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71.
72.
MnO/C composite coatings were grown by the metalorganic chemical vapor deposition process on ceramic alumina in argon ambient. Characterization by various techniques confirms that these coatings are homogeneous composites comprising nanometer-sized MnO particles embedded in a matrix of nanometer-sized graphite. Components of the MnO/C composite coating crystalline disordered, but are electrically quite conductive. Resistance vs. temperature measurements show that coating resistance increases exponentially from a few hundred ohms at room temperature to a few megaohms at 30 K. Logarithmic plots of reduced activation energy vs. temperature show that the coating material undergoes a metal–insulator transition. The reduced activation energy exponent for the film under zero magnetic field was 2.1, which is unusually high, implying that conduction is suppressed at much faster rate than the Mott or the Efros–Shklovskii hopping mechanism. Magnetoconductance vs. magnetic field plots obtained at various temperatures show a high magnetoconductance (∼28.8%) at 100 K, which is unusually large for a disordered system, wherein magnetoresistance is attributed typically to weak localization. A plausible explanation for the unusual behavior observed in the carbonaceous disordered composite material is proposed. 相似文献
73.
Numerical investigations of combined free convection and surface radiation in enclosures for Rayleigh–Benard configuration of air are carried out using FLUENT 6.3, with a view to determine the onset of convection and to propose correlations for convection and radiation Nusselt numbers based on a detailed parametric study. The onset of Rayleigh–Benard convection is delayed with an increase in the emissivity of the sidewalls. The effect of surface radiation on the onset of convection however diminishes with aspect ratio (AR) and for AR = 8, the effect of surface radiation ceases. Post-onset, the effect of surface radiation on the convection heat transfer becomes insignificant beyond an aspect ratio of 5. 相似文献
74.
A multiphase model based on unsaturated flow in a hygroscopic porous medium, which accounts for the important physical phenomena that take place during thermal treatment of meat, is developed. Frozen meat is considered as a porous solid comprising of water, fat and protein with gas trapped in its pores. As it is heated, water and fat melt, and, are gradually released from the solid protein matrix to the pore space. With further rise in temperature, liquid water evaporates. Since four fluid components (liquid water phase, liquid fat phase, water vapor and air) are present in the pore space, a mass balance equation is written for each component. Local thermal equilibrium assumption leads to one energy balance equation for the whole system. The model is validated for double-sided contact heating of hamburger patties by comparing temperature and moisture profiles with experimental studies. Dominant modes of transport are identified. 相似文献
75.
Depolarization current characteristics of solution grown pure ethyl cellulose (EC) films of about 20μm thickness have been studied as a function of electrode materials at constant poling field (5 × 104 V/cm) and poling temperature 40°C. Thermally stimulated current (TSC) thermograms of EC consists of two well resolved peaks
(located at 60°C and 140°C) for Al-Al system, which are attributed to the deorientation of strongly attached ethoxy groups
of glycosidal units and diffusion of space charges either at electrodes or due to their thermal release at higher temperatures
from the defect levels. For dissimilar electrode combinations (Al-Ag/Cu/Au/Sn/Pb), an indication of peak of lower magnitude
at around (50–70°C) alongwith a higher temperature peak (140–155°C), have been observed. TSC parameters are found to change
with the choice of electrode material. The dependence of dark current at 40°C in metal-ethyl cellulose-metal systems on applied
voltage in the range (2·0–5·0) × 104V/cm has also been studied. The results of current-voltage measurement on EC have been interpreted to show that the Schottky-Richardson
mechanism is the controlling transport mechanism. Zero field current density extrapolated fromI-E
1/2 plots are found to vary with metal work function. 相似文献
76.
In this paper, we present a collision free MAC protocol for wireless networks with smart antennas that provides proportional
service differentiation to various classes of traffic based on their respective bandwidth demand. The proposed protocol works
for diverse physical parameters such as number of interfaces at each node, number of communication frequencies, and antenna
beamwidth. To the best of our knowledge, this is the first work that provides link layer differentiated services for wireless
networks with smart antennas and explores the influence of the physical parameters and network topology on the performance
of the MAC layer.
