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   75549篇
  免费   5700篇
  国内免费   7245篇
化学   26606篇
晶体学   290篇
力学   6851篇
综合类   1317篇
数学   30499篇
物理学   22931篇
  2023年   643篇
  2022年   1242篇
  2021年   1367篇
  2020年   1493篇
  2019年   1777篇
  2018年   1434篇
  2017年   1696篇
  2016年   1944篇
  2015年   1734篇
  2014年   2563篇
  2013年   4954篇
  2012年   2935篇
  2011年   3414篇
  2010年   2946篇
  2009年   4157篇
  2008年   4638篇
  2007年   4805篇
  2006年   4534篇
  2005年   3804篇
  2004年   3487篇
  2003年   3565篇
  2002年   3273篇
  2001年   2772篇
  2000年   2711篇
  1999年   2431篇
  1998年   2268篇
  1997年   1862篇
  1996年   1671篇
  1995年   1456篇
  1994年   1358篇
  1993年   1150篇
  1992年   1104篇
  1991年   857篇
  1990年   721篇
  1989年   618篇
  1988年   580篇
  1987年   456篇
  1986年   386篇
  1985年   461篇
  1984年   454篇
  1983年   223篇
  1982年   366篇
  1981年   416篇
  1980年   318篇
  1979年   309篇
  1978年   229篇
  1977年   214篇
  1976年   161篇
  1974年   116篇
  1973年   106篇
排序方式: 共有10000条查询结果,搜索用时 26 毫秒
51.
Based on a semiclassical theory, investigations were made of the dynamics and spectral composition of pulsed generation with self-injection of priming radiation from the active part of a three-mirror linear resonator, the passive part of which contains an active loss modulator and serves as the output reflector of the laser. It is shown that there exists a range of resonator parameters at which pulsed lasing has virtually a single frequency irrespective of the detuning of the frequencies of the priming radiation and of the nearest eigenmode of the composite resonator. Considering graphically the phase conditions of generation, it is established that among pulsed lasers with self-injection of priming radiation which are constructed on the basis of three-mirror linear and branched resonators, the most efficient for creating single-frequency generation are those in which the length of the main resonator, where generation of the pulse occurs, is larger than the length of the additional one intended for forming the priming radiation. With an inverse ratio of the lengths of the resonators, the conditions of single-frequency pulsed generation becomes dependent on the priming radiation frequency.  相似文献   
52.
(S)-2-[2-(p-Tolylsulfinyl)phenyl]acetaldehyde reacts with different O-silylated ketenethioacetals in the presence of Yb(OTf)3 yielding β-hydroxythioesters in high yields and diastereoselectivities. The obtained compounds were readily transformed into β-hydroxyacids and their corresponding diols. These Mukaiyama aldol reactions are a direct evidence of the ability of the sulfinyl group to control 1,5- and 1,6-asymmetric induction processes.  相似文献   
53.
We consider the problem of maximizing a linear fractional function on the Pareto efficient frontier of two other linear fractional functions. We present a finite pivoting-type algorithm that solves the maximization problem while computing simultaneously the efficient frontier. Application to multistage efficiency analysis is discussed. An example demonstrating the computational procedure is included.  相似文献   
54.
Franz  H.  Asthalter  T.  Dommach  M.  Ehnes  A.  Messel  K.  Sergueev  I. 《Hyperfine Interactions》2002,141(1-4):131-134
The present status of the new nuclear resonance beamline PETRA 1 at HASYLAB, DESY, Hamburg is described. Besides an overview of the experimental setup some examples of recent experiments are given. Those cover the main applications, i.e., inelastic scattering from iron alloys and quasielastic scattering from glass-forming liquids. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
55.
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters. Received 28 July 2001  相似文献   
56.
On Quantum Team Games   总被引:2,自引:0,他引:2  
Recently Liu and Simaan (2004) convex static multi-team classical games have been introduced. Here they are generalized to both nonconvex, dynamic and quantum games. Puu's incomplete information dynamical systems are modified and applied to Cournot team game. The replicator dynamics of the quantum prisoner's dilemma game is also studied.  相似文献   
57.
58.
给出2005年全国部分高校研究生数学建模竞赛D题的研究背景,对参赛论文作了简要评注,并提供了一种参考解答.  相似文献   
59.
This primer provides a self-contained exposition of the case where spatial birth-and-death processes are used for perfect simulation of locally stable point processes. Particularly, a simple dominating coupling from the past (CFTP) algorithm and the CFTP algorithms introduced in [13], [14], and [5] are studied. Some empirical results for the algorithms are discussed. Received: 30 June 2002  相似文献   
60.
In this paper, the author studies the Laplace operator on the quaternionic Heisenberg group, construct a fundamental solution for it and use this solution to prove the Lp-boundedness and the weak (1-1) boundedness of certain singular convolution operators on the quaternionic Heisenberg group.  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