1984年   12篇
  1983年   4篇
  1982年   7篇
  1981年   8篇
  1980年   9篇
  1979年   6篇
  1978年   7篇
  1977年   6篇
  1976年   3篇
  1974年   3篇
排序方式: 共有2754条查询结果,搜索用时 15 毫秒
61.
一类特殊分块矩阵为循环矩阵的循环分块矩阵的几个性质   总被引:3,自引:0,他引:3  
毛纲源 《应用数学》1995,8(3):311-316
本文给出一类特殊分块矩阵为循环矩阵的循环分块矩阵的几个性质。  相似文献   
62.
Bool阵的逆阵     
We give a characterization of a regular Boolean matrix and prove that AB = I Implies that BA = I, where A and B are Boolean matrices whose elements belong to a Boolean algebra of a set with more than two elements.  相似文献   
63.
It is known that the algebra of Schur operators on ?2 (namely operators bounded on both ?1 and ?) is not inverse-closed. When ?2=?2(X) where X is a metric space, one can consider elements of the Schur algebra with certain decay at infinity. For instance if X has the doubling property, then Q. Sun has proved that the weighted Schur algebra Aω(X) for a strictly polynomial weight ω is inverse-closed. In this paper, we prove a sharp result on left-invertibility of the these operators. Namely, if an operator AAω(X) satisfies ‖Afp?‖fp, for some 1?p?∞, then it admits a left-inverse in Aω(X). The main difficulty here is to obtain the above inequality in ?2. The author was both motivated and inspired by a previous work of Aldroubi, Baskarov and Krishtal (2008) [1], where similar results were obtained through different methods for X=Zd, under additional conditions on the decay.  相似文献   
64.
Compound matrices are encountered in many fields such as Matrix Theory, Systems Theory, Control Theory, etc. In the present paper we develop an efficient algorithm computing the Smith normal form of compound matrices. This algorithm is based on a new theorem establishing an equivalence relation between the Smith normal form of the compounds of a given matrix and the compounds of the Smith normal form of the given matrix. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
65.
Asymptotic chi-squared test statistics for testing the equality of moment vectors are developed. The test statistics proposed are generalized Wald test statistics that specialize for different settings by inserting an appropriate asymptotic variance matrix of sample moments. Scaled test statistics are also considered for dealing with nonstandard conditions. The specialization will be carried out for testing the equality of multinomial populations, and the equality of variance and correlation matrices for both normal and nonnormal data. When testing the equality of correlation matrices, a scaled version of the normal theory chi-squared statistic is proven to be an asymptotically exact chi-squared statistic in the case of elliptical data.  相似文献   
66.
We investigate the parameter dynamics of eigenvalues of Hamiltonians (‘level dynamics’) defined on symmetric spaces relevant to condensed matter and particle physics. In particular we: (1) identify the appropriate reduced manifold on which the motion takes place, (2) identify the correct Poisson structure ensuring the Hamiltonian character of the reduced dynamics, (3) determine the canonical measure on the reduced space, (4) calculate the resulting eigenvalue density.  相似文献   
67.
从提高灵敏度角度出发,理论上分析了无电极电光电场传感器电极长度与灵敏度和带宽的关系.通过比较不同结构的传输函数,验证平衡检测方式的可行性,最后选取使用平衡检测的三端口结构作为实验器件结构,从而为器件制作的可行性方案从理论上作了验证.  相似文献   
68.
Given a data matrix, we find its nearest symmetric positive-semidefinite Toeplitz matrix. In this paper, we formulate the problem as an optimization problem with a quadratic objective function and semidefinite constraints. In particular, instead of solving the so-called normal equations, our algorithm eliminates the linear feasibility equations from the start to maintain exact primal and dual feasibility during the course of the algorithm. Subsequently, the search direction is found using an inexact Gauss-Newton method rather than a Newton method on a symmetrized system and is computed using a diagonal preconditioned conjugate-gradient-type method. Computational results illustrate the robustness of the algorithm.  相似文献   
69.
首先将常用类型的模糊矩阵都纳入到了二阶占优模糊矩阵的统一框架之内,然后利用模糊矩阵的有向伴随图,指出了强连通布尔矩阵振荡的一个充要条件,依次证明了强连通的二阶占优布尔矩阵的振荡指数为2n-2,非强连通的二阶占优布尔矩阵的振荡指数为3n-4.  相似文献   
70.
For matrices whose eigenvalues are real (such as Hermitian or real symmetric matrices), we derive simple explicit estimates for the maximal (λmax) and the minimal (λmin) eigenvalues in terms of determinants of order less than 3. For 3 × 3 matrices, we derive sharper estimates, which use det A but do not require to solve cubic equations.  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