全文获取类型
收费全文 | 329110篇 |
免费 | 4331篇 |
国内免费 | 1036篇 |
专业分类
电工技术 | 6637篇 |
综合类 | 1216篇 |
化学工业 | 50263篇 |
金属工艺 | 11501篇 |
机械仪表 | 9608篇 |
建筑科学 | 8511篇 |
矿业工程 | 1184篇 |
能源动力 | 8754篇 |
轻工业 | 32021篇 |
水利工程 | 2963篇 |
石油天然气 | 5028篇 |
武器工业 | 95篇 |
无线电 | 40733篇 |
一般工业技术 | 62870篇 |
冶金工业 | 58742篇 |
原子能技术 | 6314篇 |
自动化技术 | 28037篇 |
出版年
2021年 | 2621篇 |
2019年 | 2464篇 |
2018年 | 4034篇 |
2017年 | 3919篇 |
2016年 | 4024篇 |
2015年 | 3032篇 |
2014年 | 5013篇 |
2013年 | 15024篇 |
2012年 | 8063篇 |
2011年 | 10808篇 |
2010年 | 8492篇 |
2009年 | 9745篇 |
2008年 | 10137篇 |
2007年 | 10129篇 |
2006年 | 8986篇 |
2005年 | 8279篇 |
2004年 | 8160篇 |
2003年 | 7968篇 |
2002年 | 7972篇 |
2001年 | 8130篇 |
2000年 | 7526篇 |
1999年 | 7750篇 |
1998年 | 17801篇 |
1997年 | 12982篇 |
1996年 | 10252篇 |
1995年 | 8006篇 |
1994年 | 7334篇 |
1993年 | 7041篇 |
1992年 | 5434篇 |
1991年 | 5238篇 |
1990年 | 5135篇 |
1989年 | 5004篇 |
1988年 | 4878篇 |
1987年 | 4099篇 |
1986年 | 4237篇 |
1985年 | 4957篇 |
1984年 | 4546篇 |
1983年 | 4266篇 |
1982年 | 3850篇 |
1981年 | 3988篇 |
1980年 | 3695篇 |
1979年 | 3691篇 |
1978年 | 3557篇 |
1977年 | 4131篇 |
1976年 | 5180篇 |
1975年 | 3081篇 |
1974年 | 3030篇 |
1973年 | 3023篇 |
1972年 | 2538篇 |
1971年 | 2277篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
151.
Krahenbuhl R. Howerton M.M. Dubinger J. Greenblatt A.S. 《Lightwave Technology, Journal of》2002,20(1):92-99
High-performance Y-branch digital optical switches realized in Ti:LiNbO3 are presented. Their switching response functions have been optimized in terms of switch voltage and crosstalk ratio. The optimization is based on analyzing different types of waveguide shaping and switching arrangements using coupled mode theory and computer simulations. Excellent switching characteristics are achieved with devices exploiting a specially shaped waveguide branch in a dilated switch arrangement. Demonstrated performances include switching voltage as low as 9 V with crosstalk suppression better than 45 dB and fiber-to-fiber losses as low as 4 dB. Polarization independence with crosstalk suppression better than 40 dB over a 1520- to 1570-nm wavelength range is achieved for any applied switch voltage greater than 18 V. These optimized digital optical switches have further demonstrated the capability to reshape electrical input signals at switching rates of several hundred megahertz 相似文献
152.
153.
R. Naef 《Dyes and Pigments》1985,6(4):233-249
Several bis(2-methyl-1-phenyl-3-isoindolyl)-(het)arylmethane perchlorate dye salts have been synthesised, the (het)aryl substituent representing the acceptor systems 2-benzothiazolyl, 1-methyl-2-benzimidazolyl, 4-quinolyl, 4- and 2-pyridyl as well as phenyl.The constitution of these green dye salts was supported by their 1H-NMR spectra. The variation of the electronic absorption maxima of this dye series was in accord with theoretical considerations based on SCF-CI and PMO calculations. They give rise to the statement that the bathochromic effect of the varied (het)aryl group is essentially due to a LUMO-LUMO interaction with the di-isoindolylmethane cyanine moiety, i.e. a second-order perturbation, enlarging the bathochromic shift caused by the increased twist angles inflicted on the central bonds by the bulkiness of the (het)aryl substituents (a first-order perturbation). The halochromic properties of these dyes are explicable on the same basis.The dissociation constants pK★ and pK★R+ were measured and compared with analogous di-indolyl- (1) and di-indolizinyl-hetaryl-methane dyes (4), showing little difference with regard to the former and the distinct sequence indolizinyl > indolyl > isoindolyl dye series for the latter. 相似文献
154.
Chlorogenic acid at 5° published threshold concentration (100 mg/ L) in aqueous 0.2% potassium acid tartrate was not significantly more bitter than aqueous 0.2% potassium tartrate alone when evaluated by taste panel. 相似文献
155.
156.
Metal-clad ridge waveguide (MCRW), double quantum well, separately confined heterostrucuture (DQW-SCH) lasers have been fabricated having continuous-wave (CW) threshold currents of 10?12 mA and external differential quantum efficiencies of 41?46% per uncoated facet. Light/current characteristics are linear to >70 mW, and zero-order lateral mode operation was measured at 56 mW. The CW burn-off power density is nearly double the best previously reported value. 相似文献
157.
The mean convergence of various versions of a genetic algorithm are considered. A number of convergence statements are formulated
and relevant estimates are obtained. A hypothesis concerning the form of these estimates under variation of the structure
of a genetic algorithm is put forward.
Roman Riviyanovich Sharapov. Born 1981. Graduated from the Faculty of Mechanics and Mathematics, Ural State University, in 2003. Presently, a postgraduate
at the Department of Mathematical Economics at the same university. Scientific interests: genetic algorithms, neural networks,
and financial mathematics.
Aleksandr Vyacheslavovich Lapshin. Born 1980. Graduated from the Faculty of Mechanics and Mathematics, Ural State University, in 2003. Presently, a postgraduate
at the Department of Mathematical Economics at the same university. Scientific interests: financial mathematics, genetic algorithms,
and neural networks. 相似文献
158.
Field R. D. Hartwig K. T. Necker C. T. Bingert J. F. Agnew S. R. 《Metallurgical and Materials Transactions A》2002,33(13):965-972
The equal-channel angular extrusion (ECAE) technique has been applied to a powder metallurgy (P/M) source Be alloy. Extrusions
have been successfully completed on Ni-canned billets of Be at approximately 425°C. No cracking was observed in the billets,
and significant grain refinement was achieved. In this article, microstructural features and dislocation structures are discussed
for a singlepass extrusion, including evidence of <c> and <c+a> dislocations. Significant crystallographic texture developed during ECAE, which is discussed in terms of this unique deformation
processing technique and the underlying physical processes which sustain the deformation.
S.R. AGNEW, formerly with the Oak Ridge National Laboratory, Oak Ridge, TN 37831-6115
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
159.
It is essential in the simulation of power electronics applications to model magnetic components accurately. In addition to modeling the nonlinear hysteresis behavior, eddy currents and winding losses must be included to provide a realistic model. In practice the losses in magnetic components give rise to significant temperature increases which can lead to major changes in the component behavior. In this paper a model of magnetic components is presented which integrates a nonlinear model of hysteresis, electro-magnetic windings and thermal behavior in a single model for use in circuit simulation of power electronics systems. Measurements and simulations are presented which demonstrate the accuracy of the approach for the electrical, magnetic and thermal domains across a variety of operating conditions, including static thermal conditions and dynamic self heating 相似文献
160.
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