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91.
Qing Lu N.V. Suryanarayana Christodoulous Christodoulu 《Experimental Thermal and Fluid Science》1993,7(4):354-361
A technique for measuring condensate film thickness using an ultrasonic transducer is described. In the experiment, the condensate film thickness with R-113 and FC-72 (a fluorinert compound developed by the 3M Company) condensing on the horizontal lower surface of a rectangular duct was measured at several locations. From the measured values a power law relation between the condensate film thickness and the axial distance from the leading edge of the condensing surface was derived by regression analysis. Assuming a linear temperature profile in the condensate film, local and average heat transfer coefficients were computed from the condensate film thickness. The average heat transfer coefficients were compared with the values obtained by measuring the heat transfer rate to the coolant. The two values were within ±12% of each other. As yet there is no satisfactory analytical model to predict the local heat transfer coefficient even in the annular condensation regime. One of the main difficulties in modeling the condensation is the lack of a suitable model to predict the interfacial shear stress. With the measurement of the film thickness it is possible to determine the interfacial shear stress. It is hoped that the shear stresses so determined will lead to the development of a satisfactory model for interfacial shear stress with condensation. 相似文献
92.
93.
提出了一种应用于白光数字散斑图像频域位移测量技术的数字相移方法,利用计算机本身的能力,无需增加任何设备,通过计算机生成的四幅图像进行相移计算,得到逐点分析的条纹的未去包裹图像,从该图像确定位移的方向和大小,实现了白光数字散斑图像的全自动化处理。白光数字散斑方法设备简单,对环境的要求低,无需防振和相干光源,引入本文提出的数字相移技术,由于充分利用了计算机数字图像处理的功能,在未增加任何设备的情况下实现了全自动位移测量,是一种适合工业现场测量的有发展前途的位移测试的技术。 相似文献
94.
An asymptotic analysis is presented for a dynamic problem of a semi-infinite isotropic thermoelastic solid with a small surface breaking crack. The exterior surface of the solid is subjected to a series of short thermal pulses. The crack surface is traction free and an ideal thermal contact is assumed across the crack. The stress intensity factor is asymptotically evaluated as a function of the crack depth and time. The effect of a boundary layer associated with the diffusive term is identified. The theoretical model is supplied with numerical simulations. 相似文献
95.
系统介绍了在单轴转台上测量高精度光纤陀螺分辨率的方法。该方法以GJB2426—95对光纤陀螺分辨率的定义为依据,以地球自转水平分量的余弦分量为陀螺的输入量,提出了一种正交三点寻北法。分析了光纤陀螺输出信号的特征,提出用对称测量法消除陀螺零偏并减小零漂对测量的影响。最后用IEEE推荐的测量不确定度评定方法对测量结果的不确定度进行了严格的评定。 相似文献
96.
本文报告了明渠非定常水流垂向结构的实验研究,通过 LDV 激光测速,我们给出了非定常水流的速度削面,湍流度,Eulerian质量输运速度的垂向分布。实验结果表明:在非定常周期很长时非定常流动的速度剖面,湍流强度及其粗糙度的影响基本上与定常流动相一致,当非定常流动为纯往复流动时,存在一个逆时针方向的环流,这种环流有利于底部的质量输运。 相似文献
97.
98.
This study focuses on the development of a methodology for the determination of some in situ parameters for off-road vehicle mobility on sandy soils. The stress field in the vicinity of and at the interface between a wedge and soil was determined by solving the stress equations using the method of characteristics. The governing equations were solved numerically by using backward finite difference method. The proposed method allows the prediction of any two of the in situ soil parameters δ, φ, and γ (respectively, the interfacial friction angle between the material of a wedge penetrometer and the soil, the internal friction angle, and the unit weight of the soil), given the value of any one of them and the results of penetration tests of two different apex angle wedges. The predictions and the measured values are in agreement. 相似文献
99.
In speckle photograph technology, to determine the displacement of the points on the surface of the measured body, the conventional
method is to put the film which has recorded the speckle patterns before and after displacement into a system of optical Fourier
transforms. After filtering on the spectrum plane, the experimentalist can obtain the displacement information from the interference
pattern on the image plane. Instead of setting up a complex optical Fourier transform system, we consider the speckle field
as a light intensity function of 2 dimensions, which will change with different positioning of the points. After working on
the function's discrete Fourier transform (DFT), according to one of the properties of Fourier transformation, the displacement
of the measured point is involved in the phase of its spectrum. Having extracted the displacement information from the phase,
we obtain the distribution of the displacement field. In this paper, we deduce the expression for the displacement field by
using Fourier transformation under conditions of both equal and unequal displacement and show their applications. 相似文献
100.
Ming Ruisen 《Acta Mechanica Sinica》1996,12(3):251-262
Quasi-longitudinal waves are one type of structural waves, which are important at high frequencies. This paper studies the
estimate theory and measurement technique of quasi-longitudinal waves, analyzes the bias error due to the effect of bending
waves. In a two-dimensional quasi-longitudinal wave field, the intensity vector is the sum of the effective intensity vector
and the intensity variation vector. Its axial component is proportional to two imaginary parts of cross spectral densities
and in the measurement, it is measured by a pair of two-transducer arrays. In a onedimensional quasi-longitudinal wave field,
the intensity variation is zero, the intensity is proportional to only one imaginary part of a cross spectral density and
it can be measured using a two-transducer array. If bending and quasi-longitudinal waves coexist and the contribution from
bending waves cannot be eliminated or reduced to a certain extent, the measured quasi-longitudinal wave intensity will contain
a large error. The results measured on the three-beam structure show that quasi-longitudinal wave intensity can be accurately
measured using the intensity technique when bending waves are negligible in comparison with quasi-longitudinal waves.
The project supported by the National Natural Science Foundation of China 相似文献