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   329939篇
  免费   3044篇
  国内免费   934篇
化学   164786篇
晶体学   5374篇
力学   15531篇
综合类   7篇
数学   38470篇
物理学   109749篇
  2021年   3132篇
  2020年   3330篇
  2019年   3761篇
  2018年   5198篇
  2017年   5439篇
  2016年   7368篇
  2015年   4139篇
  2014年   7028篇
  2013年   15906篇
  2012年   12376篇
  2011年   14825篇
  2010年   11014篇
  2009年   10914篇
  2008年   13233篇
  2007年   13191篇
  2006年   12137篇
  2005年   10520篇
  2004年   9832篇
  2003年   8685篇
  2002年   8672篇
  2001年   10393篇
  2000年   7656篇
  1999年   5967篇
  1998年   4974篇
  1997年   4812篇
  1996年   4479篇
  1995年   3864篇
  1994年   3820篇
  1993年   3701篇
  1992年   4097篇
  1991年   4306篇
  1990年   4096篇
  1989年   4008篇
  1988年   3779篇
  1987年   3917篇
  1986年   3683篇
  1985年   4631篇
  1984年   4681篇
  1983年   3886篇
  1982年   3973篇
  1981年   3698篇
  1980年   3647篇
  1979年   3914篇
  1978年   3902篇
  1977年   3906篇
  1976年   3882篇
  1975年   3675篇
  1974年   3615篇
  1973年   3650篇
  1972年   2604篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
212.
Limiting distributions are constructed for the log likelihood ratio of close hypotheses and for estimators from censored samples.Translated from Statisticheskie Metody Otsenivaniya i Proverki Gipotez, pp. 95–104, 1986.  相似文献   
213.
214.
ABSTRACT. Limiting adverse consequences of fishing on essential fish habitat has emerged as a key fishery management objective. The conventional approach to providing habitat protection is to create MPAs or marine reserves that prohibit all or certain types of fishing in specific areas. However, there may be more cost‐effective and flexible ways to provide habitat protection. We propose an individual habitat quota (IHQ) system for habitat conservation that would utilize economic incentives to achieve habitat conservation goals cost‐effectively. Individual quotas of habitat impact units (HIU) would be distributed to fishers with an aggregate quota set to maintain a target habitat “stock.” HIU use would be based on a proxy for marginal habitat damage. We use a dynamic, explicitly spatial fishery and habitat simulation model to explore how such a system might work. We examine how outcomes are affected by spatial heterogeneity in the fishery and the scale of habitat regulation. We find that the IHQ system is a highly cost‐effective means of ensuring a given level of habitat protection, but that spatial heterogeneity and the scale of regulation can have significant effects on the distribution of habitat protection.  相似文献   
215.
The normal form of certain polynomial matrices is found.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova Akademii Nauk SSSR, Vol. 175, pp. 63–68, 1989.  相似文献   
216.
Approximate properties of variable measures compose a base of the two-scale convergence method with respect to a variable measure, which is used in averaging on periodic thin and composite structures. The paper gives a survey of methods for verifying approximate properties. The main focus is on studying composite measures, which have been little studied. __________ Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 16, Partial Differential Equations, 2004.  相似文献   
217.
218.
219.
We present analytical solutions of the Ishimaru parabolic equation for the coherence function of electromagnetic field. The equation describes the temporal properties of the pulse at the output of an inhomogeneous dissipative scattering medium. An explicit expression for the Green's function of the problem is found. It is shown that the temporal part of the Green's function has an invariant Laguerre form. Numerical results describing the shapes of the studied temporal pulses at the output of the pass interval of the medium are also given. Time scales characterizing the shapes of the Laguerre output pulses are proposed and the influence of the parameters of the medium on the properties of the resulting pulses is analyzed.  相似文献   
220.
The paper considers the performance of multi-frequency, multi-channel, free field sound cancelling systems for the reduction of discrete frequency and periodic noise. The approach uses a method of directional active noise control. Large sound reductions from these systems have been made possible through: (a) synthetically generating the cancelling sound and synchronizing with the primary source; (b) automatic alignment of all stability regions of the control system and; (c) avoiding instability produced by these multi-channel systems.  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