全文获取类型
收费全文 | 576篇 |
免费 | 16篇 |
国内免费 | 14篇 |
专业分类
化学 | 131篇 |
晶体学 | 4篇 |
力学 | 5篇 |
综合类 | 6篇 |
数学 | 61篇 |
物理学 | 399篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 10篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 23篇 |
2013年 | 43篇 |
2012年 | 14篇 |
2011年 | 38篇 |
2010年 | 31篇 |
2009年 | 41篇 |
2008年 | 51篇 |
2007年 | 58篇 |
2006年 | 29篇 |
2005年 | 17篇 |
2004年 | 14篇 |
2003年 | 33篇 |
2002年 | 27篇 |
2001年 | 31篇 |
2000年 | 20篇 |
1999年 | 13篇 |
1998年 | 15篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
排序方式: 共有606条查询结果,搜索用时 15 毫秒
541.
Francesca Caramia Ada Francia Caterina Mainero Emanuele Tinelli Maria Giuseppina Palmieri Claudio Colonnese Luigi Bozzao Maria Donatella Caramia 《Magnetic resonance imaging》2009
Functional magnetic resonance imaging (fMRI) research has shown that brain arteriovenous malformations (AVMs) lead to reorganization of cortical motor areas. Since it is known that blood oxygenation level-dependent signal in fMRI may be influenced by the hemodynamic perturbation associated with the presence of the AVM, in the present study, a combined exploration with fMRI and transcranial magnetic stimulation was performed in a patient with a right rolandic AVM in order to explore the relationship between neuronal and hemodynamic activity. The combined protocol of investigation adopted in this study was able to provide significant information regarding neuronal activity of the different cortical areas that partake to post-lesional reorganization. 相似文献
542.
Computer simulations have played a critical role in functional magnetic resonance imaging (fMRI) research, notably in the validation of new data analysis methods. Many approaches have been used to generate fMRI simulations, but there is currently no generic framework to assess how realistic each one of these approaches may be. In this article, a statistical technique called parametric bootstrap was used to generate a simulation database that mimicked the parameters found in a real database, which comprised 40 subjects and five tasks. The simulations were evaluated by comparing the distributions of a battery of statistical measures between the real and simulated databases. Two popular simulation models were evaluated for the first time by applying the bootstrap framework. The first model was an additive mixture of multiple components and the second one implemented a non-linear motion process. In both models, the simulated components included the following brain dynamics: a baseline, physiological noise, neural activation and random noise. These models were found to successfully reproduce the relative variance of the components and the temporal autocorrelation of the fMRI time series. By contrast, the level of spatial autocorrelation was found to be drastically low using the additive model. Interestingly, the motion process in the second model intrisically generated some slow time drifts and increased the level of spatial autocorrelations. These experiments demonstrated that the bootstrap framework is a powerful new tool that can pinpoint the respective strengths and limitations of simulation models. 相似文献
543.
544.
Sharon Gustard Jalal Fadili Emma J. Williams Laurance D. Hall T. Adrian Carpenter Matthew Brett Edward T. Bullmore 《Magnetic resonance imaging》2001,19(10):389-1331
The effect of slice orientation on reproducibility and sensitivity of 3T fMRI activation using a motor task has been investigated in six normal volunteers. Four slice orientations were used; axial, oblique axial, coronal and sagittal. We applied analysis of variance (ANOVA) to suprathreshold voxel statistics to quantify variability in activation between orientations and between subjects. We also assessed signal detection accuracy in voxels across the whole brain by using a finite mixture model to fit receiver operating characteristic (ROC) curves to the data. Preliminary findings suggest that suprathreshold cluster characteristics demonstrate high motor reproducibility across subjects and orientations, although a significant difference between slice orientations in number of activated voxels was demonstrated in left motor cortex but not cerebellum. Subtle inter-orientation differences are highlighted in the ROC analyses, which are not obvious by ANOVA; the oblique axial slice orientation offers the highest signal detection accuracy, whereas coronal slices give the lowest. 相似文献
545.
