全文获取类型
收费全文 | 518460篇 |
免费 | 6053篇 |
国内免费 | 1420篇 |
专业分类
电工技术 | 10091篇 |
综合类 | 734篇 |
化学工业 | 76645篇 |
金属工艺 | 18292篇 |
机械仪表 | 15004篇 |
建筑科学 | 12916篇 |
矿业工程 | 1657篇 |
能源动力 | 14467篇 |
轻工业 | 47107篇 |
水利工程 | 4375篇 |
石油天然气 | 6433篇 |
武器工业 | 21篇 |
无线电 | 67392篇 |
一般工业技术 | 98900篇 |
冶金工业 | 98754篇 |
原子能技术 | 9607篇 |
自动化技术 | 43538篇 |
出版年
2021年 | 4062篇 |
2019年 | 3728篇 |
2018年 | 6271篇 |
2017年 | 6212篇 |
2016年 | 6399篇 |
2015年 | 4358篇 |
2014年 | 7628篇 |
2013年 | 23728篇 |
2012年 | 12418篇 |
2011年 | 17153篇 |
2010年 | 13610篇 |
2009年 | 15659篇 |
2008年 | 16414篇 |
2007年 | 16254篇 |
2006年 | 14511篇 |
2005年 | 13180篇 |
2004年 | 12916篇 |
2003年 | 12862篇 |
2002年 | 12287篇 |
2001年 | 12781篇 |
2000年 | 12026篇 |
1999年 | 12791篇 |
1998年 | 31703篇 |
1997年 | 22493篇 |
1996年 | 17437篇 |
1995年 | 13355篇 |
1994年 | 12093篇 |
1993年 | 11779篇 |
1992年 | 8613篇 |
1991年 | 8270篇 |
1990年 | 8068篇 |
1989年 | 7761篇 |
1988年 | 7538篇 |
1987年 | 6347篇 |
1986年 | 6437篇 |
1985年 | 7343篇 |
1984年 | 6629篇 |
1983年 | 6306篇 |
1982年 | 5781篇 |
1981年 | 5862篇 |
1980年 | 5500篇 |
1979年 | 5319篇 |
1978年 | 4951篇 |
1977年 | 6020篇 |
1976年 | 7941篇 |
1975年 | 4281篇 |
1974年 | 4136篇 |
1973年 | 4065篇 |
1972年 | 3480篇 |
1971年 | 2979篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
71.
G. Murali Dhar B. N. Srinivas M. S. Rana Manoj Kumar S. K. Maity 《Catalysis Today》2003,86(1-4):45-60
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication. 相似文献
72.
Examination of the wreckage of a light aircraft revealed that approximately 20 cm was missing from one tip of the aluminum
alloy propeller. Fractographic and metallographic examination of the remaining portion of the propeller revealed extensive
grain-boundary separation in the vicinity of the fracture, and grain edges and corners rounded by corrosion on the fracture
surface. Energy dispersive X-ray analysis (EDXA) revealed fluorine on, and in the vicinity of, the fracture surface. In the
ensuing litigation, it was asserted that the crash occurred because the propeller fractured in flight as the result of intergranular
attack caused by the use of a fluorine-bearing cleaner. 相似文献
73.
74.
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
75.
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
76.
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
77.
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
78.
79.
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
80.
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