全文获取类型
收费全文 | 4563篇 |
免费 | 309篇 |
国内免费 | 285篇 |
专业分类
化学 | 569篇 |
晶体学 | 7篇 |
力学 | 123篇 |
综合类 | 64篇 |
数学 | 1106篇 |
物理学 | 781篇 |
综合类 | 2507篇 |
出版年
2024年 | 3篇 |
2023年 | 22篇 |
2022年 | 49篇 |
2021年 | 63篇 |
2020年 | 92篇 |
2019年 | 59篇 |
2018年 | 79篇 |
2017年 | 72篇 |
2016年 | 99篇 |
2015年 | 97篇 |
2014年 | 150篇 |
2013年 | 231篇 |
2012年 | 194篇 |
2011年 | 244篇 |
2010年 | 251篇 |
2009年 | 297篇 |
2008年 | 277篇 |
2007年 | 375篇 |
2006年 | 344篇 |
2005年 | 294篇 |
2004年 | 242篇 |
2003年 | 239篇 |
2002年 | 188篇 |
2001年 | 160篇 |
2000年 | 147篇 |
1999年 | 109篇 |
1998年 | 89篇 |
1997年 | 85篇 |
1996年 | 89篇 |
1995年 | 52篇 |
1994年 | 77篇 |
1993年 | 53篇 |
1992年 | 49篇 |
1991年 | 39篇 |
1990年 | 53篇 |
1989年 | 43篇 |
1988年 | 23篇 |
1987年 | 31篇 |
1986年 | 8篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有5157条查询结果,搜索用时 859 毫秒
41.
In hardware design, it is necessary to simulate the anticipated behavior of the integrated circuit before it is actually cast in silicon. As simulation procedures are long due to the great number of tests to be performed, optimization of the simulation code is of prime importance. This paper describes two mathematical models for the minimization of the memory access times for a cycle-based simulator.An integrated circuit being viewed as a directed acyclic graph, the problem consists in building a graph order on the vertices, compatible with the relation order induced by the graph, in order to minimize a cost function that represents the memory access time. For both proposed cost functions, we show that the corresponding problems are NP-complete. However, we show that the special cases where the graphs are in-trees or out-trees can be solved in polynomial time. 相似文献
42.
Wei-nan E Ping-bing Ming 《应用数学学报(英文版)》2007,23(4):529-550
We study continuum and atomistic models for the elastodynamics of crystalline solids at zerotemperature.We establish sharp criterion for the regime of validity of the nonlinear elastic wave equationsderived from the well-known Cauchy-Born rule. 相似文献
43.
Michael I. Mishchenko 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,101(3):411-415
The volume integral equation formalism is used to prove the scale invariance rule for an arbitrarily sized scatterer with an arbitrary shape, morphology, and orientation. The only assumptions are that the scatterer is made of optically isotropic linear materials and is embedded in a homogeneous, linear, isotropic, and nonabsorbing infinite medium. 相似文献
44.
A simple microscopic model of charge ordering in the NaxCoO2 system is presented. The model takes into account the interplane interactions between the ordered Na ions and d electrons from the CoO2 layers as well as the nearest-neighbor intraplane Coulomb interactions between d electrons. It is shown that a driving force of charge ordering in the CoO2 layers is the interplane interaction that alone is able to describe various types of inhomogeneous charge ordering (e.g., the striped phases) as well as to predict correctly the conducting properties of the system. 相似文献
45.
Thomas Andreae 《Journal of Graph Theory》2002,39(4):222-229
For a graph A and a positive integer n, let nA denote the union of n disjoint copies of A; similarly, the union of ?0 disjoint copies of A is referred to as ?0A. It is shown that there exist (connected) graphs A and G such that nA is a minor of G for all n??, but ?0A is not a minor of G. This supplements previous examples showing that analogous statements are true if, instead of minors, isomorphic embeddings or topological minors are considered. The construction of A and G is based on the fact that there exist (infinite) graphs G1, G2,… such that Gi is not a minor of Gj for all i ≠ j. In contrast to previous examples concerning isomorphic embeddings and topological minors, the graphs A and G presented here are not locally finite. The following conjecture is suggested: for each locally finite connected graph A and each graph G, if nA is a minor of G for all n ? ?, then ?0A is a minor of G, too. If true, this would be a far‐reaching generalization of a classical result of R. Halin on families of disjoint one‐way infinite paths in graphs. © 2002 Wiley Periodicals, Inc. J Graph Theory 39: 222–229, 2002; DOI 10.1002/jgt.10016 相似文献
46.
47.
Koichi Itoh Takeji Takui 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2004,80(2):29
This review paper deals with an overview of molecule-based magnetism as a rapidly developing interdisciplinary field, topological symmetry rule as the first principle of spin alignment in organic open-shell systems in the ground state, the proposal of organic through-bond 1D and 2D ferro- and superparamagnets and the detection of the first organic high-spin molecule, m-phenylenebis(phenylmethylene) in the quintet ground state (S = 2), followed by extended organic high-spin systems with π-conjugation such as aromatic hydrocarbons having S = 3, 4, 5. The paper also describes a theoretical approach to the understanding of electronic spin structures of organic high-spin molecules by invoking both Heisenberg and Hubbard model Hamiltonians, weakly interacting intramolecular high-spin systems from both experimental and theoretical sides, the spin density distribution of the first organic high-spin molecule in terms of electron- nuclear multiple resonance spectroscopy and the detection and characterization of ionic high-spin hydrocarbons, emphasizing the establishment of high spin chemistry underlying organic molecular magnetism. 相似文献
48.
49.
基于现行法定资本体制不考虑信用投资组合的多样化和限制空头信用风险头寸的补偿能力,设计了一种考虑补偿的信用风险资本要求的计算方法.该算法根据信用等级决定风险权重,可以更精确地测定信用风险资本.采用期限分段方法建立一个期间结构,区分当前和远期信用风险,考虑多头与空头信用风险头寸间的补偿. 相似文献
50.
王志敏 《上海应用技术学院学报:自然科学版》2004,4(2):126-129
在OLAP和数据挖掘的理论基础上,介绍在开发高校CET-4和CET-6通过率模拟预测系统过程中如何应用OLAP和数据挖掘技术来实现预测功能。 相似文献