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   4682篇
  免费   1087篇
  国内免费   627篇
化学   3697篇
晶体学   67篇
力学   214篇
综合类   20篇
数学   79篇
物理学   2319篇
  2024年   17篇
  2023年   62篇
  2022年   148篇
  2021年   171篇
  2020年   249篇
  2019年   189篇
  2018年   156篇
  2017年   181篇
  2016年   255篇
  2015年   239篇
  2014年   327篇
  2013年   422篇
  2012年   325篇
  2011年   329篇
  2010年   269篇
  2009年   296篇
  2008年   313篇
  2007年   279篇
  2006年   265篇
  2005年   224篇
  2004年   249篇
  2003年   219篇
  2002年   142篇
  2001年   138篇
  2000年   127篇
  1999年   106篇
  1998年   102篇
  1997年   96篇
  1996年   90篇
  1995年   65篇
  1994年   60篇
  1993年   43篇
  1992年   51篇
  1991年   29篇
  1990年   25篇
  1989年   18篇
  1988年   20篇
  1987年   14篇
  1986年   19篇
  1985年   6篇
  1984年   8篇
  1982年   11篇
  1981年   7篇
  1980年   7篇
  1979年   9篇
  1977年   3篇
  1976年   3篇
  1975年   2篇
  1974年   4篇
  1973年   2篇
排序方式: 共有6396条查询结果,搜索用时 0 毫秒
11.
We employ an agent‐based model to show that memory and the absence of an a priori best strategy are sufficient for self‐segregation and clustering to emerge in a complex adaptive system with discrete agents that do not compete over a limited resource nor contend in a winner‐take‐all scenario. An agent starts from a corner of a two‐dimensional lattice and aims to reach a randomly selected site in the opposite side within the shortest possible time. The agent is isolated during the course of its journey and does not interact with other agents. Time‐bound obstacles appear at random lattice locations and the agent must decide whether to challenge or evade any obstacle blocking its path. The agent is capable of adapting a strategy in dealing with an obstacle. We analyze the dependence of strategy‐retention time with strategy for both memory‐based and memory‐less agents. We derive the equality spectrum to establish the environmental conditions that favor the existence of an a priori best strategy. We found that memory‐less agents do not polarize into two opposite strategy‐retention time distributions nor cluster toward a center distribution. © 2004 Wiley Periodicals, Inc. Complexity 9: 41–46, 2004  相似文献   
12.
In this paper, we examine a variant of the uncapacitated lot-sizing model of Wagner–Whitin that includes fixed charges on the stocks. Such a model is natural in a production environment where stocking is a complex operation, and appears as a subproblem in more general network design problems.

Linear-programming formulations, a dynamic program, the convex hull of integer solutions and a separation algorithm are presented. All these turn out to be very natural extensions of the corresponding results of Barany et al. (Math. Programming Stud. 22 (1984) 32) for the uncapacitated lot-sizing problem. The convex hull proof is based on showing that an extended facility location formulation is tight and by projecting it onto the original space of variables.  相似文献   

13.
The bias dependent interface charge is considered as the origin of the observed non-ideality in current–voltage and capacitance–voltage characteristics. Using the simplified model for the interface electronic structure based on defects interacting with the continuum of interface states, the microscopic origin of empirical parameters describing the bias dependent interface charge function is investigated. The results show that in non-ideal metal–semiconductor contacts the interface charge function depends on the interface disorder parameter, density of defects, barrier pinning parameter and the effective gap center. The theoretical predictions are tested against several sets of published experimental data on bias dependent ideality factor and excess capacitance in various metal–semicoductor systems.  相似文献   
14.
The occurrence of charge on recoil56Mn produced by the (n,γ) reaction in polycrystalline potassium permanganate has been examined using the ‘charge plate technique’. From considerations of capture gamma ray decay schemes and internal conversion it appears that, in a condensed medium, the recoil atom develops charge after losing much of its initial kinetic energy which allows collection on charged electrodes. Preliminary findings were presented at the International Symposium on Radiochemistry and Radiation Chemistry, RC-41 BARC, Bombay, Feb. 4–6 (1991).  相似文献   
15.
16.
基于完全信息博弈理论,阐述了寡头垄断市场的排污收费古诺模型.建立了具有政府宏观调控机制的博弈模型,并对调控效果进行了分析.  相似文献   
17.
This review summarizes the experimental data on charge radii differences among ground state and high spin isomeric states determined by high-resolution laser spectroscopic methods. A comparison is presented between radii changes obtained from the isomeric shifts in the atomic spectra and from the quadrupole moments of both ground and isomeric states under the assumption that the radii changes are determined by the difference of the quadrupole deformations. Special attention is paid to isomers arising from the break-up of nucleon pairs and isomers of odd–odd nuclei. The characteristic features of the radii changes for isomeric states of different origin are discussed.  相似文献   
18.
Advances in gauge theories and unified theories have not thrown light on the meaning of electron. The problem of the origin of electronic charge is made precise, new insights gained from Weyl space are summarized, and the origin of charge in terms of fractional spin is suggested. A new perspective on the abelian Chern-Simons theory is presented to explain charge.  相似文献   
19.
Satya Prakash 《Pramana》1989,33(1):109-131
This article summarizes the recent radiochemical investigations on mass, charge kinetic energy and fragment angular distributions in low energy fission of actinides.  相似文献   
20.
Summary We report on neutron emission in palladium and titanium electrolitically charged with deuterium. The detection of neutrons is observed after thermal treatment of the electrode. In the hypothesis that neutrons came from cold fusion processes, we estimate a fusion rate as high as 1.3·10−21 fusions/deuteron pair/second.  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