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111.
A New Neutral-Point-Clamped PWM Inverter 总被引:7,自引:0,他引:7
Nabae Akira Takahashi Isao Akagi Hirofumi 《Industry Applications, IEEE Transactions on》1981,(5):518-523
A new neutral-point-clamped pulsewidth modulation (PWM) inverter composed of main switching devices which operate as switches for PWM and auxiliary switching devices to clamp the output terminal potential to the neutral point potential has been developed. This inverter output contains less harmonic content as compared with that of a conventional type. Two inverters are compared analytically and experimentally. In addition, a new PWM technique suitable for an ac drive system is applied to this inverter. The neutral-point-clamped PWM inverter adopting the new PWM technique shows an excellent drive system efficiency, including motor efficiency, and is appropriate for a wide-range variable-speed drive system. 相似文献
112.
113.
This paper describes an approximate microstructural optimization using the ns-kriging (noise-resistant smoothed kriging) method
for minimizing the maximum stochastic variation of homogenized elastic properties of a composite material caused by microscopic
uncertainties of component materials. Since evaluation of a stochastic characteristic of a homogenized material property such
as expectation or variance will involve a high computational cost and its results include inaccuracy in using the Monte Carlo
simulation, an approximation-based optimization technique is useful for solving the optimization problem considering the multiscale
stochastic problem. Especially, the ns-kriging will work well in case of using inaccurate data for an unknown objective function.
In order to investigate applicability and effectiveness of the proposed ns-kriging based approach to the optimization problem,
it is applied to the cross-sectional shape optimization of fiber in a unidirectional FRP. From the numerical results, validity
and effectiveness of the proposed approach are confirmed. 相似文献
114.
Friction and frictional tracks on 2 µm thick SiO2 films evaporated on polymethylmethacrylate (PMMA) substrate were investigated. Diamond spherical sliders of radius 30 and 100 µm, respectively, were slid on these coatings under a load of 50 to 200g at a sliding speed of 15 cm min–1. The static and dynamic friction coefficients for SiO2 films were found to be 0.1 and 0.06, respectively, depending on the load and radius of the slider. For lower load and small slider radius the tracks on SiO2 film were groove-like, and whisker-like cracks regularly grew from the edges of the tracks. For higher loads and larger slider radius, semicircular cracks in the film were regularly found behind the slider, but in thicker film (6 µm thick), circular cracks occurred. The origin of these cracks is discussed in terms of a tension zone produced around the contact area between the slider and the substrate under frictional force. 相似文献
115.
Natsuko Sakai Tatsuo Tsunoda Natsuo Fukumoto Isao Kojima Katsuhiko Yamaji Teruhisa Horita Masahiko Ishikawa Harumi yokokawa masayuki Dokiya 《Journal of Electroceramics》1999,4(1):121-128
The morphological characteristics, chromium valence state, and cation transport in the vicinity of grain boundary in La1-xCaxCrO3 were investigated by using TEM/EDS, XPS and SIMS techniques. The width of grain boundary was around 1 nm where anomalous enrichment of calcium was observed. Higher valence state of chromium such as Cr6+(d0) was detected in the grain boundaries whereas Cr3+(d3) and Cr4+(d2) were dominant in the bulk. Very fast interdiffusion of alkaline earths was observed in the Sr2+-La0.75Ca0.25CrO3 system. All observed phenomena were correlated by assuming the A-site vacancy which may be induced by the formation of Cr6+ at grain boundaries. 相似文献
116.
117.
The reductive removal of nitric oxide from flue gases by reaction with polyacrylonitrile-based active carbon fibres (PAN-ACF) activated with sulphuric acid has been studied at 423–632 K, using a circulating flow reactor. Nitric oxide (0.67 mmol) was completely removed via reduction with 1 g activated carbon under optimum conditions in 210 and 60 min at 423 and 623 K, respectively. N2 was formed as NO was removed. Some oxygen remained on the carbon surface at 423 K, but was desorbed as CO or CO2 on subsequent heating to 623 K. The bimolecular reaction of NO reduction over PAN-ACF, and the possible active sites of oxygen surface groups are discussed in the light of a kinetic study and a comparison of the fibre activation at different temperatures. 相似文献
118.
Minoru Kumakura Isao Kaetsu Kazuhiro Asami Shuichi Suzuki 《Journal of Materials Science》1989,24(5):1809-1813
Porous polymer composite columns having porous structure were prepared by radiation cast-polymerization of hydrophilic monomers at low temperature and their characteristics were studied. The porosity of the polymer increased with decreasing monomer concentration. The elution time of water in the polymer column increased with increasing monomer concentration and with decreasing irradiation temperature. The elution time was dependent on the degree of hydration of the polymer. The polymer with a degree of hydration of 0.2 to 0.4 gave the minimum elution time. The elution time decreased with the addition of porous inorganic substances. 相似文献
119.
Interfacial area concentration is one of the most important parameters in two-phase flow. It is related to mass, momentum and energy transfer at the interface. In bubbly flow, it has close relation to bubble diameter. Interfacial area concentration was measured with particular attention to bubble diameter at inlet. The relationship between bubble diameter and interfacial area was theoretically considered. The possibilities of measurement methods of interfacial area concentration with multiprobes were discussed and a preliminary experiment for one of these methods was carried out. 相似文献
120.
Katsuyuki Matsunaga Fumiyasu Oba Isao Tanaka Hirohiko Adachi 《Journal of Electroceramics》1999,4(1):69-80
Discrete variational (DV) Xα cluster method has been employed in calculating electronic structures of ZnO. Electronic structures of the bulk and the non-polar surface model clusters are calculated with inclusion of electrostatic potentials in the bulk and near the surface, and the electronic origins of experimental spectra and chemical bonds at the surface are examined in detail. The valence band structure constructed by Zn-3d and O-2p bands is much influenced by electrostatic potentials in ZnO. It is found that the reduction of an electrostatic potential near the surface gives rise to the difference of the valence band structures between in the bulk and at the surface. The calculated density of states at the non-polar surface of ZnO, where the Zn-3d and O-2p bands are more widely separated than in the bulk, is in good agreement with the experimental UPS. In addition, a Zn-O bond at the surface is found to show stronger covalency than that in the bulk, as a result of the change of the valence band structure due to the effect of the electrostatic potential. 相似文献