全文获取类型
收费全文 | 135篇 |
免费 | 1篇 |
专业分类
化学 | 59篇 |
力学 | 13篇 |
数学 | 47篇 |
物理学 | 17篇 |
出版年
2022年 | 2篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 9篇 |
2012年 | 5篇 |
2011年 | 4篇 |
2010年 | 5篇 |
2009年 | 8篇 |
2008年 | 4篇 |
2007年 | 6篇 |
2006年 | 4篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1963年 | 1篇 |
1958年 | 1篇 |
1944年 | 1篇 |
1935年 | 1篇 |
1903年 | 1篇 |
排序方式: 共有136条查询结果,搜索用时 31 毫秒
61.
Sidney B. Lang Erling Ringgaard 《Applied Physics A: Materials Science & Processing》2012,107(3):631-638
The introduction of porosity into ferroelectric ceramics has been of great interest in recent years. In particular, studies of porous lead-zirconate-titanate ceramic (PZT) have been made. In the research reported, samples of Ferroperm Pz27 with porosities of 20, 25 and 30% were studied. Very complete measurements were made of all of the physical properties relevant for ferroelectric applications including thermal conductivity and diffusivity, heat capacity, dielectric, pyroelectric, piezoelectric and elastic properties. Scanning electron micrographs indicated a change from 3-0 to 3-3 connectivity with increasing porosity. Although most of the physical properties are degraded by the presence of porosity, both piezoelectric and pyroelectric figures-of-merit are improved because of the markedly reduced relative permittivity. Porous ferroelectric ceramics are very promising materials for a number of applications. 相似文献
62.
A planar triplet of diffraction gratings is used to transform a single laser beam into a four-beam tetrahedral magneto-optical trap. This "flat" pyramid diffractor geometry is ideal for future microfabrication. We demonstrate the technique by trapping and subsequently sub-Doppler cooling (87)Rb atoms to 30 μK. 相似文献
63.
Received May 15, 1995 / Revised version received May 20, 1998 Published online October 21, 1998 相似文献
64.
Erling Størmer 《Positivity》2007,11(1):69-75
We prove a reduction theorem for capacity of positive unital maps of finite dimensional C*−algebras, thus reducing the computation of capacity to the case when the image of a nonscalar projection is never a projection. 相似文献
65.
A semi-analytical method for upscaling two-phase immiscible flows in heterogeneous porous media is described. This method
is developed for stratified reservoirs with perfect communication between layers (the case of vertical equilibrium), in a
viscous dominant regime, where the effects of capillary forces and gravity may be neglected. The method is discussed on the
example of its basic application: waterflooding in petroleum reservoirs. We apply asymptotic analysis to a system of two-dimensional
(2D) mass conservation equations for incompressible fluids. For high anisotropy ratios, the pressure gradient in vertical
direction may be set zero, which is the only assumption of our derivation. In this way, the 2D Buckley–Leverett problem may
be reduced to a one-dimensional problem for a system of quasi-linear hyperbolic equations, of a number equal to the number
of layers in the reservoir. They are solved numerically, based on an upstream finite difference algorithm. Self-similarity
of the solution makes it possible to compute pseudofractional flow functions depending on the average saturation. The computer
partial differential equation solver COMSOL is used for comparison of the complete 2D solutions with averaged 1D simulations.
Cases of both discrete and continuous (log-normal) permeability distribution are studied. Generally, saturation profiles of
the 1D model are only slightly different from the 2D simulation results. Recovery curves and fractional flow curves fit well.
Calculations show that at a favorable mobility ratio (displaced to displacing phase) crossflow increases the recovery, while
at an unfavorable mobility ratio, the effect is the opposite. Compared with the classical Hearn method, our method is more
general and more precise, since it does not assume universal relative permeabilities and piston-like displacement, and it
presumes non-zero exchange between layers. The method generalizes also the study of Yortsos (Transp Porous Media 18:107–129,
1995), taking into account in a more consistent way the interactions between the layers. 相似文献
66.
67.
Maxime Crochemore Lucian Ilie Costas S. Iliopoulos Marcin Kubica Wojciech Rytter Tomasz Waleń 《European Journal of Combinatorics》2013
The Longest Previous Factor array gives, for each position i in a string y, the length of the longest factor (substring) of y that occurs both at i and to the left of i in y. The Longest Previous Factor array is central in many text compression techniques as well as in the most efficient algorithms for detecting motifs and repetitions occurring in a text. Computing the Longest Previous Factor array requires usually the Suffix Array and the Longest Common Prefix array. We give the first time–space optimal algorithm that computes the Longest Previous Factor array, given the Suffix Array and the Longest Common Prefix array. We also give the first linear-time algorithm that computes the permutation that applied to the Longest Common Prefix array produces the Longest Previous Factor array. 相似文献
68.
Over the years, several thermodynamic models for the thermal diffusion factors for binary mixtures have been proposed. The goal of this paper is to test some of these models in combination with different equations of state. We tested the following models: those proposed by Rutherford and Drickamer in 1954, by Dougherty and Drickamer in 1955, by Haase in 1969, by Kempers in 1989 and 2002, and by Shucla and Firoozabadi in 1998. The calculated values of thermal diffusion factors were compared with a few sets of experimental data for hydrocarbon mixtures. For calculation of the partial molar properties we applied different thermodynamic models, such as the Soave-Redlich-Kwong and the Peng-Robinson equations of state. The necessity to try different thermo-dynamic models is caused by the high sensitivity of the thermal diffusion factors to the values of the partial molar properties. Two different corrections for the determination of the partial molar volumes have been implemented; the Peneloux correction and the correction based on the principle of corresponding states. 相似文献
69.
An upscaling method is developed for two-phase immiscible incompressible flows in layered reservoirs with good communication
between the layers. It takes the effect of gravity into consideration. Waterflooding of petroleum reservoirs is used as a
basic example for application of this method. An asymptotic analysis is applied to a system of 2D flow equations for incompressible
fluids at high-anisotropy ratios, but low to moderate gravity ratios, which corresponds to the most often found reservoir
conditions. The 2D Buckley–Leverett problem is reduced to a system of 1D parabolic equations in a layered reservoir. For low-gravity
ratios, it can further be reduced to a system of hyperbolic equations. The number of the 1D equations in the system is equal
to the number of layers in the reservoir. The method is tested on different examples of displacement in a layer-cake reservoir.
Different combinations of gravity-viscous and anisotropy ratios are tested. Solutions by our method are compared with the
results of 2D simulations carried out by the COMSOL solver. The results are comparable, especially if the layers of the reservoirs
are further subdivided into sublayers, in order to account better for gravity segregation. The effects of gravity are analyzed. 相似文献
70.