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   96337篇
  免费   3601篇
  国内免费   2673篇
化学   37151篇
晶体学   945篇
力学   7738篇
综合类   118篇
数学   34403篇
物理学   22256篇
  2024年   86篇
  2023年   429篇
  2022年   645篇
  2021年   720篇
  2020年   849篇
  2019年   773篇
  2018年   10958篇
  2017年   10739篇
  2016年   6935篇
  2015年   1785篇
  2014年   1373篇
  2013年   1756篇
  2012年   5391篇
  2011年   12094篇
  2010年   6769篇
  2009年   7050篇
  2008年   7739篇
  2007年   9748篇
  2006年   1174篇
  2005年   2154篇
  2004年   2198篇
  2003年   2545篇
  2002年   1675篇
  2001年   786篇
  2000年   722篇
  1999年   578篇
  1998年   530篇
  1997年   453篇
  1996年   524篇
  1995年   405篇
  1994年   306篇
  1993年   255篇
  1992年   217篇
  1991年   220篇
  1990年   172篇
  1989年   152篇
  1988年   112篇
  1987年   113篇
  1986年   128篇
  1985年   93篇
  1984年   74篇
  1983年   62篇
  1982年   56篇
  1981年   49篇
  1980年   50篇
  1979年   45篇
  1914年   45篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Malmquist indexes can be used to estimate technical change over time. The index generally represents the average effect of technical change on all outputs in a multi-output firm. However, changes in technology do not necessarily affect all outputs involved in the analysis equally. In this paper, a method for estimating the effect of technical change on each of the different outputs is proposed. This estimation is done by a modification of quasi-Malmquist indexes. An artificial data set has been used to validate the method proposed in this paper.  相似文献   
72.
Siaw-Lynn Ng 《Order》2004,21(1):1-5
We present a characterisation of posets of size n with linear discrepancy n − 2. These are the posets that are “furthest” from a linear order without being an antichain. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   
73.
74.
We will prove a result concerning the inclusion of non-trivial invariant ideals inside non-trivial ideals of a twisted crossed product. We will also give results concerning the primeness and simplicity of crossed products of twisted actions of locally compact groups on -algebras. Received: 25 January 2002; in final form: 22 May 2002/Published online: 2 December 2002 This work is partially supported by Hong Kong RGC Direct Grant.  相似文献   
75.
The influence of the sample orientation on the effective value of the hydrostatic piezoelectric coefficients d h (i) of Sn2P2S6 crystals has been studied. The hydrostatic piezoelectric coefficients d h (1) and d′ h (3) , were measured, d h (1) =(244±3) pC/N and d′ h (3) =(92±1) pC/N. The hydrostatic piezoelectric coefficient d h (3) for orthogonal axis system was calculated to be d h (3) =(87±2) pC/N. The, optimal orientation of the sample has been found as (Xy l)−20°-cut. Maximal value of the effective hydrostatic piezoelectric coefficient d h (1) equals 260 pC/N. Double rotated samples were also studied. The orientation of the samples insensitive to the pressure has been found. The theoretical mean value of hydrostatic piezoelectric coefficient (d h ) mean corresponding to randomly oriented Sn2P2S6 grains in a poled composite has been calculated to be (d h ) mean =136 pC/N.  相似文献   
76.
In this paper we find homological restrictions on Lagrangians in cotangent bundles of spheres and Lens spaces. This research was supported by the Israel Science Foundation (grand No. 205/02).  相似文献   
77.
Scheduling the production of several items requires the determination of production quantities in different periods in the presence of resource constraints. Several approximate and heuristic algorithms have been proposed to solve this problem. However, no method for finding an optimal solution has as yet been developed. It is shown that the problem may be solved advantageously using Benders' decomposition. The subproblem in Benders' decomposition is shown to be a transportation problem, and some strategies for solving the master problem are indicated. The paper concludes with a sample problem demonstrating the application of the method.  相似文献   
78.
Summary Let Fq be a finite field with q elements. We consider formal Laurent series of Fq -coefficients with their continued fraction expansions by Fq -polynomials. We prove some arithmetic properties for almost every formal Laurent series with respect to the Haar measure. We construct a group extension of the non-archimedean continued fraction transformation and show its ergodicity. Then we get some results as an application of the individual ergodic theorem. We also discuss the convergence rate for limit behaviors.  相似文献   
79.
关于具有给定Sylow子群正规化子的有限群Ⅱ   总被引:1,自引:0,他引:1  
郭文彬 《数学学报》1996,39(4):509-513
本文在有限可解群中解决了:任意m-秩≤2的子群闭的局部群系具有性质:“如果群G的非单位Sylow子群的正规化子属于,则群G也属于的一个充分必要条件.  相似文献   
80.
We study boundary value problems for the time-harmonic form of the Maxwell equations, as well as for other related systems of equations, on arbitrary Lipschitz domains in the three-dimensional Euclidean space. The main goal is to develop the corresponding theory for Lp-integrable bounday data for optimal values of p's. We also discuss a number of relevant applications in electromagnetic scattering.  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