全文获取类型
收费全文 | 595509篇 |
免费 | 7208篇 |
国内免费 | 1811篇 |
专业分类
电工技术 | 10827篇 |
综合类 | 3180篇 |
化学工业 | 86871篇 |
金属工艺 | 23059篇 |
机械仪表 | 18451篇 |
建筑科学 | 14956篇 |
矿业工程 | 2384篇 |
能源动力 | 14780篇 |
轻工业 | 50712篇 |
水利工程 | 5885篇 |
石油天然气 | 7371篇 |
武器工业 | 75篇 |
无线电 | 74840篇 |
一般工业技术 | 112690篇 |
冶金工业 | 98306篇 |
原子能技术 | 9871篇 |
自动化技术 | 70270篇 |
出版年
2021年 | 3954篇 |
2019年 | 3813篇 |
2018年 | 20115篇 |
2017年 | 18990篇 |
2016年 | 16161篇 |
2015年 | 5060篇 |
2014年 | 7904篇 |
2013年 | 23592篇 |
2012年 | 15497篇 |
2011年 | 26153篇 |
2010年 | 21311篇 |
2009年 | 20721篇 |
2008年 | 22894篇 |
2007年 | 23533篇 |
2006年 | 14882篇 |
2005年 | 14611篇 |
2004年 | 14144篇 |
2003年 | 13912篇 |
2002年 | 12863篇 |
2001年 | 12557篇 |
2000年 | 12134篇 |
1999年 | 12487篇 |
1998年 | 29181篇 |
1997年 | 21104篇 |
1996年 | 16686篇 |
1995年 | 12975篇 |
1994年 | 11651篇 |
1993年 | 11307篇 |
1992年 | 8757篇 |
1991年 | 8303篇 |
1990年 | 8092篇 |
1989年 | 7656篇 |
1988年 | 7442篇 |
1987年 | 6377篇 |
1986年 | 6372篇 |
1985年 | 7538篇 |
1984年 | 6918篇 |
1983年 | 6397篇 |
1982年 | 5840篇 |
1981年 | 6104篇 |
1980年 | 5637篇 |
1979年 | 5491篇 |
1978年 | 5216篇 |
1977年 | 6170篇 |
1976年 | 7827篇 |
1975年 | 4669篇 |
1974年 | 4495篇 |
1973年 | 4551篇 |
1972年 | 3688篇 |
1971年 | 3366篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
R. Murgan F. Razak D. R. Tilley T. Y. Tan J. Osman M. N. A. Halif 《Computational Materials Science》2004,30(3-4):468-473
We derive an expression for transmittivity (TSHG) of second harmonic generation (SHG) signals from a ferroelectric (FE) film. Intensities of up and down fields in the medium are investigated in relation to TSHG. The derivations are made based on undepletion of input fields and nonlinear wave equation derived from the Maxwell equations. We present two cases: film without mirrors and with partial mirrors. Expressions for the newly derived nonlinear susceptibility coefficients of SHG for real crystal symmetry [J. Opt. Soc. Am. B 19 (2002) 2007] are used to get more realistic results. Variations in TSHG with respect to film thickness are illustrated. 相似文献
42.
van Schoor G. van Wyk J.D. Shaw I.S. 《Industrial Electronics, IEEE Transactions on》2003,50(3):546-553
A hybrid power compensator (HPC) consisting of a static VAr compensator and a dynamic compensator needs to be optimally controlled during the compensation of nonlinear loads. The HPC must be controlled to meet minimum requirements in terms of power factor and harmonic distortion, while at the same time minimizing its total cost. An artificial neural network (ANN) is used to control the HPC amidst a very dynamic power system environment. The performance of a reference ANN is evaluated while controlling an HPC connected to a typical nonlinear industrial load. The training and performance of the ANN is then optimized in terms of training set size, training set packing and ANN topology and the performance compared to the reference ANN. This paper highlights the importance of optimising the mentioned ANN parameters to achieve optimum ANN training and modeling accuracy. The results obtained reveals that the application of an ANN in controlling an HPC is feasible given that the ANN parameters are chosen appropriately. 相似文献
43.