Ashish Deopura received his B.Tech degree in Electrical Engineering from the Indian Institute of Technology Delhi, India, in 2003, and he
received his M.S. degree in Computer Systems Engineering from the University of Massachusetts Amherst, in 2005. He currently
works as a Modeling Engineer for OPNET Technologies located in Bethesda, MD
Professor Aura Ganz is the director of the Multimedia Networking Laboratory at the University of Massachusetts at Amherst. She has authored more
than 170 journal and conference papers in the areas of multimedia wireless networks, ubiquitous computing, telemedicine, and
security. She is a co-author of the book: “Multimedia Wireless Networks”, Prentice Hall, 2003. Some of her recent assignments
include: general co-chair of the IEEE UWBNETS workshop, general co-chair of the IEEE BROADMED workshop, general co-chair of
the Massachusetts 3rd Annual R&D Conference, keynote speaker at the NSF sponsored workshop in Mobile Computing, and invited
speaker at Personal and Local Wireless Network Solutions conference, and Motorola’s Wireless Communications Futures Forum,
Wireless Local Area Networks Conference. She has a PhD, MSc and BSc in Computer Science from the Technion in Israel. More
details can be found at: dvd1.ecs.umass.edu/wireless. 相似文献
77.
Sarat K. Swain Gyanaranjan Prusty Ashish S. Ray Lingaraj Behera 《Journal of Experimental Nanoscience》2014,9(3):240-248
Poly(methyl methacrylate)/expanded graphite (PMMA/EG) composites were prepared by the incorporation of EG in various proportions (1%, 2%, 3%, 4% and 5%) with PMMA by in situ polymerisation technique. The polymer composites were characterised by ultraviolet–visible (UV–vis) and Fourier transform infra-red spectroscopies. The structural property of PMMA/EG nanocomposites was studied by X-ray diffraction. The scanning electron microscopy and transmission electron microscopy of synthesised composites were taken in order to study their morphological properties. The conductivity of composites was measured as function of EG concentration. It was found that conductivity of composites gradually increased with the increase in EG loading. Oxygen permeability of PMMA/EG nanocomposites was calculated and it was found that the property was reduced substantially with rise of EG proportion. The thermal stability of PMMA/EG nanocomposites was improved by dispersion of EG with PMMA matrix. 相似文献
78.
Bi1-xNdxFeO3 (BNFOx, x = 0-0.15) nano-crystallites were successfully synthesised by solution combustion technique. Neodymium substitution has changed the rhombohedral symmetry of BiFeO3 to the triclinic and reduced the impurity phase. The average particle size found to vary from 74 to 26 nm when Nd concentration was increased from x = 0 to 0.15. The change in the symmetry is also confirmed by Raman spectra of nanocrystallite samples. The value of remnant magnetization has improved due to the continuing collapse of the space-modulated spin structure of BNFOx. Long-range ferromagnetic ordering in BNFOx at room temperature was also confirmed from Mössbauer spectra. 相似文献
79.
Absorption of CW Yb-fiber laser light of 1.07 μm wavelength in water has been measured at different water temperatures and laser intensities. The absorption coefficient was estimated to be 0.135 cm(-1) at 25 °C water temperature, and this was found to decrease with temperature at a rate of 5.7 × 10(-4) cm(-1) °C(-1). The absorption coefficient increased significantly when the laser beam was focused in water, and the increase depended on the distance of the focal point from the water surface. This has been attributed to the absorption and scattering losses of laser radiation in a cavity formed in water by the focused beam at laser intensities in the megawatts per square centimeter and higher range. 相似文献
80.
Smoothness assumptions in traditional image expansion cause blurring of edges and other high-frequency content that can be perceptually disturbing. Previous edge-preserving approaches are either ad hoc, statistically untenable, or computationally unattractive. We propose a new edge-driven stochastic prior image model and obtain the maximum a posteriori (MAP) estimate under this model. The MAP estimate is computationally challenging since it involves the inversion of very large matrices. An efficient algorithm is presented for expansion by dyadic factors. The technique exploits diagonalization of convolutional operators under the Fourier transform, and the sparsity of our edge prior, to speed up processing. Visual and quantitative comparison of our technique with other popular methods demonstrates its potential and promise. 相似文献