全文获取类型
收费全文 | 697271篇 |
免费 | 8284篇 |
国内免费 | 1652篇 |
专业分类
电工技术 | 12344篇 |
综合类 | 601篇 |
化学工业 | 106332篇 |
金属工艺 | 30545篇 |
机械仪表 | 22304篇 |
建筑科学 | 15743篇 |
矿业工程 | 5057篇 |
能源动力 | 17181篇 |
轻工业 | 53190篇 |
水利工程 | 8201篇 |
石油天然气 | 18037篇 |
武器工业 | 50篇 |
无线电 | 73122篇 |
一般工业技术 | 145137篇 |
冶金工业 | 125659篇 |
原子能技术 | 17764篇 |
自动化技术 | 55940篇 |
出版年
2021年 | 6697篇 |
2020年 | 4907篇 |
2019年 | 6375篇 |
2018年 | 11345篇 |
2017年 | 11337篇 |
2016年 | 11901篇 |
2015年 | 7621篇 |
2014年 | 12753篇 |
2013年 | 31072篇 |
2012年 | 19513篇 |
2011年 | 26155篇 |
2010年 | 20718篇 |
2009年 | 23219篇 |
2008年 | 23696篇 |
2007年 | 23144篇 |
2006年 | 19712篇 |
2005年 | 17924篇 |
2004年 | 17355篇 |
2003年 | 17113篇 |
2002年 | 16181篇 |
2001年 | 16228篇 |
2000年 | 15236篇 |
1999年 | 15478篇 |
1998年 | 37707篇 |
1997年 | 26932篇 |
1996年 | 20535篇 |
1995年 | 15645篇 |
1994年 | 13743篇 |
1993年 | 13613篇 |
1992年 | 10166篇 |
1991年 | 9768篇 |
1990年 | 9741篇 |
1989年 | 9389篇 |
1988年 | 8759篇 |
1987年 | 8050篇 |
1986年 | 7854篇 |
1985年 | 8621篇 |
1984年 | 8158篇 |
1983年 | 7416篇 |
1982年 | 6947篇 |
1981年 | 7118篇 |
1980年 | 6864篇 |
1979年 | 6902篇 |
1978年 | 6878篇 |
1977年 | 7781篇 |
1976年 | 9760篇 |
1975年 | 6064篇 |
1974年 | 5908篇 |
1973年 | 5984篇 |
1972年 | 5116篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
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
172.
Demiguel S. Giraudet L. Joulaud L. Decobert J. Blache F. Coupe V. Jorge F. Pagnod-Rossiaux P. Boucherez E. Achouche M. Devaux F. 《Lightwave Technology, Journal of》2002,20(12):2004-2014
The design, fabrication, and performance of double-stage taper photodiodes (DSTPs) are reported. The objective of this work is to develop devices compatible with 40-Gb/s applications. Such devices require high efficiency, ultrawide band, high optical power handling capability, and compatibility with low-cost module fabrication. The integration of mode size converters improves both the coupling efficiency and the responsivity with a large fiber mode diameter. Responsivity of 0.6 A/W and 0.45 A/W are achieved with a 6-/spl mu/m fiber mode diameter and cleaved fiber, respectively, providing relaxed alignment tolerances (/spl plusmn/1.6 /spl mu/m and /spl plusmn/2 /spl mu/m, respectively), compatible with cost-effective packaging techniques. DSTPs also offer a wide bandwidth greater than 40 GHz and transverse-electric/transverse-magnetic polarization dependence lower than 0.2 dB. Furthermore, a DSTP saturation current as high as 11 mA results in optical power handling greater than +10 dBm and a high output voltage of 0.8 V. These capabilities allow the photodiode to drive the decision circuit without the need of a broad-band electrical amplifier. The DSTP devices presented here demonstrate higher responsivities with large fiber mode diameter and better optical power handling capabilities and are compared with classical side-illuminated photodiodes. 相似文献
173.
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
174.
A 1 V switched-capacitor (SC) bandpass sigma-delta (/spl Sigma//spl Delta/) modulator is realized using a high-speed switched-opamp (SO) technique with a sampling frequency of up to 50 MHz, which is improved ten times more than prior 1 V SO designs and comparable to the performance of the state-of-the-art SC circuits that operate at much higher supply voltages. On the system level, a fast-settling double-sampling SC biquadratic filter architecture is proposed to achieve high-speed operation. A low-voltage double-sampling finite-gain-compensation technique is employed to realize a high-resolution /spl Sigma//spl Delta/ modulator using only low-DC-gain opamps to maximize the speed and to reduce power dissipation. On the circuit level, a fast-switching methodology is proposed for the design of the switchable opamps to achieve a switching frequency up to 50 MHz. Implemented in a 0.35-/spl mu/m CMOS process (V/sub TP/=0.82 V and V/sub TN/=0.65 V) and at 1 V supply, the modulator achieves a measured peak signal-to-noise-and-distortion ratio (SNDR) of 42.3 dB at 10.7 MHz with a signal bandwidth of 200 kHz, while dissipating 12 mW and occupying a chip area of 1.3 mm/sup 2/. 相似文献
175.
Mine K. Kubota N. Morimoto F. Sanada M. Zhang Qi 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(3):253-255
This short paper discusses the method of effectively canceling equal status normal mode noise not only on a sensor line but also on a transmission line of an optical instrument using a sensor with a sensordummy resistance 相似文献
176.
177.
S V Bhat 《Bulletin of Materials Science》1994,17(7):1271-1285
When examined using continuous wave electron paramagnetic resonance and nuclear magnetic resonance spectrometers, the highT
c superconductors give rise to intense, low field, ‘non-resonant’ absorption signals in the superconducting state. This phenomenon
can be used as a highly sensitive, contactless technique for the detection and characterization of superconductivity even
in samples containing only minute amounts of the superconducting phase. Further, it can also be applied to the determination
of material parameters of interest such asJ
c andH
c2 in addition to being a powerful way of distinguishing between weak-link superconductivity and bulk superconductivity. The
details of these aspects are discussed. 相似文献
178.
An instrument is proposed for continuously tracking the Sun and measuring its height by the use of a laser gyrometer as measuring
converter. The accuracy in photoelectric sighting on the Sun is improved by greatly reducing the light fluxes to be compared
by screening out the central part of the Sun's image in the focal plane.
Translated from Izmeritel'naya Tekhnika, No. 3, pp. 7–9, March, 1994. 相似文献
179.
A method is given for calculating the monitoring reliability parameters (MRP) for an engineering system with allowance for the drift in the measurement error of the means of measurement (MM). The approach is based on introducing a biased MM error distribution into the traditional formulas for the conditional probabilities of spurious and unobserved failure. The bias at the center of the distribution is determined by the systematic error at the given instant. An example is given to illustrate the performance in MRP calculation.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 12–13, January, 1994. 相似文献
180.
A.S. Fomichev I. David S.M. Lukyanov Yu.E. Penionzhkevich N.K. Skobelev O.B. Tarasov 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1994,350(3):605-607
The mass and charge identification of secondary particles with Z < 4 by a large CsI(T1) scintillation detector is performed using pulse shape analysis and time-of-flight methods. The dependence of the light output on E, A and Z is studied in the energy range of 1–20 MeV/A and special attention is paid to the integration time of the photomultiplier anode signal. It is found that the behaviour of the calibration curves strongly depends on the choice of the integration time interval. 相似文献