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   20416篇
  免费   1070篇
  国内免费   1087篇
化学   8191篇
晶体学   154篇
力学   212篇
综合类   38篇
数学   12326篇
物理学   1652篇
  2023年   126篇
  2022年   128篇
  2021年   164篇
  2020年   276篇
  2019年   570篇
  2018年   511篇
  2017年   410篇
  2016年   394篇
  2015年   496篇
  2014年   716篇
  2013年   1516篇
  2012年   876篇
  2011年   1198篇
  2010年   1030篇
  2009年   1282篇
  2008年   1494篇
  2007年   1447篇
  2006年   1122篇
  2005年   896篇
  2004年   829篇
  2003年   722篇
  2002年   836篇
  2001年   509篇
  2000年   504篇
  1999年   489篇
  1998年   457篇
  1997年   353篇
  1996年   392篇
  1995年   344篇
  1994年   336篇
  1993年   266篇
  1992年   212篇
  1991年   148篇
  1990年   155篇
  1989年   158篇
  1988年   110篇
  1987年   98篇
  1986年   108篇
  1985年   133篇
  1984年   104篇
  1983年   78篇
  1982年   91篇
  1981年   89篇
  1980年   91篇
  1979年   69篇
  1978年   62篇
  1977年   52篇
  1976年   47篇
  1974年   21篇
  1973年   18篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
In this paper we investigate the electrostatic problem of determining conductivity profiles from the knowledge of boundary currents and voltages. We obtain an improved estimate for the voltage potential of a two-dimensional conductor having finitely many circular inclusions and piecewise constant conductivity profile. We derive an asymptotic expansion for the voltage potential in terms of the reference voltage potential and the location, size, and conductivity of the inhomogeneities. This representation is used to formulate the nonlinear least squares problem for estimating the location and size of the inhomogeneities. Required boundary data for the voltage potential are generated numerically by solving a system of integral equations. Computational experiments are presented to demonstrate the effectiveness of our identification procedure.  相似文献   
132.
The family of all solutions of the three chains completion problem with a prescribed tolerance is described explicitly. It is shown that this family can be parameterized by a natural set of contractive upper triangular operators. As an application all solutions to a suboptimal nonstationary Nehari problem are described.  相似文献   
133.
In this note, we discuss the reflection principle of the Stokes system in a half space for the threedimensional case, and of the biharmonic equation. Admitting different boundary conditions, we use the reflection principle to prove uniqueness of solutions of the Stokes system or the biharmonic equation in weightedLq-spaces  相似文献   
134.
王辉  马逸龙 《分析化学》1994,22(12):1219-1222
本应用自己合成的联萘20-冠-6作为活性载体,进行了五羟色胺分子选择性电极研究。电极在10^-^5-10^-^2mol/L浓度范围内对五羟色胺具有稳定的线性响应,平均斜率为63mV/PC,检测下限为2.7×10^-^6mol/L。  相似文献   
135.
136.
Summary. In this paper we investigate a stability estimate needed in hybrid finite and boundary element methods, especially in hybrid coupled domain decomposition methods including mortar finite elements. This stability estimate is equivalent to the stability of a generalized projection in certain Sobolev spaces. Using piecewise linear trial spaces and appropriate piecewise constant test spaces, the stability of the generalized projection is proved assuming some mesh conditions locally. Received April 11, 2000 / Revised version received February 15, 2001 / Published online July 25, 2001  相似文献   
137.
Non-local approximation of the Mumford-Shah functional   总被引:3,自引:0,他引:3  
The Mumford-Shah functional, introduced to study image segmentation problems, is approximated in the sense of -convergence by a sequence of non-local integral functionals. Received June 6, 1996 / Accepted July 11, 1996  相似文献   
138.
在微波放电系统中,对NH_3-F-F_2-CF_3I体系进行研究,结果表明,向IF(X)传能的诸多媒介中,N_2(A)及N(~2D)起着主要作用,并且这一结论在经微波激发后的N_2与CF_3I的直接反应中得到了进一步证实。  相似文献   
139.
Two types of optical current transducers (OCTs) have a bulk Faraday sensor inserted into the gap of an iron core and a porcelain insulator with optical fiber. The sensor consists of Bi12SiO20 (BSO) single crystal, a polarizer, and an analyzer. The OCTs satisfied the target performance requirement for fault location and metering and demonstrated maintained performance at some power utilities in Japan and the US. We have developed a fault location system that immediately detects the fault current with the OCTs, there by locating the fault section. The OCT can easily replace the existing support insulators for the disconnecting switch without any modifications to structure height or bus-bar. For metering requiring 0.3% class accuracy, use of a BSO with right optical rotatory power combined with BSO with left optical rotatory power results in a Faraday sensor with improved temperature characteristics. The OCT demonstrated 0.3% class accuracy for metering described in the current transformer Specifications of IEEE C57–13, 1993.  相似文献   
140.
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