全文获取类型
收费全文 | 489篇 |
免费 | 18篇 |
国内免费 | 6篇 |
专业分类
化学 | 278篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 178篇 |
物理学 | 52篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 16篇 |
2020年 | 4篇 |
2019年 | 10篇 |
2018年 | 16篇 |
2017年 | 18篇 |
2016年 | 20篇 |
2015年 | 24篇 |
2014年 | 16篇 |
2013年 | 35篇 |
2012年 | 39篇 |
2011年 | 26篇 |
2010年 | 27篇 |
2009年 | 16篇 |
2008年 | 32篇 |
2007年 | 29篇 |
2006年 | 19篇 |
2005年 | 20篇 |
2004年 | 19篇 |
2003年 | 15篇 |
2002年 | 14篇 |
2001年 | 10篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有513条查询结果,搜索用时 15 毫秒
481.
Zsolt Tuza 《Graphs and Combinatorics》1991,7(1):89-93
Upper and lower bounds are given for the minimum number of perfect (induced or partial) subgraphs covering or partitioning the vertex set or the edge set of a graph ofn vertices. Also, weighted versions of the problems are investigated.Research supported in part by the OTKA Research Fund of the Hungarian Academy of Sciences, Grant No. 1812. 相似文献
482.
Karoly Bezdek Zsolt Langi Marton Naszodi Peter Papez 《Discrete and Computational Geometry》2007,38(2):201-230
We study two notions. One is that of spindle convexity. A set of circumradius not greater than one is spindle convex if, for
any pair of its points, it contains every short circular arc of radius at least one, connecting them. The other objects of
study are bodies obtained as intersections of finitely many balls of the same radius, called ball-polyhedra. We find analogues
of several results on convex polyhedral sets for ball-polyhedra. 相似文献
483.
484.
Zsolt Patakfalvi 《Discrete Mathematics》2008,308(12):2351-2365
A graph is called normal if its vertex set can be covered by cliques Q1,Q2,…,Qk and also by stable sets S1,S2,…,Sl, such that Si∩Qj≠∅ for every i,j. This notion is due to Körner, who introduced the class of normal graphs as an extension of the class of perfect graphs. Normality has also relevance in information theory. Here we prove, that the line graphs of cubic graphs are normal. 相似文献
485.
Zsolt Páles 《Journal of Mathematical Analysis and Applications》2008,344(1):55-75
The extension to infinite dimensional domains of Clarke's generalized Jacobian is the focus of this paper. First, a generalization of a Fabian-Preiss theorem to the infinite dimensional setting is obtained. As a consequence, a new formula relating the Clarke's generalized Jacobians corresponding to finite dimensional spaces K, L with K⊆L is established. Furthermore, in the infinite dimensional case, basic properties pertaining the generalized Jacobian are developed and then an identification of this set-valued map is produced. Applications of these results in the form of chain rules including sum and product rules, and a computational formula for continuous selections are derived. 相似文献
486.
Let C be a convex body in the Euclidean plane. The relative distance of points p and q is twice the Euclidean distance of p and q divided by the Euclidean length of a longest chord in C with the direction, say, from p to q. We prove that, among any seven points of a plane convex body, there are two points at relative distance at most one, and
one cannot be replaced by a smaller value. We apply our result to determine the diameter of point sets in normed planes.
Zsolt Lángi: Partially supported by the Hung. Nat. Sci. Found. (OTKA), grant no. T043556 and T037752 and by the Alberta Ingenuity
Fund. 相似文献
487.
Kotek G Berente Z Schwarcz A Vajda Z Hadjiev J Horvath I Repa I Miseta A Bogner P 《Magnetic resonance imaging》2009,27(2):279-284
The purpose of this study was to investigate the effects of biophysical factors on the diffusion and the relaxation time T(2) independently. Certain properties of the extracellular and the intracellular space may change radically in pathological conditions resulting in water diffusion changes. A tissue model consisting of red blood cells was studied. The extra- and intracellular spaces were modified osmotically and by suspending medium concentration. Diffusion measurements were evaluated with regard to the effective medium theory. Neither the nature of the protein in the extracellular space nor an increased level of intracellular hydration caused a significant net water diffusion change in the cell suspension. The relaxation time T(2) exhibited very little dependence on the extracellular volume fraction or the concentration or the nature of the protein in the extracellular space. An increased level of intracellular hydration resulted in systematically larger T(2) values. It seems probable that increases in extracellular protein concentrations or in the extent of intracellular hydration do not play a significant role in the diffusion changes detected in pathological conditions. T(2) appears to depend on the level of hydration or the total water content but is seemingly less dependent of the concentration and the nature of the extracellular protein in our model solutions. 相似文献
488.
Zuhayra M Kampen WU Henze E Soti Z Zsolnai L Huttner G Oberdorfer F 《Journal of the American Chemical Society》2006,128(2):424-425
A virtually planar water tetramer in which the water molecules are virtually tetrahedrally coordinated could be realized in the solid in a three-dimensional network of [Tc4(CO)12-(mu3-OH)4.4H2O]. The network could be produced by cocrystallization of the new cubane-like cluster [Tc(CO)3-(mu3-OH)]4 and water as a complementary component. The amphiphilic behavior of cluster and water results in a highly ordered three-dimensional network. The complementary components, the water tetramer and the cubic cluster, independently of one another form two interpenetrating tetragonal lattice networks held together exclusively by hydrogen bonds. 相似文献
489.
Wang L Warburton PL Szekeres Z Surjan P Mezey PG 《Journal of chemical information and modeling》2005,45(4):850-855
The geometrical structures and properties of conjugated polyhelicenes and annelated fused-ring carbon helices with analogous frameworks were theoretically studied at the HF/6-31G and B3LYP/6-31G levels. These studies focused on the stability of the fused-ring structures with special emphasis on the helical geometrical arrangements. To elucidate bonding patterns, the orbitals, electron density contours, and the electrostatic potential of these helical compounds were analyzed. The structure of fused polynaphthalenes arranged in a helical spiral can be regarded as part of a locally helical graphite lattice that is expected to give rise to special electronic properties along the helically layered conjugated single sheet that can be regarded as a single extended pi system but also involving local layer-to-layer pi-pi interactions that are typical in ordinary graphite. This dual feature might lead to novel materials. 相似文献
490.