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   325917篇
  免费   2016篇
  国内免费   822篇
化学   147696篇
晶体学   5302篇
力学   17287篇
综合类   1篇
数学   49128篇
物理学   109341篇
  2020年   1792篇
  2019年   2047篇
  2018年   10965篇
  2017年   11725篇
  2016年   7701篇
  2015年   3200篇
  2014年   4086篇
  2013年   10230篇
  2012年   11672篇
  2011年   21210篇
  2010年   13469篇
  2009年   13494篇
  2008年   18669篇
  2007年   22041篇
  2006年   8464篇
  2005年   13815篇
  2004年   10086篇
  2003年   9367篇
  2002年   7431篇
  2001年   7252篇
  2000年   5679篇
  1999年   4286篇
  1998年   3610篇
  1997年   3495篇
  1996年   3472篇
  1995年   3117篇
  1994年   3046篇
  1993年   3129篇
  1992年   3232篇
  1991年   3408篇
  1990年   3158篇
  1989年   3105篇
  1988年   3161篇
  1987年   3048篇
  1986年   2878篇
  1985年   3903篇
  1984年   4114篇
  1983年   3289篇
  1982年   3501篇
  1981年   3422篇
  1980年   3319篇
  1979年   3442篇
  1978年   3538篇
  1977年   3387篇
  1976年   3513篇
  1975年   3193篇
  1974年   3202篇
  1973年   3290篇
  1972年   2275篇
  1971年   1873篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
不等式约束优化问题的一个势函数   总被引:1,自引:1,他引:0  
基于Carroll(1961)建立的罚函数,本文给出了不等式约束优化问题的一个势函数,并且讨论了该函数的性质.最后证明了在此基础上建立的对偶算法具有Q-线性收敛性.  相似文献   
992.
993.
A new mechanism of pulsed laser oscillation based on ion-ion recombination is proposed. The advantages of utilizing this mechanism in a pulsed mode are considered, and the expected characteristics of the proposed lasers are estimated.  相似文献   
994.
Port cities where marine cargo terminals are located are generally near urban areas characterized by high-congestion road traffic. Changes in cargo traffic volumes into a marine terminal, or in the surrounding traffic arteries, which carry this traffic, can significantly affect the terminal's operations. Conversely, activity at the terminal can have an impact on the traffic levels and congestion for a considerable distance from the terminal. This paper demonstrates a methodology useful for studying the impact of road traffic flows on marine container terminals located in highly congested areas. This model was developed at the request of the Virginia Center for World Trade and was used to answer three planning questions in the port of Hampton Roads, Virginia, USA-what would be the impact of: opening a new section of interstate highway, a projected doubling of container traffic at one terminal, and a daily unit train in the vicinity of another terminal. The problem was made more challenging by limited data-collection funds. None the less, the model was deemed valid by a panel of traffic experts and officials from several major state and private agencies involved in marine traffic management. The model results were subsequently a factor in two major decisions related to terminal management.  相似文献   
995.
Possible orders and subgraphs of the fixed points of a distance-regular graph with the intersection array {8, 7, 5; 1, 1, 4} are found. It is shown that such a graph is not vertex-transitive.  相似文献   
996.
In part I of the paper, we have defined n-dimensional C0-manifolds in ℝn(m ≥ n) with locally-finite n-dimensional variations (a generalization of locally-rectifiable curves to dimensionn > 1) and integration of measurable differential n-forms over such manifolds. The main result of part II states that an n-dimensional manifold that is C1-embedded into ℝm has locally-finite variations and the integral of a measurable differential n-form defined in part I can be calculated by the well-known formula. Bibliography: 5 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 333, 2006, pp. 66–85.  相似文献   
997.
998.
999.
The instability of the rectilinear form of parallel weakly interacting dislocations, manifesting itself in their spontaneous wave-like bending, has been investigated. It is shown that softening of a crystal leads to the enhancement of this instability.  相似文献   
1000.
The coupling of visible nanosecond laser pulses to metallic targets irradiated in vacuum is studied. The expressions of the vapour and plasma ignition times are obtained. Two cases for vapour breakdown in the plasma ignition process are considered. The first case is that 40 generations of new electrons are born in vapour generation time before plasma formation as assumed in the literature. The second case is that 10 generations of new electrons are born in vapour generation time. Molybdenum (Mo), niobium (Nb) and aluminium (Al) targets are considered for illustrations of our results. The expression of the plasma ignition time for the Al target is substantially different from that reported in the literature. The vapour and plasma ignition threshold laser intensities are calculated and compared with those reported in the literature. Reasons for disagreement are discussed. The plasma ignition threshold estimated in the second case is noted to be in good agreement with the reported experimental result.  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