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   325328篇
  免费   2006篇
  国内免费   821篇
化学   147383篇
晶体学   5299篇
力学   17280篇
综合类   1篇
数学   49098篇
物理学   109094篇
  2020年   1787篇
  2019年   2045篇
  2018年   10959篇
  2017年   11718篇
  2016年   7692篇
  2015年   3198篇
  2014年   4077篇
  2013年   10180篇
  2012年   11635篇
  2011年   21182篇
  2010年   13452篇
  2009年   13476篇
  2008年   18637篇
  2007年   22019篇
  2006年   8438篇
  2005年   13797篇
  2004年   10067篇
  2003年   9355篇
  2002年   7412篇
  2001年   7240篇
  2000年   5664篇
  1999年   4274篇
  1998年   3607篇
  1997年   3492篇
  1996年   3463篇
  1995年   3109篇
  1994年   3038篇
  1993年   3121篇
  1992年   3225篇
  1991年   3408篇
  1990年   3155篇
  1989年   3102篇
  1988年   3159篇
  1987年   3041篇
  1986年   2875篇
  1985年   3896篇
  1984年   4109篇
  1983年   3285篇
  1982年   3495篇
  1981年   3419篇
  1980年   3314篇
  1979年   3439篇
  1978年   3534篇
  1977年   3384篇
  1976年   3511篇
  1975年   3190篇
  1974年   3196篇
  1973年   3281篇
  1972年   2274篇
  1971年   1871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