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排序方式: 共有110条查询结果,搜索用时 31 毫秒
81.
Hamidreza Shabgard Christopher W. Robak Theodore L. Bergman Amir Faghri 《Solar Energy》2012,86(3):816-830
A thermal network model is developed to predict the performance of latent heat thermal energy storage (LHTES) systems including cascaded phase change materials (PCMs) and embedded heat pipes/thermosyphons. Because the design of LHTES systems involves a compromise between the amount of energy stored, the heat transfer rate, and the quality of the released thermal energy, an exergy analysis is also carried out to identify the preferred LHTES design. It is found that the LHTES with the lowest melting temperature PCM yields the highest exergy efficiency. However, a cascaded LHTES recovers the largest amount of exergy during a 24 h charging–discharging cycle. Quantitatively, the cascaded LHTES recovers about 10% more exergy during a 24 h charging–discharging cycle compared to the best non-cascaded LHTES considered in this work. 相似文献
82.
《International Journal of Heat and Mass Transfer》2006,49(17-18):2924-2930
This paper reports on an experimental study characterizing the laminar-turbulent transition for water flow in circular microtubes. Microtubes with diameters in the range 16.6–32.2 μm of varying length were employed over the Reynolds number range 300–3400. The volume flowrate was measured for an imposed pressure differential using a timed displacement technique. Additionally, the viscous heating-induced mean fluid temperature rise was measured. Two independent approaches were used to identify transition from laminar to turbulent flow. Both methods showed transition to occur in the Reynolds number range 2100–2500, consistent with macroscale tube flow behavior. 相似文献
83.
Liquefaction is the key section on floating platform. Some experts and designers selected mixed refrigerant process for floating platform, while some recommended expander cycle. However, few of them compared the two types of processes systemically before making a choice. In this paper, the liquefaction processes of propane pre-cooled mixed refrigerant cycle (C3/MRC), mixed refrigerant cycle (MRC) and nitrogen expander cycle (N2 expander) for the special offshore associated gases in South China Sea have been designed and studied. These processes have been analyzed and compared systematically considering the main factors including the performance parameters, economic performance, layout, sensitivity to motion, suitability to different gas resources, safety and operability, accounting for the features of the floating production, storage and offloading unit for liquefied natural gas (LNG-FPSO) in marine environment. The results indicated that N2 expander has higher energy consumption and poorer economic performance, while it has much more advantages than C3/MRC and MRC for offshore application because it is simpler and more compact and thus requiring less deck area, less sensitive to LNG-FPSO motion, has better suitability for other gas resources, has higher safety and is easier to operate. Therefore, N2 expander is the most suitable offshore liquefaction process. In addition, the exergy analysis is conducted for N2 expander and the results indicate that the compression equipments and after coolers, expanders and LNG heat exchangers are the main contribution to the total exergy losses. The measures to decrease the losses for these equipments are then discussed. 相似文献
84.
A chemical reactor for the steam-gasification of carbonaceous materials (e.g. coal, coke, biomass) using high-temperature solar process heat is modeled by means of a two-phase formulation that couples radiative, convective, and conductive heat transfer to the chemical kinetics for polydisperse suspensions of reacting particles. The governing mass and energy conservation equations are solved by applying advanced Monte–Carlo and finite-volume techniques with smoothing and underrelaxation. Validation is accomplished by comparing the numerically calculated temperatures, product compositions, and chemical conversions with the experimentally measured values obtained from testing a 5 kW solar reactor prototype in a high-flux solar furnace. A unique feature of the reactor concept is that the gas-particle flow is directly exposed to concentrated solar radiation, providing efficient radiative heat transfer to the reaction site for driving the high-temperature highly endothermic process. 相似文献
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88.
《International Journal of Heat and Mass Transfer》2007,50(3-4):687-701
Mass, heat and momentum transport processes are coupled with catalytic chemical reactions in a methane steam reforming duct. It is often found that endothermic and exothermic reactions in the ducts are strongly integrated by heat transfer from adjacent catalytic combustion ducts. In this paper, a three-dimensional calculation method is developed to simulate and analyze reforming reactions of methane, and the effects on various transport processes in a steam reforming duct. The reformer conditions such as mass balances associated with the reforming reactions and gas permeation to/from the porous catalyst reforming layer are applied in the analysis. The predicted results are presented and discussed for a composite duct consisting of a porous catalyst reaction layer, the fuel gas flow duct and solid layers. Parametric studies are conducted to reveal the importance of reformer designs and operating conditions. The results show that the variables, such as porous layer configuration, temperature and catalyst loading, have significant effects on the transport processes and reformer performance. 相似文献
89.
《Journal of Microcomputer Applications》1987,10(1):55-62
In this contribution, a microprocessor based sun finder and solar tracking system is discussed. The system was designed and implemented on an 8080-based microprocessor. The paper gives the general hardware and software along with the circuitry. The system is able to locate the sun even during periods of very poor visibility. ‘Hunting’, which is usual in such schemes, has been eliminated by means of appropriate design of the motor circuit. 相似文献
90.
The surface and nonlocal effects on the nonlinear flexural free vibrations of elastically supported non-uniform cross section nanobeams are studied simultaneously. The formulations are derived based on both Euler–Bernoulli beam theory (EBT) and Timoshenko beam theory (TBT) independently using Hamilton’s principle in conjunction with Eringen’s nonlocal elasticity theory. Green’s strain tensor together with von Kármán assumptions are employed to model the geometrical nonlinearity. The differential quadrature method (DQM) as an efficient and accurate numerical tool in conjunction with a direct iterative method is adopted to obtain the nonlinear vibration frequencies of nanobeams subjected to different boundary conditions. After demonstrating the fast rate of convergence of the method, it is shown that the results are in excellent agreement with the previous studies in the limit cases. The influences of surface free energy, nonlocal parameter, length of non-uniform nanobeams, variation of nanobeam width and elastic medium parameters on the nonlinear free vibrations are investigated. 相似文献