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   148001篇
  免费   12685篇
  国内免费   7639篇
化学   73149篇
晶体学   1389篇
力学   11031篇
综合类   310篇
数学   39404篇
物理学   43042篇
  2024年   279篇
  2023年   1601篇
  2022年   2727篇
  2021年   2872篇
  2020年   3112篇
  2019年   2914篇
  2018年   12309篇
  2017年   11958篇
  2016年   9239篇
  2015年   4274篇
  2014年   4412篇
  2013年   5596篇
  2012年   10304篇
  2011年   16735篇
  2010年   9856篇
  2009年   9979篇
  2008年   10887篇
  2007年   12547篇
  2006年   3949篇
  2005年   4383篇
  2004年   3886篇
  2003年   3818篇
  2002年   2718篇
  2001年   1705篇
  2000年   1642篇
  1999年   1681篇
  1998年   1490篇
  1997年   1432篇
  1996年   1483篇
  1995年   1164篇
  1994年   994篇
  1993年   855篇
  1992年   726篇
  1991年   641篇
  1990年   550篇
  1989年   442篇
  1988年   393篇
  1987年   331篇
  1986年   306篇
  1985年   250篇
  1984年   185篇
  1983年   138篇
  1982年   121篇
  1981年   105篇
  1980年   111篇
  1979年   77篇
  1978年   64篇
  1977年   58篇
  1976年   46篇
  1973年   53篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Courses which teach discrete-event simulation are based on many different simulation languages. The requirements for a language to support teaching simulation are discussed. In particular, it is recommended that such languages separate into distinct modules those aspects of simulation which are taught as separate topics. Implementation of the separation is discussed. The SEESIM language, developed as a teaching aid, is described, and examples of its use are given. Straightforward use of SEESIM can be learned quickly, yet the language provides facilities for a staged introduction to advanced concepts of simulation.  相似文献   
12.
We give the estimate for the growth of the group Fourier transforms of the Hardy spaces and establish and Hp-multipleir theorem satisfying Michlin condition on the Heisenberg group.  相似文献   
13.
Fractional factorial split-plot (FFSP) designs have an important value of investigation for their special structures. There are two types of factors in an FFSP design: the whole-plot (WP) factors and sub-plot (SP) factors, which can form three types of two-factor interactions: WP2fi, WS2fi and SP2fi. This paper considers FFSP designs with resolution III or IV under the clear effects criterion. It derives the upper and lower bounds on the maximum numbers of clear WP2fis and WS2fis for FFSP designs, and gives some methods for constructing the desired FFSP designs. It further examines the performance of the construction methods.  相似文献   
14.
15.
We consider complete ideals supported on finite sequences of infinitely near points, in regular local rings with dimensions greater than two. We study properties of factorizations in Lipman special *-simple complete ideals. We relate it to a type of proximity, linear proximity, of the points, and give conditions in order to have unique factorization. Several examples are presented. Received: 2 February 2000 / in final form: 14 March 2001 / Published online: 18 January 2002  相似文献   
16.
17.
The principal physics goals of the Compact Muon Solenoid experiment under construction at the Large Hadron Collider at CERN in Geneva are reviewed. Procedures to search for the Standard Model Higgs boson, supersymmetric Higgses and other supersymmetric particles are described.  相似文献   
18.
Analysis of the field distributions in a single biological cell under electromagnetic wave is given. With Debye approximation, the dielectric relaxation of each part of the cell, including the extracellular and cellular media, the cell membrane and the nuclear membrane, was taken into account. Making use of some typical parameters for a cell, the voltage across nuclear and cytoplasma membranes under electromagnetic waves are calculated up to millimeter wave frequency range. The calculated result indicates that it is unlikely to generate electroporation by present available millimeter wave sources.  相似文献   
19.
In this paper, we consider a class of functional equations and prove three theorems which give the approximation properties and error estimates of the optimal polynomial approximation of slution of those functional equations.  相似文献   
20.
This paper proposes two constructive heuristics for the well-known single-level uncapacitated dynamic lot-sizing problem. The proposed heuristics, called net least period cost (nLPC) and nLPC(i), are developed by modifying the average period cost concept from Silver and Meal's heuristic, commonly known as least period cost (LPC). An improved tie-breaking stopping rule and a locally optimal decision rule are proposed in the second heuristic to enhance performance. We test the effectiveness of the proposed heuristics by using 20 benchmarking test problems frequently used in the literature. Furthermore, we perform a large-scale simulation study involving three factors, 50 experimental conditions, and 100?000 randomly generated problems to evaluate the proposed heuristics against LPC and six other well-known constructive heuristics in the literature. The simulation results show that both nLPC and nLPC(i) produce average holding and setup costs lower than or equal to those of LPC in every one of the 50 experimental conditions. The proposed heuristics also outperform each of the six other heuristics evaluated in all experimental conditions, without an increase in computational requirements. Lastly, considering that both nLPC and nLPC(i) are fairly simple for practitioners to understand and that lot-sizing heuristics have been commonly used in practice, there should be a very good chance for practical applications of the proposed heuristics.  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