全文获取类型
收费全文 | 112173篇 |
免费 | 1568篇 |
国内免费 | 1462篇 |
专业分类
电工技术 | 2183篇 |
综合类 | 160篇 |
化学工业 | 11568篇 |
金属工艺 | 6146篇 |
机械仪表 | 3523篇 |
建筑科学 | 2366篇 |
矿业工程 | 173篇 |
能源动力 | 3302篇 |
轻工业 | 6526篇 |
水利工程 | 778篇 |
石油天然气 | 755篇 |
武器工业 | 16篇 |
无线电 | 17321篇 |
一般工业技术 | 24038篇 |
冶金工业 | 26678篇 |
原子能技术 | 1485篇 |
自动化技术 | 8185篇 |
出版年
2023年 | 268篇 |
2022年 | 511篇 |
2021年 | 802篇 |
2020年 | 586篇 |
2019年 | 778篇 |
2018年 | 1274篇 |
2017年 | 1252篇 |
2016年 | 1344篇 |
2015年 | 1058篇 |
2014年 | 1677篇 |
2013年 | 5277篇 |
2012年 | 2893篇 |
2011年 | 4313篇 |
2010年 | 3487篇 |
2009年 | 4261篇 |
2008年 | 4355篇 |
2007年 | 4549篇 |
2006年 | 4121篇 |
2005年 | 3686篇 |
2004年 | 3525篇 |
2003年 | 3312篇 |
2002年 | 2941篇 |
2001年 | 3264篇 |
2000年 | 3004篇 |
1999年 | 3360篇 |
1998年 | 10010篇 |
1997年 | 6530篇 |
1996年 | 5091篇 |
1995年 | 3390篇 |
1994年 | 2964篇 |
1993年 | 2875篇 |
1992年 | 1740篇 |
1991年 | 1714篇 |
1990年 | 1613篇 |
1989年 | 1405篇 |
1988年 | 1237篇 |
1987年 | 905篇 |
1986年 | 931篇 |
1985年 | 955篇 |
1984年 | 843篇 |
1983年 | 731篇 |
1982年 | 724篇 |
1981年 | 698篇 |
1980年 | 586篇 |
1979年 | 494篇 |
1978年 | 434篇 |
1977年 | 550篇 |
1976年 | 966篇 |
1975年 | 308篇 |
1974年 | 289篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Computing must become much more human centered--for example, by presenting personalized information to users and by respecting personal preferences when controlling multiple devices or invoking various services. Appropriate representation of the information's semantics and of the functionality of devices and services will be critical to such personalized computing. Symbolic artificial intelligence techniques provide the method of choice for the required semantic-representation and reasoning capabilities. 相似文献
72.
Buttari D. Chini A. Meneghesso G. Zanoni E. Moran B. Heikman S. Zhang N.Q. Shen L. Coffie R. DenBaars S.P. Mishra U.K. 《Electron Device Letters, IEEE》2002,23(2):76-78
Pre-metal-deposition reactive ion etching (RIE) was performed on an Al0.3Ga0.7N/AlN/GaN heterostructure in order to improve the metal-to-semiconductor contact resistance. An optimum AlGaN thickness for minimizing contact resistance was determined. An initial decrease in contact resistance with etching time was explained in terms of removal of an oxide surface layer and/or by an increase in tunnelling current with the decrease of the AlGaN thickness. The presence of a dissimilar surface layer was confirmed by an initial nonuniform etch depth rate. An increase in contact resistance for deeper etches was experienced. The increase was related to depletion of the two-dimensional (2-D) electron gas (2-DEG) under the ohmics. Etch depths were measured by atomic force microscopy (AFM). The contact resistance decreased from about 0.45 Ωmm for unetched ohmics to a minimum of 0.27 Ωmm for 70 Å etched ohmics. The initial thickness of the AlGaN layer was 250 Å. The decrease in contact resistance, without excessive complications on device processing, supports RIE etching as a viable solution to improve ohmic contact resistance in AlGaN/GaN HEMTs 相似文献
73.
Liang Y.C. Wenjiang Zeng Pick Hong Ong Zhaoxia Gao Jun Cai Balasubramanian N. 《Electron Device Letters, IEEE》2002,23(12):700-703
In this letter, a concise process technology is proposed for the first time to enable the fabrication of good quality three-dimensional (3-D) suspended radio frequency (RF) micro-inductors on bulk silicon, without utilizing the lithography process on sidewall and trench-bottom patterning. Samples were fabricated to demonstrate the applicability of the proposed process technology. 相似文献
74.
