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排序方式: 共有361条查询结果,搜索用时 15 毫秒
91.
This study introduced a novel energy saving cooling system, i.e. a combined cycle coupled with a traditional vapor compression cycle with a pumped liquid two-phase cooling cycle. The system has two operation modes, i.e. the compression cycle mode driven by compressor and the pump cycle mode driven by refrigerant pump. A multi-purpose test bench was constructed to experimentally evaluate the performance of the integrated cycle system under various operation conditions. The effects of cycle working condition and the shift temperature between the two operation modes on the overall cycle performance were investigated in detail. It is found that the novel cycle system has a higher EER compared to the traditional compressor system when the ambient temperature is relatively low. The further experimental results and comparative annual energy saving analysis also indicated that the proper shift temperature is about −5 °C from the system EER and cooling capacity point of view. 相似文献
92.
This paper presents a comparative analysis on leakage losses of a rolling piston type rotary compressor with refrigerants of R290, R22 and R410a. In particular, the difference of leakage losses characteristics between R290 compressor and that of other refrigerant compressors has been studied. Leakage losses through radial clearance, clearances between rolling piston faces and the cylinder head walls, clearances between the sliding vane faces and the cylinder head walls, as well as the clearances between the sides of the sliding vane and the side walls of the chutes inside the cylinder have been studied in the present methodology. Radial leakage caused by the wall velocity has been taken into account in the present study. Simulation results indicate that smaller radial clearance is required for R290 compressor to obtain relatively high efficiency comparing to that of R22 and R410a compressors under the same condition. 相似文献
93.
This paper presents a study of refrigerant desorption leading to foam formation in refrigerant-oil mixtures undergoing controlled depressurization. An experimental apparatus was designed and constructed to allow measurements of the depressurization rate, foam height and refrigerant gas mass flux resulting from expansion and desorption from a saturated liquid mixture. Quantitative data and high-speed video analyses were used to identify the main physical mechanisms in the foaming process, namely, bubble cavitation and growth, foam growth and foam decay. The experimental results for the maximum foam height, foam lifetime and liquid supersaturation during desorption were explored as a function of the overall initial refrigerant mass fraction and system temperature. A mathematical model based on integral mass balances was proposed and compared with the experimental data with deviations smaller than 20%. 相似文献
94.
95.
This paper presents experimental results on the shut-down and start-up characteristics of a residential split system R-410A air-conditioner with a capillary tube. During shut-down, the transient characteristics are evaluated by measuring the high and low side pressures and temperatures of the system. The dynamic behavior of the system after start-up is also investigated at the standard cooling capacity rating condition of which the dry and wet bulb temperatures for the indoor and outdoor are 27/19.5 and 35/24°C, respectively. All experiments are performed in a psychrometric calorimeter. The cooling capacity, power consumption, dehumidification capacity and cycle characteristics after start-up are analyzed. The test results show that the cooling capacity and the coefficient of performance (COP) after start-up can be expressed as the combination of two exponential functions of time, approaching the cooling capacity of steady-state. 相似文献
96.
This paper addresses the problem of absorption of refrigerant vapor in a stagnant layer of lubricant oil. The bulk motion of the solute is described in terms of apparent diffusion coefficients that encompass both molecular diffusion and possible macroscopic motion induced by liquid density instability and surface tension. In absorption of refrigerant mixtures, diffusion in the vapor and liquid phases are coupled with a thermodynamic model for interfacial equilibrium. Results are compared with experimental data available in the literature for absorption of several refrigerants in polyol ester oil (POE68). The adequacy of the formulation is assessed in the light of its basic assumptions and performance of the model. 相似文献
97.
Eduardo Navarro de Andrade Eric Skowron Victor W. Goldschmidt Eckhard A. Groll 《International Journal of Refrigeration》1999,22(6):499
The concentration of oil in refrigerants (while in liquid state) can be measured with an acoustic velocity sensor. The transit time for an acoustic signal can be related to the oil concentration and temperature of the liquid mixture. The performance of the sensor is dependent on the properties of the oil and refrigerant, and their miscibility. In general, a thorough calibration becomes necessary. It is shown in this paper that for concentrations less than 10%, an approximation can be made for the estimate of concentration hence eliminating the need for an elaborate calibration procedure. 相似文献
98.
