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61.
Based on a recent loopless mounting method, a simplified
loopless and bufferless crystal mounting method is developed for
macromolecular crystallography. This simplified crystal mounting
system is composed of the following components: a home-made glass
capillary, a brass seat for holding the glass capillary, a flow
regulator, and a vacuum pump for evacuation. Compared with the
currently prevalent loop mounting method, this simplified method has
almost the same mounting procedure and thus is compatible with the
current automated crystal mounting system. The advantages of this
method include higher signal-to-noise ratio, more accurate
measurement, more rapid flash cooling, less x-ray absorption
and thus less radiation damage to the crystal. This method can be
extended to the flash-freeing of a crystal without or with soaking
it in a lower concentration of cryoprotectant, thus it may be the best
option for data collection in the absence of suitable
cryoprotectant. Therefore, it is suggested that this mounting method
should be further improved and extensively applied to
cryocrystallographic experiments. 相似文献
62.
Ina Heckelmann Zifei Lu Dr. Joseph C. A. Prentice Dr. Florian Auras Dr. Tanya K. Ronson Prof. Dr. Richard H. Friend Prof. Dr. Jonathan R. Nitschke Dr. Sascha Feldmann 《Angewandte Chemie (International ed. in English)》2023,62(12):e202301806
Organic semiconductors are promising for efficient, printable optoelectronics. However, strong excited-state quenching due to uncontrolled aggregation limits their use in devices. We report on the self-assembly of a supramolecular pseudo-cube formed from six perylene diimides (PDIs). The rigid, shape-persistent cage sets the distance and orientation of the PDIs and suppresses intramolecular rotations and vibrations, leading to non-aggregated, monomer-like properties in solution and the solid state, in contrast to the fast fluorescence quenching in the free ligand. The stabilized excited state and electronic purity in the cage enables the observation of delayed fluorescence due to a bright excited multimer, acting as excited-state reservoir in a rare case of benign inter-chromophore interactions in the cage. We show that self-assembly provides a powerful tool for retaining and controlling the electronic properties of chromophores, and to bring molecular electronics devices within reach. 相似文献
63.
This paper observes the parametric excitation on atom chip by measuring the trap loss when applying a parametric modulation. By modulating the current in chip wires, it modulates not only the trap frequency but also the trap position. It shows that the strongest resonance occurs when the modulation frequency equals to the trap frequency. The resonance amplitude increases exponentially with modulation depth. Because the Z-trap is an anharmonic trap, there exists energy selective excitation which would cause parametric cooling. We confirm this effect by observing the temperature of atom cloud dropping. 相似文献
64.
Dave KIELPINSKI 《Frontiers of Physics in China》2008,3(4):365-381
Atomic ions trapped in ultra-high vacuum form an especially well-understood and useful physical system for quantum information
processing. They provide excellent shielding of quantum information from environmental noise, while strong, well-controlled
laser interactions readily provide quantum logic gates. A number of basic quantum information protocols have been demonstrated
with trapped ions. Much current work aims at the construction of large-scale ion-trap quantum computers using complex microfabricated
trap arrays. Several groups are also actively pursuing quantum interfacing of trapped ions with photons.
相似文献
65.
M. Vatasescu F. Masnou-Seeuws 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(2):191-204
The paper contains a time-dependent investigation of the tunneling effect observed in the photoassociation spectrum of Cs2 and attributed to the 0g
-(6s, 6p
3/2) double well. When by photoassociation of two cold cesium atoms a vibrational level of the outer well is populated, tunneling
is an efficient mechanism for transferring the population to the inner well (R < 15a
0), where spontaneous emission may lead to formation of cold molecules in low vibrational levels of the a
3Σ+
u(6s, 6s) electronic state. This tunneling effect is analyzed by wavepackets propagation, first considering the double well potential
alone, and following a packet made by a superposition of states initially located at large distances. Characteristic times
for the vibration dynamics, corresponding to a beating phenomenon between the two wells, to partial “revival” at large distances,
and to maxima in the population localized in the inner well are reported and discussed. Second, we simulate the two-channels
a
3Σ+
u(6s, 6s)↦0g
-(6s, 6p
3/2) photoassociation at detunings around 2.9 cm-1: the inner well can be populated either by the excitation of a vibrational level of the external well (resonant excitation),
or by tuning the photoassociation laser at the energy of the inner well level which displays tunneling (“off-resonance excitation”).
In the first case the photoassociation is efficient, while the tunneling probability is small; in the second, the tunneling
probability is large, so that despite the poor efficiency of the photoassociation process, more population can be transferred
to the inner well. This second choice is shown to be very sensitive to the laser intensity, which could be used to control
the population of the inner well and hence the formation of ultracold molecules in low vibrational levels.
Received 19 April 2002 Published online 1st October 2002
RID="a"
ID="a"e-mail: francoise.masnou@lac.u-psud.fr 相似文献
66.
激光冷却和捕陷中性原子③ 总被引:4,自引:1,他引:3
6 激光冷却和捕陷中性原子技术的应用 前面已经提到,激光冷却和捕获中性原子技术最主要的应用是在精密计量和超冷原子物理两个方面.在精密计量方面最为典型的是可用于原子频标的"原子喷泉"(atomic fountain)技术;而在超冷原子物理方面最为典型的是玻色-爱因斯坦凝聚(Bose-Einstein condensation)和原子波激射器(atom laser)的实现. 相似文献
67.
C. Mennerat-Robilliard L. Guidoni K.I. Petsas P. Verkerk J.-Y. Courtois G. Grynberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(1):33-45
All the bright optical lattices studied so far have been designed to obtain a circularly polarized light at the bottom of
the optical potential wells. This condition minimizes the departure rate of the atoms from the fundamental adiabatic surface
and permits an oscillating regime in a large range of parameters. We present here an experimental study of cesium atoms in
a three-dimensional optical lattice, where the light is linearly polarized at the bottom of the potential wells. Temperature
measurements and pump-probe spectroscopy give similar results for this lattice and for the conventional lin lin lattice (which have circular polarizations at the bottom of the wells) despite the fact that one lattice operates in
the jumping regime and the other in the oscillating regime. We study the behaviour of the two types of lattices in a longitudinal
magnetic field, with particular emphasis on the zero field and strong field regimes. The strong field situation is very simple
because the eigenstates are then almost pure Zeeman substates and the adiabatic and diabatic potential surfaces are identical.
The comparison between the zero-field and the high-field situations shows that the diabatic potentials are more appropriate
to account for experimental observations in the novel lattice.
Received: 9 October 1997 / Accepted: 6 November 1997 相似文献
68.
69.
R. Jung S. Gerlach R. Schumann G. von Oppen U. Eichmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):415-419
We report on the first successful loading of a magneto-optical trap (MOT) with metastable He atoms from a Stark-slower. Thereby,
deceleration of the atoms relies on laser-atom interaction in an inhomogeneous electric field. We show that the results obtained
are comparable with early results from other groups achieved with a Zeeman slower. The Stark slower, which is able to fully
control the final velocity of the atomic He beam, is the first step in achieving complete spin independent kinematic control
based solely on electric fields.
Received 2 October 2002 / Received in final form 20 January 2003 Published online 29 April 2003
RID="a"
ID="a"e-mail: eichmann@mbi-berlin.de 相似文献
70.