全文获取类型
收费全文 | 281045篇 |
免费 | 3163篇 |
国内免费 | 1316篇 |
专业分类
电工技术 | 4822篇 |
综合类 | 521篇 |
化学工业 | 40828篇 |
金属工艺 | 11190篇 |
机械仪表 | 8486篇 |
建筑科学 | 6533篇 |
矿业工程 | 1587篇 |
能源动力 | 7083篇 |
轻工业 | 22704篇 |
水利工程 | 3065篇 |
石油天然气 | 5787篇 |
武器工业 | 43篇 |
无线电 | 33676篇 |
一般工业技术 | 57034篇 |
冶金工业 | 51461篇 |
原子能技术 | 7512篇 |
自动化技术 | 23192篇 |
出版年
2021年 | 2252篇 |
2019年 | 2159篇 |
2018年 | 3668篇 |
2017年 | 3753篇 |
2016年 | 3982篇 |
2015年 | 2550篇 |
2014年 | 4440篇 |
2013年 | 12122篇 |
2012年 | 7190篇 |
2011年 | 9889篇 |
2010年 | 7660篇 |
2009年 | 8875篇 |
2008年 | 9257篇 |
2007年 | 9261篇 |
2006年 | 7899篇 |
2005年 | 7337篇 |
2004年 | 7258篇 |
2003年 | 7034篇 |
2002年 | 6750篇 |
2001年 | 6889篇 |
2000年 | 6521篇 |
1999年 | 6808篇 |
1998年 | 16343篇 |
1997年 | 11614篇 |
1996年 | 8960篇 |
1995年 | 6882篇 |
1994年 | 6035篇 |
1993年 | 6068篇 |
1992年 | 4418篇 |
1991年 | 4193篇 |
1990年 | 4099篇 |
1989年 | 4078篇 |
1988年 | 3765篇 |
1987年 | 3408篇 |
1986年 | 3415篇 |
1985年 | 3764篇 |
1984年 | 3473篇 |
1983年 | 3234篇 |
1982年 | 3044篇 |
1981年 | 3059篇 |
1980年 | 3055篇 |
1979年 | 2846篇 |
1978年 | 2893篇 |
1977年 | 3159篇 |
1976年 | 4115篇 |
1975年 | 2432篇 |
1974年 | 2392篇 |
1973年 | 2412篇 |
1972年 | 2025篇 |
1971年 | 1784篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Hook T.B. Brown J. Cottrell P. Adler E. Hoyniak D. Johnson J. Mann R. 《Electron Devices, IEEE Transactions on》2003,50(9):1946-1951
Lateral scattering of retrograde well implants is shown to have an effect on the threshold voltage of nearby devices. The threshold voltage of both NMOSFETs and PMOSFETs increases in magnitude for conventional retrograde wells, but for triple-well isolated NMOSFETs the threshold voltage decreases for narrow devices near the edge of the well. Electrical data, SIMS, and SUPREM4 simulations are shown that elucidate the phenomenon. 相似文献
12.
A common computing-core representation of the discrete cosine transform and discrete sine transform is derived and a reduced-complexity algorithm is developed for computation of the proposed computing-core. A parallel architecture based on the principle of distributed arithmetic is designed further for the computation of these transforms using the common-core algorithm. The proposed scheme not only leads to a systolic-like regular and modular hardware for computing these transforms, but also offers significant improvement in area-time efficiency over the existing structures. The structure proposed here is devoid of complicated input/output mapping and does not involve any complex control. Unlike the convolution-based structures, it does not restrict the transform length to be a prime or multiple of prime and can be utilized as a reusable core for cost-effective, memory-efficient, high-throughput implementation of either of these transforms 相似文献
13.
N. P. Yeliseyeva 《Journal of Communications Technology and Electronics》2006,51(4):380-384
Rigorous analytic expressions for radiation resistance R Σ of an electric dipole are obtained for three mutually orthogonal orientations of the dipole’s axis with respect to a plane metal screen or right-angle corner of infinite dimensions. Radiation resistance R Σ of the dipole oriented arbitrarily in space is calculated and analyzed as a function of the distance from the screen. 相似文献
14.
A multi-level attention framework for tracking and segmentation of humans and objects under complex occlusions is investigated,
featuring an effective probabilistic appearance-based technique for pixel reclassification during object grouping and splitting.
A novel ’spatial-depth affinity metric’ is introduced in the conventional likelihood function, utilising information of both
spatial locations of pixels and dynamic depth ordering of the component objects in grouping. Depth ordering estimation is
achieved through a combination of top-down and bottom-up approach. Experiments on some realworld difficult scenarios of low
quality and highly compressed videos demonstrate the very promising results achieved. 相似文献
15.
V. N. Tsygankov V. V. Safonov A. I. Kozlov V. P. Gavrilov 《Inorganic Materials》2003,39(10):1076-1078
The GeO2–NiO system is studied in the stability range of Ni2GeO4 by temperature-dependent resistivity measurements, in combination with x-ray diffraction, differential thermal analysis, and thermogravimetry. The resistivity of the starting mixtures and heat-treated samples is measured in the composition range 55–90 mol % NiO. The effect of air humidity on the resistivity of the samples is examined. 相似文献
16.
A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid
meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising
the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model
is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated
by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation.
The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest.
Sponsored by The Research Council of Norway, project number 125676/410
Dedicated to the memory of Prof. Mike Crisfield, a respected colleague 相似文献
17.
Two types of photo heterojunction bipolar transistor (HBT) to directly down-convert optical signals to electronic signals have been reported in the literature: a conventional photo-HBT in which light penetrates through the area of the base-collector junction and an HBT where light shines through the base-collector edge for higher conversion efficiency. Although the performance in relation to bias conditions has been published, the detailed analyses for identifying the parameters and bias conditions that provide optimum direct down-conversion have not been examined. This paper provides a full explanation of the operation of the down-conversion for both HBT configurations based on low-frequency analyses. Such information is useful for both understanding the nonlinear mechanisms involved and designing for maximum efficiency. In addition, a new circuit has been developed from the basic HBT down-conversion circuit that provides improved performance. 相似文献
18.
Thomy V. Dubois L. Vanoverschelde C. Sozanski J.P. Pribetich J. 《IEEE sensors journal》2004,4(6):772-778
This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented. 相似文献
19.
20.
Rankin D.M. Gulliver T.A. Taylor D.P. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(9):2230-2235
This article investigates the asymptotic performance of single parity-check (SPC) product codes (PCs) from a decoding point of view. Specifically, the probability of bit error is bounded before and after the decoding of each dimension, similar to the analysis of "iterated codes" by Elias (1954). It is shown that the asymptotic probability of bit error can be driven to zero as the number of dimensions, and hence the block length, increases at signal-to-noise ratios (SNRs) within 2 dB of capacity over the additive white Gaussian noise (AWGN) channel. 相似文献