全文获取类型
收费全文 | 841886篇 |
免费 | 11959篇 |
国内免费 | 2624篇 |
专业分类
电工技术 | 15273篇 |
综合类 | 1431篇 |
化学工业 | 125349篇 |
金属工艺 | 30183篇 |
机械仪表 | 23905篇 |
建筑科学 | 21862篇 |
矿业工程 | 3304篇 |
能源动力 | 22567篇 |
轻工业 | 76423篇 |
水利工程 | 7762篇 |
石油天然气 | 10745篇 |
武器工业 | 53篇 |
无线电 | 98666篇 |
一般工业技术 | 155697篇 |
冶金工业 | 171564篇 |
原子能技术 | 14388篇 |
自动化技术 | 77297篇 |
出版年
2021年 | 6744篇 |
2020年 | 4831篇 |
2019年 | 6167篇 |
2018年 | 10714篇 |
2017年 | 10708篇 |
2016年 | 11652篇 |
2015年 | 8551篇 |
2014年 | 13257篇 |
2013年 | 38202篇 |
2012年 | 22676篇 |
2011年 | 31427篇 |
2010年 | 23681篇 |
2009年 | 26640篇 |
2008年 | 27557篇 |
2007年 | 27460篇 |
2006年 | 24345篇 |
2005年 | 24739篇 |
2004年 | 23374篇 |
2003年 | 22614篇 |
2002年 | 20695篇 |
2001年 | 20625篇 |
2000年 | 18759篇 |
1999年 | 20070篇 |
1998年 | 52511篇 |
1997年 | 37036篇 |
1996年 | 28441篇 |
1995年 | 21497篇 |
1994年 | 18776篇 |
1993年 | 18332篇 |
1992年 | 12967篇 |
1991年 | 12416篇 |
1990年 | 11959篇 |
1989年 | 11596篇 |
1988年 | 10947篇 |
1987年 | 9513篇 |
1986年 | 9358篇 |
1985年 | 10912篇 |
1984年 | 10129篇 |
1983年 | 8909篇 |
1982年 | 8379篇 |
1981年 | 8510篇 |
1980年 | 8061篇 |
1979年 | 7763篇 |
1978年 | 7401篇 |
1977年 | 9317篇 |
1976年 | 12860篇 |
1975年 | 6362篇 |
1974年 | 6011篇 |
1973年 | 6001篇 |
1972年 | 4894篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
This publication consists of an analysis and a synthesis by the amplitude law of linear and planar ring printed antennas array. The analysis of the structure is based on the modified cavity model which allows taking into account the fringing fields effects. The synthesis problem is solved by the simulated annealing method based on a random process research controlled by temperature parameter. The feeding network amplitude permitting to produce an optimal radiation pattern is then given. Various synthesis results for linear and planar arrays are presented. 相似文献
982.
Peak-to-average power reduction in space division multiplexing based OFDM systems through spatial shifting 总被引:2,自引:0,他引:2
A new method to reduce the peak-to-average power ratio (PAPR) in space division multiplexing systems applying orthogonal frequency division multiplexing is proposed. The method applies spatial shifting to partial transmit sequences to achieve a decreased PAPR on all transmit branches. 相似文献
983.
A new frequency notched ultra-wideband microstrip slot antenna with a parasitic tuning stub is proposed. The antenna is similar in configuration to a conventional microstrip slot antenna; by introducing a parasitic open-circuit tuning stub, flexible frequency notched function is achieved. Several properties of the antenna, such as frequency notched function, antenna transfer function and gain, have been investigated. As is reported, the operation bandwidth of the antenna is 2.91-11.16 GHz, in which a frequency notched band of 5.10-5.85 GHz has been achieved. Furthermore, good ultra-wideband linear transmission performance over the entire operation frequency range has also been achieved. 相似文献
984.
O Bernard B Chachuat A Hélias B Le Dantec B Sialve J-P Steyer L Lardon P Neveu S Lambert J Gallop M Dixon P Ratini A Quintabà S Frattesi J M Lema E Roca G Ruiz J Rodriguez A Franco P Vanrolleghem U Zaher D J W De Pauw K De Neve K Lievens D Dochaine O Schoefs H Fibrianto R Farina V Alcaraz Gonzalez V Gonzalez Alvarez P Lemaire J A Martinez F Esandi O Duclaud J F Lavigne 《Water science and technology》2005,52(1-2):457-464
The TELEMAC project brings new methodologies from the Information and Science Technologies field to the world of water treatment. TELEMAC offers an advanced remote management system which adapts to most of the anaerobic wastewater treatment plants that do not benefit from a local expert in wastewater treatment. The TELEMAC system takes advantage of new sensors to better monitor the process dynamics and to run automatic controllers that stabilise the treatment plant, meet the depollution requirements and provide a biogas quality suitable for cogeneration. If the automatic system detects a failure which cannot be solved automatically or locally by a technician, then an expert from the TELEMAC Control Centre is contacted via the internet and manages the problem. 相似文献
985.
