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   2475篇
  免费   59篇
  国内免费   155篇
化学   827篇
力学   74篇
综合类   12篇
数学   1271篇
物理学   505篇
  2024年   6篇
  2023年   23篇
  2022年   36篇
  2021年   66篇
  2020年   43篇
  2019年   60篇
  2018年   50篇
  2017年   69篇
  2016年   83篇
  2015年   70篇
  2014年   132篇
  2013年   216篇
  2012年   134篇
  2011年   130篇
  2010年   114篇
  2009年   199篇
  2008年   181篇
  2007年   192篇
  2006年   144篇
  2005年   95篇
  2004年   90篇
  2003年   68篇
  2002年   59篇
  2001年   46篇
  2000年   50篇
  1999年   40篇
  1998年   35篇
  1997年   36篇
  1996年   42篇
  1995年   28篇
  1994年   19篇
  1993年   14篇
  1992年   27篇
  1991年   12篇
  1990年   12篇
  1989年   10篇
  1988年   5篇
  1987年   5篇
  1986年   1篇
  1985年   5篇
  1984年   8篇
  1983年   7篇
  1982年   9篇
  1981年   8篇
  1980年   3篇
  1979年   3篇
  1978年   2篇
  1976年   1篇
  1974年   1篇
排序方式: 共有2689条查询结果,搜索用时 148 毫秒
11.
We consider a large class of partially hyperbolic systems containing, among others, affine maps, frame flows on negatively curved manifolds, and mostly contracting diffeomorphisms. If the rate of mixing is sufficiently high, the system satisfies many classical limit theorems of probability theory.

  相似文献   

12.
In a Young–Michelson tandem interferometer a Michelson interferometer is illuminated through a pair of Young slits. The pattern produced by this set-up is analyzed theoretically. The consequences of small misalignments and uncompensated arms in the Michelson interferometer are studied. The effects of the spatial and temporal partial coherence of the source are also explored. Experimental results using a laser source are shown to be in good agreement with the predicted theoretical calculations.  相似文献   
13.
The asymptotic behaviour of partial sums of generalized hypergeometric series of unit argument is investigated.

  相似文献   

14.
In this paper we consider a class of nonlinear delay partial difference equations and a class of linear delay partial difference equations with variable coefficients, which may change sign. We obtain oscillation criteria for these equations. There are no results for the oscillation of these equations up to now.  相似文献   
15.
孙建设 《大学数学》2007,23(1):52-55
给出了函数f(x)和g(x)单调性的证明.据此,得到了著名的Minc H和Sathre L不等式最好的界.  相似文献   
16.
四种多变量校准方法在FTIR多组分分析中的性能比较   总被引:1,自引:0,他引:1  
本文对四种多变量校准方法--经典最小二乘法(CLS),偏最小二乘法(PLS),卡尔曼滤波法(KFM)以及人工神经网络法(ANN)--在多组分浓度分析方面的性能进行了比较。选择五种红外谱图严重混叠的大气有机毒物--1,3-丁二烯,苯,邻二甲苯,氯苯和丙烯醛--作为分析对象。分别计算各种方法对该5组分体系的平均预测误差MPE和平均相对误差MRE进行比较。结果表明,偏最小二乘法在处理这类问题中是最稳健的方法。  相似文献   
17.
We consider a spatially distributed hybrid system consisting of a convection/reaction system in which the reaction switches discontinuously in time between modes, independently at each spatial point on reaching “switching thresholds”. The model involves a novel formulation for evolution of the free boundary between the modal regions.  相似文献   
18.
This paper reports the results of experimental and modeling efforts to characterize partial oxidation of methane to produce synthesis gas (H2 and CO) using metal-substituted hexaaluminate catalysts in short-contact-time reactors. Hexaaluminate catalysts offer excellent high-temperature stability compared to the equivalent metal-based catalysts. The hexaaluminates are synthesized by a metal-exchange process using alumoxane precursors that enable a wide range of metal substitutions. Of all the combinations tested, RhSr-substituted hexaaluminates yielded the best performance. The catalysts are supported on alumina porous-foam structures, which are positioned within a tube furnace to control the operating temperature. Two-stage combinations of RhSr- and Ni-substituted hexaaluminates are shown to improve conversion activity and selectivity compared to a single-catalyst system.  相似文献   
19.
In this paper, specific issues related to high-density perpendicular magnetic recording processes, such as transition noise properties and cross-track correlation lengths, were investigated with the help of micromagnetic analysis. The effects of media parameters were taken into consideration, including intergranular exchange coupling, and exchange distribution, irregular grain shapes, magnetization saturation distribution, and anisotropy distribution. The micromagnetic simulation results showed that the effect of anisotropy distribution on transition noise is more significant than magnetization saturation distribution, and it is crucial to reduce this effect to achieve a high signal-to-noise ratio. Additionally, a new method to further estimate the partial erasure threshold was proposed to approximate the partial erasure effects, and the relation between the microtrack jitter and total track jitter was investigated.  相似文献   
20.
The aim of this article is to study the quasistatic evolutionof a Maxwell–Norton three-dimensional viscoelastic solidwith contact constraints. After introducing the appropiate functionalframework, we will discretize the problem in time using an implicitscheme whose resultant variational inequality is well posed.By using monotonicity arguments together with compensated compactnesstechniques, we will prove that the corresponding discrete solutionconverges to a solution of the continuous problem.  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