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1.
A tomographic reconstruction method based on Monte Carlo random searching guided by the information contained in the projections
of radiographed objects is presented. In order to solve the optimization problem, a multiscale algorithm is proposed to reduce
computation. The reconstruction is performed in a coarse-to-fine multigrid scale that initializes each resolution level with
the reconstruction of the previous coarser level, which substantially improves the performance. The method was applied to
a real case reconstructing the internal structure of a small metallic object with internal components, showing excellent results. 相似文献
2.
Exterior tomographic data are taken over lines outside a central region, and such data occur in the industrial nondestructive evaluation of large objects such as rockets. We explain, using microlocal analysis, which singularities are well reconstructed from exterior data, and we explain how this phenomenon is reflected in the singular value decomposition for the exterior transform [E.T. Quinto, Singular value decompositions and inversion methods for the exterior Radon transform and a spherical transform, J. Math. Anal. Appl. 95 (1983) 437–448]. We extend Lambda Tomography to exterior data and to limited angle exterior data. The algorithm is tested on industrial data from Perceptics, Inc. 相似文献
3.
X-ray microtomography coupled with image analysis was used to quantify the adsorption of vapours on activated carbon beds.
This technique was tested using three different challenges: CCl4, water vapour and a mixture of water- and organic vapour. It is shown that the used technique allows determining the adsorption
front progress in the case of organic vapour and mixture of water and organic vapour whereas the existence of this front was
not so obvious in the case of water vapour. Experimental results obtained for organic vapours were interpreted on the basis
of the Wheeler-Jonas equation: a good agreement was found between experimental and theoretical breakthrough times. 相似文献
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In recent years, Radon-type transforms that integrate functions over various sets of ellipses/ellipsoids have been considered in synthetic aperture radar, ultrasound reflection tomography, and radio tomography. In this paper, we consider the transform that integrates a given function in Rn over a set of solid ellipses (when n=2) or solid ellipsoids of rotation (when n?3) with a fixed eccentricity and foci restricted to a hyperplane. Inversion formulas are obtained for appropriate classes of functions that are even with respect to the hyperplane. Stability estimates and local uniqueness results are also provided. 相似文献
10.
The tomographic reconstruction of supersonic flows faces two challenges. Firstly, techniques used in the past, such as the
direct Fourier method (DFM) (Gottlieb and Gustafsson in On the direct Fourier method for computer tomography, 1998; Morton
in Tomographic imaging of supersonic flows, 1995) or various backprojection (Kak and Slaney in Principles of computerized
tomographic imaging, vol. 33 in Classics in Applied Mathematics, 2001) techniques, have only been able to reconstruct areas
of the flow which are upstream of any opaque objects, such as a model. Secondly, shock waves create sharp discontinuities
in flow properties, which can be difficult to reconstruct both in position and in magnitude with limited data. This paper
will present a reconstruction method, matrix inversion using ray-tracing and least squares conjugate gradient (MI-RLS), which uses geometric ray-tracing and a sparse matrix iterative solver (Paige and Saunders in ACM Trans. Math. Softw.
8(1):43–71, 1982) to overcome both of these challenges. It will be shown, through testing with a phantom object described
in tomographic literature, that the results compare favourably to those produced by the DFM technique. Finally, the method
will be used to reconstruct three-dimensional density fields from interferometric shock layer images, with good resolution
(Faletič in Tomographic reconstruction of shock layer flows, 2005).
This paper was based on work that was presented at the 3rd International Symposium on Interdisciplinary Shock Wave Research,
Canberra, Australia, March 1–3, 2006. 相似文献