全文获取类型
收费全文 | 94221篇 |
免费 | 8305篇 |
国内免费 | 5248篇 |
专业分类
电工技术 | 6313篇 |
技术理论 | 8篇 |
综合类 | 6989篇 |
化学工业 | 13701篇 |
金属工艺 | 5503篇 |
机械仪表 | 5669篇 |
建筑科学 | 6687篇 |
矿业工程 | 2513篇 |
能源动力 | 2425篇 |
轻工业 | 8584篇 |
水利工程 | 1970篇 |
石油天然气 | 4127篇 |
武器工业 | 930篇 |
无线电 | 10194篇 |
一般工业技术 | 9246篇 |
冶金工业 | 3632篇 |
原子能技术 | 1022篇 |
自动化技术 | 18261篇 |
出版年
2024年 | 331篇 |
2023年 | 1330篇 |
2022年 | 2678篇 |
2021年 | 3604篇 |
2020年 | 2724篇 |
2019年 | 2224篇 |
2018年 | 2513篇 |
2017年 | 2702篇 |
2016年 | 2515篇 |
2015年 | 3710篇 |
2014年 | 4601篇 |
2013年 | 5681篇 |
2012年 | 6640篇 |
2011年 | 8366篇 |
2010年 | 7222篇 |
2009年 | 6899篇 |
2008年 | 6668篇 |
2007年 | 6133篇 |
2006年 | 5520篇 |
2005年 | 4738篇 |
2004年 | 3593篇 |
2003年 | 3087篇 |
2002年 | 2793篇 |
2001年 | 2299篇 |
2000年 | 1756篇 |
1999年 | 1483篇 |
1998年 | 1145篇 |
1997年 | 949篇 |
1996年 | 815篇 |
1995年 | 632篇 |
1994年 | 523篇 |
1993年 | 369篇 |
1992年 | 285篇 |
1991年 | 259篇 |
1990年 | 211篇 |
1989年 | 150篇 |
1988年 | 112篇 |
1987年 | 72篇 |
1986年 | 78篇 |
1985年 | 50篇 |
1984年 | 51篇 |
1983年 | 31篇 |
1982年 | 42篇 |
1981年 | 39篇 |
1980年 | 36篇 |
1979年 | 17篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 17篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
141.
142.
An experimental study of an optical burst switching network based on wavelength-selective optical switches 总被引:1,自引:0,他引:1
Li Xinwan Chen Jianping Wu Guiling Wang Hui Ye Ailun 《Communications Magazine, IEEE》2005,43(5):S3-10
In this article we report the system structure and test results of an experimental optical burst switching network with three edge router's and one core node. Wavelength-selective switches developed for this system and their characteristics are depicted. The implementation and performance of our new scheme for the just-in-time protocol are described. We also report experimental results of FTP and VOD services on this system. Some parameters, including traffic rate, average burst data length, and assembly time, are studied. 相似文献
143.
144.
Eng Leong Tan Ding Yu Heh 《Microwave and Wireless Components Letters, IEEE》2008,18(5):296-298
This letter presents an unconditionally stable alternating direction implicit finite-difference time-domain (ADI-FDTD) method with fourth order accuracy in time. Analytical proof of unconditional stability and detailed analysis of numerical dispersion are presented. Compared to second order ADI-FDTD and six-steps SS-FDTD, the fourth order ADI-FDTD generally achieves lower phase velocity error for sufficiently fine mesh. Using finer mesh gridding also reduces the phase velocity error floor, which dictates the accuracy limit due to spatial discretization errors when the time step size is reduced further. 相似文献
145.
146.
In this paper, we present a control methodology for a class of discrete time nonlinear systems that depend on a possibly exogenous scheduling variable. This class of systems consists of an interpolation of nonlinear dynamic equations in strict feedback form, and it may represent systems with a time-varying nonlinear structure. Moreover, this class of systems is able to represent some cases of gain scheduling control, Takagi-Sugeno fuzzy systems, as well as input-output realizations of nonlinear systems which are approximated via localized linearizations. We present two control theorems, one using what we call a “global” approach (akin to traditional backstepping), and a “local” approach, our main result, where backstepping is again used but the control law is an interpolation of local control terms. An aircraft wing rock regulation problem with varying angle of attack is used to illustrate and compare the two approaches. 相似文献
147.
结合兰州市的水泥标准稠度用水量方法测定 (代用法 )的实例 ,分析代用法测定标准稠度用水量的缺点 ,并对此方法提出了一些改进措施 相似文献
148.
Hui Chen D.T.K. Tong 《Photonics Technology Letters, IEEE》2005,17(4):801-803
Symmetric interference in two-dimensional multimode silicon waveguides is experimentally investigated. For a 100/spl times/100 /spl mu/m/sup 2/ cross section, 2700-/spl mu/m-long waveguide fabricated on silicon-on-insulator substrate, an 8/spl times/8 matrix of replicated images with high contrast ratio is demonstrated for 1530-1570 nm wavelength range. Symmetric interference results in reduced device length, and the actual device length is consistent with the theoretical expectation. The device also exhibits stable imaging in terms of good loss uniformity, and low wavelength and polarization dependencies among the replicated images. 相似文献
149.
Shawn Hu Author Vitae Author Vitae 《Automatica》2007,43(7):1243-1248
This paper is concerned with stability analysis of discrete-time networked control systems over a communication channel subject to packet loss whose behavior is modeled by an i.i.d Bernoulli process with a packet dropping probability bounded by a constant. A necessary and sufficient condition for stability is obtained. A packet dropping margin is introduced as a measure of stability robustness of a system against packet dropping, and a formula for it is derived. A design method is proposed for achieving a large margin subject to a constraint that the system has a set of prescribed nominal closed-loop poles. 相似文献
150.
We report the growth of highly C-axis orientation of Sr
x
Ba1−x
Nb2O6 (SBN) thin films on p-type (100) Si substrates by using a potassium-substituted SBN template layer with the sol–gel method. The crystallization of SBN thin films was found closely related to the potassium ion doping concentration and the postannealing temperature of the K-SBN template layer. Secondary ion mass spectrometry analysis showed that potassium elements were accumulated at the interface of the template layer and silicon substrate. SBN films postannealed at 750 °C with K-SBN template layer has a smaller full width at half maximum of X-ray rocking curve of 2.45° than that of 5.40° for the pure SBN films. By introducing a template layer, the surface morphologies of SBN films fabricated on silicon substrate were greatly improved. 相似文献