全文获取类型
收费全文 | 2060篇 |
免费 | 59篇 |
国内免费 | 22篇 |
专业分类
化学 | 1384篇 |
晶体学 | 10篇 |
力学 | 53篇 |
数学 | 292篇 |
物理学 | 402篇 |
出版年
2022年 | 14篇 |
2021年 | 27篇 |
2020年 | 33篇 |
2019年 | 31篇 |
2018年 | 15篇 |
2017年 | 23篇 |
2016年 | 46篇 |
2015年 | 28篇 |
2014年 | 33篇 |
2013年 | 77篇 |
2012年 | 93篇 |
2011年 | 119篇 |
2010年 | 82篇 |
2009年 | 48篇 |
2008年 | 87篇 |
2007年 | 112篇 |
2006年 | 127篇 |
2005年 | 118篇 |
2004年 | 105篇 |
2003年 | 76篇 |
2002年 | 86篇 |
2001年 | 46篇 |
2000年 | 31篇 |
1999年 | 33篇 |
1998年 | 18篇 |
1997年 | 24篇 |
1996年 | 36篇 |
1995年 | 15篇 |
1994年 | 22篇 |
1993年 | 31篇 |
1992年 | 25篇 |
1991年 | 25篇 |
1990年 | 18篇 |
1988年 | 19篇 |
1987年 | 11篇 |
1986年 | 22篇 |
1985年 | 21篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 25篇 |
1981年 | 25篇 |
1980年 | 19篇 |
1979年 | 30篇 |
1978年 | 32篇 |
1977年 | 31篇 |
1976年 | 26篇 |
1975年 | 14篇 |
1974年 | 17篇 |
1973年 | 26篇 |
1972年 | 11篇 |
排序方式: 共有2141条查询结果,搜索用时 15 毫秒
1.
2.
P. Murzyn C. R. Pidgeon P. J. Phillips J. -P. Wells N. T. Gordon T. Ashley J. H. Jefferson T. M. Burke J. Giess M. Merrick B. N. Murdin C. D. Maxey 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):220
We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τs300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τs is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τs in non-degenerate lightly n-type Hg0.78Cd0.22Te of approximately the same band gap as InSb, and find that τs varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τs, imply that the Elliott–Yafet model dominates in these materials. 相似文献
3.
Direct measurement of fluid velocity gradients at a wall by PIV image processing with stereo reconstruction 总被引:1,自引:0,他引:1
Velocity gradient is typically estimated in Particle Image Velocimetry (PIV) by differentiating a measured velocity field,
which amplifies noise in the measured velocities. If gradients near a boundary are sought, such noise is usually greater than
in bulk fluid, because of small tracer displacement, uncertainty in the effective positions of velocity vectors, intense deformation
of tracer patterns, and laser reflection. We consider here a modified form of the Particle Image Distortion (PID) method todirectly calculate velocity gradients at a fixed wall, and refer it as “PIV/IG” (“Interface Gradiometry”). Results from synthetic
2D PIV images suggest our method achieves higher SNR and accuracy than velocity differentiation. Also, we have developed a
procedure to reconstruct three-dimensional velocity gradient at a fixed wall the two non-zero components from PIV/IG data
obtained in stereo views; these equations simplify considerably thanks to the no-slip condition. Experimental data from the
bottom wall of turbulent open channel flow appear to suffer from a form of pixel locking. As with standard PIV, this underlines
the importance of adequate tracer diameter in the images, sufficient seeding density, and of dynamic range of the camera sensor. 相似文献
4.
An efficient synthesis approach is developed which permits thecalculation of the steady-state frequency response of an assembly whichis comprised of linear components and nonlinear joints. Receptancematrices are used to characterize the linear components, which permitscondensation of the system to just the joint degrees-of-freedom.Furthermore, the calculated nonlinear joint forces are then used tostudy the power flow in the assembly, as well as detailed dynamicbehavior within the components. Integrated into the technique is acontinuation scheme which permits efficient parametric studies. 相似文献
5.
Thomas M. F. Case G. S. Bland J. Herring A. D. F. Stirling W. G. Tixier S. Boni P. Ward R. C. C. Wells M. R. Langridge S. 《Hyperfine Interactions》2002,141(1-4):471-476
Hyperfine Interactions - Multilayers of Ce/Fe and U/Fe were fabricated by sputtering and studied by X-ray diffraction and reflectivity, Mössbauer spectroscopy and polarised neutron... 相似文献
6.
The many facets of linear programming 总被引:1,自引:0,他引:1
Michael J. Todd 《Mathematical Programming》2002,91(3):417-436
We examine the history of linear programming from computational, geometric, and complexity points of view, looking at simplex,
ellipsoid, interior-point, and other methods.
Received: June 22, 2000 / Accepted: April 4, 2001?Published online October 2, 2001 相似文献
7.
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
8.
Todd Rowland 《Complexity》2006,12(2):13-29
We present a network experiment that investigates the computational power of cellular automata on the simplest irregular lattice. One cellular automaton whose apparent complexity increased is Rule 60, the left neighbor Xor operator. It went from being nested to complex. That makes Xor a candidate for universal computational power. We present the evidence in terms of the size of cycle lengths, transients, and size of boolean expressions. © 2006 Wiley Periodicals, Inc. Complexity 12: 13–29, 2006 相似文献
9.
10.
An overview is given on the stepwise learning programmes undertaken to identify the main sources of error associated with the determination of the mandatory organic contaminants in the marine monitoring programmes. Details are given on the preparation and use of LRMs and CRMs to maintain analytical control and quantify the laboratory errors in relation to the measurement of changes in the environment. 相似文献