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51.
针对强湍流信道下信号衰落的特点,分析了对数正态分布模型与K分布模型的适用范围.基于K分布模型建立大气光通信接收信号模型,并给出了自适应最优门限检测方法.采用四阶和六阶累计量对强湍流信道参量进行估计,采用二阶累计量对其它高斯噪音进行估计,得到K分布参量及高斯噪音统计量的预测值,实现自适应门限更新.基于Monte Calro算法进行仿真,给出了门限更新算法对通信系统误码率的影响,同时分析了信号采样率对估计参量偏差的影响.计算表明,在强湍流情况下,大气光通信系统的误码率性能得到极大的改善,优于基于MLSD检测的接收机. 相似文献
52.
53.
Mustafa Barri George K. El Khoury Helge I. Andersson Bjrnar Pettersen 《国际流体数值方法杂志》2010,64(7):777-792
Direct numerical simulation (DNS) has been performed to study the channel flow over a backward‐facing step at a Reynolds number Reb=5600 based on the step height h and the inflow bulk velocity Ub. A dynamic method has been used in order to generate realistic turbulent inflow conditions. The results upstream of the step compared well with the fully developed channel flow. Downstream of the step our results show excellent agreement with experimental data. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
54.
Xiaolei Cai Meili Liu Yipeng Ji Guodong Ding Long Zhang 《Journal of Dispersion Science and Technology》2017,38(10):1435-1447
Huge amounts of produced water are generated in offshore oil production. The Compact Flotation Unit (CFU) is an excellent pretreatment technology of produced water with high separation efficiency, low residence, and small split ratio. The Computational Fluid Dynamics-population balance model (CFD-PBM) method is used in the present work to study the oil–water separation characteristics in the self-developed Beijing Institute of Petrochemical Technology Compact Flotation Unit (BIPTCFU) at both micro-scale and macro-scale, which would help us gain more insights into the mechanism and the influence of flow field on the oil–water separation process such as the oil droplets’ diameter distribution and separation efficiency. The effects of the inlet diameter, the height of the preliminary separation zone, and the width of the annular space on the oil–water separation characteristics of CFU were discussed systematically. It is illustrated that the appropriate increase of inlet velocity, decrease of annular gap width, and increase of the height in the preliminary separation zone can effectively promote the collision and coalescence process of oil droplets. However, the overlarge height of the preliminary separation zone and the too narrow width of the annular space will both have a significant negative effect on the migration and separation of oil and water and lead to the decrease of separation efficiency. 相似文献
55.
Stabilization of spiral wave and turbulence in the excitable media using parameter perturbation scheme 下载免费PDF全文
This paper proposes a scheme of parameter perturbation to suppress the stable rotating spiral wave, meandering spiral wave and turbulence in the excitable media, which is described by the modified Fitzhug-Nagumo (MFHN) model. The controllable parameter in the MFHN model is perturbed with a weak pulse and the pulse period is decided by the rotating period of the spiral wave approximatively. It is confirmed that the spiral wave and spiral turbulence can be suppressed greatly. Drift and instability of spiral wave can be observed in the numerical simulation tests before the whole media become homogeneous finally. 相似文献
56.
Kinetic modeling of a high power fast-axial-flow CO2 laser with computational fluid dynamics method 总被引:1,自引:0,他引:1
A new computational fluid dynamics (CFD) method for the simulation of fast-axial-flow CO2 laser is developed.The model which is solved by CFD software uses a set of dynamic differential equations to describe the dynamic process in one discharge tube.The velocity,temperature,pressure and turbulence energy distributions in discharge passage are presented.There is a good agreement between the theoretical prediction and the experimental results.This result indicates that the parameters of the laser have significant effect on the flow distribution in the discharge passage.It is helpful to optimize the output of high power CO2 laser by mastering its kinetic characteristics. 相似文献
57.
ZHAO YuXin YI ShiHe TIAN LiFeng HE Lin & CHENG ZhongYu College of Aerospace Material Engineering National University of Defense Technology Changsha China 《中国科学G辑(英文版)》2008,51(8):1134-1143
Flow visualization of supersonic mixing layer has been studied based on the high spatiotemporal resolution Nano-based Planar Laser Scattering(NPLS) method in SML-1 wind tunnel. The corresponding images distinctly reproduced the flow structure of laminar,transitional and turbulent region,with which the fractal measurement can be implemented. Two methods of measuring fractal dimension were introduced and compared. The fractal dimension of the transitional region and the fully developing turbulence region of supersonic mixing layer were measured based on the box-counting method. In the transitional region,the fractal dimension will increase with turbulent intensity. In the fully developing turbulent region,the fractal dimension will not vary apparently for different flow structures,which em-bodies the self-similarity of supersonic turbulence. 相似文献
58.
Multi-Fractal Formalism for Quasi-Self-Similar Functions 总被引:1,自引:0,他引:1
The study of multi-fractal functions has proved important in several domains of physics. Some physical phenomena such as fully developed turbulence or diffusion limited aggregates seem to exhibit some sort of self-similarity. The validity of the multi-fractal formalism has been proved to be valid for self-similar functions. But, multi-fractals encountered in physics or image processing are not exactly self-similar. For this reason, we extend the validity of the multi-fractal formalism for a class of some non-self-similar functions. Our functions are written as the superposition of similar structures at different scales, reminiscent of some possible modelization of turbulence or cascade models. Their expressions look also like wavelet decompositions. For the computation of their spectrum of singularities, it is unknown how to construct Gibbs measures. However, it suffices to use measures constructed according the Frostman's method. Besides, we compute the box dimension of the graphs. 相似文献
59.
B. Castaing 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):357-358
Usual turbulence experiments, based on the Taylor hypothesis, differ from true Eulerian measurements. This is the origin of
the apparent discrepancy between a recent two point correlation analysis and the multiplicative cascade picture. Indeed, both
Eulerian and Lagrangian observations perfectly agree with this picture.
Received 19 June 2002 / Received in final form 29 July 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: bcastain@ens-lyon.fr 相似文献
60.
Infinite Prandtl Number Convection 总被引:1,自引:0,他引:1
We prove an inequality of the type NCR
1/3(1+log+
R)2/3 for the Nusselt number N in terms of the Rayleigh number R for the equations describing three-dimensional Rayleigh–Bénard convection in the limit of infinite Prandtl number. 相似文献