全文获取类型
收费全文 | 747651篇 |
免费 | 8952篇 |
国内免费 | 1930篇 |
专业分类
电工技术 | 13528篇 |
综合类 | 641篇 |
化学工业 | 116467篇 |
金属工艺 | 29452篇 |
机械仪表 | 23734篇 |
建筑科学 | 17550篇 |
矿业工程 | 4736篇 |
能源动力 | 19708篇 |
轻工业 | 64026篇 |
水利工程 | 8406篇 |
石油天然气 | 16559篇 |
武器工业 | 44篇 |
无线电 | 83790篇 |
一般工业技术 | 148663篇 |
冶金工业 | 130952篇 |
原子能技术 | 16876篇 |
自动化技术 | 63401篇 |
出版年
2021年 | 6705篇 |
2020年 | 5028篇 |
2019年 | 6412篇 |
2018年 | 10961篇 |
2017年 | 11158篇 |
2016年 | 11881篇 |
2015年 | 7586篇 |
2014年 | 12771篇 |
2013年 | 34877篇 |
2012年 | 20290篇 |
2011年 | 27851篇 |
2010年 | 22169篇 |
2009年 | 24663篇 |
2008年 | 25309篇 |
2007年 | 25012篇 |
2006年 | 22049篇 |
2005年 | 20023篇 |
2004年 | 19096篇 |
2003年 | 18700篇 |
2002年 | 17890篇 |
2001年 | 17787篇 |
2000年 | 16796篇 |
1999年 | 16990篇 |
1998年 | 39346篇 |
1997年 | 28253篇 |
1996年 | 21899篇 |
1995年 | 16792篇 |
1994年 | 15038篇 |
1993年 | 14738篇 |
1992年 | 11252篇 |
1991年 | 10767篇 |
1990年 | 10599篇 |
1989年 | 10235篇 |
1988年 | 9881篇 |
1987年 | 8682篇 |
1986年 | 8402篇 |
1985年 | 9747篇 |
1984年 | 8846篇 |
1983年 | 8377篇 |
1982年 | 7568篇 |
1981年 | 7713篇 |
1980年 | 7278篇 |
1979年 | 7312篇 |
1978年 | 7105篇 |
1977年 | 7898篇 |
1976年 | 9890篇 |
1975年 | 6330篇 |
1974年 | 6056篇 |
1973年 | 6187篇 |
1972年 | 5165篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Seidel A.R. Bisogno F.E. Pinheiro H. do Prado R.N. 《Industrial Electronics, IEEE Transactions on》2003,50(6):1267-1274
This paper presents a simple alternative for an electronic ballast operating in self-sustained oscillating mode with dimming capability for fluorescent lamps. A simple modification in one of the gate drivers side circuit allows the lamp to dim without compromising the simplicity, reliability, and low cost which characterize the self-oscillating electronic ballast (SOEB). A qualitative analysis is presented to explain the behavior of the proposed self-oscillating electronic ballast with dimming feature. In addition, the stability and the key equations for the design are derived using the extended Nyquist criterion and describing function method. Experimental results from two 40-W electronic ballasts are presented to demonstrate the performance and to validate the analysis carried out. 相似文献
82.
Scale Up from Small Oven-Drying Tests of Mineral Concentrate to Pilot-Scale Drying with a Heated Pad
While Fickian diffusion models are commonly used in other applications, there are few reports of them being applied to the batch drying of a mineral concentrate. Diffusion coefficients estimated from small-scale oven-drying tests were used to predict the drying behavior of a concentrate sample 1 m × 1 m in area and 50 cm deep, with a heated bottom pad. These pilot-scale tests included both daily turning of the sample and turning every three days. The excellent quantitative agreement between the predicted and observed pilot-scale behavior gives a high level of confidence in the model predictions and suggests that a Fickian diffusion model is adequate to predict the behavior of mineral concentrates at the low moisture contents used here. 相似文献
83.
In this paper a digital filter is proposed for the generation of smooth set points for motion control systems. The proposed nonlinear filter produces profiles with bounded velocity and acceleration starting from rough reference signals (steps and ramps). An actual implementation of the filter for a tile printing machine is presented and experimental results are reported. 相似文献
84.
