全文获取类型
收费全文 | 1318篇 |
免费 | 41篇 |
国内免费 | 6篇 |
专业分类
化学 | 888篇 |
晶体学 | 9篇 |
力学 | 25篇 |
数学 | 126篇 |
物理学 | 317篇 |
出版年
2023年 | 8篇 |
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 15篇 |
2019年 | 31篇 |
2018年 | 15篇 |
2017年 | 14篇 |
2016年 | 33篇 |
2015年 | 24篇 |
2014年 | 29篇 |
2013年 | 57篇 |
2012年 | 76篇 |
2011年 | 101篇 |
2010年 | 46篇 |
2009年 | 33篇 |
2008年 | 68篇 |
2007年 | 65篇 |
2006年 | 85篇 |
2005年 | 82篇 |
2004年 | 71篇 |
2003年 | 58篇 |
2002年 | 78篇 |
2001年 | 42篇 |
2000年 | 25篇 |
1999年 | 17篇 |
1998年 | 9篇 |
1997年 | 16篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 16篇 |
1992年 | 16篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 11篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1976年 | 12篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1969年 | 6篇 |
排序方式: 共有1365条查询结果,搜索用时 15 毫秒
61.
62.
Meyer BS 《Physical review letters》2002,89(23):231101
Matter expanding sufficiently rapidly and at high enough entropy per nucleon can enter a heavy-element synthesis regime heretofore unexplored. In this extreme regime, more similar to nucleosynthesis in the early universe than to that typical in stellar explosive environments, there is a persistent disequilibrium between free nucleons and abundant alpha particles, which allows heavy r-process nucleus production even in matter with more protons than neutrons. This observation bears on the issue of the site of the r process, on the variability of abundance yields from r-process events, and on constraints on neutrino physics derived from nucleosynthesis. 相似文献
63.
64.
T-ray computed tomography 总被引:6,自引:0,他引:6
We demonstrate a tomographic imaging modality that uses pulsed terahertz (THz) radiation to probe the optical properties of three-dimensional (3D) structures in the far-infrared. This THz-wave computed tomography (T-ray CT) system provides sectional images of objects in a manner analogous to conventional CT techniques such as x-ray CT. The transmitted amplitude and phase of broadband pulses of THz radiation are measured at multiple projection angles. The filtered backprojection algorithm is then used to reconstruct the target object, including both its 3D structure and its frequency-dependent far-infrared optical properties. 相似文献
65.
Roth BJ 《Chaos (Woodbury, N.Y.)》2002,12(3):973-981
Insidious experimental artifacts and invalid theoretical assumptions complicate the comparison of numerical predictions and observed data. Such difficulties are particularly troublesome when studying electrical stimulation of the heart. During unipolar stimulation of cardiac tissue, the artifacts include nonlinearity of membrane dyes, optical signals blocked by the stimulating electrode, averaging of optical signals with depth, lateral averaging of optical signals, limitations of the current source, and the use of excitation-contraction uncouplers. The assumptions involve electroporation, membrane models, electrode size, the perfusing bath, incorrect model parameters, the applicability of a continuum model, and tissue damage. Comparisons of theory and experiment during far-field stimulation are limited by many of these same factors, plus artifacts from plunge and epicardial recording electrodes and assumptions about the fiber angle at an insulating boundary. These pitfalls must be overcome in order to understand quantitatively how the heart responds to an electrical stimulus. (c) 2002 American Institute of Physics. 相似文献
66.
67.
M. K. Olsen S. A. Haine A. S. Bradley J. J. Hope 《The European physical journal. Special topics》2008,160(1):331-342
The development of the Raman atom laser promises to make available new techniques for accessing and manipulating the quantum
statistical properties of Bose-Einstein
condensates. In this work we show how, combined with the already existing methods for the manipulation
of quantum states of light which are central to quantum optics, the Raman input-output coupling mechanisms potentially enable
the production of quadrature squeezed and sub-Poissonian atomic beams, and entanglement between atomic and optical fields.
We also propose a method of measuring the quantum statistics of the atomic beam by transferring them to an optical field.
Finally, by combning these techniques, we propose a method of teleporting the atom laser beam from one trapped condensate
to another. 相似文献
68.
Bradley Plohr 《Physics letters. [Part B]》1979,85(4):361-363
For SU(2) gauge fields over the 4-dimensional sphere with a finite number of points x1, x2, ..., and xN removed, there are gauge transformations which modify the topological charge concentrated at xj by adding nj, where n1, n2, …, and nN. are integers such that ΣNj = 1nj = 0. However, the reduction modulo Z of the topological charge at a point is well defined, being given in terms of the secondary characteristic classes of Chern and Simons, except when the topological charge is indeterminate. 相似文献
69.
This paper reports the results of the third part of a field study of human responses to traffic noise. The influence of traffic noise level, community size, and socio-economic status were investigated in a controlled manner determined by subject selection procedures. Human responses were obtained from interviewer administered questionnaires, and were as spatially and temporally coincident with the noise measurements as possible. Noise measurements were obtained from several days of rapidly sampled digital recordings. Traffic noise level was the major predictor of the intensity of elicited responses. A number of other significant effects were observed largely related to community size. These were explained as due to parallel variations in the perceived necessity of vehicles, the annoyance with aircraft noise, and the logarithm of the vehicle flow rate. The results did demonstrate effects related to community size, and thus it is unwise to extrapolate the results of large city noise studies to small communities and rural areas. 相似文献
70.
3 nsec laser pulses, of bandwidth 1.3 nm, are obtained from a 10 J, 600 keV coaxial diode electron-beam pumping arrangement. Uniform pumping, with a well defined cylindrical geometry, facilitates experimental investigation of the laser parameters. Gas heating limits the laser repetition rate. While mirror damage at present limits the peak power to ∽ 1 MW, higher powers seem available. The addition of helium results in a drastic reduction of peak molecular xenon fluorescence. 相似文献