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   7848篇
  免费   372篇
  国内免费   636篇
化学   670篇
晶体学   6篇
力学   367篇
综合类   54篇
数学   6662篇
物理学   1097篇
  2023年   80篇
  2022年   52篇
  2021年   74篇
  2020年   149篇
  2019年   161篇
  2018年   191篇
  2017年   195篇
  2016年   224篇
  2015年   148篇
  2014年   309篇
  2013年   544篇
  2012年   317篇
  2011年   338篇
  2010年   315篇
  2009年   495篇
  2008年   577篇
  2007年   518篇
  2006年   472篇
  2005年   421篇
  2004年   299篇
  2003年   364篇
  2002年   314篇
  2001年   228篇
  2000年   236篇
  1999年   251篇
  1998年   195篇
  1997年   219篇
  1996年   121篇
  1995年   114篇
  1994年   99篇
  1993年   67篇
  1992年   57篇
  1991年   60篇
  1990年   66篇
  1989年   49篇
  1988年   53篇
  1987年   39篇
  1986年   38篇
  1985年   50篇
  1984年   56篇
  1983年   18篇
  1982年   36篇
  1981年   32篇
  1980年   33篇
  1979年   25篇
  1978年   30篇
  1977年   38篇
  1976年   25篇
  1974年   14篇
  1973年   15篇
排序方式: 共有8856条查询结果,搜索用时 31 毫秒
101.
The paper deals with the class of linear differential equations of any even order 2α+42α+4, α∈N0αN0, which are associated with the so-called ultraspherical-type polynomials. These polynomials form an orthogonal system on the interval [−1,1][1,1] with respect to the ultraspherical weight function (1−x2)α(1x2)α and additional point masses of equal size at the two endpoints. The differential equations of “ultraspherical-type” were developed by R. Koekoek in 1994 by utilizing special function methods. In the present paper, a new and completely elementary representation of these higher-order differential equations is presented. This result is used to deduce the orthogonality relation of the ultraspherical-type polynomials directly from the differential equation property. Moreover, we introduce two types of factorizations of the corresponding differential operators of order 2α+42α+4 into a product of α+2α+2 linear second-order operators.  相似文献   
102.
Based on a refinement of the notion of internal sets in Colombeau's theory, so-called strongly internal sets, we introduce the space of generalized smooth functions, a maximal extension of Colombeau generalized functions. Generalized smooth functions as morphisms between sets of generalized points form a sub-category of the category of topological spaces. In particular, they can be composed unrestrictedly.  相似文献   
103.
We consider a Dirichlet problem in a planar domain with a hole of diameter proportional to a real parameter ?   and we denote by u?u? the corresponding solution. The behavior of u?u? for ?   small and positive can be described in terms of real analytic functions of two variables evaluated at (?,1/log??)(?,1/log??). We show that under suitable assumptions on the geometry and on the boundary data one can get rid of the logarithmic behavior displayed by u?u? for ?   small and describe u?u? by real analytic functions of ?. Then it is natural to ask what happens when ? is negative. The case of boundary data depending on ? is also considered. The aim is to study real analytic families of harmonic functions which are not necessarily solutions of a particular boundary value problem.  相似文献   
104.
We consider sequences of random variables whose probability generating functions have only roots on the unit circle, which has only been sporadically studied in the literature. We show that the random variables are asymptotically normally distributed if and only if the fourth central and normalized (by the standard deviation) moment tends to 3, in contrast to the common scenario for polynomials with only real roots for which a central limit theorem holds if and only if the variance is unbounded. We also derive a representation theorem for all possible limit laws and apply our results to many concrete examples in the literature, ranging from combinatorial structures to numerical analysis, and from probability to analysis of algorithms. © 2013 Wiley Periodicals, Inc. Random Struct. Alg., 46,707–738, 2015  相似文献   
105.
本文首先由超空间上Cauchy-Pompeiu公式定义了超空间上高阶Teodorescu算子,研究了此类算子的一些基本性质.其次,利用此类算子,我们得到了$k$-超正则函数的Almansi型展开. 最后运用这个展开,我们证明了$k$-超正则函数的Morera型定理、开拓定理和唯一性定理.  相似文献   
106.
In the present paper, we introduce some new subclasses of meromorphic starlike,convex, close-to-convex and quasi-convex functions of β-reciprocal in terms of the linear operator using subordination. We obtain the coefficient estimates, convolution properties, integral preserving properties and inclusion relationships of the classes. The results presented here include several results as their special cases.  相似文献   
107.
108.
Mammals, including human beings, have evolved a unique viviparous reproductive system and a highly developed central nervous system. How did these unique characteristics emerge in mammalian evolution, and what kinds of changes did occur in the mammalian genomes as evolution proceeded? A key conceptual term in approaching these issues is “mammalian-specific genomic functions”, a concept covering both mammalian-specific epigenetics and genetics. Genomic imprinting and LTR retrotransposon-derived genes are reviewed as the representative, mammalian-specific genomic functions that are essential not only for the current mammalian developmental system, but also mammalian evolution itself. First, the essential roles of genomic imprinting in mammalian development, especially related to viviparous reproduction via placental function, as well as the emergence of genomic imprinting in mammalian evolution, are discussed. Second, we introduce the novel concept of “mammalian-specific traits generated by mammalian-specific genes from LTR retrotransposons”, based on the finding that LTR retrotransposons served as a critical driving force in the mammalian evolution via generating mammalian-specific genes.  相似文献   
109.
空间理性八节点块体元   总被引:1,自引:0,他引:1  
推导出空间八节点块体理性有限元列式,采用具有直到三次多项式的空间问题的微分方程的解作为插值的近似函数,数例结果表明空间理性八节点块体元的有效性。  相似文献   
110.
Singularly perturbed systems with structural perturbations are analyzed for stability. New sufficient conditions of asymptotic stability and uniform asymptotic stability are established. The systems in question are widely used in control theory, engineering, etc  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