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   770篇
  免费   15篇
  国内免费   31篇
化学   21篇
力学   20篇
综合类   1篇
数学   744篇
物理学   30篇
  2024年   1篇
  2023年   11篇
  2022年   15篇
  2021年   14篇
  2020年   15篇
  2019年   13篇
  2018年   15篇
  2017年   11篇
  2016年   8篇
  2015年   11篇
  2014年   24篇
  2013年   49篇
  2012年   48篇
  2011年   44篇
  2010年   37篇
  2009年   59篇
  2008年   42篇
  2007年   68篇
  2006年   53篇
  2005年   25篇
  2004年   21篇
  2003年   23篇
  2002年   22篇
  2001年   28篇
  2000年   29篇
  1999年   24篇
  1998年   19篇
  1997年   20篇
  1996年   9篇
  1995年   11篇
  1994年   17篇
  1993年   2篇
  1992年   2篇
  1991年   1篇
  1990年   1篇
  1989年   4篇
  1986年   1篇
  1985年   5篇
  1984年   2篇
  1982年   5篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1978年   2篇
排序方式: 共有816条查询结果,搜索用时 15 毫秒
61.
In this paper, we establish local Hölder estimate for non-negative solutions of the singular equation (M.P) below, for m in the range of exponents . Since we have trouble in finding the local energy inequality of v directly, we use the fact that the operator σ(−Δ) can be thought as the normal derivative of some extension v? of v to the upper half space (Caffarelli and Silvestre, 2007 [5]), i.e., v is regarded as boundary value of v? the solution of some local extension problem. Therefore, the local Hölder estimate of v can be obtained by the same regularity of v?. In addition, it enables us to describe the behavior of solution of non-local fast diffusion equation near their extinction time.  相似文献   
62.
63.
Minimally nonideal matrices are a key to understanding when the set covering problem can be solved using linear programming. The complete classification of minimally nonideal matrices is an open problem. One of the most important results on these matrices comes from a theorem of Lehman, which gives a property of the core of a minimally nonideal matrix. Cornuéjols and Novick gave a conjecture on the possible cores of minimally nonideal matrices. This paper disproves their conjecture by constructing a new infinite family of square minimally nonideal matrices. In particular, we show that there exists a minimally nonideal matrix with r ones in each row and column for any r?3.  相似文献   
64.
Set valued probability and fuzzy valued probability theory is used for analyzing and modeling highly uncertain probability systems. In this paper the set valued probability and fuzzy valued probability are defined over the measurable space. They are derived from a set and fuzzy valued measure using restricted arithmetics. The range of set valued probability is the set of subsets of the unit interval and the range of fuzzy valued probability is the set of fuzzy sets of the unit interval. The expectation with respect to set valued and fuzzy valued probability is defined and some properties are discussed. Also, the fuzzy model is applied to binomial model for the price of a risky security.  相似文献   
65.
在决策信息系统中引入拓扑结构,借助拓扑学的基本概念(拓扑、内部和闭包等)研究决策问题,用它们刻画决策信息系统中的一些重要概念(决策协调集、决策约简集、下近似协调集、下近似约简集、上近似协调集、上近似约简集),并利用它们把这些重要概念推广到最一般的情况,建立起相应的约简理论.  相似文献   
66.
L-双拓扑空间中的配超紧性   总被引:1,自引:0,他引:1  
借助相关远域族给出L-双拓扑空间中配超紧性的定义,研究它们的等价刻画和基本性质,证明配超紧性是弱拓扑不变性.  相似文献   
67.
This paper presents a Hilbert-style system for the logic of first-degree entailment defined in a Fmla-Fmla framework. The effective use of this formulation as a basis for a whole family of systems extending the logic of first-degree entailment in various directions is shown. By systematizing this family, some new systems are uncovered, and some other well-established logics (such as the first-degree entailment fragment of Priest's Logic of Paradox) obtain new axiomatization. Semantics for the key systems from the family is formulated.  相似文献   
68.
In this paper we analyze some classes of abstract simplicial complexes relying on algebraic models arising from module theory. To this regard, we consider a left-module on a unitary ring and find models of abstract complexes and related set operators having specific regularity properties, which are strictly interrelated to the algebraic properties of both the module and the ring.Next, taking inspiration from the aforementioned models, we carry out our analysis from modules to arbitrary sets. In such a more general perspective, we start with an abstract simplicial complex and an associated set operator. Endowing such a set operator with the corresponding properties obtained in our module instances, we investigate in detail and prove several properties of three subclasses of abstract complexes.More specifically, we provide uniformity conditions in relation to the cardinality of the maximal members of such classes. By means of the notion of OSS-bijection, we prove a correspondence theorem between a subclass of closure operators and one of the aforementioned families of abstract complexes, which is similar to the classic correspondence theorem between closure operators and Moore systems. Next, we show an extension property of a binary relation induced by set systems when they belong to one of the above families.Finally, we provide a representation result in terms of pairings between sets for one of the three classes of abstract simplicial complexes studied in this work.  相似文献   
69.
There has recently been work by multiple groups in extracting the properties associated with cardinal invariants of the continuum and translating these properties into similar analogous combinatorial properties of computational oracles. Each property yields a highness notion in the Turing degrees. In this paper we study the highness notions that result from the translation of the evasion number and its dual, the prediction number, as well as two versions of the rearrangement number. When translated appropriately, these yield four new highness notions. We will define these new notions, show some of their basic properties and place them in the computability-theoretic version of Cichoń's diagram.  相似文献   
70.
给出了整数环上一类三阶矩阵方程有解的充要条件.  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