全文获取类型
收费全文 | 906831篇 |
免费 | 12629篇 |
国内免费 | 2081篇 |
专业分类
电工技术 | 16543篇 |
综合类 | 806篇 |
化学工业 | 138335篇 |
金属工艺 | 35283篇 |
机械仪表 | 27530篇 |
建筑科学 | 21565篇 |
矿业工程 | 5556篇 |
能源动力 | 23700篇 |
轻工业 | 75973篇 |
水利工程 | 10104篇 |
石油天然气 | 19113篇 |
武器工业 | 64篇 |
无线电 | 99521篇 |
一般工业技术 | 178849篇 |
冶金工业 | 171325篇 |
原子能技术 | 20007篇 |
自动化技术 | 77267篇 |
出版年
2021年 | 8316篇 |
2020年 | 6139篇 |
2019年 | 7867篇 |
2018年 | 13438篇 |
2017年 | 13475篇 |
2016年 | 14186篇 |
2015年 | 9372篇 |
2014年 | 15602篇 |
2013年 | 41495篇 |
2012年 | 24385篇 |
2011年 | 33422篇 |
2010年 | 26650篇 |
2009年 | 29744篇 |
2008年 | 30381篇 |
2007年 | 29986篇 |
2006年 | 26047篇 |
2005年 | 23764篇 |
2004年 | 22733篇 |
2003年 | 22390篇 |
2002年 | 21455篇 |
2001年 | 21139篇 |
2000年 | 19970篇 |
1999年 | 20560篇 |
1998年 | 51133篇 |
1997年 | 36432篇 |
1996年 | 28139篇 |
1995年 | 21283篇 |
1994年 | 18854篇 |
1993年 | 18474篇 |
1992年 | 13704篇 |
1991年 | 12985篇 |
1990年 | 12865篇 |
1989年 | 12453篇 |
1988年 | 11824篇 |
1987年 | 10627篇 |
1986年 | 10379篇 |
1985年 | 11682篇 |
1984年 | 10677篇 |
1983年 | 9908篇 |
1982年 | 9136篇 |
1981年 | 9274篇 |
1980年 | 8838篇 |
1979年 | 8781篇 |
1978年 | 8587篇 |
1977年 | 9908篇 |
1976年 | 12841篇 |
1975年 | 7582篇 |
1974年 | 7214篇 |
1973年 | 7369篇 |
1972年 | 6170篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
971.
A probabilistic image model is proposed. According to the model, the noise of the boundaries has the principal effect on the precision with which the dimensions of optical monitoring objects are measured. Results of theoretical and experimental investigations of measurement precision are presented. An approach to the determination of monitoring reliability and the selection of the resolution of a machine vision system based on structural requirements is formulated. 相似文献
972.
Finite element piezothermoelasticity analysis and the active control of FGM plates with integrated piezoelectric sensors and actuators 总被引:3,自引:0,他引:3
An efficient finite element model is presented for the static and dynamic piezothermoelastic analysis and control of FGM
plates under temperature gradient environments using integrated piezoelectric sensor/actuator layers. The properties of an FGM plate are functionally graded in the thickness
direction according to a volume fraction power law distribution. A constant displacement-cum-velocity feedback control algorithm that couples the direct and inverse piezoelectric effects is applied to provide active feedback
control of the integrated FGM plate in a closed loop system. Numerical results for the static and dynamic control are presented
for the FGM plate, which consists of zirconia and aluminum. The effects of the constituent volume fractions and the influence
of feedback control gain on the static and dynamic responses of the FGM plates are examined.
Received: 13 March 2002 / Accepted: 5 March 2003
The work described in this paper was supported by a grant awarded by the Research Grants Council of the Hong Kong Special
Administrative Region, China (Project No. CityU 1024/01E). 相似文献
973.
Seidel A.R. Bisogno F.E. Pinheiro H. do Prado R.N. 《Industrial Electronics, IEEE Transactions on》2003,50(6):1267-1274
This paper presents a simple alternative for an electronic ballast operating in self-sustained oscillating mode with dimming capability for fluorescent lamps. A simple modification in one of the gate drivers side circuit allows the lamp to dim without compromising the simplicity, reliability, and low cost which characterize the self-oscillating electronic ballast (SOEB). A qualitative analysis is presented to explain the behavior of the proposed self-oscillating electronic ballast with dimming feature. In addition, the stability and the key equations for the design are derived using the extended Nyquist criterion and describing function method. Experimental results from two 40-W electronic ballasts are presented to demonstrate the performance and to validate the analysis carried out. 相似文献
974.
