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   50326篇
  免费   4544篇
  国内免费   3813篇
化学   3207篇
晶体学   42篇
力学   3593篇
综合类   391篇
数学   23826篇
物理学   9293篇
综合类   18331篇
  2024年   87篇
  2023年   401篇
  2022年   480篇
  2021年   693篇
  2020年   1190篇
  2019年   1217篇
  2018年   1094篇
  2017年   1114篇
  2016年   1231篇
  2015年   1178篇
  2014年   2136篇
  2013年   3596篇
  2012年   2513篇
  2011年   2907篇
  2010年   2540篇
  2009年   3028篇
  2008年   3030篇
  2007年   3295篇
  2006年   2942篇
  2005年   2824篇
  2004年   2466篇
  2003年   2316篇
  2002年   2094篇
  2001年   1650篇
  2000年   1591篇
  1999年   1512篇
  1998年   1322篇
  1997年   1204篇
  1996年   984篇
  1995年   915篇
  1994年   770篇
  1993年   615篇
  1992年   602篇
  1991年   536篇
  1990年   506篇
  1989年   388篇
  1988年   339篇
  1987年   246篇
  1986年   178篇
  1985年   150篇
  1984年   129篇
  1983年   64篇
  1982年   116篇
  1981年   103篇
  1980年   83篇
  1979年   83篇
  1978年   48篇
  1977年   50篇
  1976年   44篇
  1973年   17篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
姜正禄 《数学学报》1998,41(2):375-384
本文证明了周期单元中带有某些硬相互作用的相对论Boltzmann方程初值问题在初值满足质量、能量和熵有限的条件下具有一个整体温和解.  相似文献   
182.
本文通过使用化多时滞为单时滞的技巧,研究了一类广泛的非线性泛函微分方程解的振动性,所得结果包含和改进了Hunt,Yorke等多人的结果.  相似文献   
183.
The purpose of this paper is to give the Reid ``Roundabout Theorem' for quadratic functionals with general boundary conditions. In particular, we describe the so-called coupled point and regularity condition introduced in [16] in terms of Riccati equation solutions. Accepted 27 February 1996  相似文献   
184.
1IntroductionThebrainofmankindhasmanycognitivefunctionssuchaslearning,asociationandoptimizationetc..Theneuronisthemostfoundam...  相似文献   
185.
In the present article, we aim at treating the existence of fundamental solutions of linear partial differential operators with constant coefficients from the viewpoint of setting up explicit formulae yielding fundamental solutions.  相似文献   
186.
对一类变形的变分不等式:求,使得提出了一类投影收缩算法,并得到了该算法的收敛性及相关性质.  相似文献   
187.
An analytic and numerical study of the behavior of the linear nonhomogeneous wave equation of the form ε2utt = Δu + tf with high wave speed (ε 1) is carried out. This study was initially motivated by meteorological observations which have indicated the presence of large spatial scale gravity waves in the neighborhood of a number of summer and winter storms, mainly from visible images of ripples in clouds in satellite photos. There is a question as to whether the presence of these waves is caused by the nearby storms. Since the linear wave equation is an approximation to the full system describing pressure waves in the atmosphere, yet is considerably more tractable, we have chosen to analyze the behavior of the linear nonhomogeneous wave equation with high wave speed. The analysis is shown to be valid in one, two, and three space dimensions. Partly because of the high wave speed, the solution is known to consist of behavior which changes on two different time scales, one rapid and one slow. Additionally, because of the presence of the nonhomogeneous forcing term tf, we show that there is a component of the solution which will vary only on a very large spatial scale. Since even the linearized wave equation can give rise to persistent large spatial scale waves under the right conditions, the implication is that certain storms could be responsible for the generation of large-scale waves. Numerical simulations in one and two dimensions confirm analytic results.  相似文献   
188.
本文在A.Blanco等人的算法的基础上,提出了max-min神经网络的一种改进了的反馈学习算法,严格证明了该算法的迭代收敛性,理论分析及实例计算结果均表明,本文算法具有算法简单,收敛速度快,输出误差小等显著特点。  相似文献   
189.
A new scheme for controlling photodissociation through preparation of a variationally optimized linear superposition of field free vibrational eigenstates is applied for selective control of IBr and HI dissociation. The dependence of photodissociation on various field parameters and initial conditions is examined to investigate the mechanistic basis of selective control. The parametric equations of motion approach for determining vibrational dynamics as a function of field parameters without having to solve the time dependent Schrödinger equation explicitly for each field parameter separately is outlined and its use to identify field characteristics which will provide the requisite population mix represented by the optimal linear superposition of vibrational states is advocated.  相似文献   
190.
Modified Stern-Volmer equation is obeyed by bovine serum albumin (BSA)-iodide system showing selective quenching of tryptophanyl fluorescence of BSA. The fraction of accessible protein fluorescence is 0.56 and the effective Stern-Volmer constant is 290 M-1 at pH 7.4 in 0.005 M phosphate buffer at 25°C. Collisional quenching is operative both in the BSA -I−1 system and the model system, tryptophan-I−1. It is supported by the observed relationship between the ratio of quenching rate constants (k q ) and diffusion coefficients and alsok q with bulk viscosity.  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