全文获取类型
收费全文 | 531476篇 |
免费 | 6340篇 |
国内免费 | 1738篇 |
专业分类
电工技术 | 9504篇 |
综合类 | 2964篇 |
化学工业 | 79514篇 |
金属工艺 | 21344篇 |
机械仪表 | 15793篇 |
建筑科学 | 13657篇 |
矿业工程 | 2214篇 |
能源动力 | 13440篇 |
轻工业 | 46682篇 |
水利工程 | 5174篇 |
石油天然气 | 6590篇 |
武器工业 | 10篇 |
无线电 | 63896篇 |
一般工业技术 | 100016篇 |
冶金工业 | 86890篇 |
原子能技术 | 9158篇 |
自动化技术 | 62708篇 |
出版年
2021年 | 3314篇 |
2019年 | 3134篇 |
2018年 | 19031篇 |
2017年 | 17845篇 |
2016年 | 14848篇 |
2015年 | 4416篇 |
2014年 | 6803篇 |
2013年 | 20832篇 |
2012年 | 13951篇 |
2011年 | 24129篇 |
2010年 | 19838篇 |
2009年 | 19184篇 |
2008年 | 20716篇 |
2007年 | 21525篇 |
2006年 | 12672篇 |
2005年 | 12735篇 |
2004年 | 12356篇 |
2003年 | 11892篇 |
2002年 | 11133篇 |
2001年 | 10838篇 |
2000年 | 10436篇 |
1999年 | 10790篇 |
1998年 | 26107篇 |
1997年 | 18796篇 |
1996年 | 14726篇 |
1995年 | 11317篇 |
1994年 | 10112篇 |
1993年 | 9784篇 |
1992年 | 7329篇 |
1991年 | 7090篇 |
1990年 | 6872篇 |
1989年 | 6746篇 |
1988年 | 6584篇 |
1987年 | 5625篇 |
1986年 | 5675篇 |
1985年 | 6661篇 |
1984年 | 6064篇 |
1983年 | 5602篇 |
1982年 | 5115篇 |
1981年 | 5330篇 |
1980年 | 4917篇 |
1979年 | 4895篇 |
1978年 | 4672篇 |
1977年 | 5556篇 |
1976年 | 7100篇 |
1975年 | 4031篇 |
1974年 | 3932篇 |
1973年 | 3998篇 |
1972年 | 3327篇 |
1971年 | 3014篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
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
63.
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
64.
Hambleton P.J. Ng B.K. Plimmer S.A. David J.P.R. Rees G.J. 《Electron Devices, IEEE Transactions on》2003,50(2):347-351
The nonlocal enhancement in the velocities of charge carriers to ionization is shown to outweigh the opposing effects of dead space, increasing the avalanche speed of short avalanche photodiodes (APDs) over the predictions of a conventional local model which ignores both of these effects. The trends in the measured gain-bandwidth product of two short InAlAs APDs reported in the literature support this result. Relatively large speed benefits are predicted to result from further small reductions in the lengths of short multiplication regions. 相似文献
65.
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
66.
Starting from a microscopic Hamiltonian defined on a semi-infinite cubic lattice, and employing a mean-field approximation, the surface parameters relevant for wetting in confined ternary mixtures are derived. These are found in terms of the microscopic coupling constants, and yield a physical interpretation of their origins. In comparison with the standard expression for the surface free-energy density, several new terms arising from the derivation are identified. The influence of the surface parameters on a predicted unbinding transition in a mixture of oil, water, and amphiphile demonstrate that existing results are robust to the addition of the extra surface terms. 相似文献
67.
68.
du Burck F. Lopez O. El Basri A. 《IEEE transactions on instrumentation and measurement》2003,52(2):288-291
We have developed a narrow-band controller in the MHz range, based on a field-programmable gate array. It is used to control the probe beam intensity in frequency-modulated spectroscopy experiments with an acoustooptic modulator. The residual amplitude modulation at the modulation frequency (2.5 MHz) is reduced by 50 dB. The first-harmonic detection of the signals is operated in saturation spectroscopy of I/sub 2/ at 514.5 nm and 501.7 nm. A reduction of the background noise and a large increase in the signal-to-noise ratio are obtained. 相似文献
69.
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
70.
Dispersion-relation-preserving FDTD algorithms for large-scale three-dimensional problems 总被引:1,自引:0,他引:1
We introduce dispersion-relation-preserving (DRP) algorithms to minimize the numerical dispersion error in large-scale three-dimensional (3D) finite-difference time-domain (FDTD) simulations. The dispersion error is first expanded in spherical harmonics in terms of the propagation angle and the leading order terms of the series are made equal to zero. Frequency-dependent FDTD coefficients are then obtained and subsequently expanded in a polynomial (Taylor) series in the frequency variable. An inverse Fourier transformation is used to allow for the incorporation of the new coefficients into the FDTD updates. Butterworth or Chebyshev filters are subsequently employed to fine-tune the FDTD coefficients for a given narrowband or broadband range of frequencies of interest. Numerical results are used to compare the proposed 3D DRP-FDTD schemes against traditional high-order FDTD schemes. 相似文献