全文获取类型
收费全文 | 135926篇 |
免费 | 1100篇 |
国内免费 | 683篇 |
专业分类
化学 | 51124篇 |
晶体学 | 1795篇 |
力学 | 9864篇 |
综合类 | 8篇 |
数学 | 36336篇 |
物理学 | 38582篇 |
出版年
2022年 | 537篇 |
2021年 | 481篇 |
2020年 | 451篇 |
2019年 | 429篇 |
2018年 | 10939篇 |
2017年 | 10697篇 |
2016年 | 6899篇 |
2015年 | 1470篇 |
2014年 | 1263篇 |
2013年 | 2781篇 |
2012年 | 6054篇 |
2011年 | 13404篇 |
2010年 | 7681篇 |
2009年 | 8148篇 |
2008年 | 9261篇 |
2007年 | 11238篇 |
2006年 | 2653篇 |
2005年 | 3449篇 |
2004年 | 3462篇 |
2003年 | 3682篇 |
2002年 | 2627篇 |
2001年 | 3239篇 |
2000年 | 2432篇 |
1999年 | 1700篇 |
1998年 | 1265篇 |
1997年 | 1197篇 |
1996年 | 1079篇 |
1995年 | 897篇 |
1994年 | 778篇 |
1993年 | 716篇 |
1992年 | 1004篇 |
1991年 | 1006篇 |
1990年 | 898篇 |
1989年 | 806篇 |
1988年 | 789篇 |
1987年 | 853篇 |
1986年 | 711篇 |
1985年 | 931篇 |
1984年 | 870篇 |
1983年 | 604篇 |
1982年 | 603篇 |
1981年 | 571篇 |
1980年 | 541篇 |
1979年 | 665篇 |
1978年 | 684篇 |
1977年 | 678篇 |
1976年 | 592篇 |
1975年 | 497篇 |
1974年 | 534篇 |
1973年 | 476篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
91.
New heuristics for over-constrained flight to gate assignments 总被引:1,自引:0,他引:1
We consider the over-constrained Airport Gate Assignment Problem where the number of flights exceed the number of gates available, and where the objectives are to minimize the number of ungated flights and the total walking distances. The problem is formulated as a binary quadratic programming problem. We design a greedy algorithm and use a Tabu Search meta-heuristic to solve the problem. The greedy algorithm minimizes ungated flights while we devise a new neighbourhood search technique, the Interval Exchange Move, which allows us flexibility in seeking good solutions, especially when flight schedules are dense in time. Experiments conducted give good results. 相似文献
92.
W Y Hung S Kucherenko N J Samsatli N Shah 《The Journal of the Operational Research Society》2004,55(8):801-813
In this paper, we present a new modelling approach for realistic supply chain simulation. The model provides an experimental environment for informed comparison between different supply chain policies. A basic simulation model for a generic node, from which a supply chain network can be built, has been developed using an object-oriented approach. This generic model allows the incorporation of the information and physical systems and decision-making policies used by each node. The object-oriented approach gives the flexibility in specifying the supply chain configuration and operation decisions, and policies. Stochastic simulations are achieved by applying Latin Supercube Sampling to the uncertain variables in descending order of importance, which reduces the number of simulations required. We also present a case study to show that the model is applicable to a real-life situation for dynamic stochastic studies. 相似文献
93.
V E Krivonozhko O B Utkin A V Volodin I A Sablin M Patrin 《The Journal of the Operational Research Society》2004,55(10):1049-1058
The aim of the paper is to present and substantiate a technique to visualize DEA modelling results without any loss of mathematical rigour. The proposed family of parametric optimization methods allows one to construct an intersection of the multidimensional frontier with a two-dimensional plane determined by any pair of given directions. This approach reduces the efficiency analysis of production units to the investigation of well-known functions in economics. We also propose constructive methods to calculate marginal rates of substitution, marginal rates of transformation and so on. 相似文献
94.
95.
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
96.
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
97.
In 1983, a preconditioner was proposed [J. Comput. Phys. 49 (1983) 443] based on the Laplace operator for solving the discrete Helmholtz equation efficiently with CGNR. The preconditioner is especially effective for low wavenumber cases where the linear system is slightly indefinite. Laird [Preconditioned iterative solution of the 2D Helmholtz equation, First Year's Report, St. Hugh's College, Oxford, 2001] proposed a preconditioner where an extra term is added to the Laplace operator. This term is similar to the zeroth order term in the Helmholtz equation but with reversed sign. In this paper, both approaches are further generalized to a new class of preconditioners, the so-called “shifted Laplace” preconditioners of the form Δφ−k2φ with
. Numerical experiments for various wavenumbers indicate the effectiveness of the preconditioner. The preconditioner is evaluated in combination with GMRES, Bi-CGSTAB, and CGNR. 相似文献
98.
Curtis T. Mcmullen 《Acta Mathematica》2003,191(2):191-223
99.
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
100.
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