A VQ-based blind image restoration algorithm 总被引:5,自引:0,他引:5
Learning-based algorithms for image restoration and blind image restoration are proposed. Such algorithms deviate from the traditional approaches in this area, by utilizing priors that are learned from similar images. Original images and their degraded versions by the known degradation operator (restoration problem) are utilized for designing the VQ codebooks. The codevectors are designed using the blurred images. For each such vector, the high frequency information obtained from the original images is also available. During restoration, the high frequency information of a given degraded image is estimated from its low frequency information based on the codebooks. For the blind restoration problem, a number of codebooks are designed corresponding to various versions of the blurring function. Given a noisy and blurred image, one of the codebooks is chosen based on a similarity measure, therefore providing the identification of the blur. To make the restoration process computationally efficient, the principal component analysis (PCA) and VQ-nearest neighbor approaches are utilized. Simulation results are presented to demonstrate the effectiveness of the proposed algorithms. 相似文献
44.
45.
A nonstationary model of SO2 absorption from a gas phase to a countercurrent falling film of absorbing slurry was developed. Laminar, wavy and turbulent film structures were considered based on published information. Resistances to the mass transfer on the gas and the liquid sides of the interphase were considered, together with chemical reactions in the liquid phase. Relevant chemical equilibria in the liquid phase were modeled. Original experimental data on the neutralization reagent dissolution rate presented as a polydispersed two‐phase system of solids and on the rate of dissolved sulfite oxidation were used. The model was verified with experimental data from a laboratory‐scale falling‐film absorber using a single vertical tube under various geometrical and operating conditions, and a very good agreement was found with the experiment. Parametric sensitivity analysis showed the critical parts of the model. 相似文献
46.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献
47.
This paper extends an analysis developed for tubular permanent-magnet machines to account for the effect of fringing associated with the finite length of the ferromagnetic armature core. The magnetic field distribution, established by using an analytical technique formulated in the cylindrical coordinate system, provides an accurate means of evaluating the effect of the fringing flux on the thrust force and the back-electromotive force. Finite-element calculations confirm the analytically derived results. In Part II of the paper, the analysis is used to predict the cogging force that results from end effects and to facilitate minimization of the force. 相似文献
48.
49.
Anaerobic co-digestion of organic wastes from households, slaughterhouses and meat processing industries was optimised in a half technical scale plant. The plant was operated for 130 days using two different substrates under organic loading rates of 10 and 12 kgCOD.m(-3).d(-1). Since the substrates were rich in fat and protein components (TKN: 12 g.kg(-1) the treatment was challenging. The process was monitored on-line and in the laboratory. It was demonstrated that an intensive and stable co-digestion of partly hydrolysed organic waste and protein rich slaughterhouse waste can be achieved in the balance of inconsistent pH and buffering NH4-N. In the first experimental period the reduction of the substrate COD was almost complete in an overall stable process (COD reduction >82%). In the second period methane productivity increased, but certain intermediate products accumulated constantly. Process design options for a second digestion phase for advanced degradation were investigated. Potential causes for slow and reduced propionic and valeric acid degradation were assessed. Recommendations for full-scale process implementation can be made from the experimental results reported. The highly loaded and stable codigestion of these substrates may be a good technical and economic treatment alternative. 相似文献
50.
Lorenzetto G. Galtarossa A. Palmieri L. Santagiustina M. Someda C.G. Fiorone R. 《Lightwave Technology, Journal of》2003,21(2):424-431
First-order polarization-mode dispersion (PMD) compensation by means of a polarization controller and a differential delay line is not sufficient to guarantee error-free transmission for 40-Gb/s channels when higher order effects severely increase signal distortion. Higher order mitigation is possible by cascading more than one first-order block. However, only two-stage or three-stage devices remain simple enough to be actually controlled. The performance of such higher order PMD compensators is evaluated by means of numerical simulations. Two different feedback signals have been used, demonstrating that first-order and higher order PMD distortion of nonreturn-to-zero (NRZ) pulses at 40 Gb/s can be strongly mitigated for instantaneous values of the differential group delay (DGD) up to the bit slot, when the compensator is properly controlled. 相似文献