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   2473篇
  免费   148篇
  国内免费   15篇
化学   1965篇
晶体学   30篇
力学   56篇
综合类   1篇
数学   208篇
物理学   376篇
  2023年   11篇
  2022年   22篇
  2021年   26篇
  2020年   39篇
  2019年   68篇
  2018年   21篇
  2017年   26篇
  2016年   82篇
  2015年   77篇
  2014年   94篇
  2013年   145篇
  2012年   181篇
  2011年   252篇
  2010年   167篇
  2009年   104篇
  2008年   192篇
  2007年   129篇
  2006年   127篇
  2005年   142篇
  2004年   105篇
  2003年   74篇
  2002年   101篇
  2001年   43篇
  2000年   56篇
  1999年   32篇
  1998年   26篇
  1997年   10篇
  1996年   20篇
  1995年   18篇
  1994年   15篇
  1993年   18篇
  1992年   10篇
  1991年   18篇
  1990年   17篇
  1989年   11篇
  1988年   14篇
  1987年   6篇
  1986年   9篇
  1985年   12篇
  1984年   7篇
  1983年   7篇
  1982年   7篇
  1981年   12篇
  1979年   8篇
  1978年   5篇
  1977年   10篇
  1976年   8篇
  1974年   7篇
  1973年   4篇
  1914年   4篇
排序方式: 共有2636条查询结果,搜索用时 109 毫秒
11.
In this paper we study an initial-boundary-value problem for a hyperbolic integro-differential equation with random memory and a random noise. We establish the existence, uniqueness and exponential stability of solutions. Our method consists of finite-dimensional approximation and energy estimates.  相似文献   
12.
13.
Finite element analysis of fluid flow with moving free surface has been performed in 2‐D and 3‐D. The new VOF‐based numerical algorithm that has been proposed by the present authors (Int. J. Numer. Meth. Fluids, submitted) was applied to several 2‐D and 3‐D free surface flow problems. The proposed free surface tracking scheme is based on two numerical tools; the orientation vector to represent the free surface orientation in each cell and the baby‐cell to determine the fluid volume flux at each cell boundary. The proposed numerical algorithm has been applied to 2‐D and 3‐D cavity filling and sloshing problems in order to demonstrate the versatility and effectiveness of the scheme. The proposed numerical algorithm resolved successfully the free surfaces interacting with each other. The simulated results demonstrated applicability of the proposed numerical algorithm to the practical problems of large free surface motion. It has been also demonstrated that the proposed free surface tracking scheme can be easily implemented in any irregular non‐uniform grid systems and can be extended to 3‐D free surface flow problems without additional efforts. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
14.
A Kind of direct methods is presented for the solution of optimal control problems with state constraints.These methods are sequential quadratic programming methods.At every iteration a quadratic programming which is obtained by quadratic approximation to Lagrangian function and Linear approximations to constraints is solved to get a search direction for a merit function.The merit function is formulated by augmenting the Lagrangian funetion with a penalty term.A line search is carried out along the search direction to determine a step length such that the merit function is decreased.The methods presented in this paper include continuous sequential quadratic programming methods and discreate sequential quadrade programming methods.  相似文献   
15.
16.
17.
18.
We present cross sections for heavy flavour production through photon gluon fusion in electron proton collisions at HERA energy. The electron photon vertex is taken into account explicitly, and theQ 2 of the exchanged photon ranges from nearly zero (almost real photon) to the kinematically allowed maximum. In our approach the scale is set by the mass of the produced quarks. Our formalism is also applicable to the production of light quarks as long as the invariant mass of the pair is sufficiently high, so we also give cross sections for \(u\bar u,d\bar d\) and \(s\bar s\) production.  相似文献   
19.
A new class of chiral dienophiles, 5-alkoxy-2(5H)-furanones, has been developed. Both enantiomers of 5-menthyloxy-2(5H)-ftiranone are readily available in enantiomerically pure form, starting from furfural and d- or l-menthol. Excellent diastereoselectivities (d.e. β99%) are obtained in thermal Diels-Alder reactions with several cyclic and acyclic dienes. The use of silyl dienol ethers has resulted in new routes to enantiomerically pure cyclohexanones in a highly regioselective manner.  相似文献   
20.
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