全文获取类型
收费全文 | 229篇 |
免费 | 3篇 |
专业分类
化学 | 110篇 |
晶体学 | 3篇 |
力学 | 7篇 |
数学 | 26篇 |
物理学 | 86篇 |
出版年
2019年 | 3篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 7篇 |
2012年 | 2篇 |
2011年 | 6篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 4篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1975年 | 2篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1968年 | 4篇 |
1967年 | 2篇 |
1965年 | 2篇 |
1927年 | 2篇 |
1926年 | 4篇 |
排序方式: 共有232条查询结果,搜索用时 15 毫秒
91.
Fritz Haake Felix Izrailev Nils Lehmann Dirk Saher Hans-Jürgen Sommers 《Zeitschrift für Physik B Condensed Matter》1992,88(3):359-370
We present analytical and numerical results for the level density of a certain class of random non-Hermitian matrices =H+i. The conservative partH belongs to the Gaussian orthogonal ensemble while the damping piece is quadratic in Gaussian random numbers and may describe the decay of resonances through various channels. In the limit of a large matrix dimension the level density assumes a surprisingly simple dependence on the relative strength of the damping and the number of channels. Moreover, we identify situations with cubic repulsion between the complex eigenvalues of , to within a logarithmic correction. 相似文献
92.
Pavlovskaya G Blue AK Gibbs SJ Haake M Cros F Malier L Meersmann T 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,137(1):258-264
In recent years, optically pumped xenon-129 has received a great deal of attention as a contrast agent in gas-phase imaging. This report is about the other NMR active xenon isotope (i.e., xenon-131, S = 32) which exhibits distinctive features for imaging applications in material sciences that are not obtainable from xenon-129 (S = (1/2)). The spin dynamics of xenon-131 in gas and liquid phases is largely determined by quadrupolar interactions which depend strongly on the surface of the surrounding materials. This leads to a surface dependent dispersion of relaxation rates, which can be substantial for this isotope. The dephasing of the coherence due to quadrupolar interactions may be used to yield surface specific contrast for imaging. Although optical pumping is not practical for this isotope because of its fast quadrupolar relaxation, a high spin density of liquid xenon close to the critical point (289 K) overcomes the sensitivity problems of xenon-131. We report the first xenon-131 magnetic resonance images and have tested this technique on various meso-porous aerogels as host structures. Aerogels of different densities and changing levels of hydration can clearly be distinguished from the images obtained. 相似文献
93.
We analyze traces of powers of the time evolution operator of a periodically kicked top. Semiclassically, such traces are related to periodic orbits of the classical map. We derive the semiclassical traces in a coherent state basis and show how the periodic orbits can be recovered via a Fourier transform. A breakdown of the stationary phase approximation is detected. The quasi energy spectrum remains elusive due to lack of knowledge of sufficiently many periodic orbits. Divergencies of periodic orbit formulas are avoided by appealing to the finiteness of the quantum mechanical Hilbert space. The traces also enter the coefficients of the characteristic polynominal of the Floquet operator. Statistical properties of these coefficients give rise to a new criterion for the distinction of chaos and regular motion. 相似文献
94.
95.
96.
97.
98.
The atomic magnetic susceptibility χA of homogeneous β-phases of Co?Al and Co?Ga has been measured in the temperature range from 10 to 300°K. Below 50 at.% Co, χA can be described adequately by a Curie law, and for higher Co concentrations a Curie-Weiss law is obeyed. The results are interpreted in terms of a defect structure based on the antistructure cobalt concentration. This treatment is shown to be superior to previous models in that it is now possible to treat the whole range of homogeneous β-phase alloys with a single model. The relationship between the effective magneton number and the Co antistructure atom concentration is linear for both the Co?Al and Co?Ga β-phase above the stoichiometric ratio of Co. 相似文献
99.
100.
Toennes SW Schneider K Kauert GF Wunder C Moeller MR Theunissen EL Ramaekers JG 《Analytical and bioanalytical chemistry》2011,400(1):145-152
Cannabis is not only the most widely used illicit drug worldwide but is also regularly consumed along with ethanol. In previous
studies, it was assumed that cannabis users develop cross-tolerance to ethanol effects. The present study was designed to
compare the effects of ethanol in comparison to and in combination with a cannabis joint and investigate changes in pharmacokinetics.
In this study, 19 heavy cannabis users participated and received three alcohol dosing conditions that were calculated to achieve
steady blood alcohol concentrations (BAC) of about 0, 0.5 and 0.7 g/l during a 5-h time window. Subjects smoked a Δ9-tetrahydrocannabinol (THC) cigarette (400 μg/kg) 3 h post-onset of alcohol dosing. Blood samples were taken between 0 and
4 h after smoking. During the first hour, samples were collected every 15 min and every 30 min thereafter. Mean steady-state
BACs reached 0, 0.36 and 0.5 g/l. The apparent elimination half-life of THC was slightly prolonged (1.59 vs. 1.93 h, p < 0.05) and the concentration 1 h after smoking was slightly lower (24 vs. 17 ng/ml, p < 0.05) with the higher ethanol dose. The prolonged THC elimination might be explained by a small ethanol-mediated change
in distribution to and from deep compartments. Concentrations and pharmacokinetics of 11-hydroxy-THC and 11-nor-9-carboxy-THC
(THCA) were not significantly influenced by ethanol. However, THCA concentrations appeared lower in both ethanol conditions,
which might also be attributable to changes in distribution. Though not significant in the present study, this might be relevant
in the interpretation of cannabinoid concentrations in blood. 相似文献