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881.
A. Szolnoki M. Perc 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(3):337-344
We study the evolution of cooperation in structured populations within popular models of social dilemmas, whereby simple coevolutionary
rules are introduced that may enhance players abilities to enforce their strategy on the opponent. Coevolution thus here refers
to an evolutionary process affecting the teaching activity of players that accompanies the evolution of their strategies.
Particularly, we increase the teaching activity of a player after it has successfully reproduced, yet we do so depending on
the disseminated strategy. We separately consider coevolution affecting either only the cooperators or only the defectors,
and show that both options promote cooperation irrespective of the applied game. Opposite to intuitive reasoning, however,
we reveal that the coevolutionary promotion of players spreading defection is, in the long run, more beneficial for cooperation
than the likewise promotion of cooperators. We explain the contradictive impact of the two considered coevolutionary rules
by examining the differences between resulting heterogeneities that segregate participating players, and furthermore, demonstrate
that the influential individuals completely determine the final outcome of the games. Our findings are immune to changes defining
the type of considered social dilemmas and highlight that the heterogeneity of players, resulting in a positive feedback mechanism,
is a fundamental property promoting cooperation in groups of selfish individuals. 相似文献
882.
F. Schweitzer L. Behera 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(3):301-318
In nonlinear voter models the transitions between two states depend in a nonlinear manner on the frequencies of these states
in the neighborhood. We investigate the role of these nonlinearities on the global outcome of the dynamics for a homogeneous
network where each node is connected to m = 4 neighbors. The paper unfolds in two directions. We first develop a general stochastic
framework for frequency dependent processes from which we derive the macroscopic dynamics for key variables, such as global
frequencies and correlations. Explicit expressions for both the mean-field limit and the pair approximation are obtained.
We then apply these equations to determine a phase diagram in the parameter space that distinguishes between different dynamic
regimes. The pair approximation allows us to identify three regimes for nonlinear voter models: (i) complete invasion; (ii)
random coexistence; and – most interestingly – (iii) correlated coexistence. These findings are contrasted with predictions
from the mean-field phase diagram and are confirmed by extensive computer simulations of the microscopic dynamics. 相似文献
883.
S. M. Ikhdair 《The European Physical Journal A - Hadrons and Nuclei》2009,40(2):143-149
We study the effect of spatially dependent mass functions over the solution of the Klein-Gordon equation in the (3 + 1 -dimensions
for spinless bosonic particles where the mixed scalar-vector Coulomb-like field potentials and masses are directly proportional
and inversely proportional to the distance from the force center. The exact bound-state energy eigenvalues and the corresponding
wave functions of the Klein-Gordon equation for mixed scalar-vector and pure scalar Coulomb-like field potentials are obtained
by means of the Nikiforov-Uvarov (NU) method. The energy spectrum is discussed for different scalar-vector potential mixing
cases and also for the constant-mass case. 相似文献
884.
Sayan K. Chakrabarti Pulak Ranjan Giri Kumar S. Gupta 《The European Physical Journal C - Particles and Fields》2009,60(2):169-173
We analyze the possibility of inequivalent boundary conditions for a scalar field propagating in the BTZ black-hole space-time.
We find that for certain ranges of the black-hole parameters, the Klein–Gordon operator admits a one-parameter family of self-adjoint
extensions. For this range, the BTZ space-time is not quantum mechanically complete. We suggest a physically motivated method
for determining the spectra of the Klein–Gordon operator. 相似文献
885.
Choon-Lin Ho 《Annals of Physics》2009,324(5):1095-1104
The four exactly solvable models related to non-sinusoidal coordinates, namely, the Coulomb, Eckart, Rosen-Morse type I and II models are normally being treated separately, despite the similarity of the functional forms of the potentials, their eigenvalues and eigenfunctions. Based on an extension of the prepotential approach to exactly and quasi-exactly solvable models proposed previously, we show how these models can be derived and solved in a simple and unified way. 相似文献
886.
