全文获取类型
收费全文 | 208576篇 |
免费 | 15553篇 |
国内免费 | 7899篇 |
专业分类
电工技术 | 11444篇 |
技术理论 | 14篇 |
综合类 | 11325篇 |
化学工业 | 35841篇 |
金属工艺 | 10636篇 |
机械仪表 | 12101篇 |
建筑科学 | 16551篇 |
矿业工程 | 4975篇 |
能源动力 | 5889篇 |
轻工业 | 12916篇 |
水利工程 | 3265篇 |
石油天然气 | 11116篇 |
武器工业 | 1398篇 |
无线电 | 25636篇 |
一般工业技术 | 26822篇 |
冶金工业 | 12278篇 |
原子能技术 | 2146篇 |
自动化技术 | 27675篇 |
出版年
2024年 | 888篇 |
2023年 | 3279篇 |
2022年 | 5850篇 |
2021年 | 7985篇 |
2020年 | 5843篇 |
2019年 | 5050篇 |
2018年 | 5446篇 |
2017年 | 6238篇 |
2016年 | 5741篇 |
2015年 | 7352篇 |
2014年 | 9604篇 |
2013年 | 12365篇 |
2012年 | 12349篇 |
2011年 | 14019篇 |
2010年 | 11741篇 |
2009年 | 11560篇 |
2008年 | 10989篇 |
2007年 | 10605篇 |
2006年 | 10988篇 |
2005年 | 9710篇 |
2004年 | 6635篇 |
2003年 | 5817篇 |
2002年 | 5297篇 |
2001年 | 4775篇 |
2000年 | 4895篇 |
1999年 | 5680篇 |
1998年 | 5659篇 |
1997年 | 4576篇 |
1996年 | 4104篇 |
1995年 | 3379篇 |
1994年 | 2835篇 |
1993年 | 2287篇 |
1992年 | 1719篇 |
1991年 | 1299篇 |
1990年 | 1031篇 |
1989年 | 895篇 |
1988年 | 700篇 |
1987年 | 519篇 |
1986年 | 405篇 |
1985年 | 351篇 |
1984年 | 213篇 |
1983年 | 200篇 |
1982年 | 169篇 |
1981年 | 157篇 |
1980年 | 150篇 |
1979年 | 97篇 |
1978年 | 67篇 |
1977年 | 94篇 |
1976年 | 175篇 |
1975年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Juin-Hung Chen Hen-Wai Tsao 《Lightwave Technology, Journal of》1998,16(7):1137-1148
This paper presents a design method of optical frequency modulation (FM) subcarrier (with super carrier) transmission modem. The nonideal link characteristics, including laser chirping, fiber dispersion, voltage controlled oscillator (VCO) phase noise, relative intensity noise (RIN), and equivalent network model of laser diode of such a system that may bring about signal distortion are discussed first. We then propose a hierarchical methods to establish the system equivalent model. Finally this FM modem is applied to a GSM wireless system, in which multichannel signals are transmitted over fiber between radio port and basestation, and system performance is appraised by its dynamic range. It is found that optical FM subcarrier (with super carrier) transmission technique can improve the system dynamic range, compared with the intensity modulated direct detection (IMDD) method, and this is a economical and efficient method 相似文献
102.
T. -Y. Chen 《Structural and Multidisciplinary Optimization》1992,4(3-4):179-185
A design optimization procedure using a sequential linear programming technique is proposed in this paper to design minimum weight structures subjected to frequency response and static displacement constraints. The merit of the proposed approach is that the reanalyses of the static and dynamic responses, as well as the computations of the static and dynamic sensitivity data, are performed in a reduced approximate model. A significant saving of computer time for large scale structures is expected. Two numerical examples show good results of this method. 相似文献
103.
Haitao Zhang Zonghai Chen Yongji Wang Ming Li Ting Qin 《International Journal of Adaptive Control and Signal Processing》2006,20(2):53-76
Laguerre Functional Model has many advantages such as good approximation capability for the variances of system time‐delay, order and other structural parameters, low computational complexity, and the facility of online parameter identification, etc., so this model is suitable for complex industrial process control. A series of successful applications have been gained in linear and non‐linear predictive control fields by the control algorithm based on Laguerre Functional Model, however, former researchers have not systemically brought forward the theoretical analyses of the stability, robustness, and steady‐state performance of this algorithm, which are the keys to guarantee the feasibility of the control algorithm fundamentally. Aimed at this problem, we introduce the principles of the Incremental Mode Linear Laguerre Predictive Control (IMLLPC) algorithm, and then systemically propose the theoretical analyses and proofs of the stability and robustness of the algorithm, in addition, we also put forward the steady‐state performance analysis. At last, the control performances of this algorithm on two different physical industrial plants are presented in detail, and a number of experimental results validate the feasibility and superiority of IMLLPC algorithm. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
104.
STUDYONRESIDUESOF~(14)C-FENITROTHIONINMODELRICE-FISHECOSYSTEMANDFIELDRICE-FISHECOSYSTEMZhangZhongliang(张仲良);WangHuaxin(王化新);G?.. 相似文献
105.
Wang F.-Y. Gildea K. Jungnitz H. Chen D.D. 《Industrial Electronics, IEEE Transactions on》1994,41(6):641-653
The manufacturing message specification (MMS) is the ISO standard communication protocol specific to manufacturing. To analyze MMS design and performance, service unit automats are introduced to represent individual MMS services, while service connection Petri Nets (PNs) are constructed from these automats to describe MMS service connections and processes. This approach makes MMS protocol specification and analysis possible in terms of well-developed concepts and methods in PN theory. It leads to a distributed and hierarchical model of MMS software system by integrating service connection PNs. A generalized stochastic PN for MMS performance evaluation is obtained by incorporating service parameters and time factors into the model. A technique based on T-invariants is used to simplify the performance analysis 相似文献
106.
Ma Z.J. Chen J.C. Liu Z.H. Krick J.T. Cheng Y.C. Hu C. Ko P.K. 《Electron Device Letters, IEEE》1994,15(3):109-111
It has been reported that high-temperature (~1100°C) N2 O-annealed oxide can block boron penetration from poly-Si gates to the silicon substrate. However, this high-temperature step may be inappropriate for the low thermal budgets required of deep-submicron ULSI MOSFETs. Low-temperature (900~950°C) N2O-annealed gate oxide is also a good barrier to boron penetration. For the first time, the change in channel doping profile due to compensation of arsenic and boron ionized impurities was resolved using MOS C-V measurement techniques. It was found that the higher the nitrogen concentration incorporated at Si/SiO2 interface, the more effective is the suppression of boron penetration. The experimental results also suggest that, for 60~110 Å gate oxides, a certain amount of nitrogen (~2.2%) incorporated near the Si/SiO2 interface is essential to effectively prevent boron diffusing into the underlying silicon substrate 相似文献
107.
Shye Lin Wu Chung Len Lee Tan Fu Lei Chen C.F. Chen L.J. Ho K.Z. Ling Y.C. 《Electron Device Letters, IEEE》1994,15(4):120-122
In this study, it is demonstrated that the incorporation of fluorine can enhance poly-Si/Si interfacial oxide break-up in the poly-Si emitter contacted p+-n shallow junction formation. The annealing temperature for breaking up the poly-Si/Si interfacial oxide has been found to be as low as 900°C. As a result, the junction depth of the BF2-implanted device is much larger than that of the boron-implanted device 相似文献
108.
109.
110.