全文获取类型
收费全文 | 217篇 |
免费 | 6篇 |
国内免费 | 3篇 |
专业分类
化学 | 134篇 |
力学 | 2篇 |
数学 | 15篇 |
物理学 | 75篇 |
出版年
2016年 | 5篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 10篇 |
2011年 | 19篇 |
2010年 | 8篇 |
2009年 | 5篇 |
2008年 | 9篇 |
2007年 | 7篇 |
2006年 | 11篇 |
2005年 | 9篇 |
2004年 | 12篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1995年 | 2篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 4篇 |
1968年 | 2篇 |
1967年 | 1篇 |
1966年 | 3篇 |
1955年 | 1篇 |
1937年 | 1篇 |
1932年 | 1篇 |
1907年 | 1篇 |
1896年 | 2篇 |
排序方式: 共有226条查询结果,搜索用时 15 毫秒
81.
Sisyphus amplification, familiar from quantum optics, has recently been reported as a mechanism to explain the enhanced quality factor of a classical resonant (tank) circuit coupled to a superconducting flux qubit. Here we present data from a coupled system, comprising a quantum mechanical rf SQUID (flux qubit) reactively monitored by an ultrahigh quality factor noise driven rf resonator and excited by microwaves. The system exhibits enhancement of the tank-circuit resonance, bringing it significantly closer (within 1%) to the lasing limit, than previously reported results. 相似文献
82.
The distribution of solute arrival times, W(t;x), at position x in disordered porous media does not generally follow Gaussian statistics. A previous publication determined W(t;x) in the absence of diffusion from a synthesis of critical path, percolation scaling, and cluster statistics of percolation.
In that publication, W(t;x) as obtained from theory, was compared with simulations in the particular case of advective solute transport through a two-dimensional
model porous medium at the percolation threshold for various lengths x. The simulations also did not include the effects of diffusion. Our prediction was apparently verified. In the current work
we present numerical results related to moments of W(x;t), the spatial solute distribution at arbitrary time, and extend the theory to consider effects of molecular diffusion in
an asymptotic sense for large Peclet numbers, Pe. However, results for the scaling of the dispersion coefficient in the range 1<Pe<100 agree with those of other authors, while results for the dispersivity as a function of spatial scale also appear to explain
experiment. 相似文献
83.
Skinner TE Kobzar K Luy B Bendall MR Bermel W Khaneja N Glaser SJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,179(2):241-249
An optimal control algorithm for generating purely phase-modulated pulses is derived. The methodology is applied to obtain broadband excitation with unprecedented tolerance to RF inhomogeneity. Design criteria were transformation of Iz-->Ix over resonance offsets of +/-25 kHz for constant RF amplitude anywhere in the range 10-20 kHz, with a pulse length of 1 ms. Simulations transform Iz to greater than 0.99 Ix over the targetted ranges of resonance offset and RF variability. Phase deviations in the final magnetization are less than 2-3 degrees over almost the entire range, with sporadic deviations of 6-9 degrees at a few offsets for the lowest RF (10 kHz) in the optimized range. Experimental performance of the new pulse is in excellent agreement with the simulations, and the robustness of the excitation pulse and a derived refocusing pulse are demonstrated by insertion into conventional HSQC and HMBC-type experiments. 相似文献
84.
Wandering is a typical feature of wing-tip vortices and it consists in random fluctuations of the vortex core. Consequently, vortices
measured by static measuring techniques appear to be more diffuse than in reality, so that a correction method is needed.
In the present paper statistical simulations of the wandering of a Lamb-Oseen vortex are first performed by representing the
vortex core locations through bi-variate normal probability density functions. It is found that wandering amplitudes smaller
than 60% of the core radius are well predicted by using the ratio between the RMS value of the mean cross-velocity and its
slope measured at the mean vortex center. Furthermore, the principal axes of wandering can be accurately evaluated from the
opposite of the cross-correlation coefficient between the spanwise and the normal velocities measured at the mean vortex center.
The correction of the wandering smoothing effects is then carried out through four different algorithms that perform the deconvolution
of the mean velocity field with the probability density function that represents the wandering. The corrections performed
are very accurate for the simulations with wandering amplitudes smaller than 60% of the core radius, whereas errors become
larger with increasing wandering amplitudes. Subsequently, the whole procedure to evaluate wandering and to correct the mean
velocity field is applied to static measurements, carried out with a fast-response five-hole pressure probe, of a tip vortex
generated from a NACA 0012 half-wing model. It is found that the wandering is predominantly in the upward-outboard to downward-inboard
direction. Furthermore, the wandering amplitude grows with increasing streamwise distance from the wing, whereas it decreases
with increasing angle of attack and free-stream velocity. 相似文献
85.
86.
87.
88.
The influence of the tin octanoate catalyst on the physical and thermal properties of RTV 5370 polysiloxane rubbers has been studied. To assess the likely influence of crosslinking on a number of physical and thermal properties in polysiloxanes, “model siloxane networks” (representing networks of well defined composition/structure) have been formulated by the hydrosilylation of polysiloxane diols of known average molecular weight with tetraethoxysilane curing agent. It was found that linear swell and the crystallisation melting transitions of these systems were both significantly affected by changes in crosslink density. A selection of RTV5370 foamed rubbers with different tin concentrations were prepared in a similar manner to assess the influence of the tin catalyst. For these materials it was found that the area of the crystalline melting transition decreased with increasing tin concentration, an effect indicative of increased crosslinking. Samples with double the standard amount of tin (10% wt catalyst) show a shift in the crystallisation transition to higher temperature with no further effect beyond this concentration. Furthermore, the storage modulus (E') of the rubbers at room temperature appears to be independent of the tin catalyst concentration. Through correlation with the data from the model siloxanes, these results suggests that increasing the catalyst concentration appears to induce additional crosslinking interactions that are stable at low temperatures but not stable at room temperature. 相似文献
89.
90.