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   4978篇
  免费   664篇
  国内免费   165篇
化学   140篇
力学   467篇
综合类   53篇
数学   3571篇
物理学   1203篇
无线电   373篇
  2024年   6篇
  2023年   44篇
  2022年   77篇
  2021年   115篇
  2020年   162篇
  2019年   140篇
  2018年   148篇
  2017年   156篇
  2016年   178篇
  2015年   115篇
  2014年   213篇
  2013年   557篇
  2012年   255篇
  2011年   231篇
  2010年   233篇
  2009年   235篇
  2008年   230篇
  2007年   245篇
  2006年   246篇
  2005年   243篇
  2004年   181篇
  2003年   183篇
  2002年   165篇
  2001年   169篇
  2000年   181篇
  1999年   117篇
  1998年   123篇
  1997年   108篇
  1996年   76篇
  1995年   73篇
  1994年   67篇
  1993年   50篇
  1992年   56篇
  1991年   46篇
  1990年   39篇
  1989年   33篇
  1988年   31篇
  1987年   24篇
  1986年   26篇
  1985年   43篇
  1984年   37篇
  1983年   15篇
  1982年   22篇
  1981年   16篇
  1980年   13篇
  1979年   16篇
  1978年   12篇
  1977年   19篇
  1976年   11篇
  1973年   6篇
排序方式: 共有5807条查询结果,搜索用时 15 毫秒
51.
Consider discrete storage processes that are modulated by environmental processes. Environmental processes cause interruptions in the input and/or output processes of the discrete storage processes. Due to the difficulties encountered in the exact analysis of such discrete storage systems, often Poisson flow and/or fluid flow models with the same modulating environmental processes are proposed as approximations for these systems. The analysis of Poisson flow and fluid flow models is much easier than that of the discrete storage processes. In this paper we give sufficient conditions under which the content of the discrete storage processes can be bounded by the Poisson flow and the fluid flow models. For example, we show that Poisson flow models and the fluid flow models developed by Kosten (and by Anick, Mitra and Sondhi) can be used to bound the performance of infinite (finite) source packetized voice/data communication systems. We also show that a Poisson flow model and the fluid flow model developed by Mitra can be used to bound the buffer content of a two stage automatic transfer line. The potential use of the bounding techniques presented in this paper, of course, transcends well beyond these examples.Supported in part by NSF grant DMS-9308149.  相似文献   
52.
We prove that the Hudson-Parthasarathy equation corresponds, up to unitary equivalence, to the strong resolvent limit of Schrödinger Hamiltonians in Fock space and that the symmetric form of this equation corresponds to the weak limit of the Schrödinger Hamiltonians.Translated fromMatematicheskie Zametki, Vol. 60, No. 5, pp. 726–750, November, 1996.  相似文献   
53.
In a general measure-theoretic context, it is proved that the action of a stochastic map on a pair of probability distributions can be characterized by the criterion of decreasing mixing distance.  相似文献   
54.
A class of circuit-switching open queueing networks is discussed. The main result of the paper is that if extra message flows are not too intensive and the path distribution is mainly concentrated on the paths of (graph) distance 1 (nearest neighbour connections), then the network has a unique stationary working regime, no matter how large the configuration graph of the network is. Standard properties of this regime are established such as decay of correlation and continuity.  相似文献   
55.
56.
We consider the relaxation dynamics of two quantum levels coupled to a stochastic bath. We emphasize that even if the matrix elements of the fluctuating Hamiltonian are Gaussian, a second-order cumulant truncation is not exact. For various stochastic models, including the case of a spin-1/2 particle in a fluctuating magnetic field, we calculate 1/T 1, the population relaxation rate, and 1/T 2, the phase relaxation rate, up to fourth order in perturbation theory. We show that unlike the commonly accepted second-order result that 1/T 21/2T 1, when fourth-order terms are included, in some instances 1/T 2<1/2T 1.  相似文献   
57.
In this paper, we establish the discrete approximation of continuous-state nonlinear branching processes in Lévy random environments by using tightness and convergence sequence in infinite dimensional product space via stochastic differential equations. Taking α-stable branching as an example, the conditions which are given to discretize continuous-state nonlinear branching processes in Lévy random environments are verified. © 2022 Chinese Academy of Sciences. All rights reserved.  相似文献   
58.
梁青 《应用数学和力学》2022,43(9):1034-1044
该文讨论了一类带扰动的随机脉冲泛函微分方程解的渐近性.通过比较扰动方程的解和原方程的解,得到了两者逼近的充分条件.首先,两者在有限的时间区间上相互逼近;其次,当扰动趋于零时,区间长度趋于无穷大,在这个区间上两个解仍然是相互逼近的.最后,举例说明了结果的有效性.  相似文献   
59.
形状记忆合金(SMA)是二十一世纪具有形状记忆效应的新型智能材料.针对具有非对称约束的SMA梁,本文构造了碰撞振动系统.在无碰撞和有碰撞两种情况下,利用随机平均法给出了近似解析结果.数值模拟作为验证解析结果的工具.结果表明,系统能量的概率响应曲线具有非光滑特性.当约束位置发生变化时,系统会出现随机P分岔和D分岔.  相似文献   
60.
In this paper, we study the stability of multistage stochastic programming with recourse in a way that is different from that used in studying stability of two-stage stochastic programs. Here, we transform the multistage programs into mathematical programs in the space n ×L p with a simple objective function and multistage stochastic constraints. By investigating the continuity of the multistage multifunction defined by the multistage stochastic constraints and applying epi-convergence theory we obtain stability results for linear and linear-quadratic multistage stochastic programs.Project supported by the National Natural Science Foundation of China.  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