全文获取类型
收费全文 | 6135篇 |
免费 | 648篇 |
国内免费 | 453篇 |
专业分类
化学 | 1966篇 |
晶体学 | 42篇 |
力学 | 1132篇 |
综合类 | 110篇 |
数学 | 1360篇 |
物理学 | 2626篇 |
出版年
2024年 | 8篇 |
2023年 | 123篇 |
2022年 | 123篇 |
2021年 | 162篇 |
2020年 | 208篇 |
2019年 | 126篇 |
2018年 | 127篇 |
2017年 | 212篇 |
2016年 | 235篇 |
2015年 | 190篇 |
2014年 | 396篇 |
2013年 | 455篇 |
2012年 | 344篇 |
2011年 | 407篇 |
2010年 | 289篇 |
2009年 | 434篇 |
2008年 | 455篇 |
2007年 | 432篇 |
2006年 | 333篇 |
2005年 | 302篇 |
2004年 | 269篇 |
2003年 | 236篇 |
2002年 | 209篇 |
2001年 | 162篇 |
2000年 | 144篇 |
1999年 | 137篇 |
1998年 | 94篇 |
1997年 | 99篇 |
1996年 | 80篇 |
1995年 | 66篇 |
1994年 | 58篇 |
1993年 | 39篇 |
1992年 | 59篇 |
1991年 | 33篇 |
1990年 | 25篇 |
1989年 | 24篇 |
1988年 | 31篇 |
1987年 | 13篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1957年 | 1篇 |
排序方式: 共有7236条查询结果,搜索用时 234 毫秒
31.
A simple and accurate algorithm (phase scanning method) is proposed for 3D surface contouring and dynamic response determination of a vibrating object. A sinusoidal fringe pattern is projected onto a low-frequency vibrating object by a programmable liquid crystal display projector. The fringe patterns are captured by a high-speed CCD camera with a telecentric gauging lens. Phase values are evaluated point by point using phase scanning method. From the phase values of each point on the object, the contour of the specimen at different instants of vibration can be retrieved. In this paper, a small vibrating coin is used to demonstrate the validity of the method and the experimental results are compared with test results on a stationary coin using four-step phase shifting and fast Fourier transform methods. The technique is especially useful in applications where the vibrating object has a complicated shape. 相似文献
32.
33.
A review of the optimal stopping problem with more than a single decision maker (DM) is presented in this paper. We classify
the existing literature according to the arrival of the offers, the utility of the DMs, the length of the sequence of offers,
the nature of the game and the number of offers to be selected. We enumerate various definitions for this problem and describe
some dynamic approaches.
Fouad Ben Abdelaziz is on leave from the Institut Superieur de Gestion, University of Tunis, Tunisia e-mail: foued.benabdelaz@isg.run.tn. 相似文献
34.
This paper deals with the optimal control of a one-machine two-product manufacturing system with setup changes, operating in a continuous time dynamic environment. The system is deterministic. When production is switched from one product to the other, a known constant setup time and a setup cost are incurred. Each product has specified constant processing time and constant demand rate, as well as an infinite supply of raw material. The problem is formulated as a feedback control problem. The objective is to minimize the total backlog, inventory and setup costs incurred over a finite horizon. The optimal solution provides the optimal production rate and setup switching epochs as a function of the state of the system (backlog and inventory levels). For the steady state, the optimal cyclic schedule is determined. To solve the transient case, the system's state space is partitioned into mutually exclusive regions such that with each region, the optimal control policy is determined analytically. 相似文献
35.
An initial boundary value problem for the dynamic system of anisotropic elasticity in a half space is studied in the paper. A novel method of finding an exact solution of this problem for a special polynomial form of initial data and inhomogeneous term of the system is described. On the base of this method the simulation of elastic waves in different homogeneous anisotropic half spaces is implemented. 相似文献
36.
This paper proposes a floating-point genetic algorithm (FPGA) to solve the unit commitment problem (UCP). Based on the characteristics of typical load demand, a floating-point chromosome representation and an encoding–decoding scheme are designed to reduce the complexities in handling the minimum up/down time limits. Strategic parameters of the FPGA are characterized in detail, i.e., the evaluation function and its constraints, population size, operation styles of selection, crossover operation and probability, mutation operation and probability. A dynamic combination scheme of genetic operators is formulated to explore and exploit the FPGA in the non-convex solution space and multimodal objective function. Experiment results show that the FPGA is a more effective technique among the various styles of genetic algorithms, which can be applied to the practical scheduling tasks in utility power systems. 相似文献
37.
本文采用解析的方法计算了应变Si1-xGex层中p型杂质电离度与Ge组分x、温度T以及掺杂浓度N的关系.发现常温时,在同一Ge组分下,随着掺杂浓度的升高,杂质的电离度的先变小,而后又迅速上升到1.在同一掺杂浓度下,轻掺杂时,杂质的电离度随Ge组分的增加先变大,而后几乎不变;重掺杂时,杂质电离能变为0后,杂质电离度为1.低温下,轻掺杂时,载流子低温冻析效应较为明显,杂质的电离度普遍较小,当掺杂浓度大于Mott转换点时,载流子冻析效应不再明显,电离率迅速上升到1.在同一Ge组分下,随着掺杂浓度的升高,杂质的电离度先变小,后变大,而后又迅速上升到1.在同一掺杂浓度下,轻掺杂时,杂质的电离度随Ge组分的增加变大;重掺杂时,杂质电离能变为0后,杂质电离度为1. 相似文献
38.
39.
Considering a plane hyperbolic system with time-periodic coefficients, we construct a version of the direct Lyapunov method with the condition on the derivative of the Lyapunov functional along the trajectories of the system which is weakened by use of periodicity of the coefficients. We exhibit an illustrative example. 相似文献
40.
基于RBC模型的动态随机一般均衡的数值解 总被引:1,自引:0,他引:1
以一般均衡为框架,引入随机变量的动态随机一般均衡系统,由于模型的庞大和函数形式的复杂,往往不能给出明确的数值解.本文给出几种操作性强的、有效的寻求一般化模型数值解的方法,并通过介绍模型参数确定的办法,使得理论的模型有了现实的含义. 相似文献