全文获取类型
收费全文 | 395010篇 |
免费 | 7801篇 |
国内免费 | 2777篇 |
专业分类
电工技术 | 7716篇 |
技术理论 | 5篇 |
综合类 | 1352篇 |
化学工业 | 60913篇 |
金属工艺 | 17081篇 |
机械仪表 | 13455篇 |
建筑科学 | 9329篇 |
矿业工程 | 1830篇 |
能源动力 | 10107篇 |
轻工业 | 34239篇 |
水利工程 | 3676篇 |
石油天然气 | 6599篇 |
武器工业 | 260篇 |
无线电 | 48713篇 |
一般工业技术 | 76380篇 |
冶金工业 | 74355篇 |
原子能技术 | 7305篇 |
自动化技术 | 32273篇 |
出版年
2022年 | 2691篇 |
2021年 | 4491篇 |
2020年 | 3137篇 |
2019年 | 3813篇 |
2018年 | 5649篇 |
2017年 | 5608篇 |
2016年 | 6316篇 |
2015年 | 4780篇 |
2014年 | 7740篇 |
2013年 | 18021篇 |
2012年 | 12776篇 |
2011年 | 16799篇 |
2010年 | 13254篇 |
2009年 | 14401篇 |
2008年 | 15129篇 |
2007年 | 14810篇 |
2006年 | 13224篇 |
2005年 | 11657篇 |
2004年 | 10639篇 |
2003年 | 10035篇 |
2002年 | 9588篇 |
2001年 | 9791篇 |
2000年 | 9051篇 |
1999年 | 9372篇 |
1998年 | 22961篇 |
1997年 | 16089篇 |
1996年 | 12367篇 |
1995年 | 8902篇 |
1994年 | 8034篇 |
1993年 | 7800篇 |
1992年 | 5630篇 |
1991年 | 5407篇 |
1990年 | 5400篇 |
1989年 | 5179篇 |
1988年 | 4759篇 |
1987年 | 3948篇 |
1986年 | 3971篇 |
1985年 | 4350篇 |
1984年 | 4134篇 |
1983年 | 3766篇 |
1982年 | 3356篇 |
1981年 | 3562篇 |
1980年 | 3176篇 |
1979年 | 3293篇 |
1978年 | 3139篇 |
1977年 | 3366篇 |
1976年 | 4670篇 |
1975年 | 2744篇 |
1974年 | 2552篇 |
1973年 | 2563篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
L. A. Dombrovskii 《High Temperature》2003,41(6):819-824
Theoretical models of heat transfer by radiation through a vapor gap under conditions of film boiling of liquid are treated, namely, a general wave model for a gap of arbitrary thickness and an approximate model of geometrical optics. Calculations are performed of heat transfer by radiation under conditions of film boiling of water on hot surfaces of refractory metal and molten oxide. Practical recommendations are given to calculate the distribution of the power of absorbed radiation in a water layer. 相似文献
62.
63.
Bong Keun Kim Wan Kyun Chung 《Industrial Electronics, IEEE Transactions on》2003,50(6):1207-1216
Disturbance-observer (DOB)-based controller design is one of the most popular methods in the field of motion control. In this paper, the generalized disturbance compensation framework, named the robust internal-loop compensator (RIC) is introduced and an advanced design method of a DOB is proposed based on the RIC. The mixed sensitivity optimization problem, which is the main issue of DOB design, is also solved through the parametrization of the DOB in the RIC framework. Differently from conventional methods, the Q-filter is separated from the mixed sensitivity optimization problem and a systematic design law for the DOB is proposed. This guarantees the robustness and optimality of the DOB and enables the design for unstable plants. 相似文献
64.
Demiguel S. Giraudet L. Joulaud L. Decobert J. Blache F. Coupe V. Jorge F. Pagnod-Rossiaux P. Boucherez E. Achouche M. Devaux F. 《Lightwave Technology, Journal of》2002,20(12):2004-2014
The design, fabrication, and performance of double-stage taper photodiodes (DSTPs) are reported. The objective of this work is to develop devices compatible with 40-Gb/s applications. Such devices require high efficiency, ultrawide band, high optical power handling capability, and compatibility with low-cost module fabrication. The integration of mode size converters improves both the coupling efficiency and the responsivity with a large fiber mode diameter. Responsivity of 0.6 A/W and 0.45 A/W are achieved with a 6-/spl mu/m fiber mode diameter and cleaved fiber, respectively, providing relaxed alignment tolerances (/spl plusmn/1.6 /spl mu/m and /spl plusmn/2 /spl mu/m, respectively), compatible with cost-effective packaging techniques. DSTPs also offer a wide bandwidth greater than 40 GHz and transverse-electric/transverse-magnetic polarization dependence lower than 0.2 dB. Furthermore, a DSTP saturation current as high as 11 mA results in optical power handling greater than +10 dBm and a high output voltage of 0.8 V. These capabilities allow the photodiode to drive the decision circuit without the need of a broad-band electrical amplifier. The DSTP devices presented here demonstrate higher responsivities with large fiber mode diameter and better optical power handling capabilities and are compared with classical side-illuminated photodiodes. 相似文献
65.
Passaro V.M.N. Armenise M.N. Nesheva D. Savatinova I.T. Pun E.Y.B. 《Lightwave Technology, Journal of》2002,20(1):71-77
Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r33=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided 相似文献
66.
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
67.
Varani L. Reggiani L. Kuhn T. Gonzalez T. Pardo D. 《Electron Devices, IEEE Transactions on》1994,41(11):1916-1925
We present a microscopic interpretation of electronic noise in semiconductor materials and two-terminal devices. The theory is based on Monte Carlo simulations of the carrier motion self-consistently coupled with a Poisson solver. Current and voltage noise operations are applied and their respective representations discussed. As application we consider the cases of homogeneous materials, resistors, n+nn + structures, and Schottky-barrier diodes. Phenomena associated with coupling between fluctuations in carrier velocity and self-consistent electric field are quantitatively investigated for the first time. At increasing applied fields hot-carrier effects are found to be of relevant importance in all the cases considered here. As a general result, noise spectroscopy is found to be a source of valuable information to investigate and characterize transport properties of semiconductor materials and devices 相似文献
68.
69.
70.