全文获取类型
收费全文 | 24201篇 |
免费 | 2777篇 |
国内免费 | 916篇 |
专业分类
化学 | 4603篇 |
晶体学 | 111篇 |
力学 | 8256篇 |
综合类 | 278篇 |
数学 | 7350篇 |
物理学 | 7296篇 |
出版年
2024年 | 41篇 |
2023年 | 294篇 |
2022年 | 502篇 |
2021年 | 569篇 |
2020年 | 615篇 |
2019年 | 515篇 |
2018年 | 567篇 |
2017年 | 785篇 |
2016年 | 871篇 |
2015年 | 863篇 |
2014年 | 1090篇 |
2013年 | 1758篇 |
2012年 | 1239篇 |
2011年 | 1435篇 |
2010年 | 1122篇 |
2009年 | 1384篇 |
2008年 | 1400篇 |
2007年 | 1421篇 |
2006年 | 1199篇 |
2005年 | 984篇 |
2004年 | 1027篇 |
2003年 | 955篇 |
2002年 | 827篇 |
2001年 | 631篇 |
2000年 | 656篇 |
1999年 | 590篇 |
1998年 | 557篇 |
1997年 | 483篇 |
1996年 | 466篇 |
1995年 | 405篇 |
1994年 | 346篇 |
1993年 | 303篇 |
1992年 | 279篇 |
1991年 | 232篇 |
1990年 | 204篇 |
1989年 | 164篇 |
1988年 | 162篇 |
1987年 | 116篇 |
1986年 | 108篇 |
1985年 | 137篇 |
1984年 | 102篇 |
1983年 | 63篇 |
1982年 | 109篇 |
1981年 | 46篇 |
1980年 | 58篇 |
1979年 | 50篇 |
1978年 | 33篇 |
1977年 | 35篇 |
1976年 | 41篇 |
1957年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Plasma-assisted flow control is of high industrial interest, but practical applications at full scale require a large surface of interaction. Nanosecond pulsed Dielectric Barrier Discharge (DBD) have demonstrated promising results of flow control, but their interacting region is limited to only a few cm2. In this paper, the conditions to extend a surface nanosecond DBD are documented. It is shown that a sliding discharge regime can fully fill an inter-electrode distance of 40 mm. This discharge regime promotes the formation of two hemispheric pressure waves originating from both air-exposed electrodes while an horizontal region of pressure gradient is also observed. 相似文献
3.
4.
David K Bisset 《国际流体数值方法杂志》2002,39(10):961-977
Turbulent flow simulation methods based on finite differences are attractive for their simplicity, flexibility and efficiency, but not always for accuracy or stability. This paper demonstrates that a good compromise is possible with the advected grid explicit (AGE) method. Starting from the same initial field as a previous spectral DNS, AGE method simulations of a planar turbulent wake were carried out as DNS, and then at three levels of reduced resolution. The latter cases were in a sense large‐eddy simulations (LES), although no specific sub‐grid‐scale model was used. Results for the two DNS methods, including variances and power spectra, were very similar, but the AGE simulation required much less computational effort. Small‐scale information was lost in the reduced resolution runs, but large‐scale mean and instantaneous properties were reproduced quite well, with further large reductions in computational effort. Quality of results becomes more sensitive to the value chosen for one of the AGE method parameters as resolution is reduced, from which it is inferred that the numerical stability procedure controlled by the parameter is acting in part as a sub‐grid‐scale model. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
5.
William J. Reed 《Natural Resource Modeling》1989,3(4):463-480
It is assumed that the probability of destruction of a biological asset by natural hazards can be reduced through investment in protection. Specifically a model, in which the hazard rate depends on both the age of the asset and the accumulated invested protection capital, is assumed. The protection capital depreciates through time and its effectiveness in reducing the hazard rate is subject to diminishing returns. It is shown how the investment schedule to maximize the expected net present value of the asset can be determined using the methods of deterministic optimal control, with the survival probability regarded as a state variable. The optimal investment pattern involves “bang-bang-singular” control. A numerical scheme for determining jointly the optimal investment policy and the optimal harvest (or replacement) age is outlined and a numerical example involving forest fire protection is given. 相似文献
6.
A convective flow CO laser composed of polytetrafluoroethylene discharge tubes, nickel–chromium steel components, a cupric heat exchanger and other components is described. Operating in liquid nitrogen condition, output power of 60 W has been obtained from a non-selective cavity. 相似文献
7.
介绍了车用压差式气体流量传感器的结构设计和电测电路,指出了传感器的使用范围,由实验测出了特性曲线.该仪器可检测车用发动机曲轴箱窜气量,适用于发动机不解体故障诊断. 相似文献
8.
We consider the optimal service control of a multiclass M/G/1 queueing system in which customers are served nonpreemptively and the system cost rate is additive across classes and increasing convex in the numbers present in each class. Following Whittle's approach to a class of restless bandit problems, we develop a Langrangian relaxation of the service control problem which serves to motivate the development of a class of index heuristics. The index for a particular customer class is characterised as a fair charge for service of that class. The paper develops these indices and reports an extensive numerical investigation which exhibits strong performance of the index heuristics for both discounted and average costs. 相似文献
9.
Geng Sheng WANG 《数学学报(英文版)》2005,21(5):1005-1014
This work is concerned with Pontryagin's maximum principle of optimal control problems governed by some non-well-posed semilinear heat equations. A type of approach to the non-well-posed optimal control problem is given. 相似文献
10.