全文获取类型
收费全文 | 510810篇 |
免费 | 6224篇 |
国内免费 | 1447篇 |
专业分类
化学 | 271663篇 |
晶体学 | 8151篇 |
力学 | 22347篇 |
综合类 | 8篇 |
数学 | 58463篇 |
物理学 | 157849篇 |
出版年
2021年 | 4145篇 |
2020年 | 4576篇 |
2019年 | 5021篇 |
2018年 | 6740篇 |
2017年 | 6866篇 |
2016年 | 10064篇 |
2015年 | 6232篇 |
2014年 | 9597篇 |
2013年 | 23711篇 |
2012年 | 17998篇 |
2011年 | 21637篇 |
2010年 | 15355篇 |
2009年 | 14990篇 |
2008年 | 19285篇 |
2007年 | 19372篇 |
2006年 | 17875篇 |
2005年 | 15768篇 |
2004年 | 14495篇 |
2003年 | 12726篇 |
2002年 | 12575篇 |
2001年 | 14752篇 |
2000年 | 11271篇 |
1999年 | 8825篇 |
1998年 | 7277篇 |
1997年 | 7135篇 |
1996年 | 6928篇 |
1995年 | 6045篇 |
1994年 | 5922篇 |
1993年 | 5795篇 |
1992年 | 6529篇 |
1991年 | 6512篇 |
1990年 | 6294篇 |
1989年 | 6253篇 |
1988年 | 5976篇 |
1987年 | 6111篇 |
1986年 | 5723篇 |
1985年 | 7494篇 |
1984年 | 7486篇 |
1983年 | 6249篇 |
1982年 | 6520篇 |
1981年 | 6207篇 |
1980年 | 6082篇 |
1979年 | 6434篇 |
1978年 | 6725篇 |
1977年 | 6522篇 |
1976年 | 6454篇 |
1975年 | 6134篇 |
1974年 | 6038篇 |
1973年 | 6088篇 |
1972年 | 4212篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
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
872.
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
873.
874.
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
875.
The essential self-adjointness on a natural domain of the sharp-time Wick powers of the relativistic free field in two space-time dimension is proven. Other results on Wick powers are reviewed and discussed. 相似文献
876.
877.
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
878.
In this work, the effect of flexibility on the trajectory of a planar two-link manipulator is studied using integrated computer-aided design/analysis (CAD/CAE) procedures. The solid models and finite element models of the parts of the manipulator are created by using the CAD/CAE software I-DEAS. The assembly is defined, and knowing the payload and the end point trajectory, the velocities and accelerations of the parts, joint forces and driving torques are calculated using the rigid body dynamics. All the time dependent nodal forces acting on the parts including distributed gravity and inertia forces are created in files with the I-DEAS program file format. The finite element vibration analysis of the parts is performed by I-DEAS. The end point vibrations and the deviations from the rigid-body trajectory are analyzed for different types of end point acceleration curves. A circular trajectory is considered as an example. It is observed that the precision of the manipulator can be increased by testing different end point acceleration curves without changing the trajectory and the duration of the end point work. The procedure explained in this work can be used for this purpose successfully. 相似文献
879.
M. A. Efendiev J. Fuhrmann S. V. Zelik 《Mathematical Methods in the Applied Sciences》2004,27(8):907-930
For the Boussinesq approximation of the equations of coupled heat and fluid flow in a porous medium we show that the corresponding system of partial differential equations possesses a global attractor. We give lower and upper bounds of the Hausdorff dimension of the attractor depending on a physical parameter of the system, namely the Rayleigh number of the flow. Numerical experiments confirm the theoretical findings and raise new questions on the structure of the solutions of the system. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
880.