全文获取类型
收费全文 | 77547篇 |
免费 | 7075篇 |
国内免费 | 11212篇 |
专业分类
化学 | 50797篇 |
晶体学 | 730篇 |
力学 | 3854篇 |
综合类 | 1363篇 |
数学 | 19082篇 |
物理学 | 20008篇 |
出版年
2023年 | 821篇 |
2022年 | 1925篇 |
2021年 | 2402篇 |
2020年 | 1869篇 |
2019年 | 1824篇 |
2018年 | 1576篇 |
2017年 | 2004篇 |
2016年 | 2315篇 |
2015年 | 2184篇 |
2014年 | 3171篇 |
2013年 | 5021篇 |
2012年 | 4234篇 |
2011年 | 4023篇 |
2010年 | 3609篇 |
2009年 | 4520篇 |
2008年 | 4885篇 |
2007年 | 5266篇 |
2006年 | 4282篇 |
2005年 | 3589篇 |
2004年 | 3397篇 |
2003年 | 3055篇 |
2002年 | 5337篇 |
2001年 | 2745篇 |
2000年 | 2161篇 |
1999年 | 1908篇 |
1998年 | 1773篇 |
1997年 | 1477篇 |
1996年 | 1436篇 |
1995年 | 1292篇 |
1994年 | 1142篇 |
1993年 | 1076篇 |
1992年 | 1068篇 |
1991年 | 814篇 |
1990年 | 693篇 |
1989年 | 597篇 |
1988年 | 586篇 |
1987年 | 480篇 |
1986年 | 466篇 |
1985年 | 544篇 |
1984年 | 426篇 |
1983年 | 280篇 |
1982年 | 371篇 |
1981年 | 534篇 |
1980年 | 461篇 |
1979年 | 509篇 |
1978年 | 404篇 |
1977年 | 305篇 |
1976年 | 257篇 |
1974年 | 131篇 |
1973年 | 200篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
In this paper we give a realization of some symmetric space G/K as a closed submanifold P of G. We also give several equivalent representations of the submanifold P. Some properties of the set gK∩P are also discussed, where gK is a coset space in G. 相似文献
72.
In this paper, by using qualitative analysis, we investigate the number of limit cycles of perturbed cubic Hamiltonian system with perturbation in the form of (2n+2m) or (2n+2m+1)th degree polynomials . We show that the perturbed systems has at most (n+m) limit cycles, and has at most n limit cycles if m=1. If m=1, n=1 and m=1, n=2, the general conditions for the number of existing limit cycles and the stability of the limit cycles will be established, respectively. Such conditions depend on the coefficients of the perturbed terms. In order to illustrate our results, two numerical examples on the location and stability of the limit cycles are given. 相似文献
73.
一类机器人系统的最优控制 总被引:1,自引:1,他引:0
王辉 《数学的实践与认识》2002,32(3):455-459
本文通过把结构阻尼系数当作控制变量来讨论一类弹性机器人系统的最优控制问题 ,并利用Banach空间几何性质证明了最优控制元的存在唯一性 相似文献
74.
Summary In 1980 Dahmen-DeVore-Scherer introduced a modulus of continuity which turns out to reflect invariance properties of compound cubature rules effectively. Accordingly, sharp error bounds are derived, the existence of relevant counterexamples being a consequence of a quantitative resonance principle, established previously. 相似文献
75.
Camillo Costantini 《Topology and its Applications》2006,153(7):1056-1078
For X a metrizable space and (Y,ρ) a metric space, with Y pathwise connected, we compute the density of (C(X,(Y,ρ)),σ)—the space of all continuous functions from X to (Y,ρ), endowed with the supremum metric σ. Also, for (X,d) a metric space and (Y,‖⋅‖) a normed space, we compute the density of (UC((X,d),(Y,ρ)),σ) (the space of all uniformly continuous functions from (X,d) to (Y,ρ), where ρ is the metric induced on Y by ‖⋅‖). We also prove that the latter result extends only partially to the case where (Y,ρ) is an arbitrary pathwise connected metric space.To carry such an investigation out, the notions of generalized compact and generalized totally bounded metric space, introduced by the author and A. Barbati in a former paper, turn out to play a crucial rôle. Moreover, we show that the first-mentioned concept provides a precise characterization of those metrizable spaces which attain their extent. 相似文献
76.
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
77.
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
78.
79.
论大学物理实验体系建设与教学改革 总被引:3,自引:1,他引:2
传统的物理实验是按普通物理、电子线路和近代物理等内容进行划分,这种体系突出了学科的系统性,但忽视了学科之间的兼容互补性,各学科相互独立,限制了学生跨学科思维能力和创新能力的培养,建立现代物理实验教学新体系是大学物理实验教学改革的必然趋势.新的物理实验体系应依照训练层次,划分为引导性实验、基本实验、综合性实验、设计性实验、研究性实验.并需要注重时代性和先进性,改革和更新大学物理实验教学内容,改革实验教学与管理模式,形成新的运行机制,从而达到学生素质和能力的提高. 相似文献
80.