全文获取类型
收费全文 | 19895篇 |
免费 | 2140篇 |
国内免费 | 1467篇 |
专业分类
化学 | 2801篇 |
晶体学 | 62篇 |
力学 | 1264篇 |
综合类 | 479篇 |
数学 | 9548篇 |
物理学 | 4244篇 |
无线电 | 5104篇 |
出版年
2024年 | 45篇 |
2023年 | 169篇 |
2022年 | 321篇 |
2021年 | 458篇 |
2020年 | 470篇 |
2019年 | 432篇 |
2018年 | 440篇 |
2017年 | 576篇 |
2016年 | 704篇 |
2015年 | 593篇 |
2014年 | 1014篇 |
2013年 | 1316篇 |
2012年 | 1056篇 |
2011年 | 1255篇 |
2010年 | 1125篇 |
2009年 | 1285篇 |
2008年 | 1315篇 |
2007年 | 1316篇 |
2006年 | 1291篇 |
2005年 | 1009篇 |
2004年 | 887篇 |
2003年 | 892篇 |
2002年 | 771篇 |
2001年 | 689篇 |
2000年 | 561篇 |
1999年 | 518篇 |
1998年 | 434篇 |
1997年 | 368篇 |
1996年 | 327篇 |
1995年 | 276篇 |
1994年 | 213篇 |
1993年 | 178篇 |
1992年 | 182篇 |
1991年 | 129篇 |
1990年 | 104篇 |
1989年 | 91篇 |
1988年 | 75篇 |
1987年 | 64篇 |
1986年 | 37篇 |
1985年 | 66篇 |
1984年 | 57篇 |
1983年 | 34篇 |
1982年 | 62篇 |
1981年 | 45篇 |
1980年 | 49篇 |
1979年 | 63篇 |
1978年 | 33篇 |
1977年 | 34篇 |
1976年 | 18篇 |
1974年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
研究了链状聚合物的长短键结构呈准周期排列的电子谱。利用紧束缚近似和转移矩阵方法通过理论证明和计算表明:这种准周期排列聚合物的电子谱,当长短键长度相差很小时,具有类似于金属晶体的能带结构;相差很大时,具有无序系统一维能级结构;而对于一般情形,其电子谱与上两者均异,形成所谓的类Cantor集。这3类不同的谱结构反映在链状聚合物的宏观物理性质上也将有所不同,它无疑会影响聚合物的稳定性及相关(超)导电性能,深入研究这方面问题将有助于对有机超导的认识。 相似文献
992.
We develop a notion of an n-fold monoidal category and show that it corresponds in a precise way to the notion of an n-fold loop space. Specifically, the group completion of the nerve of such a category is an n-fold loop space, and free n-fold monoidal categories give rise to a finite simplicial operad of the same homotopy type as the classical little cubes operad used to parametrize the higher H-space structure of an n-fold loop space. We also show directly that this operad has the same homotopy type as the n-th Smith filtration of the Barratt-Eccles operad and the n-th filtration of Berger's complete graph operad. Moreover, this operad contains an equivalent preoperad which gives rise to Milgram's small model for when n=2 and is very closely related to Milgram's model of for n>2. 相似文献
993.
在电工与电子技术课程中融入素质教学的实践 总被引:1,自引:0,他引:1
陈新华 《电气电子教学学报》2001,23(2):50-51
针对当前教育改革的形势,对在《电工电子技术》课程改革中推行素质 教育的重要性和必要性进行了论述,结合实践介绍了把素质教育融入课程教学改革中的新模式。 相似文献
994.
L.?Marié J.?Burguete F.?DaviaudEmail author J.?Léorat 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(4):469-485
A numerical study of the magnetic induction equation has
been performed on von Kármán type flows. These flows are
generated by two co-axial counter-rotating propellers in
cylindrical containers. Such devices are currently used in the
von Kármán sodium (VKS) experiment designed to study dynamo
action in an unconstrained flow. The mean velocity fields have
been measured for different configurations and are introduced in
a periodic cylindrical kinematic dynamo code. Depending on the
driving configuration, on the poloidal to toroidal flow ratio
and on the conductivity of boundaries, some flows are observed
to sustain growing magnetic fields for magnetic Reynolds numbers
accessible to a sodium experiment. The response of the flow to
an external magnetic field has also been studied: The results
are in excellent agreement with experimental results in the
single propeller case but can differ in the two propellers case. 相似文献
995.
F. Crisciani R. Purini 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):571-575
The present note deals with Munk's ocean model and proposes an alternative approach to find its solution, with special regard
to the western boundary layer. We introduce a suitable “distance” between the related Sverdrup streamfunction and all the
admissible streamfunctions which are valid in the western boundary layer. We prove that such distance has a minimum that singles
out a unique solution. Unlike the traditional method, this procedure works without assuming a priori any dynamic boundary
condition.
Received 16 July 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: fulcri@itt.ts.cnr.it 相似文献
996.
Guoen Hu 《Journal of Mathematical Analysis and Applications》2003,283(2):351-361
boundedness is considered for the commutator of higher-dimensional Marcinkiewicz integral. Some conditions implying the and the boundedness for the commutator of the Marcinkiewicz integral are obtained. 相似文献
997.
Roman Barták 《Annals of Operations Research》2003,118(1-4):101-119
Global constraints provide strong filtering algorithms to reduce the search space when solving large combinatorial problems. In this paper we propose to make the global constraints dynamic, i.e., to allow extending the set of constrained variables during search. We describe a generic dynamisation technique for an arbitrary monotonic global constraint and we compare it with the semantic-based dynamisation for the alldifferent constraint. At the end we sketch a dynamisation technique for non-monotonic global constraints. A comparison with existing methods to model dynamic problems is given as well. 相似文献
998.
周英告 《高校应用数学学报(英文版)》2003,18(1):53-58
§ 1 IntroductionConsiderthenonautonomousdelaylogisticdifferenceequationΔyn =pnyn( 1 - yτ(n) ) ,n =0 ,1 ,2 ,...,( 1 1 )wherepn ∞n =0 isasequenceofpositiverealnumbers ,τ(n) ∞n =0 isanondecreasingsequenceofintegers,τ(n) <nandlimn→∞τ(n) =∞ ,Δyn=yn +1- yn.Motivatedbyplausibleapplications… 相似文献
999.
Closed kernel systems of the coalition matrix turn out to correspond to cones of games on which the core correspondence is
additive and on which the related barycentric solution is additive, stable and continuous. Different perfect cones corresponding
to closed kernel systems are described.
Received: December 2001/Revised: July 2002
RID="*"
ID="*" This note contains the new results, which were presented by the first author in an invited lecture at the XIV Italian
Meeting on Game Theory and Applications in Ischia, July 2001. The lecture was dedicated to Irinel Dragan on the occasion of
his seventieth birthday. 相似文献
1000.