A Bose-Einstein condensate will evolve almost adiabatically if the number of atoms is large enough, even though the trap parameters may be changing rapidly. We demonstrate this by examining a Bose-Einstein condensate in a two-dimensional rapidly contracting circular box. We show that as a result of the contraction the condensate will oscillate about the instantaneous ground state. These oscillations will be small though when the number of atoms is large. Approximate analytic expressions are found for the evolving condensate wavefunction, both before and after the contraction has begun. 相似文献
887.
Zhenya Yan 《Physics letters. A》2009,373(29):2432-2437
The three-dimensional extended quantum Zakharov-Kuznetsov (ZK) equation was investigated in dense quantum plasmas which arises from the dimensionless hydrodynamics equations describing the nonlinear propagation of the quantum ion-acoustic waves. With the aid of symbolic computation, many types of new analytical solutions of the extended quantum ZK equation are constructed in terms of some powerful ansatze, which include new doubly periodic wave, solitary wave, shock wave, rational wave, and singular wave solutions. Moreover, we analyze the nonlinear wave propagation of the obtained solutions for some chosen parameters. 相似文献
888.
An evolutionary snowdrift game (SG) that incorporates bounded rationality and limited information in the evolutionary process is proposed and studied. Based on SG in a well-mixed population and defining the winning action at a turn to be the one that gets a higher payoff, the most recent m winning actions can be used as a public information based on which the competing agents decide their next actions. This defines a strategy pool from which each agent picks a number of strategies as their tool in adapting to the competing environment. The payoff parameter r in SG serves to set the maximum number of winners per turn. Due to the bounded rationality and limited information, the cooperative frequency shows steps and plateaux as a function of r and these features tend to be smoothed out as m increases. These features are results of an interplay between a restricted subset of m-bit histories that the system can visit at a value of r and the limited capacity that agents can adapt. The standard deviation in the number of agents taking the cooperative action is also studied. For general values of r, our model generates a realization of the binary-agent-resource model. The idea of introducing bounded rationality into a two-person game to realize the minority game or binary-agent-resource model could be a useful tool for future research. 相似文献
889.
A large sample study of spin relaxation and magnetometric sensitivity of paraffin-coated Cs vapor cells 总被引:1,自引:0,他引:1
N. Castagna G. Bison G. Di Domenico A. Hofer P. Knowles C. Macchione H. Saudan A. Weis 《Applied physics. B, Lasers and optics》2009,96(4):763-772
We have manufactured more than 250 nominally identical paraffin-coated Cs vapor cells (28 mm inner diameter bulbs) for multi-channel
atomic magnetometer applications. We describe our dedicated cell characterization apparatus. For each cell we have determined
the intrinsic longitudinal, Γ
01, and transverse, Γ
02, relaxation rates. Our best cell shows Γ
01/2π≈0.5 Hz, and Γ
02/2π≈2 Hz. We find a strong correlation of both relaxation rates which we explain in terms of reservoir and spin exchange relaxation.
For each cell we have determined the optimal combination of rf and laser powers which yield the highest sensitivity to magnetic
field changes. Out of all produced cells, 90% are found to have magnetometric sensitivities in the range of 9 to 30 fT
. Noise analysis shows that the magnetometers operated with such cells have a sensitivity close to the fundamental photon
shot noise limit. 相似文献
890.
分别以硅-二氧化硅和锗-二氧化硅复合靶作为溅射靶,采用磁控溅射技术在p型硅衬底上淀积了含纳米硅的氧化硅薄膜和含纳米锗的氧化硅薄膜.各样品分别在氮气氛中经过300至1100℃不同温度的退火处理.使用高分辨透射电子显微镜可以观察到经900和1100℃退火的含纳米硅的氧化硅薄膜中的纳米硅粒,和经900和1100℃退火的含纳米锗的氧化硅薄膜中的纳米锗粒.经过不同温度退火处理的含纳米硅的氧化硅和含纳米锗的氧化硅薄膜的光致发光谱均具有相似的峰型,且它们的发光峰位均位于580nm(2.1eV)附近.可以认为含纳米硅的氧化硅和含纳米锗的氧化硅薄膜的光发射主要来自于SiO2层中发光中心上的复合发光,对实验结果进行了合理的解释 相似文献