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排序方式: 共有183条查询结果,搜索用时 15 毫秒
1.
Ehsani M. Bilgic M.O. Khan S. Laskai L. Seung Gi Jeong 《Power Electronics, IEEE Transactions on》1995,10(4):511-518
The bang-bang controlled capacitor coupled converter (C3) is described in this paper. Due to the converter's inherent commutating property, the C3 can accommodate thyristors as well as high-power gate turn-off switches, due to zero-current switching transitions. The zero-current switching is achieved at no current stress increase, therefore, the topology is considered appropriate for high-power processing. DC and small signal AC models are derived for the bang-bang controlled C3, a design procedure is proposed, and simulation results are discussed. Finally, oscillograms from a proof of principle prototype circuit are presented 相似文献
2.
Commutation of SR motors 总被引:3,自引:0,他引:3
Commutation schemes for most common types of switched reluctance (SR) motors are presented. Commutation can be achieved using two- or three-positions sensors and a simple commutation logic in a similar fashion to brushless electronically commutated motors. The commutation logic can be easily housed on a programmable logic array (PLA) or similar device. Two-quadrant operation, usually with two position sensors with variable phase shift and dwell angles, can be tuned up to achieve optimum efficiency at low cost. Four-quadrant operation with multimode commutation schemes, such as normal, boost, longdwell, and brake, which cover most of the SR drive applications, can be easily implemented with simple logic control and feedback from low-resolution position sensors. The speed range can be increased beyond the limit reachable with pulse-width modulation (PWM). A 100% increase in the speed range can be easily obtained by switching modes 相似文献
3.
Metallurgical and Materials Transactions A - In this research, it was found that the C/SiC transition interface thickness increases without a significant decrease in toughness by modifying the... 相似文献
4.
Mohammad Reza Ehsani Hamed Bateni Ghazal Razi Parchikolaei 《Korean Journal of Chemical Engineering》2012,29(7):855-861
The effect of some operating conditions such as temperature, gas hourly space velocity (GHSV), CH4/O2 ratio and diluents gas (mol% N2) on ethylene production by oxidative coupling of methane (OCM) in a fixed bed reactor at atmospheric pressure was studied over Mn/Na2WO4/SiO2 catalyst. Based on the properties of neural networks, an artificial neural network was used for model developing from experimental data. To prevent network complexity and effective data input to the network, principal component analysis method was used and the number of output parameters was reduced from 4 to 2. A feed-forward back-propagation network was used for simulating the relations between process operating conditions and those aspects of catalytic performance including conversion of methane, C2 products selectivity, C2 yielding and C2H4/C2H6 ratio. Levenberg-Marquardt method is presented to train the network. For the first output, an optimum network with 4-9-1 topology and for the second output, an optimum network with 4-6-1 topology was prepared. After simulating the process as well as using ANNs, the operating conditions were optimized and a genetic algorithm based on maximum yield of C2 was used. The average error in comparing the experimental and simulated values for methane conversion, C2 products selectivity, yield of C2 and C2H4/C2H6 ratio, was estimated as 2.73%, 10.66%, 5.48% and 10.28%, respectively. 相似文献
5.
Composites of multi-walled carbon nanotubes (MWCNTs) and poly ortho aminophenol (POAP) with good uniformity for use as electrodes in electrochemical capacitors were prepared by electropolymerization by using the ionic surfactant as electrolyte, for dispersing CNTs within conducting polymer/carbon nanotube composite films. The capacitance properties were investigated with cyclic voltammetry (CV), discharge tests and ac impedance spectroscopy. The composite electrode shows much higher specific capacitance, better power characteristics and is more promising for application in the capacitor than a pure POAP electrode. The effect and role of MWCNT in the composite electrode are discussed in detail. In comparison with a Ni–POAP/glassy carbon (GC), a Ni–MWCNT–POAP/GC electrode shows a better catalytic performance for the electrocatalytic oxidation of methanol. 相似文献
6.
7.
A. Nadjafi Maryam Negari R. S. Mamoory A. Simchi N. Ehsani 《Powder Metallurgy and Metal Ceramics》2007,46(9-10):423-428
Microwave energy is highly efficient for heating and processing different materials. In recent years, this type of heat transfer has been used in sintering process. Rapid and highly efficient heating, time and energy saving, and improved properties of sintered materials are advantages of microwave sintering. In this paper, Fe and Fe-Cu powder compact samples (cylindrical and bone shapes) are sintered both in microwave and electrical tube furnaces. The microwave generator has 2.45 GHz frequency and 1 KW power. Times are selected in the range of 5–25 min for microwave sintering and 5–40 min for electrical heating. The sintering temperature is set at 1120°C. Samples are sintered in the reducing atmosphere of 95% N2 + 5% H2 mixture. The density, hardness, and tensile strength of the samples are measured. The results are compared. The results show that the microwave-sintered materials have a finer microstructure. The microwave-sintered materials have 6–8% higher density, 5–10 HV5 higher hardness, and about 10% higher tensile strength than conventionally sintered materials. 相似文献
8.
Equilibrium data for carbon dioxide and methane adsorption on nanoporous metal organic framework Cu‐BTC powder and tablets were measured in a magnetic suspension balance in the temperature range of 308–373 K and a pressure range of 0–7 bar and fitted with Langmuir model. The tablets adsorption loading is 0.63 mol kg–1 for methane and 3.1 mol kg–1 for carbon dioxide at 1 bar and 308 K, while these values are 0.77 and 3.9 mol kg–1 for powder in the same conditions. Isosteric heats of adsorption were 22.8 and 15.0 kJ mol–1 for carbon dioxide and methane, respectively, on both adsorbents, which indicates a strong adsorption of carbon dioxide. Also, single and binary breakthrough curves were measured in the same temperature range and atmospheric pressure by using Cu‐BTC tablets as adsorbent. A complete model was used in the simulation of breakthrough curves and good agreement was observed with experimental data. 相似文献
9.
10.
Bass J. T. Ehsani M. Miller Timothy J. E. 《Industrial Electronics, IEEE Transactions on》1986,(3):212-216
This paper describes a technique for stabilizing the operation of variable-reluctance stepping-motor drives operating without a shaft-position sensor. In such systems there is a trade-off between the system efficiency and the torque margin (or pull-out torque) which depends on the width of the phase conduction pulse width. The scheme described in the paper permits the motor to run in the steady state with both narrow conduction pulse widths and high efficiency. Under transient or overload conditions the conduction pulse width is increased in response to a change in the dc link current, providing an increase in available torque. Tests on a small motor drive have produced a steady-state torque margin of over 300 percent and of 200 percent under step-change conditions. 相似文献