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   1324篇
  免费   168篇
  国内免费   100篇
化学   228篇
晶体学   14篇
力学   172篇
综合类   54篇
数学   595篇
物理学   529篇
  2024年   5篇
  2023年   10篇
  2022年   37篇
  2021年   30篇
  2020年   13篇
  2019年   24篇
  2018年   15篇
  2017年   38篇
  2016年   45篇
  2015年   28篇
  2014年   58篇
  2013年   91篇
  2012年   63篇
  2011年   78篇
  2010年   76篇
  2009年   83篇
  2008年   99篇
  2007年   80篇
  2006年   78篇
  2005年   73篇
  2004年   41篇
  2003年   65篇
  2002年   49篇
  2001年   43篇
  2000年   54篇
  1999年   47篇
  1998年   37篇
  1997年   23篇
  1996年   27篇
  1995年   29篇
  1994年   23篇
  1993年   21篇
  1992年   20篇
  1991年   17篇
  1990年   13篇
  1989年   13篇
  1988年   16篇
  1987年   7篇
  1986年   4篇
  1985年   2篇
  1984年   4篇
  1983年   3篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
  1976年   2篇
  1974年   1篇
  1973年   1篇
排序方式: 共有1592条查询结果,搜索用时 15 毫秒
61.
A Theorem is given on the number of passages passing throgh a multiply-connected region,which corrects a wrong conjecture in a former paper of the author.  相似文献   
62.
The truncated Newton algorithm was devised by Dembo and Steihaug (Ref. 1) for solving large sparse unconstrained optimization problems. When far from a minimum, an accurate solution to the Newton equations may not be justified. Dembo's method solves these equations by the conjugate direction method, but truncates the iteration when a required degree of accuracy has been obtained. We present favorable numerical results obtained with the algorithm and compare them with existing codes for large-scale optimization.  相似文献   
63.
In this paper we prove that a class of trust region methods presented in part Ⅰ is superlinearly convergent. Numerical tests are reported thereafter. Results by solving a set of typical problems selected from literatures have demonstrated that our algorithm is effective.  相似文献   
64.
A tolerance region is a map from the sample space of one statistical model to the event space of a second statistical model having the same parameter. This paper derives an optimum β-expectation tolerance region for the multivariate regression model. A measure of power is proposed and evaluated.  相似文献   
65.
Let T be a homogeneous tree of homogeneity q+1. Let denote the boundary of T, consisting of all infinite geodesics b=[b 0,b 1,b 2,] beginning at the root, 0. For each b, 1, and a0 we define the approach region ,a (b) to be the set of all vertices t such that, for some j, t is a descendant of b j and the geodesic distance of t to b j is at most (–1)j+a. If >1, we view these as tangential approach regions to b with degree of tangency . We consider potentials Gf on T for which the Riesz mass f satisfies the growth condition T f p (t)q –|t|<, where p>1 and 0<<1, or p=1 and 0<1. For 11/, we show that Gf(s) has limit zero as s approaches a boundary point b within ,a (b) except for a subset E of of -dimensional Hausdorff measure 0, where H (E)=sup>0inf i q –|t i|:E a subset of the boundary points passing through t i for some i,|t i |>log q (1/).  相似文献   
66.
一种基于正负差图像的运动目标检测新方法   总被引:1,自引:1,他引:1       下载免费PDF全文
运动目标检测领域中现有的差图像法是利用绝对值差图像检测差图像上运动目标区域,用现有方法检测时易受噪声干扰,而且当摄像机有自运动时需要进行背景运动补偿。因此,提出一种新算法,即首先分别计算正差图像与负差图像,然后利用运动目标区域在正差图像与负差图像中的幅值、形状以及运动等信息的对称性对其进行检测,最后给出针对飞机尾焰序列图像进行检测的结果。实验结果表明:该方法可提高运动目标检测的可靠性与效率。  相似文献   
67.
Research into microdisk lasers demonstrates new achievements both in the technology and in the associated physical effects and applications. Melting and rounding of the disk edge boosts the Q-factors due to improved surface smoothness. In-plane cavity shape is widely used as a design instrument. Optimal shaping of pumped area lowers the threshold power. Photonic molecules made of several microdisks as “photonic atoms” show lasing at several closely spaced frequencies. A microdisk with a single quantum dot as an active region is considered as the most promising system for realisation of a single photon emitter necessary for quantum computing. These new effects and devices can be simulated with accurate numerical techniques, developed recently for “warm-cavity” linear modelling, that are able to bring a new vision of the physics of lasing.  相似文献   
68.
再入飞行器驻点流光辐射特性的理论建模   总被引:1,自引:0,他引:1  
本文用直接模拟蒙特卡罗法,对再入体驻点区域的流场、光辐射特性进行了研究.针对头部锥体驻点区(包括激波层),建立了流场中的化学反应模型,中性粒子和等离子体的热运动、粒子间碰撞的理论模型,碰撞激发辐射和化学发光辐射的物理模型.给出了样本粒子运动方向和速率、粒子碰撞对的选择等蒙特卡罗法概率模型和计算方法.  相似文献   
69.
Expressions are derived for the tunnel electric current between two metals produced by the adiabatic transitions of the electrons through a bridge electron level. A new possible physical phenomenon is discussed, viz. electronically driven oscillations of the electron bridge level between two molecular wires.  相似文献   
70.
Digital image correlation (DIC) has received a widespread research and application in experimental mechanics. In DIC, the performance of subpixel registration algorithm (e.g., Newton-Raphson method, quasi-Newton method) relies heavily on the initial guess of deformation. In the case of small inter-frame deformation, the initial guess could be found by simple search scheme, the coarse-fine search for instance. While for large inter-frame deformation, it is difficult for simple search scheme to robustly estimate displacement parameters and deformation parameters simultaneously with low computational cost. In this paper, we proposed three improving strategies, i.e. Q-stage evolutionary strategy (T), parameter control strategy (C) and space expanding strategy (E), and then combined them into three population-based intelligent algorithms (PIAs), i.e. genetic algorithm (GA), differential evolution (DE) and particle swarm optimization (PSO), and finally derived eighteen different algorithms to calculate the initial guess for qN. The eighteen algorithms were compared in three sets of experiments including large rigid body translation, finite uniaxial strain and large rigid body rotation, and the results showed the effectiveness of proposed improving strategies. Among all compared algorithms, DE-TCE is the best which is robust, convenient and efficient for large inter-frame deformation measurement.  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