全文获取类型
收费全文 | 565590篇 |
免费 | 5850篇 |
国内免费 | 1600篇 |
专业分类
化学 | 272216篇 |
晶体学 | 7769篇 |
力学 | 29114篇 |
综合类 | 13篇 |
数学 | 95689篇 |
物理学 | 168239篇 |
出版年
2021年 | 3749篇 |
2020年 | 4188篇 |
2019年 | 4524篇 |
2018年 | 20252篇 |
2017年 | 20525篇 |
2016年 | 16450篇 |
2015年 | 6838篇 |
2014年 | 8879篇 |
2013年 | 20504篇 |
2012年 | 21492篇 |
2011年 | 35907篇 |
2010年 | 23073篇 |
2009年 | 23339篇 |
2008年 | 30420篇 |
2007年 | 34382篇 |
2006年 | 16567篇 |
2005年 | 20709篇 |
2004年 | 17303篇 |
2003年 | 16094篇 |
2002年 | 13634篇 |
2001年 | 13739篇 |
2000年 | 10545篇 |
1999年 | 8060篇 |
1998年 | 6750篇 |
1997年 | 6445篇 |
1996年 | 6350篇 |
1995年 | 5642篇 |
1994年 | 5528篇 |
1993年 | 5342篇 |
1992年 | 5926篇 |
1991年 | 6041篇 |
1990年 | 5760篇 |
1989年 | 5582篇 |
1988年 | 5618篇 |
1987年 | 5495篇 |
1986年 | 5203篇 |
1985年 | 6677篇 |
1984年 | 6816篇 |
1983年 | 5417篇 |
1982年 | 5502篇 |
1981年 | 5474篇 |
1980年 | 5067篇 |
1979年 | 5424篇 |
1978年 | 5560篇 |
1977年 | 5391篇 |
1976年 | 5364篇 |
1975年 | 4934篇 |
1974年 | 4901篇 |
1973年 | 4946篇 |
1972年 | 3484篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
In basin modelling the thermodynamics of a multicomponent multiphase fluid flux are computationally too expensive when derived from an equation of state and the Gibbs equality constraints. In this article we present a novel implicit molar mass formulation technique using binary mixture thermodynamics. The two proposed solution methods, with and without cross derivative terms between components, are based on a preconditioned Newton‐GMRES scheme for each time‐step with analytical computation of the derivatives. These new algorithms reduce significantly the numerical effort for the computation of the molar masses, and we illustrate the behavior of these methods with numerical computations. Copyright © 2004 John Wiley & Sons Ltd. 相似文献
942.
A preconditioning approach based on the artificial compressibility formulation is extended to solve the governing equations for unsteady turbulent reactive flows with heat release, at low Mach numbers, on an unstructured hybrid grid context. Premixed reactants are considered and a flamelet approach for combustion modelling is adopted using a continuous quenched mean reaction rate. An overlapped cell‐vertex finite volume method is adopted as a discretisation scheme. Artificial dissipation terms for hybrid grids are explicitly added to ensure a stable, discretised set of equations. A second‐order, explicit, hybrid Runge–Kutta scheme is applied for the time marching in pseudo‐time. A time derivative of the dependent variable is added to recover the time accuracy of the preconditioned set of equations. This derivative is discretised by an implicit, second‐order scheme. The resulting scheme is applied to the calculation of an infinite planar (one‐dimensional) turbulent premixed flame propagating freely in reactants whose turbulence is supposed to be frozen, homogeneous and isotropic. The accuracy of the results obtained with the proposed method proves to be excellent when compared to the data available in the literature. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
943.
K.B. Welter Q. Wu Y. You K. Abel D. McCreary S.M. Bajorek J.N. Reyes Jr 《International Journal of Multiphase Flow》2004,30(12):407-1484
This article describes a comprehensive literature review of liquid entrainment in horizontal pipes with vertical-up branches. Deficiencies in the available data and correlations were identified. The Air–water Test Loop for Advanced Thermal–hydraulic Studies (ATLATS) was constructed and entrainment onset and steady-state data were collected for a wide range of flow conditions. Using new insights gained from experimental testing, the authors developed a model for predicting the onset of entrainment and steady-state entrainment rate. Previously published correlations, along with the new model, are compared against all available data. The new model shows very good agreement with the onset data, but is not very good at predicting branch quality at high liquid flow rates. 相似文献
944.
