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391.
392.
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394.
Determination of the helium-4 mass in a Penning trap 总被引:2,自引:0,他引:2
S. Brunner T. Engel A. Schmitt G. Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(2):181-188
The determination of the rotational quadrupole alignment of diatomic molecules via REMPI detection is investigated. In this process a high focal intensity usually increases the detection probability. At high
intensities the AC Stark effect may cause a splitting of the normally degenerate mJ sublevels of a rotational state J beyond the spectral width of the exciting radiation. This leads to a selective detection of only certain mJ states with the consequence that deduced alignment factors can be misleading. From the theoretical considerations line profiles
are explicitly calculated for dynamic polarizabilities which represent the B
1Σ+
u←X
1Σ+
g transition of H2, in order to fit an experimental (3+1) REMPI spectrum and to predict (1+1') line shapes as a function of laser intensity.
It is further shown that the deduced quadrupole alignment factor
A
0
(2) is significantly changed by the second order AC Stark effect when the intensities are chosen high enough to observe asymmetric
broadened line profiles. Different combinations of relative linear polarizations of the exciting and ionizing laser beams
are discussed.
Received 1st August 2000 and Received in final form 2 May 2001 相似文献
395.
T.J. Davis 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):289-297
The problem of atom diffraction from a reflecting magnetic diffraction grating is solved in the thin phase-grating approximation.
The general problem for scalar diffraction is modelled using a semi-classical method in which the grating potential is separated
into a reflecting term and a diffracting term. The trajectory of the atom in the reflecting potential is solved classically
and the atom wave function in the diffracting potential found by integrating the phase change along the classical trajectory.
The diffraction orders are obtained after Fourier transforming the result. This can be done independently of the grating potential
resulting in a general formula for the diffraction efficiencies. The general result is applied to the problem of atom diffraction
from a magnetic grating. Several approximations are required to reduce the problem to a form amenable to analytic solution.
The results are compared with an accurate numerical method.
Received 1st February 2001 and Received in final form 8 March 2001 相似文献
396.
G. Fuhr B. Ronacher R. Krahe S. Fest S.G. Shirley S. Rogaschewski 《Applied Physics A: Materials Science & Processing》1999,68(4):379-385
Locusta migratoria L. ). The handling of living insects, the survival, and physiological response after treatment are described. We selectively
interrupted the d-receptor of the tympanal organ, which is the receptor system responsible for the locust’s sensitivity in
the high-frequency range (>10 kHz). The effects of the laser treatment were tested by determining hearing thresholds in electrophysiological
recordings from the tympanal nerves. In agreement with the literature, the interruption of the d-receptors led to a significant
shift towards higher values of the thresholds in the high-frequency range. Future perspectives and biological applications
of UV-laser ablation are discussed.
Received: 10 Dezember 1998 / Accepted: 15 December 1998 / Published online: 24 February 1999 相似文献
397.
Photomechanical damage in absorbing regions or particles surrounded by a non-absorbing medium is investigated experimentally
and theoretically. The damage mechanism is based on the generation of thermoelastic pressure by absorption of pulsed laser
radiation under conditions of stress confinement. Principles of photoacoustic sound generation predict that the acoustic wave
generated in a finite-size absorbing region must contain both compressive and tensile stresses. Time-resolved imaging experiments
were performed to examine whether the tensile stress causes cavitation in absorbers of spherical or cylindrical shape. The
samples were absorbing water droplets and gelatin cylinders suspended in oil. They were irradiated with 6-ns-long pulses from
an optical parametric oscillator. Photoacoustic cavitation was observed near the center of the absorbers, even if the estimated
temperature caused by absorption of the laser pulse did not exceed the boiling point. The experimental findings are supported
by theoretical simulations that reveal strong tensile stress in the interior of the absorbers, near the center of symmetry.
Tensile stress amplitudes depend on the shape of the absorber, the laser pulse duration, and the ratio of absorber size to
optical absorption length. The photoacoustic damage mechanism has implications for the interaction of ns and sub-nslaser pulses
with pigmented structures in biological tissue.
Received: 9 October 1998 / Accepted: 5 January 1999 / Published online: 31 March 1999 相似文献
398.
F. Lison D. Haubrich P. Schuh D. Meschede 《Applied physics. B, Lasers and optics》1999,69(5-6):501-504
We have demonstrated the partly directed reflection of a slow cesium atomic beam by using the natural magnetic stray field
above a Nd-Fe-B surface. From these experiments we determine the reflectivity and a minimum value for the magnetic stray field
directly at the surface.
Received: 5 July 1999 / Revised version: 6 October 1999 / Published online: 3 November 1999 相似文献
399.
J.H. Thywissen M. Olshanii G. Zabow M. Drndić K.S. Johnson R.M. Westervelt M. Prentiss 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(3):361-367
We describe how tightly confining magnetic waveguides for atoms can be created with microfabricated or nanofabricated wires.
Rubidium atoms guided in the devices we have fabricated would have a transverse mode energy spacing of K. We discuss the creation of a single-mode waveguide for atom interferometry whose depth is comparable to magneto-optical
trap (MOT) temperatures. We also discuss the application of microfabricated waveguides to low-dimensional systems of quantum
degenerate gases, and show that confinement can be strong enough to observe fermionization in a strongly interacting bosonic
ensemble.
Received 1st December 1998 and Received in final form 23 February 1999 相似文献
400.
Manipulation of cold atoms by an adaptable magnetic reflector 总被引:1,自引:0,他引:1
P. Rosenbusch B.V. Hall I.G. Hughes C.V. Saba E.A. Hinds 《Applied physics. B, Lasers and optics》2000,70(5):709-720
Adaptive optics for cold atoms has been experimentally realized by applying a bias magnetic field to a static magnetic mirror.
The mirror consist of a 12-mm-diameter piece of commercial videotape, having a sine wave of wavelength 25.4 μm recorded in
a single track across its width, curved to form a concave reflector with radius of curvature R=54 mm. We have studied the
performance of the mirror by monitoring the evolution of a 24 μK cloud of 85Rb atoms bouncing on it. A uniform static external magnetic field was added to the mirror field causing a corrugated potential
from which the atoms bounce with increased angular spread. The characteristic angular distribution of the surface normal is
mapped at the peak of the bounce for atoms dropped from a height of R/2 and at the peak of the second bounce for a drop height
of R/4. In a second experiment a time-dependent magnetic field was applied and the angular distribution of the cloud was measured
as a function of field frequency. In this scheme we demonstrate a corrugated potential whose time-dependent magnitude behaves
like a diffraction grating of variable depth. Finally a rotating field was added to generate a corrugated potential that moves
with a velocity given by the product of the external field rotation frequency and the videotape wavelength. This travelling
grating provides a new method of manipulation as cold atoms are transported across the surface by surfing along the moving
wave. Two theoretical methods have been developed to predict the behaviour of atoms reflecting from these stationary, variable
magnitude and moving corrugated potentials. A simple analytic theory provides excellent agreement for reflection from a stationary
corrugated potential and gives good agreement when extended to the case of a travelling grating. A Monte Carlo simulation
was also performed by brute force numeric integration of the equations of motion for atoms reflecting from all three corrugated
potential cases.
Received: 1 December 1999 / Revised version: 3 February 2000 / Published online: 5 April 2000 相似文献