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   10964篇
  免费   1547篇
  国内免费   769篇
化学   3110篇
晶体学   1158篇
力学   1161篇
综合类   159篇
数学   4560篇
物理学   3132篇
  2024年   16篇
  2023年   113篇
  2022年   243篇
  2021年   302篇
  2020年   355篇
  2019年   271篇
  2018年   246篇
  2017年   337篇
  2016年   471篇
  2015年   337篇
  2014年   523篇
  2013年   800篇
  2012年   601篇
  2011年   691篇
  2010年   611篇
  2009年   646篇
  2008年   718篇
  2007年   682篇
  2006年   674篇
  2005年   591篇
  2004年   502篇
  2003年   452篇
  2002年   369篇
  2001年   317篇
  2000年   353篇
  1999年   271篇
  1998年   252篇
  1997年   224篇
  1996年   151篇
  1995年   151篇
  1994年   118篇
  1993年   102篇
  1992年   88篇
  1991年   109篇
  1990年   75篇
  1989年   56篇
  1988年   71篇
  1987年   48篇
  1986年   42篇
  1985年   52篇
  1984年   38篇
  1983年   22篇
  1982年   38篇
  1981年   17篇
  1980年   34篇
  1979年   22篇
  1978年   13篇
  1977年   24篇
  1976年   19篇
  1975年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
在有限执行假设下对最优契约的扩展模型研究   总被引:1,自引:0,他引:1  
张勇  吴传文 《运筹与管理》2005,14(1):123-127,122
本文运用违约保证金条款改进了代理人事前报酬契约;在契约有限执行的假设下,扩展了代理人的逆向选择模型,并运用扩展逆向选择模型分析了改进后的最优报酬契约。文章指出,改进后的最优报酬契约严格优于委托人为防范代理人违约而被迫采用的非负参与性约束条件下的最优报酬契约。  相似文献   
122.
本文利用不连续罚函数方法将带有不等式约束的全局优化问题的求解转化为 讨论一非线性方程的求根问题,从而得到若干个全局最优性条件.  相似文献   
123.
We present an iterative algorithm (BIN) for scaling all the rows and columns of a real symmetric matrix to unit 2-norm. We study the theoretical convergence properties and its relation to optimal conditioning. Numerical experiments show that BIN requires 2–4 matrix–vector multiplications to obtain an adequate scaling, and in many cases significantly reduces the condition number, more than other scaling algorithms. We present generalizations to complex, nonsymmetric and rectangular matrices.  相似文献   
124.
本利用矩阵对的标准相关分解,得到了矩阵方程(A^TXB,B^TXB)=(C,D)反对称解存在的充分必要条件及通解表达式,同时给出了解关于已知矩阵的最佳逼近.  相似文献   
125.
Zinc oxide (ZnO) films were deposited on glass substrates by the sol-gel dip coating method using acrylamide route. The films were characterized by X-ray diffraction studies which indicated wurtzite structure. Optical absorption measurements indicated band gap in the range 3.17-3.32 eV. XPS studies indicated the formation of ZnO. The resistivity of the films were in the range 1000-10,000 ohm cm.  相似文献   
126.
A modified Kinetic Lattice Monte Carlo model has been developed to predict growth rate regimes and defect formation in the case of the homo-epitaxial growth of close packed crystalline structures. The model is an improvement over standard Monte Carlo algorithms, which usually retain fixed atom positions and bond partners indicative of perfect crystal lattices. Indeed, we extend the concepts of Monte Carlo growth simulations on super-lattices containing additional sites (defect sites) with respect to those of the reference material. This extension implies a reconsideration of the energetic mapping, which is extensively presented, and allows to describe a complex phenomenology that is out of accessibility of standard stochastic approaches. Results obtained using the Kawasaki and the Bond-Counting rules for the transition probability of the Monte Carlo event are discussed in details. These results demonstrate how the defect types (local or extended), the formation mechanisms and the defect generation regimes can be characterized using our approach.  相似文献   
127.
Shaping command input or preshaping is used for reducing system oscillation in motion control. Desired systems inputs are altered so that the system finishes the requested move without residual oscillation. This technique, developed by N.C. Singer and W.P. Seering, is used for example in the aerospace field, in particular in flexible structure control. This paper presents the study of ZV shaper for explicit fractional derivative systems (generalized derivative systems). A robustness study of ZV shaper is then presented and applied to improve second generation CRONE control response time. Results from simulation and from a DC motor bench are also given.  相似文献   
128.
Functional Quantization and Small Ball Probabilities for Gaussian Processes   总被引:1,自引:0,他引:1  
Quantization consists in studying the L r -error induced by the approximation of a random vector X by a vector (quantized version) taking a finite number n of values. We investigate this problem for Gaussian random vectors in an infinite dimensional Banach space and in particular, for Gaussian processes. A precise link proved by Fehringer(4) and Dereich et al. (3) relates lower and upper bounds for small ball probabilities with upper and lower bounds for the quantization error, respectively. We establish a complete relationship by showing that the same holds for the direction from the quantization error to small ball probabilities. This allows us to compute the exact rate of convergence to zero of the minimal L r -quantization error from logarithmic small ball asymptotics and vice versa.  相似文献   
129.
In this paper we consider an obstacle control problem where the state satisfies a quasilinear elliptic variational inequality and the control function is the obstacle. The state is chosen to be close to the desire profile while the H2 norms of the obstacle is not too large. Existence and necessary conditions for the optimal control are established.  相似文献   
130.
We prove that simply connected open manifolds of bounded geometry, linear growth and sublinear filling growth (e.g. finite filling area) are simply connected at infinity.  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