全文获取类型
收费全文 | 4577篇 |
免费 | 369篇 |
国内免费 | 222篇 |
专业分类
化学 | 216篇 |
晶体学 | 4篇 |
力学 | 214篇 |
综合类 | 41篇 |
数学 | 3665篇 |
物理学 | 1028篇 |
出版年
2024年 | 12篇 |
2023年 | 66篇 |
2022年 | 94篇 |
2021年 | 75篇 |
2020年 | 156篇 |
2019年 | 148篇 |
2018年 | 146篇 |
2017年 | 137篇 |
2016年 | 111篇 |
2015年 | 105篇 |
2014年 | 175篇 |
2013年 | 362篇 |
2012年 | 170篇 |
2011年 | 257篇 |
2010年 | 228篇 |
2009年 | 381篇 |
2008年 | 360篇 |
2007年 | 297篇 |
2006年 | 265篇 |
2005年 | 187篇 |
2004年 | 208篇 |
2003年 | 192篇 |
2002年 | 162篇 |
2001年 | 123篇 |
2000年 | 110篇 |
1999年 | 108篇 |
1998年 | 85篇 |
1997年 | 85篇 |
1996年 | 60篇 |
1995年 | 31篇 |
1994年 | 39篇 |
1993年 | 34篇 |
1992年 | 33篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 20篇 |
1988年 | 16篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1973年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有5168条查询结果,搜索用时 15 毫秒
21.
A signed graph has a plus or minus sign on each edge. A simple cycle is positive or negative depending on whether it contains an even or odd number of negative edges, respectively. We consider embeddings of a signed graph in the projective plane for which a simple cycle is essential if and only if it is negative. We characterize those signed graphs that have such a projective-planar embedding. Our characterization is in terms of a related signed graph formed by considering the theta subgraphs in the given graph. 相似文献
22.
We derive a test problem for evaluating the ability of time-steppingmethods to preserve the statistical properties of systems inmolecular dynamics. We consider a family of deterministic systemsconsisting of a finite number of particles interacting on acompact interval. The particles are given random initial conditionsand interact through instantaneous energy- and momentum-conservingcollisions. As the number of particles, the particle density,and the mean particle speed go to infinity, the trajectory ofa tracer particle is shown to converge to a stationary Gaussianstochastic process. We approximate this system by one describedby a system of ordinary differential equations and provide numericalevidence that it converges to the same stochastic process. Wesimulate the latter system with a variety of numerical integrators,including the symplectic Euler method, a fourth-order Runge-Kuttamethod, and an energyconserving step-and-project method. Weassess the methods' ability to recapture the system's limitingstatistics and observe that symplectic Euler performs significantlybetter than the others for comparable computational expense. 相似文献
23.
In the present paper we give necessary and sufficient conditions for the subgroup separability of the fundamental group of a finite graph of groups with finitely generated abelian vertex groups.
24.
A.R.ELAMROUSS 《数学学报(英文版)》2005,21(1):129-142
This paper contains a generalization of the well-known Palais-Smale and Cerami compactness conditions. The compactness condition introduced is used to prove some general existence theorems for critical points. Some applications are given to differential equations. 相似文献
25.
Zhu Da xin 《数学年刊B辑(英文版)》1994,15(3):293-298
ACOMPLETEMETRICOFPOSITIVECURVATUREONR~nANDEXISTENCEOFCLOSEDGEODESICS¥ZHUDAXIN(DepartmentofMathematics,TianjinUniversitylTianj?.. 相似文献
26.
Let P(G,λ) be the chromatic polynomial of a graph G with n vertices, independence number α and clique number ω. We show that for every λ≥n, ()α≤≤ ()
n
−ω. We characterize the graphs that yield the lower bound or the upper bound.?These results give new bounds on the mean colour
number μ(G) of G: n− (n−ω)()
n
−ω≤μ(G)≤n−α() α.
Received: December 12, 2000 / Accepted: October 18, 2001?Published online February 14, 2002 相似文献
27.
28.
Based on the theory of calculus of variation, some suffcient conditions are given for some Euler-Lagrangcequations to be equivalently represented by finite or even infinite many Hamiltonian canonical equations. Meanwhile,some further applications for equations such as the KdV equation, MKdV equation, the general linear Euler Lagrangeequation and the cylindric shell equations are given. 相似文献
29.
A tree T is arbitrarily vertex decomposable if for any sequence τ of positive integers adding up to the order of T there is a sequence of vertex-disjoint subtrees of T whose orders are given by τ. An on-line version of the problem of characterizing arbitrarily vertex decomposable trees is completely solved here. 相似文献
30.
The notion of balanced bipartitions of the vertices in a tree T was introduced and studied by Reid (Networks 34 (1999) 264). Reid proved that the set of balance vertices of a tree T consists of a single vertex or two adjacent vertices. In this note, we give a simple proof of that result. 相似文献