全文获取类型
收费全文 | 19273篇 |
免费 | 3018篇 |
国内免费 | 1090篇 |
专业分类
化学 | 2545篇 |
晶体学 | 96篇 |
力学 | 1563篇 |
综合类 | 208篇 |
数学 | 7359篇 |
物理学 | 5130篇 |
无线电 | 6480篇 |
出版年
2024年 | 33篇 |
2023年 | 182篇 |
2022年 | 313篇 |
2021年 | 432篇 |
2020年 | 550篇 |
2019年 | 540篇 |
2018年 | 529篇 |
2017年 | 695篇 |
2016年 | 769篇 |
2015年 | 733篇 |
2014年 | 1072篇 |
2013年 | 1766篇 |
2012年 | 1210篇 |
2011年 | 1312篇 |
2010年 | 1072篇 |
2009年 | 1121篇 |
2008年 | 1220篇 |
2007年 | 1231篇 |
2006年 | 1091篇 |
2005年 | 966篇 |
2004年 | 832篇 |
2003年 | 833篇 |
2002年 | 730篇 |
2001年 | 633篇 |
2000年 | 573篇 |
1999年 | 505篇 |
1998年 | 380篇 |
1997年 | 345篇 |
1996年 | 298篇 |
1995年 | 224篇 |
1994年 | 185篇 |
1993年 | 140篇 |
1992年 | 124篇 |
1991年 | 127篇 |
1990年 | 83篇 |
1989年 | 63篇 |
1988年 | 44篇 |
1987年 | 50篇 |
1986年 | 41篇 |
1985年 | 71篇 |
1984年 | 48篇 |
1983年 | 28篇 |
1982年 | 37篇 |
1981年 | 38篇 |
1980年 | 10篇 |
1979年 | 23篇 |
1978年 | 18篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 159 毫秒
111.
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
112.
External difference families (EDFs) are a type of new combinatorial designs originated from cryptography. In this paper, some
earlier ideas of recursive and cyclotomic constructions of combinatorial designs are extended, and a number of classes of
EDFs and disjoint difference families are presented. A link between a subclass of EDFs and a special type of (almost) difference
sets is set up. 相似文献
113.
本文针对一类非饱和土壤水流问题,提出了基于二次插值的特征差分格式,得到了严谨的L2模误差估计.并作了数值试验,指明方法的有效性. 相似文献
114.
Masanobu Haraguchi David F. P. Pile Toshihiro Okamoto Masuo Fukui Dmitri K. Gramotnev 《Optical Review》2006,13(4):228-230
We have numerically shown the existence of coupled wedge plasmons (CWPs) which propagates along a nano gap of a twin metal
wedge. The CWPs are formed by wedge plasmons which can interact with each other. The dispersion relations of the wavenumber,
propagation distance, and beam area of CWPs, are described and show that the characteristics of CWPs are similar to those
of wedge plasmons and of gap plasmons. We also propose a new plasmon waveguide composed of twin metal wedges with a nano gap. 相似文献
115.
High even order generalizations of the traditional upwind method are introduced to solve second order ODE-BVPs without recasting
the problem as a first order system. Both theoretical analysis and numerical comparison with central difference schemes of
the same order show that these new methods may avoid typical oscillations and achieve high accuracy. Singular perturbation
problems are taken into account to emphasize the main features of the proposed methods.
AMS subject classification (2000) 65L10, 65L12, 65L50 相似文献
116.
In this paper, we analyze the manufacturing lead time in a production system with BMAP (Batch Markovian Arrival process) input and post-operation operated under the N-policy. We use the factorization principle to derive the waiting time distribution (hence the manufacturing lead time) and the mean performance measures. A numerical example is provided. 相似文献
117.
We construct a new family of cyclic difference sets with parameters ((3
d
– 1)/2, (3
d – 1 – 1)/2, (3
d – 2 – 1)/2) for each odd d. The difference sets are constructed with certain maps that form Jacobi sums. These new difference sets are similar to Maschietti's hyperoval difference sets, of the Segre type, in characteristic two. We conclude by calculating the 3-ranks of the new difference sets. 相似文献
118.
Eckhard Steffen 《Discrete Mathematics》2004,280(1-3):191-214
Cubic bridgeless graphs with chromatic index four are called uncolorable. We introduce parameters measuring the uncolorability of those graphs and relate them to each other. For k=2,3, let ck be the maximum size of a k-colorable subgraph of a cubic graph G=(V,E). We consider r3=|E|−c3 and
. We show that on one side r3 and r2 bound each other, but on the other side that the difference between them can be arbitrarily large. We also compare them to the oddness ω of G, the smallest possible number of odd circuits in a 2-factor of G. We construct cyclically 5-edge connected cubic graphs where r3 and ω are arbitrarily far apart, and show that for each 1c<2 there is a cubic graph such that ωcr3. For k=2,3, let ζk denote the largest fraction of edges that can be k-colored. We give best possible bounds for these parameters, and relate them to each other. 相似文献
119.
具有时滞的非自治的捕食-食饵系统的全局吸引 总被引:1,自引:0,他引:1
考虑一个具有离散时滞的非自治的捕食—食饵系统。系统是由3种群组成的,其中一个为捕食者,另两个为食饵种群。本文的目的是给出时滞对系统的持续生存是无害的,从而确定了系统的周期解全局吸引的条件。 相似文献
120.
Influence of annealing and chain defects on the melting behaviour of poly(vinylidene fluoride) 总被引:2,自引:0,他引:2
C. Marega 《European Polymer Journal》2003,39(8):1713-1720
The melting behaviour of poly(vinylidene fluoride) (PVDF) was investigated by differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering in order to study the influence of the chain defects content and of the temperature of annealing on the crystallization and melting behaviour.All the DSC scans show a double endotherm and the analysis of the data suggests that the low temperature endotherm is due to the melting of a population of thin lamellae, whose thickness increases during the annealing, but a high content of chain defects prevents the lamellar thickening and the main effect in this case is the crystallization of thin lamellae from a portion of polymer which did not crystallize during the quenching from the melt. Furthermore, the two melting endotherms, which are observed, can be partially ascribed to a melting-recrystallization process.Furthermore, stepwise isothermal cooling was performed in a differential scanning calorimeter followed by melting scans of fractionated PVDF samples to point out the possible presence of a series of endothermic peaks. 相似文献