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   10996篇
  免费   1500篇
  国内免费   647篇
化学   1268篇
晶体学   95篇
力学   3714篇
综合类   165篇
数学   3146篇
物理学   4755篇
  2024年   16篇
  2023年   80篇
  2022年   192篇
  2021年   293篇
  2020年   303篇
  2019年   243篇
  2018年   253篇
  2017年   375篇
  2016年   454篇
  2015年   354篇
  2014年   474篇
  2013年   686篇
  2012年   577篇
  2011年   682篇
  2010年   529篇
  2009年   644篇
  2008年   648篇
  2007年   699篇
  2006年   715篇
  2005年   615篇
  2004年   528篇
  2003年   496篇
  2002年   461篇
  2001年   414篇
  2000年   353篇
  1999年   320篇
  1998年   277篇
  1997年   231篇
  1996年   189篇
  1995年   175篇
  1994年   146篇
  1993年   105篇
  1992年   89篇
  1991年   76篇
  1990年   79篇
  1989年   34篇
  1988年   41篇
  1987年   47篇
  1986年   34篇
  1985年   39篇
  1984年   31篇
  1983年   11篇
  1982年   23篇
  1981年   9篇
  1980年   12篇
  1979年   19篇
  1978年   19篇
  1977年   13篇
  1976年   15篇
  1974年   6篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
柯尔莫哥洛夫检验在混凝土强度检测中的应用   总被引:1,自引:0,他引:1  
回弹法是检测混凝土强度的一种常用方法,回弹法的测量精度依赖于数据本身的真实性。本文提出了一种利用柯尔莫哥洛夫检验控制测量数据误差的方法。  相似文献   
982.
A variation of the Polak method of feasible directions for solving nonlinear programming problems is shown to be related to the Topkis and Veinott method of feasible directions. This new method is proven to converge to a Fritz John point under rather weak assumptions. Finally, numerical results show that the method converges with fewer iterations than that of Polak with a proper choice of parameters.  相似文献   
983.
We develop an empirical test aimed at detecting nonergodicity from a single sample of a spin system. We show that the test is asymptotically correct, and we give explicit asymptotics for the error probability. The key tool consists in some new large-deviation estimates.  相似文献   
984.
In this paper a class of goodness-of-fit tests for the Rayleigh distribution is proposed. The tests are based on a weighted integral involving the empirical Laplace transform. The consistency of the tests as well as their asymptotic distribution under the null hypothesis are investigated. As the decay of the weight function tends to infinity the test statistics approach limit values. In a particular case the resulting limit statistic is related to the first nonzero component of Neyman’s smooth test for this distribution. The new tests are compared with other omnibus tests for the Rayleigh distribution.  相似文献   
985.
The estimation problems for the conventional step-up method (the observed breakdown voltages are not given at all) and the new step-up method (some of the observed breakdown voltages are given) are analyzed when the underlying probability distribution (of breakdown voltage level) is assumed to be gumbel distributions for minima and maxima. The new step-up test method has advantages compared to the conventional method: (1) the confidence intervals of the estimates become smaller and (2) the estimates can be obtained with higher probability. In some case of real step-up breakdown voltage test, a fit of the gumbel distribution to the data case is found to be superior to that of the normal distribution, which suggests the usefulness of the gumbel distribution for the underlying distribution in the step-up breakdown voltage test.  相似文献   
986.
 复合片钻头的钻速与其切削齿的自锐性密切相关,钻头台架试验反映了这种内在联系,并用平均钻速(v)和平均钻速变化率(α)等指标对复合片自锐性能进行描述与评价。试验结果表明,复合片的自锐性在微观上取决于聚晶体发生串晶断裂和沿晶界断裂的程度,宏观上则依赖于复合片双层结构间在耐磨性能上互为因果的关系。  相似文献   
987.
We describe a new parallel method for solving global optimization problems. The formulation of the decision rules of this method is presented. We examine convergence conditions of the proposed algorithm and establish conditions which guarantee a considerable speedup with respect to the sequential version of the algorithm. We also present some numerical experiments executed on Alliant FX/80 for one class of multiextremal functions.The authors are greatly indebted to R. G. Strongin who stimulated the fulfillment of this research. They also would like to thank the anonymous referees for their useful suggestions.The research of the first author was partially supported by Grant 9494/NC/89 from the Italian Government under the Italian-Soviet Agreement about the Cultural and Scientific Exchange in 1990–1991. He thanks the Systems Department, University of Calabria, where he was a Visitor.  相似文献   
988.
实验利用光注入多量子陆半导体激光器产生的载流子消耗和带间载流子吸收产生的交叉增益调制效,实现波长转换,转换光的光强变化幅度与偏置电流有关。通过调节偏置电流的大小,能使转换光与注入信号光在同向和反向间进行切换。  相似文献   
989.
We describe an automatic quadrature routine which is specifically designed for real functions having a certain type of infinite oscillating tails. The algorithm is designed to integrate a vector function over an infinite interval. A FORTRAN implementation of the algorithm is included.The algorithm combines an adaptive subdivision strategy with extrapolation and requires that the decay of all the functions in the vector is the same. The algorithm is based on the assumption that the oscillating behavior is due to a periodic function with the property that it changes sign when evaluated at points of distance half a period. We assume that this period is known. The algorithm offers a choice of three different quasi-linear extrapolation procedures, namely the Euler transformation and two modifications of this transformation.This work was supported by The Norwegian Research Council for Science and the Humanities.  相似文献   
990.
厚非线性介质瞬态热光非线性效应的研究   总被引:1,自引:0,他引:1       下载免费PDF全文
瞬态热光非线性效应是指由脉冲宽度可以和非线性效应的建立时间相比拟的纳秒脉冲激光入射产生的热光非线性效应.用Zscan法测量了不同厚度、不同束腰半径碘的酒精溶液的瞬态热光非线性效应曲线.从声波的传播方程和光波的非线性传播方程出发,用数值计算方法模拟了这一非线性过程.并对实验结果和数值模拟结果进行了比较 关键词: 瞬态热光非线性效应 非线性光学 数值计算  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