全文获取类型
收费全文 | 35302篇 |
免费 | 5002篇 |
国内免费 | 1362篇 |
专业分类
化学 | 3967篇 |
晶体学 | 124篇 |
力学 | 2530篇 |
综合类 | 335篇 |
数学 | 8990篇 |
物理学 | 7619篇 |
无线电 | 18101篇 |
出版年
2024年 | 85篇 |
2023年 | 400篇 |
2022年 | 662篇 |
2021年 | 886篇 |
2020年 | 960篇 |
2019年 | 789篇 |
2018年 | 776篇 |
2017年 | 1274篇 |
2016年 | 1478篇 |
2015年 | 1550篇 |
2014年 | 2416篇 |
2013年 | 2617篇 |
2012年 | 2458篇 |
2011年 | 2467篇 |
2010年 | 1927篇 |
2009年 | 2028篇 |
2008年 | 2271篇 |
2007年 | 2172篇 |
2006年 | 1980篇 |
2005年 | 1688篇 |
2004年 | 1471篇 |
2003年 | 1563篇 |
2002年 | 1189篇 |
2001年 | 979篇 |
2000年 | 868篇 |
1999年 | 757篇 |
1998年 | 596篇 |
1997年 | 526篇 |
1996年 | 449篇 |
1995年 | 387篇 |
1994年 | 304篇 |
1993年 | 223篇 |
1992年 | 169篇 |
1991年 | 174篇 |
1990年 | 125篇 |
1989年 | 105篇 |
1988年 | 94篇 |
1987年 | 84篇 |
1986年 | 71篇 |
1985年 | 116篇 |
1984年 | 66篇 |
1983年 | 46篇 |
1982年 | 59篇 |
1981年 | 47篇 |
1980年 | 55篇 |
1979年 | 61篇 |
1978年 | 40篇 |
1977年 | 45篇 |
1976年 | 47篇 |
1974年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
When a circuit is tested using random or pseudorandom patterns, it is essential to determine the amount of time (test length) required to test it adequately. We present a methodology for predicting different statistics of random pattern test length. While earlier methods allowed estimation only of upper bounds of test length and only for exhaustive fault coverage, the technique presented here is capable of providing estimates of all statistics of interest (including expected value and variance) for all coverage specifications.Our methodology is based on sampling models developed for fault coverage estimation [1]. Test length is viewed as awaiting time on fault coverage. Based on this relation we derive the distribution of test length as a function of fault coverage. Methods of approximating expected value and variance of test length are presented. Accuracy of these approximations can be controlled by the user. A practical technique for predicting expected test length is developed. This technique is based on clustering faults into equal detectability subsets. A simple and effective algorithm for fault clustering is also presented. The sampling model is applied to each cluster independently and the results are then aggregated to yield test lengths for the whole circuit. Results of experiments with several circuits (both ISCAS '85 benchmarks and other practical circuits) are also provided.This work was done while the author was with the Department of Electrical Engineering, Southern Illinois University, Carbondale, IL 62901. 相似文献
203.
S. Scott Collis Kaveh Ghayour Matthias Heinkenschloss Michael Ulbrich Stefan Ulbrich 《国际流体数值方法杂志》2002,40(11):1401-1429
The control of complex, unsteady flows is a pacing technology for advances in fluid mechanics. Recently, optimal control theory has become popular as a means of predicting best case controls that can guide the design of practical flow control systems. However, most of the prior work in this area has focused on incompressible flow which precludes many of the important physical flow phenomena that must be controlled in practice including the coupling of fluid dynamics, acoustics, and heat transfer. This paper presents the formulation and numerical solution of a class of optimal boundary control problems governed by the unsteady two‐dimensional compressible Navier–Stokes equations. Fundamental issues including the choice of the control space and the associated regularization term in the objective function, as well as issues in the gradient computation via the adjoint equation method are discussed. Numerical results are presented for a model problem consisting of two counter‐rotating viscous vortices above an infinite wall which, due to the self‐induced velocity field, propagate downward and interact with the wall. The wall boundary control is the temporal and spatial distribution of wall‐normal velocity. Optimal controls for objective functions that target kinetic energy, heat transfer, and wall shear stress are presented along with the influence of control regularization for each case. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
204.
一类随机环境中的随机游动 总被引:5,自引:2,他引:3
在Solomn的模型的基础上对一类随机环境中随机游动进行了讨论,并得出了一个常返性准则和一些极限性质。 相似文献
205.
206.
ZHANG Zu-fan DU Hui-ping JIANG Ze Chongqing University of Posts Telecommunications Chongqing China University of Electronic Science Technology of China Chengdu China 《中国邮电高校学报(英文版)》2006,13(4):29-33
1 Introduction The calling dwell time characteristic is critical for the user network planning and deployment, e.g., global system for mobile communications (GSM), as well as the next generation wireless multimedia networks, such as, the currently standar… 相似文献
207.
208.
为适应网络发展的需要 ,有线宽带运营商需要通过一套完整的宽带网络计费管理系统 ,从硬件到软件、从前台到后台对各个方面进行管理 ,实现统一、规范、快速的信息化、网络化电脑管理 ,降低运营成本 ,提高工作效率 ,以过硬的服务质量、优惠的价格、丰富的内容吸引用户。 相似文献
209.
ZhaoHongzhong ZhouJianxiong LiWeimin FuQiang 《电子科学学刊(英文版)》2003,20(6):401-406
High acceleration of radar targets is analyzed using Acceleration Ambiguity Function(AAF). The acceleration resolution based on AAF is defined. The AAF and acceleration resolution of rectangle pulse signal are derivated and the conclusion that its acceleration resolution is in inverse proportion with the square of its duration is drawn. In the end, these conclusions are applied to the parameter designing and performance evaluation for a certain type of pulse Doppler radar. 相似文献
210.