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   69202篇
  免费   5945篇
  国内免费   7571篇
化学   45335篇
晶体学   1291篇
力学   1717篇
综合类   982篇
数学   13975篇
物理学   19418篇
  2023年   524篇
  2022年   971篇
  2021年   2250篇
  2020年   1571篇
  2019年   1620篇
  2018年   1285篇
  2017年   1470篇
  2016年   1750篇
  2015年   1849篇
  2014年   2519篇
  2013年   4655篇
  2012年   3192篇
  2011年   3731篇
  2010年   3549篇
  2009年   4330篇
  2008年   4478篇
  2007年   4674篇
  2006年   3991篇
  2005年   3113篇
  2004年   2864篇
  2003年   2791篇
  2002年   5042篇
  2001年   2408篇
  2000年   1986篇
  1999年   1582篇
  1998年   1479篇
  1997年   1147篇
  1996年   1157篇
  1995年   1005篇
  1994年   969篇
  1993年   920篇
  1992年   914篇
  1991年   647篇
  1990年   479篇
  1989年   462篇
  1988年   417篇
  1987年   331篇
  1986年   304篇
  1985年   422篇
  1984年   343篇
  1983年   174篇
  1982年   353篇
  1981年   530篇
  1980年   476篇
  1979年   502篇
  1978年   393篇
  1977年   302篇
  1976年   261篇
  1974年   85篇
  1973年   173篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
161.
162.
Let G be a 2-connected graph with minimum degree at least 3. We prove that there exists an even circuit C in G with factorization F={F1,F2} such that GE(F1) is 2-connected.  相似文献   
163.
The authors study the bifurcation problems of rough heteroclinic loop connecting three saddle points for the case β1 > 1, β2 > 1, β3 < 1 and β1β2β3 < 1. The existence, number, coexistence and incoexistence of 2-point-loop, 1-homoclinic orbit and 1-periodic orbit are studied. Meanwhile, the bifurcation surfaces and existence regions are given.  相似文献   
164.
The local adsorption geometry of CO adsorbed in different states on Ni(1 0 0) and on Ni(1 0 0) precovered with atomic hydrogen has been determined by C 1s (and O 1s) scanned-energy mode photoelectron diffraction, using the photoelectron binding energy changes to characterise the different states. The results confirm previous spectroscopic assignments of local atop and bridge sites both with and without coadsorbed hydrogen. The measured Ni–C bondlengths for the Ni(1 0 0)/CO states show an increase of 0.16 ± 0.04 Å in going from atop to bridge sites, while comparison with similar results for Ni(1 1 1)/CO for threefold coordinated adsorption sites show a further lengthening of the bond by 0.05 ± 0.04 Å. These changes in the Ni–CO chemisorption bondlength with bond order (for approximately constant adsorption energy) are consistent with the standard Pauling rules. However, comparison of CO adsorbed in the atop geometry with and without coadsorbed hydrogen shows that the coadsorption increases the Ni–C bondlength by only 0.06 ± 0.04 Å, despite the decrease in adsorption energy of a factor of 2 or more. This result is also reproduced by density functional theory slab calculations. The results of both the experiments and the density functional theory calculations show that CO adsorption onto the Ni(1 0 0)/H surface is accompanied by significant structural modification; the low desorption energy may then be attributed to the energy cost of this restructuring rather than weak local bonding.  相似文献   
165.
In this paper we study the ergodic properties of the linear action of lattices Γ of SL(2,ℚp) on ℚp × ℚp and distribution results for orbits of Γ. Following Serre, one can define a “geodesic flow” for an associated tree (actually associated to GL(2,ℚp)). The approach we use is based on an extension of this approach to “frame flows” which are a natural compact group extension of the geodesic flow.  相似文献   
166.
This paper deals with maximum principle for some optimal control problem governed by some elliptic variational inequalities. Some state constraints are discussed. The basic techniques used here are based on those in [1] and a new penalty functional defined in this paper.  相似文献   
167.
The content of residual monomers is one of the most important characteristics of polymer dispersions. As a result of the similar physicochemical parameters of ethyl acrylate and methyl methacrylate, it is very difficult to determine the residual monomers in acrylate dispersions obtained by emulsion polymerization of both monomers. Gas chromatography with capillary columns, however, permits separation of these monomers and their quantitative determination in acrylate dispersions.  相似文献   
168.
This paper is a continuation of [8]. In Section 1, three kinds of communication are introdnced for two states and the relations among them are investigated. In Section 2, two kinds of period of a state are introdnced and it is obtained that the period is a “class property” ,i.e. two states x and y belong to same class implies the period of x is equal to the period of y.  相似文献   
169.
The questions raised by A. M. Turing in his paper on thought and machines are discussed. Human thought is considered in turn as a concept of normal language usage, as a basic concept of psychology, and as the basis of intellectual activity. It is concluded that neither of these notions of thought identifies something specific that a human being can or cannot do. The imitation game proposed by Turing for deciding whether a machine can think is found to result from an arbitrary empoverishment of the channel of communication between the interrogator and the item under investigation. Turing's notions of thinking are shown to lead to logical difficulties. An alternative view of consciousness, that would place it beyond the reach of any finite test, is finally discussed.  相似文献   
170.
利用TRS方法对双奇核164Lu的位能面进行了计算,确认了164Lu核的一条三轴超形变带,结果与实验较好地符合,同时指出了三轴超形变带的一个具体的组态  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