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   67475篇
  免费   7606篇
  国内免费   5409篇
化学   43467篇
晶体学   553篇
力学   1869篇
综合类   805篇
数学   15328篇
物理学   18468篇
  2023年   710篇
  2022年   862篇
  2021年   2343篇
  2020年   2046篇
  2019年   1997篇
  2018年   1621篇
  2017年   1513篇
  2016年   2134篇
  2015年   2220篇
  2014年   2952篇
  2013年   4809篇
  2012年   3221篇
  2011年   3653篇
  2010年   3265篇
  2009年   3897篇
  2008年   4170篇
  2007年   4296篇
  2006年   3565篇
  2005年   2596篇
  2004年   2456篇
  2003年   2419篇
  2002年   4600篇
  2001年   2145篇
  2000年   1658篇
  1999年   1480篇
  1998年   1424篇
  1997年   1010篇
  1996年   944篇
  1995年   1024篇
  1994年   897篇
  1993年   843篇
  1992年   825篇
  1991年   507篇
  1990年   442篇
  1989年   419篇
  1988年   374篇
  1987年   297篇
  1986年   311篇
  1985年   460篇
  1984年   352篇
  1983年   198篇
  1982年   388篇
  1981年   542篇
  1980年   504篇
  1979年   540篇
  1978年   434篇
  1977年   316篇
  1976年   280篇
  1974年   93篇
  1973年   169篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
951.
Takayuki Hibi 《Order》1987,3(4):383-389
A finite poset Q is called integral over a field k if there exists an ASL (algebra with straightening laws) domain on Q{–} over k. We classify all trees (rank one connected posets without cycles) which are integral over an infinite field.  相似文献   
952.
In this work, some results related to superatomic Boolean interval algebras are presented, and proved in a topological way. Let x be an uncountable cardinal. To each I x, we can associate a superatomic interval Boolean algebra B I of cardinality x in such a way that the following properties are equivalent: (i) I I x, (ii) B I is a quotient algebra of B J, and (iii) there is an homomorphism f from B J into B I such that for every atom b of B I, there is an atom a of B J satisfying f(a)=b. As a corollary, there are 2 x isomorphism types of superatomic interval Boolean algebras of cardinality x. This case is quite different from the countable one.  相似文献   
953.
954.
A new model (called the Temperley-Lieb interactions model) is introduced, in two-dimensional lattice statistics, on a square lattice . The Temperley-Lieb equivalence of this model to the six-vertex, self-dual Potts, critical hard-hexagons and critical nonintersecting string models is established. A graphical equivalence of this model to the six-vertex model generalizes this equivalence to noncritical cases of the above models. The order parameters of a specialization of this model are studied.  相似文献   
955.
The growth kinetics is characterized and the moving species is identified for the formation of Ni2Si by Rapid Thermal Annealing (RTA) of sequentially deposited Si and Ni films on a 100 Si substrate. The interfacial Ni2Si layer grows as the square root of time, indicating that the suicide growth process is diffusion-limited. The activation energy is 1.25±0.2 eV in the RTA temperature range of 350–450° C. The results extend those of conventional steady-state furnace annealing quite fittingly, and a common activation energy of 1.3±0.2 eV is deduced from 225° to 450° C. The marker experiment shows that Ni is the dominant moving species during Ni2Si formation by RTA, as is the case for furnace annealing. It is concluded that the two annealing techniques induce the same growth mechanisms in Ni2Si formation.  相似文献   
956.
    
Submillimeter laser-Stark spectra have been observed for the isotopic species of methyl fluoride,13CH3F, using the 337 m line of the HCN laser. We have identified the multiplet transitions as JK=18K17K in the ground vibrational state. Ten distinct families with K=8, 9, 10, 11, 12, 13, 14, 15, 16 and 17 have been observed. Zero-field frequencies for all the transitions are given and in most cases with better accuracy than predicted from the previous constants.  相似文献   
957.
评论了聚合物系统中非辐射能量传递类型,影响能量传递的因素,以及能量传递同聚合物光化学的关系,附22篇文献。  相似文献   
958.
This is one in a series of papers studying measures of information in the so-called mixed theory of information (i.e. considering the events as well as their probabilities) on the open domain (i.e. without empty sets and zero probabilities). In this paper we find all-recursive, 3-semisymmetric inset entropies on the open domain. We do this by solving the fundamental equation of inset information of degree () on the open domain.Dedicated to Professor János Aczél on his 60th birthday.  相似文献   
959.
We study the dynamics of a two-parameter family of noninvertible maps of the plane, derived from a model in population dynamics. We prove that, as one parameter varies with the other held fixed, the nonwandering set changes from the empty set to an unstable Cantor set on which the map is topologically equivalent to the shift endomorphism on two symbols. With the help of some numerical work, we trace the genealogies of the periodic points of the family of period 5, and describe their stability types and bifurcations. Among our results we find that the family has a fixed point which undergoes fold, flip and Hopf bifurcations, and that certain families of period five points are interconnected through a codimension-two cusp bifurcation.  相似文献   
960.
First we propose a model of visual perception essentially based on the Keldysh-Chernavsky-Sossinsky three-channel theorem, from which three-dimensionality of space follows. Second, we associate with a system of subgroups H 1, ..., Hs of a given group G a geometric object, called a group crystal, in order to visualize G. How this notion works is illustrated via the Burnside problem.  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