M. Deserno 《The European physical journal. E, Soft matter》2001,6(2):163-168
The classical instability of a charged spherical droplet is reconsidered in the presence of counterions. An ensemble of such
droplets is studied within a simplified cell model. Screening of the electric field by the counterions is found to increase
the equilibrium droplet size. Furthermore, if the ions can enter the droplet, a first-order phase transition occurs upon increasing
Bjerrum length, surface tension or droplet density, leading to a phase separation. Simple scaling properties of the free energy
give the shape of the phase boundary and show the system to be scale-invariant there. Pearl-necklace structures of hydrophobic
polyelectrolytes are discussed as an application.
Received 30 August 2001 相似文献
546.
A. Benfredj D. Gamra S. Romdhane T. Barhoumi C. Guthmann J.L. Monge H. Bouchriha 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):385-391
The effect of a magnetic field (6 kG) on the delayed fluorescence in a 1,4-Dibromonaphtalene at 300 K and 20 K is analysed
using a new approach of calculation of the triplet-triplet annihilation rate constant. The agreement of the best fit between
experiment and theory allows reaching at 300 K and 20 K respectively the lifetimes and the interaction constant of the triplets
pairs.
Received 12 March 1999 and Received in final form 27 April 2000 相似文献
547.
M.-P. Gorza S. Saltiel H. Failache M. Ducloy 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):113-126
A theory of van der Waals (vdW) interaction between an atom (in ground or excited state) and a birefringent dielectric surface
with an arbitrary orientation of the principal optic axis (C-axis) is presented. Our theoretical approach is based on quantum-mechanical linear response theory, using generalized susceptibilities
for both atom and electromagnetic field. Resonant atom-surface coupling is predicted for excited-state atoms interacting with
a dispersive dielectric surface, when an atom de-excitation channel gets into resonance with a surface polariton mode. In
the non-retarded regime, this resonant coupling can lead to enhanced attractive or repulsive vdW surface forces, as well as
to a dissipative coupling increasing the excited-state relaxation. We show that the strongly non-scalar character of the interaction
with the birefringent surface produces a C-axis-dependent symmetry-breaking of the atomic wavefunction. Changes of the C-axis orientation may also lead to a frequency shift of the surface polariton mode, allowing for tuning on or off the resonant coupling, resulting in a special type of engineering of surface forces. This is analysed here in the case of
cesium 6D
3/2 level interacting with a sapphire interface, where it is shown that an adequate choice of the sapphire C-axis orientation allows one to transform vdW surface attraction into repulsion, and to interpret recent experimental observations
based on selective reflection methods [H. Failache etal., Phys. Rev. Lett. 83, 5467 (1999)].
Received 24 January 2001 相似文献
548.
549.
A.S. Leal D. Kröner L. González 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):185-190
The selective preparation of an enantiomer starting from a pure state of H2POSH representing a 50%:50% mixture of two enantiomers with opposite chiralities is extended to its deuterated counterpart,
H2POSD. A one-dimensional model involving the torsional angle of S-H/D around a pre-oriented P-S axis is used. The design of
an appropriate sequence of ultrashort infrared laser pulses to achieve molecular handedness for H2POSH/D is based on the characteristic level splitting and tunneling times of both molecules. A simple scheme of two linearly
polarized laser pulses involving a three level system serves to convert the different isotopomers to opposite enantiomers,
for any given mixture of H2POSH and H2POSD molecules.
Received 31 August 2000 and Received in final form 23 November 2000 相似文献
550.
T.A. Beu J. Onoe K. Takeuchi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):205-212
Non-orthogonal tight-binding molecular-dynamics is employed to calculate structural and vibrational properties of C36 and its oligomers (C36)
M = 2, 3, 4
. The lowest energy configuration of the C
36
cage is confirmed to have D
6h
symmetry. For the dimer, too, the D
2h
structure reported in the literature is found. The vibrational spectrum is identified with the power spectrum of the displacement
autocorrelation function. Additional vibrational properties are extracted from the dynamical matrix. For the monomer, fair
agreement with available ab initio calculations is achieved, with comparatively smaller deviations in the Raman-frequencies than for published semi-empirical
calculations. The features of the vibrational modes are correlated with the structural properties of the oligomers.
Received 24 November 2000 and Received in final form 24 August 2001 相似文献