75.
76.
The behavior of two series of concrete slabs exposed to sulfate-bearing soils was investigated by a numerical model called
STADIUM. In addition to the diffusion of ions and moisture, the model also accounts for the effects of dissolution/precipitation
reactions on the transport mechanisms. The simulations yielded by the model were compared to the actual degradation of the
slabs after 8 years of exposure. The microstructural alterations of concrete resulting from the penetration of magnesium,
chloride and sulfate ions were studied by backscatter mode scanning electron microscope observations and energy-dispersive
X-ray analyses. The comparison of both series of data indicates that the model can reliably predict the various features of
the microstructural alterations of concrete.
Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’. 相似文献
Résumé Le comportement de deux séries de dalles sur sol en béton exposées à des sols chimiquement agressifs a été étudié à l'aide d'un code de calcul numérique appelé STADIUM. Ce modèle permet de décrire le transport couplé de l'eau et des ions dans des matériaux poreux non-saturés en prenant en considération l'influence des réactions chimiques. Les résultats des simultations de la dégradation du béton après huit ans d'exposition à des ions chlore, sulfate et magnésium. Les observations ont été réalisées par microscopie électronique à balayage. Des analyses par dispersion des rayons X ont également été effectuées. Les données démontrent clairement que le modèle perment de prédire avec précision le comportement du béton soumis à différents types d'agression chimique.
Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’. 相似文献
77.
Ignatius Y. Chan 《Microscopy research and technique》1987,5(2):181-188
A new transmission electron microscopy (TEM) specimen preparation procedure for high temperature experiments using a controlled atmosphere specimen holder (HTCASH) has been developed. It is designed for studying the microstructure of catalyst specimens before and after treatments in various gases. The procedure involved (1) finding a new formula for the embedding material, (2) devising a new method of making specimen supports, and (3) developing a method for removing the embedding material after the specimen has been microtomed. These techniques were then brought together to produce the ideal specimens for the HTCASH experiments. As an extra benefit, this procedure is also suitable for preparing specimens for ultrahigh resolution imaging experiments. The application of the new procedure in HTCASH experiments is illustrated through a high temperature reduction of a Co/SiO2-923 catalyst. 相似文献
78.
Francois P.-L. Monerie M. Vassallo C. Durteste Y. Alard F.R. 《Lightwave Technology, Journal of》1989,7(3):500-513
Depending on the spectal width of the source illuminating an interferometer, measurement procedures can utilize either the whole interferogram, or only the fringe envelope, or only the fringe quick oscillations. With an ultraband spectrum source, a simplified adaptation of the methods of Fourier transform spectroscopy yields the variations of the test-fiber propagation constant over the whole wavelength-interval of the source. Chromatic dispersion can then be computed from a single interferogram. With narrower spectrum sources, only the fringe envelopes are utilized and yield measurements of mode delay, with application to chromatic and polarization mode dispersion. In this case, however, interferograms at several wavelengths are necessary. With even narrower spectrum sources, the fringe quick oscillations provide measurements of phase shifts, related to changes in the mode propagation constant, when outside perturbations are applied to the test fiber. A direct method for measuring the third-order nonlinear susceptibilities is discussed. In this case the outside perturbation is an intense pump laser field 相似文献
79.
A minimal integrated filter containing four MOS transistors as the only circuit elements is presented. Voltage tuning is used to set the cutoff frequency and band-edge peaking. A filter test chip occupies an active area of 0006mm2, has acutoff frequency of 40 MHz and dissipates 580W. 相似文献
80.
Tang Helen H. Y.; McNally Gavan P.; Richardson Rick 《Canadian Metallurgical Quarterly》2007,121(6):1421
The authors studied the role of gamma-aminobutyric acid (GABA) in 2 types of forgetting of fear in the developing rat. One type of forgetting studied was that observed after an intermediate retention interval (the "Kamin effect"); the other type studied was that observed after a longer interval (infantile amnesia). Rats were given pairings of an auditory conditioned stimulus with shock, and learned fear was assessed by freezing. Forgetting at an intermediate retention interval (1 hr) was not alleviated by the GABAA receptor partial inverse agonist FG7142 (0, 1, 5, or 10 mg/kg), whereas forgetting at a longer retention interval (48 hr) was alleviated. These results suggest that in the developing rat, forgetting observed at different retention intervals is mediated by different physiological mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献