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   3761篇
  免费   306篇
  国内免费   398篇
化学   1165篇
晶体学   8篇
力学   54篇
综合类   88篇
数学   2703篇
物理学   447篇
  2024年   4篇
  2023年   46篇
  2022年   80篇
  2021年   126篇
  2020年   105篇
  2019年   123篇
  2018年   134篇
  2017年   133篇
  2016年   143篇
  2015年   79篇
  2014年   211篇
  2013年   385篇
  2012年   167篇
  2011年   222篇
  2010年   170篇
  2009年   222篇
  2008年   225篇
  2007年   257篇
  2006年   213篇
  2005年   205篇
  2004年   172篇
  2003年   163篇
  2002年   141篇
  2001年   99篇
  2000年   107篇
  1999年   90篇
  1998年   96篇
  1997年   54篇
  1996年   65篇
  1995年   39篇
  1994年   33篇
  1993年   24篇
  1992年   17篇
  1991年   15篇
  1990年   7篇
  1989年   16篇
  1988年   11篇
  1987年   10篇
  1986年   3篇
  1985年   18篇
  1984年   8篇
  1983年   2篇
  1982年   3篇
  1981年   3篇
  1980年   7篇
  1979年   3篇
  1978年   2篇
  1976年   3篇
  1959年   1篇
  1936年   1篇
排序方式: 共有4465条查询结果,搜索用时 31 毫秒
11.
期货经纪公司保证金的一种确定方法   总被引:1,自引:0,他引:1  
本文基于马尔可夫链在存储论中的应用,结合Ergodic定理,得到确定期货经纪公司保证金的Ergodic模型,即一个双目标规划问题,然后应用乘积最大化准则,将该模型转化为单目标规划问题来求解。该方法考虑期货经纪公司承担的风险和对投资者的吸引程度,为保证金的确定提供新的思路。  相似文献   
12.
Let H and K be indefinite inner product spaces. This paper shows that a bijective map φ:B(H)→B(K) satisfies φ(AB B A) =φ(A)φ(5) φ(B) φ(A) for every pair A,B ∈B(H) if and only if either φ(A) = cU AU for all A or φ(A) = cUA U for all A; φsatisfies φ(AB A) = φ(A)φ(B) φ(A) for every pair A,B ∈B(H) if and only if either φ(A) = UAV for all A or φ(A) = UA V for all A, where A denotes the indefinite conjugate of A, U and V are bounded invertible linear or conjugate linear operators with U U = c-1I and V V = cI for some nonzero real number c.  相似文献   
13.
Defining speed of diffusion as the amount of time it takes to get from one penetration level to a higher one, we introduce a dynamic model in which we study the link between pricing policy, speed of diffusion, and number of competitors in the market. Our analysis shows that, in the case of strategic (oligopolistic) competition, the speed of diffusion has an important influence on the optimal pricing policy. In particular, we find that higher speeds of diffusion create an incentive to strategically interacting firms to lower their prices.  相似文献   
14.
A laser system containing four CW Nd:YAG double-rod lasers, transforming optics and a fibre with input-output optics has been designed and investigated. It is shown that reduction of the beam parameter product of the non-Gaussian beams in the image space of the lens has made it possible to collect the emission of four lasers to the same fibre. Independent laser operation has provided the output power control in the range of 10–900 W with a stable light spot size on the input end of the fibre.  相似文献   
15.
This paper presents a unified analysis of decomposition algorithms for continuously differentiable optimization problems defined on Cartesian products of convex feasible sets. The decomposition algorithms are analyzed using the framework of cost approx imation algorithms. A convergence analysis is made for three decomposition algorithms: a sequential algorithm which extends the classical Gauss-Seidel scheme, a synchronized parallel algorithm which extends the Jacobi method, and a partially asynchronous parallel algorithm. The analysis validates inexact computations in both the subproblem and line search phases, and includes convergence rate results. The range of feasible step lengths within each algorithm is shown to have a direct correspondence to the increasing degree of parallelism and asynchronism, and the resulting usage of more outdated information in the algorithms.  相似文献   
16.
Summary It is shown that the outer automorphism group of a Coxeter groupW of finite rank is finite if the Coxeter graph contains no infinite bonds. A key step in the proof is to show that if the group is irreducible andΠ 1 andΠ 2 any two bases of the root system ofW, thenΠ 2 = ±ωΠ 1 for some ω εW. The proof of this latter fact employs some properties of the dominance order on the root system introduced by Brink and Howlett. This article was processed by the author using the Springer-Verlag TEX PJour1g macro package 1991.  相似文献   
17.
THE RADICALS OF HOPF MODULE ALGEBRAS   总被引:1,自引:0,他引:1  
THERADICALSOFHOPFMODULEALGEBRASZHANGSHOUCHUAN*AbstractThecharacterizationofH-primeradicalisgiveninmanyways.Meantime,therelati...  相似文献   
18.
We consider the question of factorizability in tensor product spaces, and argue that the correlations associated with entangled states are even more problematic in the general case involving any tensor product of Hilbert spaces, than in the Einstein, Podolsky, and Rosen case with only two [1].  相似文献   
19.
Let G be a graph and let Pm(G) denote the number of perfect matchings of G.We denote the path with m vertices by Pm and the Cartesian product of graphs G and H by G×H. In this paper, as the continuance of our paper [W. Yan, F. Zhang, Enumeration of perfect matchings of graphs with reflective symmetry by Pfaffians, Adv. Appl. Math. 32 (2004) 175-188], we enumerate perfect matchings in a type of Cartesian products of graphs by the Pfaffian method, which was discovered by Kasteleyn. Here are some of our results:1. Let T be a tree and let Cn denote the cycle with n vertices. Then Pm(C4×T)=∏(2+α2), where the product ranges over all eigenvalues α of T. Moreover, we prove that Pm(C4×T) is always a square or double a square.2. Let T be a tree. Then Pm(P4×T)=∏(1+3α2+α4), where the product ranges over all non-negative eigenvalues α of T.3. Let T be a tree with a perfect matching. Then Pm(P3×T)=∏(2+α2), where the product ranges over all positive eigenvalues α of T. Moreover, we prove that Pm(C4×T)=[Pm(P3×T)]2.  相似文献   
20.
连通图的离散度是用s(G)来表示的,s(G)=max{ω(G-S)-|S|:ω(G-S)>1,SV(G)}.给出了两个完全图乘积的和一个完全图与路的乘积的离散度.还给出了两个完全图乘积的坚韧度.  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