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   125175篇
  免费   2394篇
  国内免费   392篇
化学   55405篇
晶体学   1004篇
力学   8101篇
数学   38796篇
物理学   24655篇
  2023年   392篇
  2022年   307篇
  2021年   521篇
  2020年   698篇
  2019年   672篇
  2018年   11066篇
  2017年   10736篇
  2016年   7417篇
  2015年   2274篇
  2014年   1752篇
  2013年   3359篇
  2012年   7130篇
  2011年   13558篇
  2010年   7513篇
  2009年   7546篇
  2008年   9349篇
  2007年   11402篇
  2006年   2876篇
  2005年   3854篇
  2004年   3733篇
  2003年   3734篇
  2002年   2560篇
  2001年   1165篇
  2000年   1065篇
  1999年   704篇
  1998年   603篇
  1997年   524篇
  1996年   675篇
  1995年   421篇
  1994年   432篇
  1993年   453篇
  1992年   442篇
  1991年   401篇
  1990年   374篇
  1989年   371篇
  1988年   319篇
  1987年   321篇
  1986年   286篇
  1985年   445篇
  1984年   407篇
  1983年   284篇
  1982年   383篇
  1981年   364篇
  1980年   345篇
  1979年   334篇
  1978年   309篇
  1976年   301篇
  1975年   267篇
  1974年   267篇
  1973年   272篇
排序方式: 共有10000条查询结果,搜索用时 445 毫秒
941.
The angular distributions of the (p, d), (d, t) and(3He, ) reactions on13C have been analysed within the framework of DWBA in which additional information on nuclear vertex constants was introduced. Although all these reactions seem to be similar single nucleon transfer, their mechanism is shown to be quite different and so is the information extracted thereof. While from the (p, d) reactions spectroscopic factors may be extracted unambiguously, from the (d, t) reactions it is possible to obtain directly the values of vertex constants only, which in turn are consistent with those determined by extrapolation of the experimental cross sections of the (p, d) reactions to the pole.In the case of (3He, ) reactions, however, the analysis indicates inadequacy of the DWBA concerning the calculations of central partial amplitudes. For a more reliable extraction of structural information, besides the correct normalization of peripheral amplitudes, a contribution of more complex mechanisms must be taken into account.  相似文献   
942.
943.
944.
945.
946.
947.
948.
The production of the neutralK ? (892) resonances by 200 GeVK ? andπ ? has been studied over the kinematic range 0.0<x f<1.0 andp t 2 <5.0 GeV2. Longitudinal and transverse momentum distributions are presented. In addition the decay angular distributions inK ? fragmentation to \(\bar K^{0*} \) have been investigated.  相似文献   
949.
This paper is concerned with a combined production-transportation scheduling problem. The problem comprises a simple, two-machine, automated manufacturing cell, which either stands alone or is a subunit of a complete flexible manufacturing system. The cell consists of two machines in series with a dedicated part-handling device such as a crane or robotic arm for transferring parts from the first machine to the second. The loading of a new piece on the first machine and the ejection of a finished piece from the second machine are performed by dedicated automated mechanisms. The introduction of parts into the system is done n at a time, whereby the parts are reshuffled into a sequence that minimizes completion time. All processing and transfer times are considered deterministic—a reasonable assumption for a cell comprising a robotic transfer device and two CNC machining units. What complicates the problem is the assumption of a non-negligible time for the transfer device to return (empty) from the second machine to the first. The operation is a generalization of a two-machine flowshop problem, and is formulated as a specially structured, asymmetric travelling salesman problem. An approximate polynomial time 0(n log n) algorithm is proffered. The procedure incorporates a lower bound using the Gilmore–Gomory algorithm for the no-wait, two-machine flowshop problem.  相似文献   
950.
In this note, we characterize the regular probability measures satisfying the Choquet-Deny convolution equation =* on Abelian topological semigroups for a given probability measure .  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