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   242845篇
  免费   3756篇
  国内免费   804篇
化学   127278篇
晶体学   3474篇
力学   9863篇
综合类   15篇
数学   35457篇
物理学   71318篇
  2021年   1718篇
  2020年   2061篇
  2019年   2159篇
  2018年   4051篇
  2017年   4202篇
  2016年   5264篇
  2015年   3712篇
  2014年   4903篇
  2013年   11024篇
  2012年   11709篇
  2011年   12314篇
  2010年   8479篇
  2009年   7885篇
  2008年   9864篇
  2007年   9818篇
  2006年   9107篇
  2005年   12007篇
  2004年   10702篇
  2003年   8356篇
  2002年   6353篇
  2001年   6257篇
  2000年   4657篇
  1999年   3574篇
  1998年   2971篇
  1997年   2797篇
  1996年   2725篇
  1995年   2439篇
  1994年   2468篇
  1993年   2376篇
  1992年   2794篇
  1991年   2658篇
  1990年   2583篇
  1989年   2490篇
  1988年   2437篇
  1987年   2416篇
  1986年   2266篇
  1985年   3024篇
  1984年   3030篇
  1983年   2642篇
  1982年   2821篇
  1981年   2611篇
  1980年   2555篇
  1979年   2696篇
  1978年   2713篇
  1977年   2602篇
  1976年   2743篇
  1975年   2605篇
  1974年   2567篇
  1973年   2751篇
  1972年   1749篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
951.
Using a generalization of the classical ballot theorem, Niu and Cooper [7] established a duality relation between the joint distribution of several variables associated with the busy cycle inM/G/1 (with a modified first service) and the corresponding joint distribution of several related variables in its dualGI/M/1. In this note, we generalize this duality relation toGI/G/1 queues with modified first services; this clarifies the original result, and shows that the generalized ballot theorem is superfluous for the duality relation.  相似文献   
952.
This paper has two objectives. We introduce a new global optimization algorithm reformulating optimization problems in terms of boundary-value problems. Then, we apply this algorithm to a pointwise control problem of the viscous Burgers equation, where the control weight coefficient is progressively decreased. The results are compared with those obtained with a genetic algorithm and an LM-BFGS algorithm in order to check the efficiency of our method and the necessity of using global optimization techniques.  相似文献   
953.
954.
We study linear dynamical systems with multidimensional time in Banach spaces. Using Taylor functional calculus we prove that under additional assumptions hyperbolic systems have shadowing property.  相似文献   
955.
The behavior of the intensity of anomalous and galactic cosmic rays in the outer heliosphere is compared. The previous hypothesis, according to which the lowest energy galactic cosmic rays affected by large-scale electric fields far beyond the termination shock wave of the solar wind may contribute to the behavior of the anomalous component intensity, is analyzed.  相似文献   
956.
New results are presented of an experimental investigation of the spectrum of 36P → 37P two-photon microwave transition in Rydberg atoms of sodium in a constant electric field. Depending on the conditions of excitation of the initial 36P state (the constant electric field is switched on either before or after the exciting laser pulse) and polarization of laser radiation, a strong variation is observed of the amplitudes of individual two-photon transitions between the fine-structure Stark components of the 36P and 37P states. This effect is an analog of the Paschen-Back effect in a strong magnetic field and is due to the break of L-S coupling and to the variation of the wave functions of Rydberg electrons in an electric field. It is also found that the break of L-S coupling affects considerably the shape of double Stark resonance arising upon intersection of the virtual intermediate level of two-photon transition with the real intermediate 37S level.  相似文献   
957.
The O-(arylcarbamoyl)butyrhydroximoyl chlorides were synthesized, and the x-ray structural analysis (XSA) of one of them — O-(o-tolylcarbamoyl)butyrhydroximoyl chloride — was performed. It was established from the data of the XSA and the PMR spectra that all synthesized compounds are the Z isomers.Institute of Physiologically Active Substances, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 315–319, February, 1992.  相似文献   
958.
959.
As a consequence of Jensen's inequality, centered operators of probabilistic type (also called Bernstein-type operators) approximate convex functions from above. Starting from this fact, we consider several pairs of classical operators and determine, in each case, which one is better to approximate convex functions. In almost all the discussed examples, the conclusion follows from a simple argument concerning composition of operators. However, when comparing Szász-Mirakyan operators with Bernstein operators over the positive semi-axis, the result is derived from the convex ordering of the involved probability distributions. Analogous results for non-centered operators are also considered.  相似文献   
960.
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