全文获取类型
收费全文 | 7599篇 |
免费 | 859篇 |
国内免费 | 353篇 |
专业分类
化学 | 1547篇 |
晶体学 | 18篇 |
力学 | 457篇 |
综合类 | 76篇 |
数学 | 4530篇 |
物理学 | 2183篇 |
出版年
2024年 | 7篇 |
2023年 | 36篇 |
2022年 | 125篇 |
2021年 | 120篇 |
2020年 | 115篇 |
2019年 | 266篇 |
2018年 | 301篇 |
2017年 | 148篇 |
2016年 | 159篇 |
2015年 | 184篇 |
2014年 | 412篇 |
2013年 | 496篇 |
2012年 | 409篇 |
2011年 | 648篇 |
2010年 | 518篇 |
2009年 | 605篇 |
2008年 | 610篇 |
2007年 | 652篇 |
2006年 | 513篇 |
2005年 | 343篇 |
2004年 | 311篇 |
2003年 | 288篇 |
2002年 | 199篇 |
2001年 | 149篇 |
2000年 | 152篇 |
1999年 | 142篇 |
1998年 | 146篇 |
1997年 | 102篇 |
1996年 | 109篇 |
1995年 | 77篇 |
1994年 | 67篇 |
1993年 | 65篇 |
1992年 | 54篇 |
1991年 | 42篇 |
1990年 | 26篇 |
1989年 | 29篇 |
1988年 | 29篇 |
1987年 | 28篇 |
1986年 | 22篇 |
1985年 | 25篇 |
1984年 | 17篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有8811条查询结果,搜索用时 31 毫秒
11.
Michael Carr 《Topology and its Applications》2006,153(12):2155-2168
Given a graph Γ, we construct a simple, convex polytope, dubbed graph-associahedra, whose face poset is based on the connected subgraphs of Γ. This provides a natural generalization of the Stasheff associahedron and the Bott-Taubes cyclohedron. Moreover, we show that for any simplicial Coxeter system, the minimal blow-ups of its associated Coxeter complex has a tiling by graph-associahedra. The geometric and combinatorial properties of the complex as well as of the polyhedra are given. These spaces are natural generalizations of the Deligne-Knudsen-Mumford compactification of the real moduli space of curves. 相似文献
12.
Yevhen Zelenyuk 《Topology and its Applications》2006,153(14):2382-2385
We introduce the notion of a partially selective ultrafilter and prove that (a) if G is an extremally disconnected topological group and p is a converging nonprincipal ultrafilter on G containing a countable discrete subset, then p is partially selective, and (b) the existence of a nonprincipal partially selective ultrafilter on a countable set implies the existence of a P-point in ω∗. Thus it is consistent with ZFC that there is no extremally disconnected topological group containing a countable discrete nonclosed subset. 相似文献
13.
带干扰的多险种风险模型 总被引:2,自引:0,他引:2
由于保险公司风险经营规模不断扩大,用单一险种的模型来描述风险过程存在局限性,本文讨论了带干扰多险种风险模型,应用鞅论方法,得出伦德伯格不等式和最终破产概率公式。 相似文献
14.
15.
16.
Parallel to Cox's [JRSS B34 (1972) 187-230] proportional hazards model, generalized logistic models have been discussed by Anderson [Bull. Int. Statist. Inst. 48 (1979) 35-53] and others. The essential assumption is that the two densities ratio has a known parametric form. A nice property of this model is that it naturally relates to the logistic regression model for categorical data. In astronomic, demographic, epidemiological, and other studies the variable of interest is often truncated by an associated variable. This paper studies generalized logistic models for the two-sample truncated data problem, where the two lifetime densities ratio is assumed to have the form exp{α+φ(x;β)}. Here φ is a known function of x and β, and the baseline density is unspecified. We develop a semiparametric maximum likelihood method for the case where the two samples have a common truncation distribution. It is shown that inferences for β do not depend the nonparametric components. We also derive an iterative algorithm to maximize the semiparametric likelihood for the general case where different truncation distributions are allowed. We further discuss how to check goodness of fit of the generalized logistic model. The developed methods are illustrated and evaluated using both simulated and real data. 相似文献
17.
F. Balibrea 《Topology and its Applications》2006,153(12):2092-2095
Recently, Forti, Paganoni and Smítal constructed an example of a triangular map of the unite square, F(x,y)=(f(x),g(x,y)), possessing periodic orbits of all periods and such that no infinite ω-limit set of F contains a periodic point. In this note we show that the above quoted map F has a homoclinic orbit. As a consequence, we answer in the negative the problem presented by A.N. Sharkovsky in the eighties whether, for a triangular map of the square, existence of a homoclinic orbit implies the existence of an infinite ω-limit set containing a periodic point. It is well known that, for a continuous map of the interval, the answer is positive. 相似文献
18.
19.
平行机半在线排序问题研究(Ⅰ) 总被引:15,自引:1,他引:14
对半在线平行机排序问题的研究进展作了详细综述和进一步探讨。文章给出半在线排序问题的背景、定义、分类和求解。介绍它们定义和在不同机器环境和目标函数下半在线排序问题分类,以及第一类半在线模型的近似算法的设计及其竞争比分析。 相似文献
20.