Managing sewerage systems is a highly complex task due to the dynamic nature of the facilities. Their performance strongly depends on the know-how applied by the operators. In order to define optimal operational settings, two decision support tools based on mathematical models have been developed. Moreover, easy-to-use interfaces have been created as well, aiding operators who presumably do not have the necessary skills to use modelling software. The two developed programs simulate the behaviour of both wastewater treatment plants (WWTP) and sewer network systems, respectively. They have essentially the same structure, including raw data management and statistical analysis, a simulation layer using the application programming interface of the applied software and a layer responsible for the representation of the obtained results. Four user modes are provided in the two software including the simulation of historical data using the applied and novel operational settings, as well as modes concerning prediction of possible operation periods and updates. Concerning the WWTP software, it was successfully installed in Nantes (France) in June 2004. Moreover, the one managing sewer networks has been deployed in Saint-Malo (France) in January 2005. This paper presents the structure of the developed software and the first results obtained during the commissioning phase. 相似文献
85.
Third generation (3G) mobile communication systems are now just starting to be introduced. With a maximum data rate of 2 Mbit/s they will make wireless access to broadband data services like the Internet or video applications feasible. Most of the different physical layer technologies summarised under the acronym 3G are based on wideband-CDMA (W-CDMA), in contrast to existing second generation systems, which mostly use TDMA and FDMA. This has severe consequences for the design of the transceiver front-ends. During standardisation these were assumed to have an adequate RF performance yet they still present a performance bottleneck for the system. Starting with a short introduction to UMTS (Universal Mobile Telecommunications System)-the 3G standard to be deployed in Europe and already operating in Japan-this paper describes by way of example some of the test cases specified for UMTS and their impact on the analogue front-end. It is shown that accurate simulation of all the analogue and digital signal processing is necessary in order to predict the RF performance needed of today's commercial RFICs. The paper then presents and reviews some actual design examples. Finally, possible technologies and techniques for application in future mobile terminals are discussed 相似文献
86.
The theory of characteristic modes for aperture problems is used in this paper to solve the equivalent magnetic current and aperture fields due to a conducting cylinder with multiple slots. It is assumed that these slots are illuminated by either a transverse electric (TE) or a transverse magnetic (TM) plane wave and the media inside and outside the cylinder exhibit different electromagnetic properties. The formulation is given for the general case and numerical results for a limited number of slots are presented 相似文献
87.
Crosstalk between microstrip transmission lines 总被引:1,自引:0,他引:1
Hill D.A. Cavcey K.H. Johnk R.T. 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(4):314-321
Methods for prediction of crosstalk between microstrip transmission lines are reviewed and simplified for the weak-coupling case. Classical coupled transmission line theory is used for uniform lines, and potential and induced EMF methods are used for crosstalk between nonuniform lines. It is shown that the potential method is equivalent to classical coupled transmission line theory for the case of uniform lines. An experiment was performed for uniform coupled microstrip lines for frequencies from 50 MHz to 5 GHz, and good agreement between theory and measurement was obtained for both near- and far-end crosstalk 相似文献
88.
Younan N.H. Cox B.I. Taylor C.D. Prather W.D. 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(4):394-398
Efficient numerical solution techniques have been developed and used to examine the electromagnetic fields that can be developed in the working volume of the CW Ellipticus antenna operated at frequencies from 100 kHz to 1 GHz. An exponentially tapered transition section is designed to obtain the desired illumination pattern in the working volume. The input transition section is needed for impedance matching and to drive efficiently the Ellipticus antenna. A parametric study is performed to ascertain the performance of the Ellipticus antenna for frequencies up to 1 GHz 相似文献
89.
90.
A. A. Kovalev A. F. Kotyuk B. N. Levinskii A. A. Liberman 《Measurement Techniques》1994,37(2):151-158
The authors survey published results on the application of metal diffraction gratings as laser power or energy dividers when the laser beam is split into two approximately equal pans. The normal incidence of laser radiation on metal diffraction gratings of various profiles in the case of three propagating diffraction orders n=0, ±1 is discussed, along with the case of oblique incidence with only two propagating diffraction orders n=0 and n =–1.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 22–26, February, 1994. 相似文献