全文获取类型
收费全文 | 1103篇 |
免费 | 92篇 |
国内免费 | 45篇 |
专业分类
化学 | 119篇 |
晶体学 | 1篇 |
力学 | 70篇 |
综合类 | 7篇 |
数学 | 388篇 |
物理学 | 655篇 |
出版年
2024年 | 3篇 |
2023年 | 29篇 |
2022年 | 30篇 |
2021年 | 22篇 |
2020年 | 37篇 |
2019年 | 25篇 |
2018年 | 15篇 |
2017年 | 31篇 |
2016年 | 30篇 |
2015年 | 42篇 |
2014年 | 72篇 |
2013年 | 89篇 |
2012年 | 61篇 |
2011年 | 79篇 |
2010年 | 79篇 |
2009年 | 78篇 |
2008年 | 70篇 |
2007年 | 81篇 |
2006年 | 66篇 |
2005年 | 46篇 |
2004年 | 44篇 |
2003年 | 29篇 |
2002年 | 26篇 |
2001年 | 16篇 |
2000年 | 22篇 |
1999年 | 21篇 |
1998年 | 21篇 |
1997年 | 17篇 |
1996年 | 14篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1240条查询结果,搜索用时 15 毫秒
101.
Generation scheduling (GS) in power systems is a tough optimisation problem which continues to present a challenge for efficient solution techniques. The solution is to define on/off decisions and generation levels for each electricity generator of a power system for each scheduling interval. The solution procedure requires simultaneous consideration of binary decision and continuous variables. In recent years researchers have focused much attention on developing new hybrid approaches using evolutionary and traditional exact methods for this type of mixed-integer problems. This paper investigates how the optimum or near optimum solution for the GS problem may be quickly identified. A design is proposed which uses a variety of metaheuristic, heuristics and mathematical programming techniques within a hybrid framework. The results obtained for two case studies are promising and show that the hybrid approach offers an effective alternative for solving the GS problems within a realistic timeframe. 相似文献
102.
Lei Wang Rui-Min Xu Bo Yan 《International Journal of Infrared and Millimeter Waves》2007,28(12):1133-1141
An accurate small-signal modeling approach applied to GaAs-based pHEMT devices is presented. The procedure for extracting
equivalent-circuit model parameters is illustrated in detail. A genetic algorithm (GA) program is developed to optimize the
model parameters in order to improve the modeling accuracy. The validity of modeling approach is verified by comparing the
simulated and measured result of two pHEMTs and a fabricated ka-band power amplifier. The conclusion can be drawn that the
proposed modeling method is rather accurate and efficient. 相似文献
103.
S. Lorenzo-Freire J.M. Alonso-Meijide B. Casas-Méndez M.G. Fiestras-Janeiro 《European Journal of Operational Research》2007
In this paper, we provide a new characterization of the Deegan–Packel power index, which uses a new monotonicity property, and two characterizations of the Johnston power index by employing some usual properties of the literature and two new transfer properties. Finally, a real-world numerical example taken from the political field illustrates the main differences between these two indices. 相似文献
104.
Ngc-Minh Lê 《Computational Geometry》1997,8(6):279-298
We introduce the simple abstract Voronoi diagram in 3-space as an abstraction of the usual Voronoi diagram. We show that the 3-dimensional simple abstract Voronoi diagram of n sites can be computed in O(n2) expected time using O(n2) expected space by a randomized algorithm. The algorithm is based on the randomized incremental construction technique of Clarkson and Shor (1989). We apply the algorithm to some concrete types of such diagrams: power diagrams, diagrams under ellipsoid convex distance functions, and diagrams under the Hausdorff distance for sites that are parallel segments all having the same length. 相似文献
105.
Vibration isolation plays an important role in both the vibration and noise control of building services equipment. To evaluate vibration isolation performance, the force transmissibility method is commonly adopted. However, increasing the damping effect in the force transmissibility method reduces both the resonance peak value and the isolation performance in the “isolation region”. The limitation of the method is that the transmitted displacement of a floor structure and the interaction of mounting points are neglected. To include the floor displacement and the interaction of mounting points, Mak and Su recently proposed the power transmissibility method to assess the performance of vibration isolation. In this paper, the effect of viscous damping on power transmissibility is investigated. A practical procedure for experimentally determining the damping ratio is also given. 相似文献
106.
107.
利用旋转涂膜方法制备了以P3HT:PCBM为有源层的聚合物太阳能电池, 器件结构为ITO/PEDOT:PSS/P3HT:PCBM/Al(氧化铟锡导电玻璃/聚二氧乙基噻吩:聚对苯乙烯磺酸/聚三已基噻酚:富勒烯衍生物/铝),研究了退火温度对聚合物太阳能电池性能的影响. 实验发现: 聚合物薄膜经过120 °C退火10 min处理后, 开路电压(Voc)达到0.64 V, 短路电流密度(Jsc)为10.25 mA·cm-2, 填充因子(FF) 38.1%, 光电转换效率(PCE)达到2.00%. 为了讨论其内在机制, 对不同退火条件下聚合物薄膜进行了各种表征. 从紫外-可见吸收光谱中发现, 退火处理使P3HT在可见光范围内吸收加强且吸收峰展宽, 特别是在560和610 nm处的吸收强度明显增大; X射线衍射(XRD)结果表明, 120 °C退火后P3HT在(100)晶面上的衍射强度是未退火薄膜的2.8倍, 有利于光生载流子的输运; 原子力显微镜(AFM)研究结果表明, 退火显著增大了P3HT与PCBM的相分离程度, 提高了激子解离的几率; 傅里叶变换红外(FTIR)光谱验证了退火并没有引起聚合物材料物性的变化. 相似文献
108.
109.
In this article the flows of perfect gas behind converging and diverging strong shock waves under isothermal condition in
the cases of spherical and cylindrical symmetry are examined. A diverging shock wave is formed by energy supply according
to a power law. These waves propagate in a uniform medium at rest and all conservation laws hold at the fronts of these shock
waves. It was established that in the case of converging waves for any value of the ratios of specific heats the solution of the problem under consideration exists and is unique. When the problem has more than one solution. In the case of diverging shock waves the solution exists and is unique for any from the interval and any value of power in the energy input law.
Received 4 August 1996 / Accepted 28 May 1996 相似文献
110.
The fundamental assumption of the paper is that the extra stress tensor of an electrorheological fluid is an isotropic tensor valued function of the rate of strain tensor D and the vector n (which characterizes the orientation
and length N of the fibers formed by application of an electric field). The resulting constitutive equation for is supplemented by the solution of the previously studied time evolution equation for n. Plastic behavior for the shear and normal stresses is predicted. Anticipating that the action of increasing shear rate
is i) to orient the fibers more and more in the direction of flow and ii) simultaneously to break up the fibers leads to the conclusion that for
the same behavior is encountered as without an electric field. Using realistically possible approximation formulas for the dependence of
and N on
leads to the Bingham behavior for
and power law behavior for large shear rates.
相似文献
Basim Abu-JdayilEmail: |