全文获取类型
收费全文 | 7572篇 |
免费 | 409篇 |
国内免费 | 504篇 |
专业分类
化学 | 343篇 |
晶体学 | 1篇 |
力学 | 308篇 |
综合类 | 77篇 |
数学 | 4081篇 |
物理学 | 570篇 |
综合类 | 3105篇 |
出版年
2024年 | 16篇 |
2023年 | 68篇 |
2022年 | 111篇 |
2021年 | 103篇 |
2020年 | 142篇 |
2019年 | 148篇 |
2018年 | 151篇 |
2017年 | 181篇 |
2016年 | 154篇 |
2015年 | 127篇 |
2014年 | 282篇 |
2013年 | 458篇 |
2012年 | 300篇 |
2011年 | 402篇 |
2010年 | 384篇 |
2009年 | 478篇 |
2008年 | 481篇 |
2007年 | 529篇 |
2006年 | 471篇 |
2005年 | 367篇 |
2004年 | 357篇 |
2003年 | 328篇 |
2002年 | 294篇 |
2001年 | 278篇 |
2000年 | 265篇 |
1999年 | 227篇 |
1998年 | 234篇 |
1997年 | 176篇 |
1996年 | 156篇 |
1995年 | 104篇 |
1994年 | 104篇 |
1993年 | 72篇 |
1992年 | 80篇 |
1991年 | 76篇 |
1990年 | 60篇 |
1989年 | 78篇 |
1988年 | 42篇 |
1987年 | 30篇 |
1986年 | 23篇 |
1985年 | 26篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 23篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1978年 | 14篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1936年 | 3篇 |
排序方式: 共有8485条查询结果,搜索用时 31 毫秒
21.
T-型树谱唯一性的一个简单刻画 总被引:1,自引:0,他引:1
图G称为谱唯一的,如果任何与G谱相同的图一定与G同构.一棵树称为T-型树如果其仅有一个最大度为3的顶点.本文给出了T-型树谱唯一性的一个简单刻画,从而完全解决了T-型树的谱唯一性问题. 相似文献
22.
Signed graphs for portfolio analysis in risk management 总被引:1,自引:0,他引:1
Harary Frank; Lim Meng-Hiot; Wunsch Donald C. 《IMA Journal of Management Mathematics》2002,13(3):201-210
We introduce the notion of structural balance for signed graphsin the context of portfolio analysis. A portfolio of securitiescan be represented as a signed graph with the nodes denotingthe securities and the edges representing the correlation betweenthe securities. With signed graphs, the characteristics of aportfolio from a risk management perspective can be uncoveredfor analysis purposes. It is shown that a portfolio characterizedby a signed graph of positive and negative edges that is structurallybalanced is characteristically more predictable. Investors whoundertake a portfolio position with all positively correlatedsecurities do so with the intention to speculate on the upside(or downside). If the portfolio consists of negative edges andis balanced, then it is likely that the position has a hedgingdisposition within it. On the other hand, an unbalanced signedgraph is representative of an investment portfolio which ischaracteristically unpredictable. 相似文献
23.
曾六川 《数学年刊A辑(中文版)》2002,(6)
设X是p一致凸Banach空间,具有弱一致正规结构与非严格的Opial性质.又设C是X的非空凸弱紧子集.在适当的条件下,证明了C上每个渐近正则半群T={T(t):t∈S}都有不动点进一步,在类似的条件下,也讨论了一致凸Banach空间中渐近正则半群的不动点的存在性. 相似文献
24.
对高师体育教育专业学生培养的思考 总被引:1,自引:0,他引:1
指出了在高师体育专业学生培养过程中存在的问题,提出了以知识为基础,知识、能力、素质三者和谐统一的理想人才模式,为达到这个目标,提出的对策有:深化课程体系改革;完善对学生的管理;加强教师队伍建设;进行思想品德、人文素质教育;注重实践,促进学生能力发展. 相似文献
25.
V. V. Kozlov 《Functional Analysis and Its Applications》2005,39(4):271-283
We discuss the symplectic geometry of linear Hamiltonian systems with nondegenerate Hamiltonians. These systems can be reduced to linear second-order differential equations characteristic of linear oscillation theory. This reduction is related to the problem on the signatures of restrictions of quadratic forms to Lagrangian planes. We study vortex symplectic planes invariant with respect to linear Hamiltonian systems. These planes are determined by the solutions of quadratic matrix equations of a special form. New conditions for gyroscopic stabilization are found. 相似文献
26.
James Murdock 《Journal of Differential Equations》2004,205(2):424-465
Hypernormal forms (unique normal forms, simplest normal forms) are investigated both from the standpoint of foundational theory and algorithms suitable for use with computer algebra. The Baider theory of the Campbell-Hausdorff group is refined, by a study of its subgroups, to determine the smallest substages into which the hypernormalization process can be divided. This leads to a linear algebra algorithm to compute the generators needed for each substage with the least amount of work. A concrete interpretation of Jan Sanders’ spectral sequence for hypernormal forms is presented. Examples are given, and a proof is given for a little-known theorem of Belitskii expressing the hypernormal form space (in the inner product style) as the kernel of a higher-order differential operator. 相似文献
27.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
28.
A graph G is N2‐locally connected if for every vertex ν in G, the edges not incident with ν but having at least one end adjacent to ν in G induce a connected graph. In 1990, Ryjá?ek conjectured that every 3‐connected N2‐locally connected claw‐free graph is Hamiltonian. This conjecture is proved in this note. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 142–146, 2005 相似文献
29.
30.
Karl Gustafson 《Numerical Linear Algebra with Applications》2004,11(7):649-659
Given the operator product BA in which both A and B are symmetric positive‐definite operators, for which symmetric positive‐definite operators C is BA symmetric positive‐definite in the C inner product 〈x, y〉C? This question arises naturally in preconditioned iterative solution methods, and will be answered completely here. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献