全文获取类型
收费全文 | 480551篇 |
免费 | 15716篇 |
国内免费 | 8001篇 |
专业分类
电工技术 | 14851篇 |
技术理论 | 9篇 |
综合类 | 9084篇 |
化学工业 | 70196篇 |
金属工艺 | 24150篇 |
机械仪表 | 19311篇 |
建筑科学 | 17494篇 |
矿业工程 | 4541篇 |
能源动力 | 11944篇 |
轻工业 | 37745篇 |
水利工程 | 5407篇 |
石油天然气 | 11332篇 |
武器工业 | 1067篇 |
无线电 | 59267篇 |
一般工业技术 | 85847篇 |
冶金工业 | 78346篇 |
原子能技术 | 9538篇 |
自动化技术 | 44139篇 |
出版年
2023年 | 2920篇 |
2022年 | 5760篇 |
2021年 | 8240篇 |
2020年 | 6105篇 |
2019年 | 5899篇 |
2018年 | 8206篇 |
2017年 | 8543篇 |
2016年 | 8340篇 |
2015年 | 8169篇 |
2014年 | 11412篇 |
2013年 | 22938篇 |
2012年 | 16610篇 |
2011年 | 20399篇 |
2010年 | 16983篇 |
2009年 | 17928篇 |
2008年 | 18439篇 |
2007年 | 18121篇 |
2006年 | 16705篇 |
2005年 | 14995篇 |
2004年 | 13088篇 |
2003年 | 13000篇 |
2002年 | 12786篇 |
2001年 | 12633篇 |
2000年 | 11370篇 |
1999年 | 11861篇 |
1998年 | 25275篇 |
1997年 | 17893篇 |
1996年 | 14234篇 |
1995年 | 10635篇 |
1994年 | 9318篇 |
1993年 | 8903篇 |
1992年 | 6451篇 |
1991年 | 6253篇 |
1990年 | 5813篇 |
1989年 | 5516篇 |
1988年 | 5224篇 |
1987年 | 4404篇 |
1986年 | 4287篇 |
1985年 | 4831篇 |
1984年 | 4377篇 |
1983年 | 3942篇 |
1982年 | 3757篇 |
1981年 | 3777篇 |
1980年 | 3519篇 |
1979年 | 3405篇 |
1978年 | 3337篇 |
1977年 | 3981篇 |
1976年 | 5701篇 |
1975年 | 2862篇 |
1974年 | 2737篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
This letter further discusses the difference between different definitions of voltage unbalance. Contrary to an earlier letter (see P. Pillay et al., ibid., vol.5, p.50-1, 2001), it is concluded that different definitions may give significantly different results. The two IEEE definitions that were not discussed in the earlier letter give different results and both deviate significantly from the true value (ratio of negative, and positive-sequence voltage) when a zero-sequence component is present. 相似文献
93.
94.
95.
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
96.
97.
H. Koizumi 《International Journal of Heat and Mass Transfer》2002,45(5):937-949
I have experimentally studied the influence of the buoyancy force and inlet flow conditions on the laminar-turbulent transition process of fully developed air flow in a heated horizontal tube with uniform wall heat flux at modified Rayleigh number 3.1×106. Eight time-series of the air temperature were simultaneously obtained using eight thermocouples positioned within the tube along a vertical line passing through the tube's axis. I have studied the time and space dependence of the transition behavior by analyzing these instantaneous time-series. By calculating a set of Lyapunov exponents and the correlation dimension of the time-series of a single thermocouple, these transitional flows are found to be chaotic. 相似文献
98.
The carrier sense multiple access with collision detection (CSMA-CD) protocol cannot be applied directly to radio channels because of the difficulty in sensing remote carrier in the presence of local transmission. Only recently, a new protocol called the CSMA with timesplit collision detection (CSMA-TCD) was introduced to overcome this problem on radio channels. This paper presents an extension of the CSMA-TCD protocol, called CSMA-TCD with multitone tree search (CSMA-TCD-MTTS). In CSMA-TCD, a preamble is transmitted before data transmission. For CSMA-TCD-MTTS, the preamble is modulated with one out ofN tones. In case of a collision, a resolution algorithm splits the terminals involved into anN -degree tree according to the tone chosen. This paper presents the throughput and approximate delay analysis of the CSMA-TCD-MTTS protocol. 相似文献
99.
In this paper, the authors present the results of experiments which clearly demonstrate a technical basis confirming that the carrier frequency harmonics data can be used for diagnostics relative to motor stator insulation degradation. 相似文献
100.
N. A. Sivov A. I. Martynenko G. N. Bondarenko M. P. Filatova E. Yu. Kabanova N. I. Popova A. N. Sivov E. B. Kruts’ko 《Petroleum Chemistry》2006,46(1):41-59
Structures and compositions of the monomers guanidine acrylate and guanidine methacrylate, their homopolymers, and copolymers with diallyldimethylammonium chloride enriched in acrylate comonomer units were determined. It was shown that ampholytic copolymers, owing to their ionic nature, contained comonomeric guanidine acrylate or methacrylate units and diallyldimethylammonium chloride units, as well as the acrylate comonomer with the diallyl counterion and polymeric acrylate and diallyl ion pairs. It follows from IR and 1H NMR data that guanidine methacrylate has the same structure (with two hydrogen bonds) in the solid state and in solutions. Guanidine acrylate structures in the solid state and in dimethylsulfoxide are identical and analogous to guanidine methacrylate structure in this solvent. In water, the guanidine acrylate structure has another type of hydrogen bonding (with one hydrogen bond, where the proton is shifted toward the guanidine group). These features of hydrogen bonding of guanidine acrylate and guanidine methacrylate are also retained in their homopolymers and copolymers with diallyldimethylammonium chloride. It was shown that the thermal stability of the copolymers was higher than that of their homopolymers, confirming the formation of intramolecular ion pairs of oppositely charged units of ampholytic copolymers. Moreover, the thermal stability of guanidine methacrylate-diallyldimethylammonium chloride copolymers is higher than that of guanidine acrylate-diallyldimethylammonium chloride copolymers. 相似文献