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91.
Jaona Randrianalisoa Dominique Baillis 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(10):1372-1388
This contribution presents a new Ray-tracing method for calculating effective radiative properties of densely packed spheres in non-absorbing or semitransparent host medium. The method is restricted to the geometric optic objects and neglects the wave effects. The effective radiative properties such as the absorption and scattering coefficients, and phase function are retrieved from the calculation of mean-free paths of scattering and absorption, and the angular scattering probability of radiation propagating in the dispersed medium. The model accounts for the two geometric effects called here as non-point scattering and ray transportation effects. The successful comparison of the current model with data of radiative properties and transmittances of particle beds in a non-absorbing medium reported in the literature confirm its suitability. It is shown that: (i) for opaque or absorbing particles (not systematically opaque), the non-point scattering is the dominant geometric effects whereas both non-point scattering and ray transportation effects occur for weakly absorbing and transparent particles. In the later cases, these two geometric effects oppose and may cancel out. This may explain why the Independent scattering theory works well for packed of quasi-transparent particles; (ii) the non-point scattering and ray transportation effects can be captured through the scattering and absorption coefficients while using the classical form of phase function. This enables using the standard radiative transfer equation (RTE); (iii) the surrounding medium absorption can be accounted for without any homogenization rule. It contributes to increasing the effective absorption coefficient of the composite medium as expected but, at the same time, it reduces the particle extinction; and (iv) the current transfer calculation predicts remarkably the results of direct Monte Carlo (MC) simulation. This study tends therefore to confirm that the RTE can be applied to densely packed media by using effective radiative properties. 相似文献
92.
93.
It is proposed that the inflow to and outflow from a permeable bed be related by an integral. For vanishing fluid velocities, it is linear and its kernel is a material property characterizing the bed. Some of the properties of the kernel are considered here. The approach is particularly useful for tilted, fractured and other inhomogeneous beds, since no continuum characteristics need be assumed. The effects of nonlinearity are also discussed. 相似文献
94.
95.
A linear stability analysis for a sedimenting bidisperse gas-solid suspension (or gas fluidized bed) is performed. Mass, momentum and energy conservation equations for each of the two species are derived using constitutive equations that are valid at high Stokes numbers, (St1 1). The homogeneous suspension becomes unstable at sufficiently large St1 to waves of particle volume fraction with the wave number in the vertical direction. Numerical calculations of the growth rate in an unbounded suspension indicate that the marginal stability limits are controlled by the small wave number (k 1) behavior. Depending on the Stokes number and the volume fractions 1 and 2 of the two species, the suspension becomes unstable due to O(k) or O(k2) contributions to the growth rate. The O(k) term corresponds to an instability due to kinematic waves similar to that predicted for bidisperse suspensions of particles in viscous liquids [22]. The O(k2) contribution represents an instability to dynamic waves similar to that obtained from an analysis of averaged equations for monodisperse fluidized beds [4]. 相似文献
96.
纸类废弃物流化床热解气化研究 总被引:8,自引:0,他引:8
为开发低污染城市生活垃圾气化熔融处理技术,对城市生活垃圾中广泛存在的废纸组分进行了流化床热解与气化试验.在400~700℃、过量空气系数0~0.8的范围内,分析反应产物特性及其变化规律.结果表明,随热解温度的提高,热解油与热解气产量增大,热解炭产量减小,热解温度达到600℃及以上时,热解气产量达到60%左右;气化温度700℃、过量空气系数0.6时,气化效率最高,达到32%,此时气化气热值为2150 kJ/Nm3,固定碳转化率80%,气化气产率为2.3 Nm3/kg. 相似文献
97.
以NiO/Al2O3为载氧体,在1 kWth串行流化床反应器上进行了煤化学链燃烧实验,通过四个参数:碳转换效率ηC,coal、煤气化产物的转换效率、碳捕集效率ηC,cap及煤燃烧效率ηcombust对煤燃烧过程进行表征,考察了燃料反应器温度tFR、过量空气系数α、隔离器水煤比SLS/C、燃料反应器水煤比SFR/C和热负荷等参数的影响。结果表明,tFR和SLS/C的增大有利于煤气化产物的转换;tFR、α和SLS/C的增大有助于ηC,coal的提高,随着SFR/C由0.8增加到1.8,ηC,coal呈先增加再减小的趋势,并在SFR/C=1.2达到最大值;ηcombust和ηC,coal变化趋势保持一致,主要受飞灰含碳量中残碳损失的影响;tFR提高有助于提高ηC,cap,而α和SLS/C的增大使得ηC,cap降低。 相似文献
98.
Satish Bhusarapu Miryan Cassanello Muthanna H. Al-Dahhan Milorad P. Dudukovic Steven Trujillo Timothy J. O’Hern 《International Journal of Multiphase Flow》2007
The trajectories of a solid tracer with the same characteristics as the circulating solids in the risers of two pilot-scale circulating fluidized beds (CFBs), obtained by the computer automated radioactive particle tracking (CARPT) technique, are examined in detail to get further insights into the complex solids dynamics of these systems. The analysis uses tools from the theory of non-linear dynamics and symbolic dynamics. Distinct features of the solids dynamics within the fast fluidization and the dilute phase transport flow regimes are highlighted and related to the operating conditions. The possibility of downflow cluster existence within the central region of the riser is particularly examined. 相似文献
99.
EXTERNAL-LOOP AIRLIFT MAGNETICALLY STABILIZED BED——MINIMUM STABILIZATION AND FLUIDIZATION CONDITIONS
Jordan Hristov 《中国颗粒学报》2005,3(4):197-203
Experimental study of an airlift with a magnetically stabilized bed in the riser bottom has been performed. External magnetic field allows easy control of magnetized bed structure and liquid circulation rate. Minimum stabilization and fluidization conditions have been determined experimentally and by a three-line graphical method. Semi-empirical data correlations of sections of the experimental curves have been performed. Scaling relationships known from non-magnetic airlift are applicable too, but with the assumption that the magnetic field affects the loop friction coefficient only. 相似文献
100.