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   597056篇
  免费   6353篇
  国内免费   1914篇
化学   314322篇
晶体学   9181篇
力学   27124篇
综合类   14篇
数学   71461篇
物理学   183221篇
  2021年   4833篇
  2020年   5406篇
  2019年   5954篇
  2018年   7663篇
  2017年   7498篇
  2016年   11445篇
  2015年   7205篇
  2014年   11239篇
  2013年   27268篇
  2012年   20710篇
  2011年   25647篇
  2010年   18056篇
  2009年   17869篇
  2008年   23443篇
  2007年   23318篇
  2006年   21707篇
  2005年   19488篇
  2004年   18079篇
  2003年   15872篇
  2002年   15802篇
  2001年   17777篇
  2000年   13508篇
  1999年   10674篇
  1998年   8935篇
  1997年   8676篇
  1996年   8307篇
  1995年   7533篇
  1994年   7428篇
  1993年   7321篇
  1992年   8014篇
  1991年   8140篇
  1990年   7765篇
  1989年   7619篇
  1988年   7658篇
  1987年   7455篇
  1986年   7029篇
  1985年   9236篇
  1984年   9562篇
  1983年   7614篇
  1982年   7833篇
  1981年   7777篇
  1980年   7302篇
  1979年   7786篇
  1978年   8024篇
  1977年   7892篇
  1976年   7882篇
  1975年   7254篇
  1974年   7249篇
  1973年   7260篇
  1972年   5164篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Dominant nonlinear electric dipole polarizations at the interaction of fundamental and second harmonic waves in centrosymmetric media without and with memory are treated in this paper. The process of forming a permanent spatially periodic quadratic susceptibility grating in the medium with memory is described from the phenomenological point of view.Dedicated to the Czechoslovak Student Movement '89.  相似文献   
112.
The variational problem of contact equilibrium of a punch and an elastic body is considered. An equivalent formulation of the problem is given in variational inequality form. Existence and uniqueness of the solution is investigated in a particular case. A penalty method is proposed for approximate solution of the problem.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 56, pp. 97–103, 1985.  相似文献   
113.
Translated from Chislennye Metody Resheniya Obratnykh Zadach Matematicheskoi Fiziki, pp. 119–127.  相似文献   
114.
Although coupled liquid chromatographygas chromatography (LC-GC) was first demonstrated ten years ago, only in the last few years has there been a sudden surge of interest in the technique. Approximately 70% of the total number of LC-GC applications have been published in the last two years (1987–88) alone. This review categorizes LC-GC publications into four main application areas: fossil fuels, foods, environmental samples, biologiical/pharmaceutical samples, and miscellaneous samples. Multidimensional separations carried out using other coupled-column chromatographic techniques (such as supercritical fluid chromatography (SFC) with GC, and on-line trace enrichment-GC) have also been included in this review.  相似文献   
115.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 51, No. 2, pp. 212–217, August, 1989.  相似文献   
116.
117.
A firm's logistics cost, including shipping and inventory-carrying, is a substantial percentage of its sales. Nevertheless, typical inventory-control methods ignore or insufficiently represent the shipping cost. This paper describes a recursive algorithm that determines the reorder cycle-time that minimizes total logistics cost. It allows for a realistic accounting of shipping cost, which is modelled here as a function of shipping distance and weight. The algorithm uses a relaxation procedure to identify a suitable initial approximation to the optimal order cycle-time and then, through a series of recursive steps, moves to the optimal result. We demonstrate the algorithm with a single item, with a group of items that share a common order cycle, and with multi-items when item demands are random variables. Experience with this algorithm indicates that it converges to the optimal result in a very few steps.  相似文献   
118.
The main notions and results which are necessary for finding higher symmetries and conservation laws for general systems of partial differential equations are given. These constitute the starting point for the subsequent papers of this volume. Some problems are also discussed.  相似文献   
119.
120.
A model equation describing the configuration of a simple plasma maintained by external radiation is studied. A branch of steady solutions of the equation was found by Eckhaus et al. to terminate at a finite critical value of the power of the external source, and this is attributed to the discontinuous nature of a nonlinear term in the governing equation. On introducing a small parameter to render the term continuous, a second branch of solutions is constructed in a neighborhood of the termination point of the original branch. This suggests that the termination point is formed as the limit of a subcritical fold in the surface of the steady solution branch.  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