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   1396篇
  免费   159篇
  国内免费   80篇
化学   234篇
晶体学   1篇
力学   34篇
综合类   159篇
数学   745篇
物理学   462篇
  2024年   3篇
  2023年   23篇
  2022年   31篇
  2021年   42篇
  2020年   36篇
  2019年   52篇
  2018年   32篇
  2017年   31篇
  2016年   40篇
  2015年   33篇
  2014年   56篇
  2013年   59篇
  2012年   37篇
  2011年   59篇
  2010年   60篇
  2009年   97篇
  2008年   76篇
  2007年   91篇
  2006年   89篇
  2005年   80篇
  2004年   62篇
  2003年   67篇
  2002年   64篇
  2001年   45篇
  2000年   38篇
  1999年   39篇
  1998年   33篇
  1997年   28篇
  1996年   31篇
  1995年   52篇
  1994年   24篇
  1993年   26篇
  1992年   17篇
  1991年   9篇
  1990年   13篇
  1989年   13篇
  1988年   8篇
  1987年   8篇
  1986年   5篇
  1985年   6篇
  1984年   3篇
  1983年   5篇
  1982年   2篇
  1981年   2篇
  1980年   3篇
  1979年   2篇
  1977年   1篇
  1973年   1篇
  1972年   1篇
排序方式: 共有1635条查询结果,搜索用时 0 毫秒
101.
We extend a quadrivalent logic of Belnap to graded truth values in order to handle graded relevance of positive and negative arguments provided in preferential information concerning ranking of a finite set of alternatives. This logic is used to design the preference modelling and exploitation phases of decision aiding with respect to the ranking problem. The graded arguments are presented on an ordinal scale and their aggregation leads to preference model in form of four graded outranking relations (true, false, unknown and contradictory). The exploitation procedure combines the min-scoring procedure with the leximin rule. Aggregation of positive and negative arguments as well as exploitation of the resulting outranking relations is concordant with an advice given by St. Ignatius of Loyola (1548) how to make a good choice.  相似文献   
102.
The aim of this paper is to give a purely logical construction of repletion, i.e. the reflection of an arbitrary set to a replete one. Replete sets within constructive logic were introduced independently by M. Hyland and P. Taylor as the most restrictive but sufficiently general notion of predomain suitable for the purposes of denotational semantics à la Scott.For any set A its repletion R(A) appears as an inductively defined subset of S2(A) (A S) S which can be expressed within the internal language of a model of type theory. More explicitly, R(A) is the least subset of S2(A) containing all point filters and closed under a class of generalised limit processes. Improvements of our construction arise from several results saying that it suffices for the purpose of repletion to consider more restrictive classes of generalised limit processes.  相似文献   
103.
There are several open problems in the study of the calculi which result from adding either of Hilbert's ?- or τ-operators to the first order intuitionistic predicate calculus. This paper provides answers to several of them. In particular, the first complete and sound semantics for these calculi are presented, in both a “quasi-extensional” version which uses choice functions in a straightforward way to interpret the ?- or τ-terms, and in a form which does not require extensionality assumptions. Unlike the classical case, the addition of either operator to intuitionistic logic is non-conservative. Several interesting consequences of the addition of each operator are proved. Finally, the independence of several other schemes in either calculus are also proved, making use of the semantics supplied earlier in the paper.  相似文献   
104.
We investigate the definability in monadic ∑11 and monadic Π11 of the problems REGk, of whether there is a regular subgraph of degree k in some given graph, and XREGk, of whether, for a given rooted graph, there is a regular subgraph of degree k in which the root has degree k, and their restrictions to graphs in which every vertex has degree at most k, namely REGkk and XREGkk, respectively, for k ≥ 2 (all our graphs are undirected). Our motivation partly stems from the fact (which we prove here) that REGkk and XREGkk are logspace equivalent to CONN and REACH, respectively, for k ≥ 3, where CONN is the problem of whether a given graph is connected and REACH is the problem of whether a given graph has a path joining two given vertices. We use monadic first - order reductions, monadic ∑11 games and a recent technique due to Fagin, Stockmeyer and Vardi to almost completely classify whether these problems are definable in monadic ∑11 and monadic Π11, and we compare the definability of these problems (in monadic ∑11 and monadic Π11 with their computational complexity (which varies from solvable using logspace to NP - complete).  相似文献   
105.
The work of Karl Menger in social science is briefly surveyed, in particular in the areas of marginal utility and diminishing value, utility, and uncertainty, a logic of imperatives based on deterrence, and a theory of voluntary associations in which cohesive groups are studied combinatorially.  相似文献   
106.
A logical approach to fuzzy sets method originated by Giles is developed. The infinitely many-valued logic tω is taken as basic. We accept, it is correct to use the strong conjunction by the logical analysis of the summation of fuzzy items. Under some broad conditions it is proved. that the sum of many fuzzy variables is a variable whose membership function is approximately equal to ?(x) = max{1 ? 12c(x ? α)2, 0}, where a and c are some constant parameters. A method of estimation of the unknown parameters is developed in a general case. The proposed fuzzy method coincides with the method of maximum likelihood if used in problems of classical mathematical statistics.  相似文献   
107.
We present an alternative, purely semantical and relatively simple, proof of the Statman's result that both intuitionistic propositional logic and its implicational fragment are PSPACE-complete.This paper was supported by grant 401/01/0218 of the Grant Agency of the Czech Republic. % Mathematics Subject Classification (2000):  相似文献   
108.

We prove that if is consistent then is consistent with the following statement: There is for every a model of cardinality which is -equivalent to exactly non-isomorphic models of cardinality . In order to get this result we introduce ladder systems and colourings different from the ``standard' counterparts, and prove the following purely combinatorial result: For each prime number and positive integer it is consistent with that there is a ``good' ladder system having exactly pairwise nonequivalent colourings.

  相似文献   

109.
电流控阈技术及三值电流型 CMOS施密特电路   总被引:1,自引:1,他引:0  
本文以开关信号理论为指导 ,对电流型 CM OS电路中如何实现阈值控制进行研究. 建立实现阈 值控制电路的电流传输开关运算 ,并用于指导电流型 CMOS施密特电路的开关级设计 .用 PSPICE程序 模拟证明了所设计的电路具有理想的施密特电路特性.  相似文献   
110.
一阶形式系统K~*及其完备性   总被引:2,自引:0,他引:2  
模糊命题演算的形式系统L*已经在模糊逻辑与模糊推理的结合研究中得到了成功的应用.本文考虑与系统L*相应的一阶逻辑理论,建立了一阶形式系统K*,并证明了这个系统的完备性.  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