全文获取类型
收费全文 | 41839篇 |
免费 | 5997篇 |
国内免费 | 5381篇 |
专业分类
化学 | 30896篇 |
晶体学 | 530篇 |
力学 | 2408篇 |
综合类 | 476篇 |
数学 | 4584篇 |
物理学 | 14323篇 |
出版年
2024年 | 99篇 |
2023年 | 749篇 |
2022年 | 1124篇 |
2021年 | 1336篇 |
2020年 | 1549篇 |
2019年 | 1547篇 |
2018年 | 1279篇 |
2017年 | 1220篇 |
2016年 | 1802篇 |
2015年 | 1799篇 |
2014年 | 2262篇 |
2013年 | 3036篇 |
2012年 | 3691篇 |
2011年 | 3889篇 |
2010年 | 2597篇 |
2009年 | 2524篇 |
2008年 | 2758篇 |
2007年 | 2598篇 |
2006年 | 2322篇 |
2005年 | 1901篇 |
2004年 | 1514篇 |
2003年 | 1256篇 |
2002年 | 1205篇 |
2001年 | 972篇 |
2000年 | 879篇 |
1999年 | 909篇 |
1998年 | 756篇 |
1997年 | 700篇 |
1996年 | 784篇 |
1995年 | 620篇 |
1994年 | 559篇 |
1993年 | 461篇 |
1992年 | 429篇 |
1991年 | 378篇 |
1990年 | 319篇 |
1989年 | 228篇 |
1988年 | 193篇 |
1987年 | 153篇 |
1986年 | 151篇 |
1985年 | 139篇 |
1984年 | 108篇 |
1983年 | 76篇 |
1982年 | 48篇 |
1981年 | 41篇 |
1980年 | 23篇 |
1978年 | 20篇 |
1977年 | 24篇 |
1976年 | 23篇 |
1975年 | 30篇 |
1974年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
131.
132.
In this paper, nonconvex multiobjective optimization problems are studied. New characterizations of a properly efficient solution in the sense of Geoffrion's are established in terms of the stability of one scalar optimization problem and the existence of an exact penalty function of a scalar constrained program, respectively. One of the characterizations is applied to derive necessary conditions for a properly efficient control-parameter pair of a nonconvex multiobjective discrete optimal control problem with linear constraints. 相似文献
133.
C.-S. Huang T. Li L. Wei Q.-S. Yan 《The European Physical Journal C - Particles and Fields》2002,23(1):195-199
It is shown that new sources of CP violation can be generated in models with more than one extra dimension. In the supersymmetric models on the space-time , where the radius moduli have auxiliary vacuum expectation values and the supersymmetry breaking is mediated by the Kaluza–Klein
states of the gauge supermultiplets, we analyze the gaugino masses and trilinear couplings for two scenarios and obtain the
result that there exist relative CP violating phases among the gaugino masses and trilinear couplings.
Received: 10 October 2001 / Published online: 20 December 2001 相似文献
134.
遥感傅里叶变换红外光谱层析技术是一项新的气体分析技术,它可用于构造气体浓度峰图形,定量分析工业污染气体总释放量等方面,随着算法的不断优化,在重构气体在空间的分布方面,遥感傅里叶变换红外光谱层析技术正在不断成长。 相似文献
135.
136.
Ying Zhang Gang Hu Shigang Chen H.A. Cerdeira 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):381-384
A method of controlling global stochasticity in Hamiltonian systems by applying nonlinear perturbation is proposed. With the
well-known standard map we demonstrate that this control method can convert global stochasticity into regular motion in a
wide chaotic region for arbitrary initial condition, in which the control signal remains very weak after a few kicks. The
system in which chaos has been controlled approximates to the original Hamiltonian system, and this approach appears robust
against small external noise. The mechanism underlying this high control efficiency is intuitively explained.
Received 15 January 2002 Published online 6 June 2002 相似文献
137.
This paper proposes a new method that extends the efficient global optimization to address stochastic black-box systems. The
method is based on a kriging meta-model that provides a global prediction of the objective values and a measure of prediction
uncertainty at every point. The criterion for the infill sample selection is an augmented expected improvement function with
desirable properties for stochastic responses. The method is empirically compared with the revised simplex search, the simultaneous
perturbation stochastic approximation, and the DIRECT methods using six test problems from the literature. An application
case study on an inventory system is also documented. The results suggest that the proposed method has excellent consistency
and efficiency in finding global optimal solutions, and is particularly useful for expensive systems. 相似文献
138.
Improving Construction for Connected Dominating Set with Steiner Tree in Wireless Sensor Networks 总被引:2,自引:0,他引:2
Manki Min Hongwei Du Xiaohua Jia Christina Xiao Huang Scott C.-H. Huang Weili Wu 《Journal of Global Optimization》2006,35(1):111-119
The connected dominating set plays an important role in ad hoc wireless networking. Many constructions for approximating the minimum connected dominating set have been proposed in the
literature. In this paper, we propose a new one with Steiner tree, which produces approximation solution within a factor of
6.8 from optimal. This approximation algorithm can also be implemented distributedly. 相似文献
139.
Yuanqiu Huang 《Discrete Applied Mathematics》2007,155(3):405-409
A stable set of a graph is a vertex set in which any two vertices are not adjacent. It was proven in [A. Brandstädt, V.B. Le, T. Szymczak, The complexity of some problems related to graph 3-colorability, Discrete Appl. Math. 89 (1998) 59-73] that the following problem is NP-complete: Given a bipartite graph G, check whether G has a stable set S such thatG-Sis a tree. In this paper we prove the following problem is polynomially solvable: Given a graph G with maximum degree 3 and containing no vertices of degree 2, check whether G has a stable set S such thatG-Sis a tree. Thus we partly answer a question posed by the authors in the above paper. Moreover, we give some structural characterizations for a graph G with maximum degree 3 that has a stable set S such that G-S is a tree. 相似文献
140.
Jiaqiang Wang Hua Fang Ying Li Junjie Li Zhiying Yan 《Journal of molecular catalysis. A, Chemical》2006,250(1-2):75-79
Cobalt-doped mesoporous titania with a crystalline framework synthesized by surfactant templating method presented highly selective (99%) and reasonable conversion rate (49%) of catalytic oxidation of para-chlorotoluene to para-chlorobenzaldehyde in acetic acid using aqueous hydrogen peroxide as oxidant for the first time. Recycling of the catalyst indicates that the catalyst can be used a number of times without losing its activity to a greater extent. By contrast, cobalt-doped mesoporous titania without a crystalline structure and cobalt doped the commercial titania, Degussa P25 prepared by impregnation method with the similar concentration of cobalt were found inactive. The effects of catalyst concentration, reaction time, reaction temperature, and solvents on the performance of the catalyst were also investigated. 相似文献