Decreasing carboxyl retention in deposits from the glow region of an acrylic acid plasma was measured by X-ray photoelectron spectroscopy and chemical derivatisation as the collection distance from the monomer vapour inlet was increased. Volatilisation of plasma polymerised acrylic acid was detected after trifluoroethanol derivatisation; this is correlated with evaporation of low molecular weight components observed previously. 相似文献
975.
The intent of a binomial effect size display (BESD) is to show "the [real-world] importance of [an] effect indexed by a correlation [r]" (R. Rosenthal, 1994, p. 242) by reexpressing this correlation as a success rate difference (SRD) (e.g., treatment group success rate - control group success rate). However, SRDs displayed in BESDs generally overestimate real-world SRDs implied by correlations of (a) dichotomous X and Y variables (φ coefficients), (b) dichotomous X and continuous Y variables (point-biserial coefficients [rphs]). and (c) continuous X and Y variables (rxys). Furthermore, overestimation biases are larger for rxys than for rphs. Differences in the sizes of biases linked to different correlations suggest that BESD SRDs reported for different correlations are not comparable. The stochastic difference index (N. Cliff, 1993: A. Vargha & H. D. Delaney, 2000) is recommended as an alternative to the BESD. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
976.
Bajko M. Chamizo R. Savary F. Skoczen B. Veness R. Jeanneret J.B. 《Applied Superconductivity, IEEE Transactions on》2004,14(2):215-218
In order to provide the necessary mechanical aperture for the LHC beam, the main dipole cold masses have to match precisely the nominal circular trajectory of the particles beam. The requirements on the dipole cold mass geometry are dictated by the LHC beam optics and by the allowed limits of mechanical deformation of the interconnection bellows. Keeping the tight tolerances that are imposed necessitates a well controlled bending process and the use of a high accuracy 3D measuring instrument for checking the geometry of the cold mass throughout many manufacturing stages up to the final inspection. The dipole cold mass pre-series production started in 2000. It is almost completed at the three sites. In this paper, we report on the problems encountered to shape correctly the cold masses, their effect on interconnection of the dipole cold masses and on the mechanical aperture. On one side measures to improve the production process in terms of accuracy and reproducibility were taken, on the other side the assembly tolerances could be relaxed following a thorough review of the machine requirements. The summary of the encountered problems, corrective actions and results obtained on the pre-series cold masses are presented and discussed. 相似文献
977.
This article describes the different methods to design regular low density parity-check (LDPC) codes with large girth. In graph terms, this corresponds to designing bipartite undirected regular graphs with large girth. Large girth speeds the convergence of iterative decoding and improves the performance at least in the high SNR range, by slowing down the onsetting of the error floor. We reviewed several existing constructions from exhaustive search to highly structured designs based on Euclidean and projective finite geometries and combinatorial designs. We describe GB and TS LDPC codes and compared the BER performance with large girth to the BER performance of random codes. These studies confirm that in the high SNR regime these codes with high girth exhibit better BER performance. The regularity of the codes provides additional advantages that we did not explore in this article like the simplicity of their hardware implementation and fast encoding. 相似文献
978.
Staker S.W. Holloway C.L. Bhobe A.U. Piket-May M. 《Electromagnetic Compatibility, IEEE Transactions on》2003,45(2):156-166
The alternating-direction implicit finite-difference time-domain (ADI-FDTD) technique is an unconditionally stable time-domain numerical scheme, allowing the /spl Delta/t time step to be increased beyond the Courant-Friedrichs-Lewy limit. Execution time of a simulation is inversely proportional to /spl Delta/t, and as such, increasing /spl Delta/t results in a decrease of execution time. The ADI-FDTD technique greatly increases the utility of the FDTD technique for electromagnetic compatibility problems. Once the basics of the ADI-FDTD technique are presented and the differences of the relative accuracy of ADI-FDTD and standard FDTD are discussed, the problems that benefit greatly from ADI-FDTD are described. A discussion is given on the true time savings of applying the ADI-FDTD technique. The feasibility of using higher order spatial and temporal techniques with ADI-FDTD is presented. The incorporation of frequency dependent material properties (material dispersion) into ADI-FDTD is also presented. The material dispersion scheme is implemented into a one-dimensional and three-dimensional problem space. The scheme is shown to be both accurate and unconditionally stable. 相似文献
979.
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
980.