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   19246篇
  免费   2278篇
  国内免费   1135篇
化学   2389篇
晶体学   36篇
力学   1542篇
综合类   301篇
数学   9473篇
物理学   4081篇
无线电   4837篇
  2024年   47篇
  2023年   201篇
  2022年   295篇
  2021年   392篇
  2020年   509篇
  2019年   508篇
  2018年   494篇
  2017年   626篇
  2016年   767篇
  2015年   588篇
  2014年   1068篇
  2013年   1752篇
  2012年   1052篇
  2011年   1215篇
  2010年   1069篇
  2009年   1134篇
  2008年   1181篇
  2007年   1287篇
  2006年   1074篇
  2005年   982篇
  2004年   833篇
  2003年   813篇
  2002年   719篇
  2001年   604篇
  2000年   558篇
  1999年   471篇
  1998年   398篇
  1997年   306篇
  1996年   296篇
  1995年   226篇
  1994年   190篇
  1993年   161篇
  1992年   145篇
  1991年   145篇
  1990年   78篇
  1989年   69篇
  1988年   47篇
  1987年   42篇
  1986年   41篇
  1985年   47篇
  1984年   44篇
  1983年   25篇
  1982年   25篇
  1981年   30篇
  1980年   16篇
  1979年   20篇
  1978年   16篇
  1977年   18篇
  1976年   11篇
  1974年   8篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
提出了一种利用Mach-Zehnder干涉仪制备自旋压缩态的方案,研究了两条干涉路径之间的相位差对自旋压缩参数的影响。结果表明,自旋压缩出现在垂直于平均自旋和 轴的方向;通过调节两条干涉路径之间的相位差和减少两条干涉路径之间的粒子数差可以有效制备粒子的自旋压缩态。  相似文献   
993.
We report on the novel application of nanoscratch characterization to provide insight into the plasticity mechanisms responsible for the behaviour of composites. Accordingly, we conduct deformation characterization with nanoscratch testing (DCNT) to study the deformation behaviour of two B4C reinforced ultrafine grained Al alloy tri-modal composites with average B4C particle sizes of ~1–6?μm and ~500?nm, respectively. To highlight the type of mechanistic information revealed in a DCNT study of composites, we concentrate on the influence of B4C particle size on deformation mechanisms.  相似文献   
994.
995.
The use of Gibbs samplers driven by improper posteriors has been a controversial issue in the statistics literature over the last few years. It has recently been demonstrated that it is possible to make valid statistical inferences through such Gibbs samplers. Furthermore, theoretical and empirical evidence has been given to support the idea that there are actually computational advantages to using these nonpositive recurrent Markov chains rather than more standard positive recurrent chains. These results provide motivation for a general study of the behavior of the Gibbs Markov chain when it is not positive recurrent. This article concerns stability relationships among the two-variable Gibbs sampler and its subchains. We show that these three Markov chains always share the same stability; that is, they are either all positive recurrent, all null recurrent, or all transient. In addition, we establish general results concerning the ways in which positive recurrent Markov chains can arise from null recurrent and transient Gibbs chains. Six examples of varying complexity are used to illustrate the results.  相似文献   
996.
The aim of this paper is that of investigating the asymptotic exponential cone of a single Metzler matrix, introduced in [23], and of defining and analysing the new concept of asymptotic exponential cone of a family of Metzler matrices (along a certain direction). These results will provide necessary and/or sufficient conditions for the solvability of an interesting algebraic problem that arises in the context of continuous-time positive switched systems and, specifically, in the investigation of the reachability property [21,22,25].  相似文献   
997.
In this work, we establish Weyl-Titchmarsh theory for symplectic difference systems. This paper extends classical Weyl-Titchmarsh theory and provides a foundation for studying spectral theory of symplectic difference systems.  相似文献   
998.
Triple quad liquid chromatography mass spectrometric assays (LC/MS/MS) have revolutionized the analysis of drug(s)/metabolite(s) with exceptional speed, sensitivity and selectivity features. From inception to date, several new and innovative features have been regularly proposed by researchers to further enhance the value in the applicability of this analytical tool. However, owing to such compressed run times and scanty sample preparation procedures, LC/MS/MS assays that are not fully optimized generally have issues of matrix effects, where ionization potential is either suppressed or enhanced due to the presence of other materials (endogenous/exogenous) in the matrix. By definition, even co‐medications, isomeric or isobaric impurities, and drug excipients used in dosing solutions could also potentially contribute to matrix effects. This article captures some of the interesting work carried out by researchers to understand and handle matrix effects. Additionally, it provides perspectives to effectively deal with matrix effects. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
999.
In this work the combined finite difference and spectral methods have been proposed for the numerical solution of the one‐dimensional wave equation with an integral condition. The time variable is approximated using a finite difference scheme. But the spectral method is employed for discretizing the space variable. The main idea behind this approach is that we can get high‐order results. The new method is used for two test problems and the numerical results are obtained to support our theoretical expectations. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007  相似文献   
1000.
一类积分微分方程概周期解的存在性和唯一性   总被引:1,自引:0,他引:1  
考虑具无穷时滞的非线性积分微分方程概周期的存在性和唯一性问题,利用矩阵测度和不动点方法获得了一类方程的概周期的存在性和唯一性的充分条件,推广了相应文献的结果.  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