全文获取类型
收费全文 | 525956篇 |
免费 | 5756篇 |
国内免费 | 2245篇 |
专业分类
电工技术 | 9065篇 |
综合类 | 2939篇 |
化学工业 | 73188篇 |
金属工艺 | 21852篇 |
机械仪表 | 15899篇 |
建筑科学 | 11873篇 |
矿业工程 | 2736篇 |
能源动力 | 11987篇 |
轻工业 | 37645篇 |
水利工程 | 5602篇 |
石油天然气 | 8373篇 |
武器工业 | 47篇 |
无线电 | 65194篇 |
一般工业技术 | 102481篇 |
冶金工业 | 94310篇 |
原子能技术 | 10583篇 |
自动化技术 | 60183篇 |
出版年
2021年 | 3174篇 |
2019年 | 3127篇 |
2018年 | 19175篇 |
2017年 | 18123篇 |
2016年 | 15202篇 |
2015年 | 4304篇 |
2014年 | 6684篇 |
2013年 | 18851篇 |
2012年 | 13601篇 |
2011年 | 23648篇 |
2010年 | 19440篇 |
2009年 | 18735篇 |
2008年 | 20538篇 |
2007年 | 21552篇 |
2006年 | 12584篇 |
2005年 | 12756篇 |
2004年 | 12677篇 |
2003年 | 12310篇 |
2002年 | 11319篇 |
2001年 | 11356篇 |
2000年 | 10759篇 |
1999年 | 11493篇 |
1998年 | 30295篇 |
1997年 | 20766篇 |
1996年 | 15989篇 |
1995年 | 11927篇 |
1994年 | 10433篇 |
1993年 | 10464篇 |
1992年 | 7300篇 |
1991年 | 7030篇 |
1990年 | 6831篇 |
1989年 | 6655篇 |
1988年 | 6133篇 |
1987年 | 5321篇 |
1986年 | 5374篇 |
1985年 | 6009篇 |
1984年 | 5410篇 |
1983年 | 4951篇 |
1982年 | 4633篇 |
1981年 | 4790篇 |
1980年 | 4570篇 |
1979年 | 4270篇 |
1978年 | 4262篇 |
1977年 | 4900篇 |
1976年 | 6526篇 |
1975年 | 3642篇 |
1974年 | 3521篇 |
1973年 | 3501篇 |
1972年 | 2969篇 |
1971年 | 2583篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Scale Up from Small Oven-Drying Tests of Mineral Concentrate to Pilot-Scale Drying with a Heated Pad
While Fickian diffusion models are commonly used in other applications, there are few reports of them being applied to the batch drying of a mineral concentrate. Diffusion coefficients estimated from small-scale oven-drying tests were used to predict the drying behavior of a concentrate sample 1 m × 1 m in area and 50 cm deep, with a heated bottom pad. These pilot-scale tests included both daily turning of the sample and turning every three days. The excellent quantitative agreement between the predicted and observed pilot-scale behavior gives a high level of confidence in the model predictions and suggests that a Fickian diffusion model is adequate to predict the behavior of mineral concentrates at the low moisture contents used here. 相似文献
102.
M. Kawasaki T. Tsukamoto Y. Kimura T. Iwasaki H. Yamane 《Journal of Materials Science》2003,38(4):739-745
The damage imposed on SiO
x
deposited nylon 6 films as a result of abrasion with a cotton cloth and Gelboflex testing was examined by evaluating the rate at which copper plates, which were enveloped by the damaged films, were corroded by H2S. Abrasion with a cotton cloth caused some micro-cracking of the SiO
x
layer and the permeation rate of H2S approached that of the uncoated nylon 6 film. Damage to the SiO
x
layer by twisting and crushing progressed gradually with the number of Gelboflex test cycles and correspondingly the corrosion rate of the copper plates increased. Comparison of the corrosion rates of the copper plates kept in the pouches made of various commercial films with those obtained for the damaged SiO
x
deposited nylon 6 films showed a clear relationship between the H2 permeation rate of the films and the corrosion rate of the copper plates by H2S. 相似文献
103.
Borges J. Phelps K.T. Rifa J. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(8):2028-2034
A binary extended 1-perfect code of length n + 1 = 2/sup t/ is additive if it is a subgroup of /spl Zopf//sub 2//sup /spl alpha// /spl times/ /spl Zopf//sub 4//sup /spl beta//. The punctured code by deleting a /spl Zopf//sub 2/ coordinate (if there is one) gives a perfect additive code. 1-perfect additive codes were completely characterized and by using that characterization we compute the possible parameters /spl alpha/, /spl beta/, rank, and dimension of the kernel for extended 1-perfect additive codes. A very special case is that of extended 1-perfect /spl Zopf//sub 4/-linear codes. 相似文献
104.
Parameterisation of slant-Haar transforms 总被引:1,自引:0,他引:1
Agaian S. Tourshan K. Noonan J.P. 《Vision, Image and Signal Processing, IEE Proceedings -》2003,150(5):11
A parameterisation of the slant-Haar transform is presented, which includes an existing version of the slant-Haar transform. An efficient algorithm for the slant-Haar transform is developed and its computational complexity is estimated. The parametric slant-Haar transforms are compared to the Karhunen-Loeve transform. The parametric slant-Haar is shown to perform better than the commonly used slant-Haar and slant-Hadamard transforms for the first-order Markov model and also performs better than the discrete cosine transform for images approximated by the generalised image correlation model 相似文献
105.
Codecasa L. D'Amore D. Maffezzoni P. Batty W. 《Components and Packaging Technologies, IEEE Transactions on》2004,27(1):87-95
In this paper, the multipoint moment matching method for model order reduction of discretized linear thermal networks is extended to distributed linear thermal networks. As a result, from the analytical canonical forms of distributed linear thermal networks, reduced thermal networks are derived analytically. This direct construction of the reduced network, from the exact analytical solutions, avoids the inevitable inaccuracies inherent in conventional surface and volume meshing. It allows nearly exact reduced thermal network construction by domain decomposition for arbitrarily complicated structures. 相似文献
106.
107.
108.
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
109.
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
110.
A spacecraft in a plasma builds up charge on all the dielectric surfaces and interfaces. Once the net charge exceeds the dielectric breakdown of the material, a discharge occurs. One of the more susceptible pieces of equipment is the antenna/receiver system. The radiated E-field may be strong enough to create an ambiguous signal which may be misinterpreted by the system electronics and cause a system malfunction. A technique is developed to monitor the radiated E-field of materials discharging in an electron environment, using vacuum chambers for measuring the material discharges which are made of highly reflective materials. These chambers affect the radiated E-field due to multiple reflections from the walls. The technique developed defines a method for correcting the effects caused by the measurement facilities. The methodology is: monitor the radiated E-field with a broadband dipole antenna, and digitize the radiated signal as a function of time. Determine the frequency response of the radiated E-field using an FFT algorithm. Measure the transmission and reflection characteristics of the two-port network inside the measurement chamber, and determine the impedance network from the measured E-parameters across the frequency band of interest. Transform the measured E-field frequency response through the impedance network to obtain the frequency response of the actual radiated discharge current. Find the inverse FFT of this response to obtain the actual radiated discharge current response. This technique aids in the prediction of the E-field coupling into receive antennas on-board actual satellites 相似文献