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831.
The acceleration of aluminum particles with a 5μm diameter in the flow field behind an incident shock wave was investigated
experimentally in a 10-m long and 70 mm inner diameter shock tube. By means of instantaneous Laser Doppler Velocimetry (LDV)
the velocity of the particles was observed directly. The light scattered by the moving particles is Doppler shifted and sent
to the laser Doppler velocimeter. The velocimeter essentially consists of a phase-stabilized Michelson interferometer used
as a sensitive spectrometer. An electro-optical circuit ensures the phase stabilization that results in a voltage signal independent
of the scattered light intensity and proportional to the mean velocity of the particles at the measurement point. Because
of the very short response time (1μs) of the LDV system used here, the latter gives a continuous real-time signal of the particle
acceleration. To avoid particle oxidation the particles were accelerated by a high-speed nitrogen gas flow. From the measured
velocity the dimensionless drag coefficient was calculated. The drag coefficient is related to the fluid dynamic force exerted
by the gas on the particles. The experimental data were compared to theoretical models from the literature. A significant
deviation between the model and the experimental data was observed. This deviation is supposed to be induced by the shock
wave, which hits the particles and breaks them into pieces of a smaller diameter. Further experiments will be carried out
in the future to check the size distribution of the particles after the shock has gone past them.
相似文献
832.
V. I. Rodchenkov D. A. Sergeev 《Journal of Applied Mechanics and Technical Physics》2009,50(4):553-557
Particle image velocimetry was used to study the structure of stationary acoustic flows on a solid surface subjected to acoustic
radiation along the normal to the prefocal and postfocal planes of a spherical concentrator. The results of model experiments
were used for rapid growth of water-soluble single crystals.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 4, pp. 11–17, July–August, 2009. 相似文献
833.
834.
本文对现有相位调制激光多普勒频移测量方法进行了改进,通过定义新的鉴频参量来同时利用相位调制信号直流和交流分量中的有用信息进行多普勒频移测量.由于相位调制信号直流分量中包含着调制信号光的Fabry-Perot干涉仪光强透过率,所以这一改进本质上是将基于Fabry-Perot干涉仪的边缘技术激光多普勒频移测量方法的优势引入到相位调制测量方法中,以提高其自身的性能.理论上证明改进后的相位调制激光多普勒频移测量方法无需对信号光的光强进行测量,所以可以进一步简化探测系统的结构和较少噪声混入的通道.另外,通过对改进前后鉴频和测量灵敏度曲线进行对比,还证明了其具有更高的测量灵敏度和动态范围.实验上对硬目标反射的频移可控信号光进行测量,不但证明了理论的正确性,而且证明了改进后的相位调制激光多普勒频移测量方法,测量动态范围提高约1倍,测量标准偏差降低约35%. 相似文献
835.
阐述了多普勒非对称空间外差光谱仪用于被动式多普勒测速的基本原理,通过综合考虑干涉条纹对比度和仪器测速灵敏度等关键因素,建立了效率函数,分别针对高斯线型和洛伦兹线型发射谱线,从理论上推导了最优单臂偏置量的选择依据,并以高斯线型目标谱线为例进行了仿真验证.同时,提出了一种基于部分干涉条纹反演多普勒速度的数据处理方法,简化了多谱线目标源的数据处理过程.结合自适应频率跟踪算法对单谱线目标源和多谱线目标源进行了仿真比较,仿真结果表明,在不考虑噪声的情况下,该方法针对多谱线目标源的多普勒测速最大绝对误差在0.004 m/s以内,与针对单谱线目标源的处理精度相当,可以满足实际应用的精度要求. 相似文献
836.
移动荷载作用下饱和土地基中的波动特性分析 总被引:1,自引:1,他引:0
基于Biot波动方程,经过Fourier变换和逆Fourier变换后可获得波数-频率域以及时间-空间域的解析解。通过数值分析的手段研究了移动荷载作用下饱和多孔弹性地基中波的传播特性。重点就弥散曲线、多谱勒效应、波的成分和动力响应频率等几个特性进行了分析,发现饱和土地基由于比弹性地基多了一项流体介质,波动特性明显差异于弹性介质。 相似文献
837.
T. A. KOWALEWSKI M. REBOW 《International Journal of Computational Fluid Dynamics》2013,27(3-4):193-210
An experimental and numerical study has been made of transient natural convection of water freezing in a cube-shaped cavity. The effect of the heat transfer through the side walls is studied in two configurations: with the cavity surrounded by air and with the cavity immersed in an external water bath of constant temperature. The experimental data for the velocity and temperature fields are obtained using liquid crystal tracers. The transient development of the ice/water interface is measured. The collected data are used as an experimental benchmark and compared with numerical results obtained from a Finite-difference code with boundary fitted grid generation. The computational model has been adopted to simulate as closely as possible the physical experiment. Hence, fully variable fluid properties are implemented in the code, and, to improve modelling of the thermal boundary conditions, the energy equation is also solved inside the bounding walls. Although the general behaviour of the calculated ice front and its volume matches observations, several details of the flow structure do not. Observed discrepancies between experimental and numerical results indicate the necessity of verifying and improving the usual assumptions for modelling ice formation. 相似文献
838.
PIV速度场坏矢量的本征正交分解处理技术 总被引:1,自引:0,他引:1
介绍了一种针对粒子图像测速(PIV)基于本征正交分解(POD)的速度场后处理技术.该技术改变了现在后处理技术将速度场坏矢量识别和修正分开实现的局面,通过迭代方法有效地实现了速度场坏点统一的识别和修复算法.算法利用POD分解的低阶模态信息重构出可以用于坏矢量识别的参考速度场,利用该参考速度场对全流场进行坏点识别并完成修正.通过对一套光滑的PIV速度场数据引入高斯分布的随机误差,测试验证了该POD方法的优越性.在坏矢量识别方面新方法较归一化中值检验有更高的正确性,能识别大面积出现的坏矢量区域.在坏矢量修补的插值算法中,新方法的计算效率又高于传统Gappy POD方法,且计算精度优于常见的矢量场内插数学方法.特别是在数据缺失的大连通区域,该方法对物理流场有很好的预测效果. 相似文献
839.
840.