A technique is described for the measurement of all components of mean velocity and Reynolds stresses, in a complex turbulent flow where achieving coincidence data acquisition is difficult. The method is based on data recorded using four orientations of the laser probe. It is shown that the measurement errors are not the same for all the components of the Reynolds tensor, but they are sufficiently small to give a good accuracy. An application to a turbomachinery flow is given to illustrate the method. 相似文献
945.
A novel super-hydrophobic stearic acid (STA) film with a water contact angle of 166o was prepared by chemical adsorption on aluminum wafer coated with polyethyleneimine (PEI) film. The micro-tribological behavior
of the super-hydrophobic STA monolayer was compared with that of the polished and PEI-coated Al surfaces. The effect of relative
humidity on the adhesion and friction was investigated as well. It was found that the STA monolayer showed decreased friction,
while the adhesive force was greatly decreased by increasing the surface roughness of the Al wafer to reduce the contact area
between the atomic force microscope (AFM) tip and the sample surface to be tested. Thus the friction and adhesion of the Al
wafer was effectively decreased by generating the STA monolayer, which indicated that it could be feasible and rational to
prepare a surface with good adhesion resistance and lubricity by properly controlling the surface morphology and the chemical
composition. Both the adhesion and friction decreased as the relative humidity was lowered from 65% to 10%, though the decrease
extent became insignificant for the STA monolayer.
The project supported by the National Natural Science Foundation of China (50375151, 50323007, 10225209) and the Chinese Academy
of Sciences (KJCX-SW-L2) 相似文献
946.
We carried out detailed calculations for photorefractive wave-mixing switches based on one of three crystals with high electro-optic coefficients, namely, BaTiO3, Strontium Barium Niobate (SBN (0.75)), and Potasium Sodium Strontium Barium Niobate (KNSBN). A comparison of results for the three crystals shows that a 0_-cut BaTiO3 crystal is suitable for a longitudinal switch and requires a voltage of about 80 for a 2-mm-thick crystal to induce sufficient phase mismatch. The electrodes must be transparent for the incident and diffracted beams. A 45_-cut SBN (0.75) crystal, however, is suitable for a lateral switch and requires a voltage of about 150 for a 1-mm-wide crystal. The electrodes do not need to be transparent. 相似文献
947.
948.
949.
V. Babin P. Bohacek E. Bender A. Krasnikov E. Mihokova M. Nikl N. Senguttuvan A. Stolovits Y. Usuki S. Zazubovich 《Radiation measurements》2004,38(4-6):533-537
Luminescence characteristics of a number of undoped and variously doped PbWO4 crystals were studied at 0.4–400 K by the time-resolved spectroscopy and compared with those of ZnWO4,CdWO4 and PbMoO4 crystals. Two types of green emission centres are detected in PbWO4 crystals. The centres of the first type are responsible for the low-temperature 2.3–2.4 eV emission observed under excitation around 3.90–3.95 eV. The structure and parameters of their relaxed excited states were determined. It was concluded that the origin of defects responsible for the green emission of the first type could vary for different crystals. The centres of the second type with the emission around 2.5 eV appear in crystals containing oxygen vacancies after the thermal destruction of Pb+-WO3 centres at T>180 K. Decomposition of the exciton and various defect-related states was also studied, and activation energies of this process were calculated. 相似文献
950.
Y. Guyot H. Loudyi S. Kazanskii J. C. Gcon C. Pdrini M. F. Joubert 《Radiation measurements》2004,38(4-6):753-757
Photoconductivity spectra of rare earth-doped insulating materials are measured using the resonant microwave cavity method. This technique is based on the detection of the cavity Q-factor changes induced by irradiation of the sample (inserted in the cavity) by a pulsed tunable laser. Results obtained with Lu2(SiO4)O:Ce3+ and BaF2:Eu2+ are presented and discussed. Photoionization thresholds at 400 nm (3.1 eV) and 310 nm (4.0 eV) are measured for Lu2(SiO4)O:Ce3+ and BaF2:Eu2+, respectively. 相似文献