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   15716篇
  免费   2467篇
  国内免费   953篇
化学   4273篇
晶体学   113篇
力学   2899篇
综合类   253篇
数学   5552篇
物理学   6046篇
  2024年   19篇
  2023年   191篇
  2022年   272篇
  2021年   421篇
  2020年   441篇
  2019年   359篇
  2018年   392篇
  2017年   624篇
  2016年   735篇
  2015年   649篇
  2014年   872篇
  2013年   1138篇
  2012年   835篇
  2011年   946篇
  2010年   837篇
  2009年   990篇
  2008年   1004篇
  2007年   1056篇
  2006年   858篇
  2005年   692篇
  2004年   721篇
  2003年   691篇
  2002年   571篇
  2001年   460篇
  2000年   467篇
  1999年   438篇
  1998年   336篇
  1997年   269篇
  1996年   252篇
  1995年   215篇
  1994年   175篇
  1993年   128篇
  1992年   99篇
  1991年   122篇
  1990年   93篇
  1989年   64篇
  1988年   85篇
  1987年   64篇
  1986年   50篇
  1985年   71篇
  1984年   48篇
  1983年   34篇
  1982年   46篇
  1981年   30篇
  1980年   56篇
  1979年   58篇
  1978年   28篇
  1977年   39篇
  1976年   39篇
  1957年   15篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Differential game formulations provide an adequate basis for a guidance law synthesis against highly maneuvering targets. This paper deals with a guidance law based on a linear-quadratic differential game formulation. This guidance law has many attractive properties: it is continuous, linear with respect to the state variables, and its gain coefficients can be precalculated offline. Nevertheless, due to the lack of hard control constraints in the formulation, the magnitude of the control can exceed the admissible level imposed by the nature of the problem. In this paper, the upper bound of the interceptor control is obtained depending on the system parameters and the penalty coefficients of the game performance index. It is shown that the interceptor can guarantee an arbitrarily small miss distance without exceeding the control constraints if it has sufficient maneuverability and if the penalty coefficients are chosen properly. By manipulating the penalty coefficients, it is possible to reduce significantly the maneuverability requirements compared to the case of zero interceptor penalty coefficient.  相似文献   
72.
The control of piecewise-deterministic processes is studied where only local boundedness of the data is assumed. Moreover the discount rate may be zero. The value function is shown to be solution to the Bellman equation in a weak sense; however the solution concept is strong enough to generate optimal policies. Continuity and compactness conditions are given for the existence of nonrelaxed optimal feedback controls.  相似文献   
73.
This paper is concerned with global stabilization of an undamped non‐linear string in the case where any velocity feedback is not available. The linearized system has an infinite number of poles and zeros on the imaginary axis. In the case where any velocity feedback is not available, a parallel compensator is effective. The stabilizer is constructed for the augmented system which consists of the controlled system and a parallel compensator. It is proved that the string can be stabilized by linear boundary control. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
74.
This paper is concerned with well‐posedness results for a mathematical model for the transversal vibrations of a two‐dimensional hybrid elastic structure consisting of a rectangular Reissner–Mindlin plate with a Timoshenko beam attached to its free edge. The model incorporates linear dynamic feedback controls along the interface between the plate and the beam. Classical semigroup methods are employed to show the unique solvability of the coupled initial‐boundary‐value problem. We also show that the energy associated with the system exhibits the property of strong stability. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
75.
We consider an initial and boundary value problem for a homogenous string subject to an internal pointwise control. The solution resulting from a non‐linear feedback is studied. We give various explicit decay estimates depending on the control position and the feedback non‐linearity. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
76.
The paper discusses the relationship between weights and control vertices of two rational NURBS curves of degree two or three with all weights larger than zero when they represent the same curve parametrically and geometrically, and gives sufficient and necessary conditions for coincidence of two rational NURBS curves in non-degeneracy case.  相似文献   
77.
统一混沌系统的控制   总被引:31,自引:2,他引:29       下载免费PDF全文
陶朝海  陆君安 《物理学报》2003,52(2):281-284
对统一混沌系统建立了自反馈控制、错位反馈控制和自适应控制方法,在理论上给予严格证明,数值仿真表明这些方法是很有效的.还纠正了文献[10]的某些不足. 关键词: 统一混沌系统 反馈 自适应 控制 Routh-Hurwitz定理  相似文献   
78.
陈平  朱登松  吴仲康  高立模 《物理实验》2003,23(2):14-15,18
通过实验观测氩离子激光器工作电流与输出光功率及其稳定性之间的关系,采用光反馈解决了反馈工作点的设置和跟踪调解,使输出光功率稳定性得到明显提高。  相似文献   
79.
80.
This paper deals with maximum principle for some optimal control problem governed by some elliptic variational inequalities. Some state constraints are discussed. The basic techniques used here are based on those in [1] and a new penalty functional defined in this paper.  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