Remotely powered addressable UHF RFID integrated system 总被引:3,自引:0,他引:3
Curty J.-P. Joehl N. Dehollain C. Declercq M.J. 《Solid-State Circuits, IEEE Journal of》2005,40(11):2193-2202
This paper presents a fully integrated remotely powered and addressable radio frequency identification (RFID) transponder working at 2.45 GHz. The achieved operating range at 4 W effective isotropically radiated power (EIRP) base-station transmit power is 12 m. The integrated circuit (IC) is implemented in a 0.5 /spl mu/m silicon-on-sapphire technology. A state-of-the-art rectifier design achieving 37% of global efficiency is embedded to supply energy to the transponder. The necessary input power to operate the transponder is about 2.7 /spl mu/W. Reader to transponder communication is obtained using on-off keying (OOK) modulation while transponder to reader communication is ensured using the amplitude shift keying (ASK) backscattering modulation technique. Inductive matching between the antenna and the transponder IC is used to further optimize the operating range. 相似文献
986.
Video Compression - From Concepts to the H.264/AVC Standard 总被引:10,自引:0,他引:10
Sullivan G.J. Wiegand T. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》2005,93(1):18-31
Over the last one and a half decades, digital video compression technologies have become an integral part of the way we create, communicate, and consume visual information. In this paper, techniques for video compression are reviewed, starting from basic concepts. The rate-distortion performance of modern video compression schemes is the result of an interaction between motion representation techniques, intra-picture prediction techniques, waveform coding of differences, and waveform coding of various refreshed regions. The paper starts with an explanation of the basic concepts of video codec design and then explains how these various features have been integrated into international standards, up to and including the most recent such standard, known as H.264/AVC. 相似文献
987.
Todd M. Alam Joshua U. Otaigbe Dave Rhoades Gregory P. Holland Brian R. Cherry Paul G. Kotula 《Polymer》2005,46(26):12468-12479
Nanostructured polymer blends prepared via anionic ring opening polymerizations of cyclic monomers in the presence of a pre-made polymer melt exhibit a number of special properties over traditional polymer blends and homopolymers. Here, we report on a simple and versatile method of in situ polymerization of macrocyclic carbonates in the presence of a maleic anhydride polypropylene (mPP) matrix and a surface-active compatibilizer (i.e. PC grafted onto a mPP backbone generated in situ) to yield a micro- and nanostructured polymer blends consisting of a polycarbonate (PC) minor phase, and a polypropylene (PP) major phase. By varying the processing conditions and concentration of the macrocyclic carbonate it was possible to reduce the size of the PC dispersions to an average minor diameter of 150 nm. NMR and TEM characterizations indicate that the PC dispersions do not influence crystal content in the PP phase. Overall, the results point to a simple strategy and versatile route to new polymeric materials with enhanced benefits. 相似文献
988.
Dynamic vulcanisation of EPDM/PE-based thermoplastic vulcanisates studied along the extruder axis 总被引:1,自引:0,他引:1
Simple blending and dynamic vulcanisation of EPDM/PE blends using the resol/SnCl2 system was studied in an extruder using a series of sampling devices. The melting of the PE pellets occurs just in front of and in the first kneading zone. Upon complete melting of the PE phase, the EPDM/PE blends reach very quickly their final morphology. Crosslinking of the EPDM phase to high levels occurs already when the PE phase is not yet fully molten. The higher the EPDM content, the higher the viscous dissipation, the higher the melt temperature and, consequently, the higher the crosslinking rate. For the EPDM/PE (50/50; w/w) TPV a transition from continuous via co-continuous to fully dispersed EPDM is observed, which is driven by crosslinking. Although the degree of crosslinking of the EPDM rubber is very high, this does not prevent phase inversion of the blend. The EPDM/PE interface is rather blurred, because PE crystalline lamellae are growing into the EPDM domains, probably because of the high compatibility between PE and EPDM (60 wt% of ethene). This study shows that dynamic vulcanisation in extruders proceeds quite differently from that in batch kneaders, where melting, mixing and crosslinking are separated in time. In extruders mass and heat transport, melting of the thermoplastic, morphology development (including dispersion and phase inversion), distribution and dissolution of (crosslinking) chemicals and crosslinking of the rubber do not occur as independent phenomena, but mutually and/or continuously interact. 相似文献
989.
Summary Electropolymerization of o-(CH3O)2C6H4 (Veratrole) in dry acetonitrile/tetrabutylammonium tetrafluoroborate at platinum electrode, yields a green polymeric conducting solid. As the pressure is increased, the material becomes more conductive, but sharp changes towards lower conductivity occur at 4.2 and 6.2 metric tons pressure, probably due to phase transitions. The photoconductivity shows an exponential increase as temperature is increased, but it shows reversible changes at 200 K, 225 K and 250 K during slow warming, also attributable to phase transitions. Photoconductivity of Polyveratrole increases with the radiation frequency, being higher under blue light than under red of infrared radiation and there is a linear increase of photoconductivity with radiation density. Conductivity transients show that the conductivity increases exponentially with time to the saturation point within few minutes, and it also decreases exponentially when the light is turned off and the circuit is open. This behaviour can be explained by formation and encounter of electron and hole as current carriers. A preliminary study indicates a piezoelectric effect for the material. absorption spectroscopy allowed the measurements of the material band gap. 相似文献
990.
Emission of coherent light at 5.1 /spl mu/m wavelength from GaAs-based quantum cascade lasers is reported. This was achieved by integrating nonlinear cascades with large second-order susceptibility in the active regions of the laser. 相似文献