全文获取类型
收费全文 | 84753篇 |
免费 | 832篇 |
国内免费 | 479篇 |
专业分类
化学 | 29279篇 |
晶体学 | 842篇 |
力学 | 6882篇 |
综合类 | 4篇 |
数学 | 32474篇 |
物理学 | 16583篇 |
出版年
2023年 | 53篇 |
2022年 | 72篇 |
2021年 | 156篇 |
2020年 | 154篇 |
2019年 | 186篇 |
2018年 | 10512篇 |
2017年 | 10335篇 |
2016年 | 6299篇 |
2015年 | 1068篇 |
2014年 | 585篇 |
2013年 | 753篇 |
2012年 | 4266篇 |
2011年 | 11036篇 |
2010年 | 5996篇 |
2009年 | 6347篇 |
2008年 | 7033篇 |
2007年 | 9097篇 |
2006年 | 630篇 |
2005年 | 1687篇 |
2004年 | 1831篇 |
2003年 | 2219篇 |
2002年 | 1264篇 |
2001年 | 403篇 |
2000年 | 419篇 |
1999年 | 234篇 |
1998年 | 259篇 |
1997年 | 220篇 |
1996年 | 273篇 |
1995年 | 174篇 |
1994年 | 126篇 |
1993年 | 164篇 |
1992年 | 102篇 |
1991年 | 108篇 |
1990年 | 94篇 |
1989年 | 109篇 |
1988年 | 92篇 |
1987年 | 90篇 |
1986年 | 90篇 |
1985年 | 80篇 |
1984年 | 67篇 |
1983年 | 60篇 |
1982年 | 62篇 |
1981年 | 66篇 |
1980年 | 68篇 |
1979年 | 65篇 |
1978年 | 46篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
142.
143.
Malmquist indexes can be used to estimate technical change over time. The index generally represents the average effect of technical change on all outputs in a multi-output firm. However, changes in technology do not necessarily affect all outputs involved in the analysis equally. In this paper, a method for estimating the effect of technical change on each of the different outputs is proposed. This estimation is done by a modification of quasi-Malmquist indexes. An artificial data set has been used to validate the method proposed in this paper. 相似文献
144.
In this paper, we study a problem central to crossdocking that aims to eliminate or minimize storage and order picking activity using JIT scheduling. The problem is modelled naturally as a machine scheduling problem. As the problem is NP-hard, and for real-time applications, we designed and implemented two heuristics. The first uses Squeaky Wheel Optimization embedded in a Genetic Algorithm and the second uses Linear Programming within a Genetic Algorithm. Both heuristics offer good solutions in experiments where comparisons are made with the CPLEX solver. 相似文献
145.
In this note we show how 1-factors in the middle two layers of the discrete cube can be used to construct 2-factors in the
Odd graph (the Kneser graph of (k − 1)-sets from a (2k − 1)-set). In particular, we use the lexical matchings of Kierstead and Trotter, and the modular matchings of Duffus, Kierstead
and Snevily, to give explicit constructions of two different 2-factorisations of the Odd graph.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
146.
Siaw-Lynn Ng 《Order》2004,21(1):1-5
We present a characterisation of posets of size n with linear discrepancy n − 2. These are the posets that are “furthest” from a linear order without being an antichain.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
147.
Curtis T. Mcmullen 《Acta Mathematica》2003,191(2):191-223
148.
We will prove a result concerning the inclusion of non-trivial invariant ideals inside non-trivial ideals of a twisted crossed
product. We will also give results concerning the primeness and simplicity of crossed products of twisted actions of locally
compact groups on -algebras.
Received: 25 January 2002; in final form: 22 May 2002/Published online: 2 December 2002
This work is partially supported by Hong Kong RGC Direct Grant. 相似文献
149.
The influence of the sample orientation on the effective value of the hydrostatic piezoelectric coefficients d
h
(i)
of Sn2P2S6 crystals has been studied. The hydrostatic piezoelectric coefficients d
h
(1)
and d′
h
(3)
, were measured, d
h
(1)
=(244±3) pC/N and d′
h
(3)
=(92±1) pC/N. The hydrostatic piezoelectric coefficient d
h
(3)
for orthogonal axis system was calculated to be d
h
(3)
=(87±2) pC/N. The, optimal orientation of the sample has been found as (Xy l)−20°-cut. Maximal value of the effective hydrostatic piezoelectric coefficient d
h
(1)
equals 260 pC/N. Double rotated samples were also studied. The orientation of the samples insensitive to the pressure has
been found. The theoretical mean value of hydrostatic piezoelectric coefficient (d
h
)
mean
corresponding to randomly oriented Sn2P2S6 grains in a poled composite has been calculated to be (d
h
)
mean
=136 pC/N. 相似文献
150.
Lev Buhovsky 《Israel Journal of Mathematics》2004,143(1):181-187
In this paper we find homological restrictions on Lagrangians in cotangent bundles of spheres and Lens spaces.
This research was supported by the Israel Science Foundation (grand No. 205/02). 相似文献