基于Java3D的虚拟现实建模方法 总被引:13,自引:1,他引:13
当前的虚拟现实建模主要用OpenGL,VRML等语言,分别存在着难以掌握学习、不易 控制等缺点。给出了一种基于Java3D构建方法,即用Java3D描述虚拟物体的几何和物理 特征,充分利用Java语言的面向对象的特征和初学者易学易用的特点来构造虚拟现实场 景。 相似文献
99.
Chi-Chuan Wang Jiin-Yuh Jang Chien-Chang Lai Yu-Juei Chang 《International Journal of Refrigeration》1999,22(4):275
An experimental study was carried out to investigate the effect of circuitry on the performance of wavy finned condensers. A total of eight arrangements were made and tested. The arrangements included six 1-circuit and two 2-circuit arrangements. For the one-circuit arrangement, the test results indicate that counter-cross flow would give better performance than other arrangements. However, heat conduction along the fins may offset the benefits of the counter-cross arrangement. This study has proposed two modifications to the counter-cross flow arrangement. For the two-circuit arrangement, a unique characteristic of “pressure gain” was observed when one circuit is completely condensed and the other is still in two-phase region.
Résumé
On a effectué une étude expérimentale afin d'étudier l'effet de la disposition du circuit sur la performance des condenseurs à ailettes ondulées. Huit dispositions ont été fabriquées et étudiées: six de ces dispositions comportaient un circuit et les deux autres dispositions avaient deux circuits. Les résultats obtenus avec les dispositions à un circuit indiquent que le flux à contre-courant sembler avoir une performance accrue par rapport aux autres dispositions. Cependant, la conduction de chaleur le long des ailettes pourrait réduire l'avantage de la disposition à contre-courant. Les auteurs propose deux modifications de la disposition à contre-courant. Une augmentation de pression a été observée avec la disposition à un circuit lorsqu'une condensation totale était obtenue dans l'un des deux circuits pendant que l'autre circuit restait en régime diphasique. 相似文献100.
Five zero ODP (ozone depletion potential) hydro-fluorocarbon refrigerants (HFC-23, HFC-143a, HFC-227ea, HFC-236fa, HFC-245fa) were tested to define their maximum usable temperature and their thermal degradation threshold. Pyrolysis is detected (a) as a pressure change at constant temperature and volume; (b) as a departure of the vapour pressure curve of the heated fluid from that of the original substance. Visual inspection of the vessel walls and fluid chemical analysis complement the method. The minimum detectable degradation rate is believed to be less than 1% in 50 h. All the fluids exhibit a variable, but excellent thermal stability up to the following temperatures at which no decomposition was observable in 50–100 h: 425 °C for HFC-227ea, 400 °C for HFC-23 and HFC-236fa, 350 °C for HFC-143a and 300 °C for HFC-245fa. Clear degradation signs were observed at temperatures 25–50 °C higher. Most of the fluids heated up to their thermal stability threshold exhibited an induction period of 5–50 h in which no decomposition was detectable but after which an observable degradation started. For a given fluid such period decreases at increasing temperatures. The use of fluids in a cyclic process in which the working medium permanence at the top temperature is very brief could take advantage of this behaviour with a reduction in degradation rates or with an increase in the limiting temperature. The influence of the decomposition products on the functionality of a thermodynamic power cycle was investigated by means of an appropriate computer code. The working fluid was assumed to be a binary mixture with 1 to 3% concentration of a light decomposition product of the methane series. Chemical species such as CH4 and CF4 with a critical temperature much lower than that of the base fluid strongly affect the cycle configuration. On the contrary species with critical temperatures closer to that of the base fluid such as CH3F, CH2F2 or CHF3 influence only marginally the cycle performance. In general a small concentration of decomposition products in the working medium is likely to be acceptable without noticeable drawbacks.