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   13396篇
  免费   269篇
  国内免费   74篇
化学   8342篇
晶体学   133篇
力学   453篇
数学   1956篇
物理学   2855篇
  2022年   131篇
  2021年   145篇
  2020年   181篇
  2019年   174篇
  2018年   135篇
  2017年   116篇
  2016年   277篇
  2015年   245篇
  2014年   310篇
  2013年   682篇
  2012年   635篇
  2011年   708篇
  2010年   361篇
  2009年   419篇
  2008年   652篇
  2007年   657篇
  2006年   620篇
  2005年   562篇
  2004年   530篇
  2003年   436篇
  2002年   385篇
  2001年   240篇
  2000年   246篇
  1999年   141篇
  1998年   137篇
  1997年   139篇
  1996年   187篇
  1995年   138篇
  1994年   195篇
  1993年   195篇
  1992年   197篇
  1991年   141篇
  1990年   142篇
  1989年   150篇
  1988年   120篇
  1987年   139篇
  1986年   126篇
  1985年   223篇
  1984年   183篇
  1983年   128篇
  1982年   157篇
  1981年   136篇
  1980年   157篇
  1979年   144篇
  1978年   150篇
  1977年   128篇
  1976年   144篇
  1975年   117篇
  1974年   143篇
  1973年   132篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
When depicted on maps as homogenous territorial wholes, ancient states are visually summarized as static entities in a way that conceals the highly fluid dynamics of polity formation, maintenance, and growth. Models derived from studies of animal behavior show that “territory” does not consist of an undifferentiated use of the landscape. Instead, the concept of territory can be parsed into a series of resource‐rich nodes linked by corridors of access, surrounded by unutilized regions and boundaries marked at points of competition. Ancient human groups also can be analyzed as having perceived and occupied landscapes through strategies of flexible networks in which nodes and corridors were surrounded by unutilized spaces around which boundaries were selectively identified and defended. This strategy is identifiable in human social groups at different levels of complexity ranging from hunter‐gatherers through ancient chiefdoms and states. © 2007 Wiley Periodicals, Inc. Complexity 12: 28–35, 2007  相似文献   
993.
In this paper we present an atomic decomposition of integrable functions. As an application we compute the distance of in to the Hardy space .

  相似文献   

994.
We examine the problem of building or fortifying a network to defend against enemy attacks in various scenarios. In particular, we examine the case in which an enemy can destroy any portion of any arc that a designer constructs on the network, subject to some interdiction budget. This problem takes the form of a three-level, two-player game, in which the designer acts first to construct a network and transmit an initial set of flows through the network. The enemy acts next to destroy a set of constructed arcs in the designer’s network, and the designer acts last to transmit a final set of flows in the network. Most studies of this nature assume that the enemy will act optimally; however, in real-world scenarios one cannot necessarily assume rationality on the part of the enemy. Hence, we prescribe optimal network design algorithms for three different profiles of enemy action: an enemy destroying arcs based on capacities, based on initial flows, or acting optimally to minimize our maximum profits obtained from transmitting flows.  相似文献   
995.
We present a new linearized model for the zero-one quadratic programming problem, whose size is linear in terms of the number of variables in the original nonlinear problem. Our derivation yields three alternative reformulations, each varying in model size and tightness. We show that our models are at least as tight as the one recently proposed in [7], and examine the theoretical relationship of our models to a standard linearization of the zero-one quadratic programming problem. Finally, we demonstrate the efficacy of solving each of these models on a set of randomly generated test instances.  相似文献   
996.
Abstract  Let p be a prime integer and M a Krull monoid with divisor class group . We represent by S the set of nontrivial divisor classes of which contain prime divisors. We present a new inequality for the elasticity of M (denoted ρ (M)) which is dependent on the cardinality of S and argue that this inequality is the best possible. If M as above has | S| = 3, then it is known that , but for large p, not all the values in this containment set can be realized. For each | S| = 3, we produce a submonoid of such that
Keywords: Krull monoid, Block monoid, Elasticity of factorization Mathematics Subject Classification (2000): 20M14, 20D60, 13F05  相似文献   
997.
In this paper we deal with nonlinear second-order boundary value problems with impulses. The impulsive functions depend implicitly on the different considered variables and the boundary value conditions are nonlinear. In both cases functional dependence on the solution is allowed. The existence results follow from the existence of a pair of well-ordered lower and upper solutions.  相似文献   
998.
This paper is a short report on the generalization of some results of our previous paper [12] to the case of spin j/2 Dirac operators in real dimension three for arbitrary odd integer j. We use an explicit formula for the local expression of such operators to study their algebraic properties, construct the compatibility conditions of the overdetermined system associated to the operator in several spatial variables, and we prove that its associated algebraic complex, dual do the BGG sequence coming from representation theory, has substantially the same pattern as the Cauchy-Fueter complex. The author is a member of the Eduard Čech Center and his research is supported by the relative grants.  相似文献   
999.
By means of several examples of structural operational semantics for a variety of languages, we justify the importance and interest of using the notions of strategies and simulations in the semantic framework provided by rewriting logic and implemented in the Maude metalanguage. On the one hand, we describe a basic strategy language for Maude and show its application to CCS, the ambient calculus, and the parallel functional language Eden. On the other hand, we show how the concept of stuttering simulation can be used inside Maude to show that a stack machine correctly implements the operational semantics of a simple functional language.  相似文献   
1000.
We prove some extension theorems for analytic objects, in particular sections of a coherent sheaf, defined in semi q-coronae of a complex space. Semi q-coronae are domains whose boundary is the union of a Levi flat part, a q-pseudoconvex part and a q-pseudoconcave part. Such results are obtained mainly using cohomological techniques.  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