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   113338篇
  免费   5793篇
  国内免费   3995篇
化学   48990篇
晶体学   1125篇
力学   8765篇
综合类   241篇
数学   35818篇
物理学   28187篇
  2024年   111篇
  2023年   759篇
  2022年   1224篇
  2021年   1400篇
  2020年   1443篇
  2019年   1330篇
  2018年   11298篇
  2017年   11064篇
  2016年   7511篇
  2015年   2445篇
  2014年   2280篇
  2013年   2868篇
  2012年   6935篇
  2011年   13423篇
  2010年   7659篇
  2009年   7948篇
  2008年   8666篇
  2007年   10568篇
  2006年   2033篇
  2005年   2807篇
  2004年   2784篇
  2003年   2918篇
  2002年   1889篇
  2001年   974篇
  2000年   973篇
  1999年   978篇
  1998年   880篇
  1997年   777篇
  1996年   898篇
  1995年   714篇
  1994年   623篇
  1993年   562篇
  1992年   501篇
  1991年   426篇
  1990年   373篇
  1989年   294篇
  1988年   274篇
  1987年   255篇
  1986年   198篇
  1985年   202篇
  1984年   178篇
  1983年   152篇
  1982年   121篇
  1981年   97篇
  1980年   96篇
  1979年   77篇
  1978年   60篇
  1976年   43篇
  1975年   47篇
  1914年   45篇
排序方式: 共有10000条查询结果,搜索用时 0 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.
In this paper, two classes of closely related multilinear singular and fractional integrals,which include the commutators as special cases, are studied and their boundedness on Herz type spaces is discussed. In fact, it is proved that these operators are actually not bounded in certain extreme cases.  相似文献   
79.
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   
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