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22.
DSM-LPDF两相湍流模型及旋流两相流动的模拟 总被引:2,自引:0,他引:2
本文由流体-颗粒速度的拉氏联合概率密度函数(PDF)输运方程出发,用Simonin建议的Langevin模型封闭颗粒所遇到流体瞬时速度的条件期望项,并用Monte Carlo方法直接求解 PDF输运方程,将其和求解流体雷诺应力方程模型的有限差分方法结合,建立了雷诺应力-拉氏PDF(DSM-LPDF,简称DL)两相湍流模型.用此模型模拟了旋流数为0.47的突扩旋流气粒两相流动,并与文献中PDPA实验和用类似于单相流动湍流模型封闭方法的时平均统一二阶矩(USM)模型的预报进行了对比. 相似文献
23.
Joint Scalar versus Joint Velocity-Scalar PDF Simulations of Bluff-Body Stabilized Flames with REDIM
Two transported PDF strategies, joint velocity-scalar PDF (JVSPDF) and joint scalar PDF (JSPDF), are investigated for bluff-body
stabilized jet-type turbulent diffusion flames with a variable degree of turbulence–chemistry interaction. Chemistry is modeled
by means of the novel reaction-diffusion manifold (REDIM) technique. A detailed chemistry mechanism is reduced, including
diffusion effects, with N
2 and CO
2 mass fractions as reduced coordinates. The second-moment closure RANS turbulence model and the modified Curl’s micro-mixing
model are not varied. Radiative heat loss effects are ignored. The results for mean velocity and velocity fluctuations in
physical space are very similar for both PDF methods. They agree well with experimental data up to the neck zone. Each of
the two PDF approaches implies a different closure for the velocity-scalar correlation. This leads to differences in the radial
profiles in physical space of mean scalars and mixture fraction variance, due to different scalar flux modeling. Differences
are visible in mean mixture fraction and mean temperature, as well as in mixture fraction variance. In principle, the JVSPDF
simulations can be closer to physical reality, as a differential model is implied for the scalar fluxes, whereas the gradient
diffusion hypothesis is implied in JSPDF simulations. Yet, in JSPDF simulations, turbulent diffusion can be tuned by means
of the turbulent Schmidt number. In the neck zone, where the turbulent flow field results deteriorate, the joint scalar PDF
results are in somewhat better agreement with experimental data, for the test cases considered. In composition space, where
results are reported as scatter plots, differences between the two PDF strategies are small in the calculations at hand, with
a little more local extinction in the joint scalar PDF results. 相似文献
24.
25.
Maxwell W. Terban Alexander M. Pütz Gökcen Savasci Ute Heinemeyer Bernd Hinrichsen Philippe Desbois Robert E. Dinnebier 《Journal of polymer science. Part A, Polymer chemistry》2020,58(13):1843-1866
Investigations of the atomic structures within polyamides started over 80 years ago and continue today. These weakly ordered materials diffract X-rays poorly and typically require postprocessing to obtain idealized samples for structural studies. An important goal remains to develop techniques to study the local structure in its natural state, with atomic resolution, and with sensitivity to subtle changes due to synthesis conditions or other technologically relevant processing procedures. Here, we compare the structures of as-produced, nonoriented polyamide 6 ([C6H11NO] n) from both hydrolytic and anionic processes. A total scattering pair distribution function approach is used to elucidate information about the atomic bonding, molecular conformation, chain packing, crystallite size, and ratio of ordered to disordered domain content. The results are compared with those from standard analytical methods. 相似文献
26.
Dr. Hui Xu Sanna Sommer Nils Lau Nyborg Broge Prof. Dr. Junkuo Gao Prof. Dr. Bo Brummerstedt Iversen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(8):2051-2058
The concept of secondary building units (SBUs) is central to all science on metal-organic frameworks (MOFs), and they are widely used to design new MOF materials. However, the presence of SBUs during MOF formation remains controversial, and the formation mechanism of MOFs remains unclear, due to limited information about the evolution of prenucleation cluster structures. Here in situ pair distribution function (PDF) analysis was used to probe UiO-66 formation under solvothermal conditions. The expected SBU—a hexanuclear zirconium cluster—is present in the metal salt precursor solution. Addition of organic ligands results in a disordered structure with correlations up to 23 Å, resembling crystalline UiO-66. Heating leads to fast cluster aggregation, and further growth and ordering results in the crystalline product. Thus, SBUs are present already at room temperature and act as building blocks for MOF formation. The proposed formation steps provide insight for further development of MOF synthesis. 相似文献
27.
D. Geyer A. Dreizler J. Janicka A.D. Permana J.Y. Chen 《Proceedings of the Combustion Institute》2005,30(1):711-718
This study reports results from experimental and numerical investigations of a partially premixed turbulent opposed methane/air jet flame. Experimentally determined properties of the scalar and the flow field are compared to the results from a Monte Carlo simulation. One-dimensional spatially resolved Raman/Rayleigh scattering serves to quantify the mean species concentrations and temperature, whereas laser Doppler velocimetry is used to measure axial and radial velocity components. The simulation is simplified by using a one-dimensional formulation. It includes a Reynolds-stress turbulence model and a Monte Carlo simulation of the joint scalar probability density function (PDF). A non-uniform Monte Carlo particle distribution is used to minimize stochastic errors. The flame is operated close to extinction with strong interactions between turbulence and chemistry. Comparisons between experimental and numerical results reveal a good agreement of mixture fraction profiles along the centreline. However, species scatter plots and mixture fraction PDFs show discrepancies between experiment and simulation. Numerical simulations over-predict the extinction limits and therefore under-predict the intermittent nature of turbulence and mixing of the scalars. 相似文献
28.
29.
Large eddy simulation is applied to the auto-ignition of a hydrogen jet issuing into a turbulent co-flowing air stream. A 19 step, nine species detailed mechanism is used for reaction. The influence of sub-grid species concentration and temperature fluctuations are accounted for by a sub-grid joint PDF for the reactive scalars, obtained from solution of a modelled transport equation. The method is able to reproduce ignition lengths and different regimes observed experimentally without any adjustment or calibration of the model constants. 相似文献
30.
Turbulent mixing of a single jet, twin jets, triple jets and multiple jets is synthetically analysed in this paper. Chung's kinetic theory of turbulence and a modified Green's function are employed to solve this problem. The probability density function of fluid elements in the velocity space of multiple plane jets and the corresponding turbulence correlations are revealed in this analysis. The calculated results are found to be in good agreement with the available experimental data. The internal physical structure of the turbulent mixing mechanism seems better understood via the kinetic theory approach. The present study provides the fundamentals for theoretical understanding of multiple-jet turbulent mixing and further application to multiple-jet turbulent combustion analysis. 相似文献