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   7799篇
  免费   790篇
  国内免费   654篇
化学   1919篇
晶体学   57篇
力学   1493篇
综合类   184篇
数学   2996篇
物理学   2594篇
  2024年   9篇
  2023年   50篇
  2022年   141篇
  2021年   171篇
  2020年   193篇
  2019年   178篇
  2018年   172篇
  2017年   216篇
  2016年   273篇
  2015年   206篇
  2014年   322篇
  2013年   538篇
  2012年   423篇
  2011年   418篇
  2010年   400篇
  2009年   515篇
  2008年   521篇
  2007年   503篇
  2006年   474篇
  2005年   390篇
  2004年   383篇
  2003年   344篇
  2002年   337篇
  2001年   308篇
  2000年   247篇
  1999年   232篇
  1998年   199篇
  1997年   170篇
  1996年   153篇
  1995年   128篇
  1994年   113篇
  1993年   74篇
  1992年   73篇
  1991年   58篇
  1990年   57篇
  1989年   50篇
  1988年   23篇
  1987年   34篇
  1986年   24篇
  1985年   16篇
  1984年   19篇
  1983年   10篇
  1982年   11篇
  1981年   20篇
  1980年   11篇
  1979年   14篇
  1978年   10篇
  1977年   3篇
  1975年   3篇
  1936年   2篇
排序方式: 共有9243条查询结果,搜索用时 15 毫秒
51.
The miniaturized calorimetric devices furnish a reduced working flat surface and permits measurements with extremely low-mass quantities. The experimental sensitivity shows relevant position dependence with x-y surface coordinates and with z-distance. The device identification is realized via a 2-D model based in Fourier general equation. Using the Marquardt method the experimental flat surface device can be identified and the fitted parameters used to simulate the behavior of the experimental system. From the model, the effects of several dissipation configurations can be evaluated. Also, via the RC-analogy, a way to 3-D experimental devices is roughly described. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
52.
In this paper,the concept of the infinitesimal realization factor is extended to the parameter-dependent performance functions in closed queueing networks. Then the concepts of realization matrix (its elements are called realization factors) and performance potential are introduced,and the relations between infinitesimal realization factors and these two quantities are discussed. This provides a united framework for both IPA and non IPA approaches. Finally,another physical meaning of the service rate is given.  相似文献   
53.
We study Pauli-Fierz Hamiltonians-self-adjoint operators describing a small quantum system interacting with a bosonic field. Using quadratic form techniques, we extend the results of Dereziński-Gérard and Gérard about the self-adjointness, the location of the essential spectrum and the existence of a ground state to a large class of Pauli-Fierz Hamiltonians.  相似文献   
54.
Many natural counting problems arise in connection with the normal form of braids—and seem to have not been much considered so far. Here we solve some of them. One of the noteworthy points is that a number of different induction schemes appear. The key technical ingredient is an analysis of the normality condition in terms of permutations and their descents, in the vein of the Solomon algebra. As was perfectly summarized by a referee, the main result asserts that the size of the automaton involved in the automatic structure of Bn associated with the normal form can be lowered from n! to p(n), the number of partitions of n.  相似文献   
55.
主范式的运算性质   总被引:3,自引:0,他引:3  
研究了极大项、极小项的运算性质 ,利用这些性质给出了求 A,A∨ B,A∧ B,A→ B,A B的主范式的公式 ,由此可用程序化的方法求任意公式的主范式 .  相似文献   
56.
In the factor analysis model with large cross-section and time-series dimensions,we pro- pose a new method to estimate the number of factors.Specially if the idiosyncratic terms satisfy a linear time series model,the estimators of the parameters can be obtained in the time series model. The theoretical properties of the estimators are also explored.A simulation study and an empirical analysis are conducted.  相似文献   
57.
We propose a method for constructing systems of polynomial equations that define submanifolds of degenerate binary forms of an arbitrary degeneracy degree. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 153, No. 2, pp. 147–157, November, 2007.  相似文献   
58.
We present some of our results for the electromagnetic properties of excited Σ hyperons, computed within the framework of the Bonn constituent-quark model, which is based on the Bethe-Salpeter approach. The seven parameters entering the model are fitted against the best-known baryon masses. Accordingly, the results for the form factors and helicity amplitudes are genuine predictions. We compare with the scarce experimental data available and discuss the processes in which Σ *'s may play an important role.  相似文献   
59.
实对称正定矩阵的复合矩阵正定性的研究已有结论,但对于一般意义下的正定矩阵的复合矩阵是否仍然是正定的研究需要利用一般的正定矩阵的标准形的复合矩阵进行讨论,给出了一般公式及具体算法,为讨论其复合矩阵的正定性提供了基础条件.  相似文献   
60.
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