全文获取类型
收费全文 | 648061篇 |
免费 | 8521篇 |
国内免费 | 2438篇 |
专业分类
电工技术 | 12236篇 |
综合类 | 735篇 |
化学工业 | 95002篇 |
金属工艺 | 24799篇 |
机械仪表 | 19151篇 |
建筑科学 | 16587篇 |
矿业工程 | 1935篇 |
能源动力 | 17059篇 |
轻工业 | 62676篇 |
水利工程 | 5500篇 |
石油天然气 | 6704篇 |
武器工业 | 76篇 |
无线电 | 82087篇 |
一般工业技术 | 118605篇 |
冶金工业 | 127685篇 |
原子能技术 | 10648篇 |
自动化技术 | 57535篇 |
出版年
2021年 | 4693篇 |
2019年 | 4491篇 |
2018年 | 7244篇 |
2017年 | 7259篇 |
2016年 | 7914篇 |
2015年 | 5530篇 |
2014年 | 9318篇 |
2013年 | 29449篇 |
2012年 | 15885篇 |
2011年 | 22206篇 |
2010年 | 17613篇 |
2009年 | 19774篇 |
2008年 | 21083篇 |
2007年 | 21060篇 |
2006年 | 19329篇 |
2005年 | 17549篇 |
2004年 | 16964篇 |
2003年 | 16811篇 |
2002年 | 16207篇 |
2001年 | 16516篇 |
2000年 | 15126篇 |
1999年 | 16477篇 |
1998年 | 40920篇 |
1997年 | 28811篇 |
1996年 | 22192篇 |
1995年 | 16772篇 |
1994年 | 14866篇 |
1993年 | 14601篇 |
1992年 | 10690篇 |
1991年 | 10180篇 |
1990年 | 9564篇 |
1989年 | 9091篇 |
1988年 | 8914篇 |
1987年 | 7555篇 |
1986年 | 7342篇 |
1985年 | 8847篇 |
1984年 | 8044篇 |
1983年 | 7281篇 |
1982年 | 6819篇 |
1981年 | 6915篇 |
1980年 | 6520篇 |
1979年 | 6058篇 |
1978年 | 5808篇 |
1977年 | 7060篇 |
1976年 | 9397篇 |
1975年 | 5085篇 |
1974年 | 4875篇 |
1973年 | 4922篇 |
1972年 | 3929篇 |
1971年 | 3616篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Towards intelligent dressing 总被引:1,自引:0,他引:1
Egana I. Mendikute A. Urionaguena X. Alberdi H. 《IEEE instrumentation & measurement magazine》2006,9(3):38-43
The aim of this article is to state the principles of an intelligent monitoring and control system for the grinding machine, comprising the dressing process as well as grinding stability. 相似文献
62.
Self-induced effects in a passive polarization-independent vertical-cavity semiconductor gate are investigated numerically and experimentally. We demonstrate all-optical seed-pulse extraction for synchronization of differential phase-shift keying and ON-OFF keying packets at 10 Gb/s. Our results provide evidence that vertical-cavity gates, exploiting saturable absorption in semiconductor quantum-wells, exhibit attractive performances in terms of efficiency, power consumption, and polarization independency. 相似文献
63.
This paper provides an overview of the main aspects of modern fluorescence microscopy. It covers the principles of fluorescence and highlights the key discoveries in the history of fluorescence microscopy. The paper also discusses the optics of fluorescence microscopes and examines the various types of detectors. It also discusses the signal and image processing challenges in fluorescence microscopy and highlights some of the present developments and future trends in the field. 相似文献
64.
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
65.
Over the last five years, many activities have focused on the unexploited field of carrying out reactions on small scales. Due to the rapid development of new components, this paper deals with recent developments only in a compressed form. An important point is the analysis of possible plant concepts for microreactors and whether these are a sensible option. Due to the enormous difference in size between the microchannels and the fluid periphera of possible components this is not just a technical question. It touches on the microtechnology concept as a whole. The direction in which the field should be developed and which measures can be taken to influence its development are questions that are addressed here with respect to the big industrial interest in microreactors. 相似文献
66.
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
67.
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
68.
Passaro V.M.N. Armenise M.N. Nesheva D. Savatinova I.T. Pun E.Y.B. 《Lightwave Technology, Journal of》2002,20(1):71-77
Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r33=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided 相似文献
69.
Near-field corrections to site attenuation 总被引:1,自引:0,他引:1
The theoretical model used for calculating normalized site attenuation for broadband antennas in ANSI C63.4-1992 and for antenna calibration in ANSI C63.5-1988 includes only the radiation terms in the electric field. The omission of the near field terms leads to errors of as much as 2.0 dB at 30 MHz for horizontally polarized antennas separated by 3 m. Corrected values of normalized site attenuation and E Dmax are presented for the 30-300 MHz frequency range 相似文献
70.
Carroll R.D. Merritt S.W. Branciforte E.J. Tanski W.J. Cullen D.E. Sacks R.N. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1994,41(3):416-418
Heterostructure Acoustic Charge Transport (HACT) devices have been fabricated with a new nondestructive sense (NDS) electrode structure that provides for the recovery of base-band signals without the use of an integrating capacitor. This electrode structure provides an output signal comprising an RF carrier at the SAW frequency, amplitude modulated by the sampled input signal which has been delayed by a period proportional to the output electrodes distance from the input diode. The output of the NDS electrode structure is subsequently demodulated to provide the base-band signal 相似文献