全文获取类型
收费全文 | 10678篇 |
免费 | 286篇 |
国内免费 | 288篇 |
专业分类
化学 | 2023篇 |
晶体学 | 78篇 |
力学 | 49篇 |
综合类 | 22篇 |
数学 | 8121篇 |
物理学 | 959篇 |
出版年
2023年 | 47篇 |
2022年 | 71篇 |
2021年 | 75篇 |
2020年 | 100篇 |
2019年 | 232篇 |
2018年 | 218篇 |
2017年 | 120篇 |
2016年 | 129篇 |
2015年 | 143篇 |
2014年 | 286篇 |
2013年 | 537篇 |
2012年 | 315篇 |
2011年 | 655篇 |
2010年 | 575篇 |
2009年 | 668篇 |
2008年 | 766篇 |
2007年 | 795篇 |
2006年 | 655篇 |
2005年 | 432篇 |
2004年 | 379篇 |
2003年 | 352篇 |
2002年 | 291篇 |
2001年 | 213篇 |
2000年 | 220篇 |
1999年 | 277篇 |
1998年 | 272篇 |
1997年 | 210篇 |
1996年 | 231篇 |
1995年 | 268篇 |
1994年 | 225篇 |
1993年 | 211篇 |
1992年 | 188篇 |
1991年 | 109篇 |
1990年 | 117篇 |
1989年 | 126篇 |
1988年 | 77篇 |
1987年 | 58篇 |
1986年 | 57篇 |
1985年 | 79篇 |
1984年 | 79篇 |
1983年 | 55篇 |
1982年 | 70篇 |
1981年 | 47篇 |
1980年 | 44篇 |
1979年 | 52篇 |
1978年 | 43篇 |
1977年 | 21篇 |
1976年 | 19篇 |
1975年 | 15篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 250 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.
14.
Summary In this paper a Gauss-Jordan algorithm with column interchanges is presented and analysed. We show that, in contrast with Gaussian elimination, the Gauss-Jordan algorithm has essentially differing properties when using column interchanges instead of row interchanges for improving the numerical stability. For solutions obtained by Gauss-Jordan with column interchanges, a more satisfactory bound for the residual norm can be given. The analysis gives theoretical evidence that the algorithm yields numerical solutions as good as those obtained by Gaussian elimination and that, in most practical situations, the residuals are equally small. This is confirmed by numerical experiments. Moreover, timing experiments on a Cyber 205 vector computer show that the algorithm presented has good vectorisation properties. 相似文献
15.
16.
The paper provides significant simplifications and extensions of results obtained by Gorsich, Genton, and Strang (J. Multivariate Anal. 80 (2002) 138) on the structure of spatial design matrices. These are the matrices implicitly defined by quadratic forms that arise naturally in modelling intrinsically stationary and isotropic spatial processes. We give concise structural formulae for these matrices, and simple generating functions for them. The generating functions provide formulae for the cumulants of the quadratic forms of interest when the process is Gaussian, second-order stationary and isotropic. We use these to study the statistical properties of the associated quadratic forms, in particular those of the classical variogram estimator, under several assumptions about the actual variogram. 相似文献
17.
Chuanming Zong 《Monatshefte für Mathematik》2002,134(3):247-255
In this article we study the simultaneous packing and covering constants of two-dimensional centrally symmetric convex domains.
Besides an identity result between translative case and lattice case and a general upper bound, exact values for some special
domains are determined. Similar to Mahler and Reinhardt’s result about packing densities, we show that the simultaneous packing
and covering constant of an octagon is larger than that of a circle.
(Received 17 January 2001; in revised form 13 July 2001) 相似文献
18.
Wincenty Turek Mieczyslaw Lapkowski Agnieszka Stolarczyk 《Applied Surface Science》2005,252(3):801-806
The goal of our studies was to determine the nature of interactions between catalytic active samples, such as polypyrrole (PPy) doped with: chloride anions, heteropolyacids such as H5PMo10V2O40, or H4SiW12O40, and oxygen particles. In order to reveal the mechanism of the linkage between the catalysts and oxygen we provided the electron paramagnetic resonance (EPR) measurements of synthesized samples in O2 and N2 flow. Moreover, the X-ray photoelectron spectroscopy (XPS) measurements were performed to show the properties of doped heteropolyacids and the state of nitrogen in polypyrrole matrix. The results of EPR studies of PPy(Cl), PPy(H4SiW12O40), PPy(H5PMo10V2O40) samples, show that the polypyrrole doped with chloride anions interacts much easier with oxygen than polypyrrole doped with heteropolyacids (in the above given order, of preference with the most active polypyrrole system first). It correlates with XPS results, which show that a molybdenium-vanadium anion is more reduced than a silicon-tungsten one. The redox reactions of heteropolyacids involve the oxidation-reduction of the conjugated polymer chain, leaving no or little place for interactions with oxygen. Polypyrrole doped with H4SiW12O40 shows some oxygen sensitivity as observed in the EPR studies, as opposed to polypyrrole doped with H5PMo10V2O40, which is in line with the XPS results. 相似文献
19.
20.
The existence of an attractor for a 2D-Navier-Stokes system with delay is proved. The theory of pullback attractors is successfully applied to obtain the results since the abstract functional framework considered turns out to be nonautonomous. However, on some occasions, the attractors may attract not only in the pullback sense but in the forward one as well. Also, this formulation allows to treat, in a unified way, terms containing various classes of delay features (constant, variable, distributed delays, etc.). As a consequence, some results for the autonomous model are deduced as particular cases of our general formulation. 相似文献