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101.
The energy landscapes of ion clouds confined in isotropic quadrupolar and octupolar traps are characterized for several representative cluster sizes. All clusters exhibit stable multishell structures that belong to separate funnels. Quadrupolar confinement leads to more homogeneous clusters and denser distributions of isomers than octupolar confinement. Statistical analysis of the transition states indicates that the barriers associated with intrashell motion are lower but more asymmetric and more cooperative compared to intershell motion. The relaxation between low-energy funnels with different arrangements of shells mostly exhibits Arrhenius kinetics, with a weak variation of the activation energy at higher temperatures. 相似文献
102.
Geobacillus thermoleovorans subsp stromboliensis, was immobilized on an Amberlite XAD-4 ion exchanger and used as a solid phase extractant for the preconcentration of U(VI) ions prior to their determination by UV-VIS spectrophotometry. Parameters affecting the preconcentration (such as the pH value of the sample solution, the concentration of U(VI), the volume and type of eluent, the flow rate and the effect of potentially interfering ions) were studied. The optimum pH for the sorption of U(VI) was found to be pH 5.0. 5.0?mL of 1 M hydrochloric acid were used to eluate the U(VI) from the column. The loading capacity is 11?mg?g?1. The limits of detection and quantification are 2.7 and 9.0?μg?L?1, respectively, and relative standard deviations are <10?%. The method was applied to the determination of U(VI) in a certified reference sample (NCS ZC-73014; tea leaves) and in natural water samples. Figure
Schematic presentation of SPE procedure using Geobacillus thermoleovorans subsp stromboliensis immobilized on an Amberlite XAD-4 as ion exchanger for preconcentration of U(VI) ions prior to their determination by UV-VIS spectrophotometry 相似文献
103.
Ilker Kucuk Atakan Tekgül Kagan Sarlar Ersin Civan Nil Kucuk Barıs Macan 《哲学杂志》2013,93(21):2736-2750
ABSTRACTLa0.7Ca0.3MnO3 perovskite and its composites with graphene nanoplatelet (GNP) were prepared using a wet chemical method. The structural, magnetic and magnetocaloric properties of La0.7Ca0.3MnO3: GNP composites were investigated to determine the effect of GNPs. The results of XRD analysis show that the synthesised powders can be almost indexed to pure phase orthorhombic La0.7Ca0.3MnO3. The magnetic measurements demonstrate that 0.7 and 1% GNP amounts cause an increase in the Curie temperature (TC), and for larger amounts of GNP, the TC monotonically decreases, except for the sample with 10% GNP. The results obtained from the Arrott plots show that the magnetic phase transition of the samples transforms from the first to second order with increasing GNP amount. The changes in the magnetocaloric properties are interpreted in terms of perovskite phase formations via structural analysis. The amounts of graphene nanoplatelets in the oxide powders are correlated with the observed magnetocaloric properties. The best magnetocaloric performance with the maximum magnetic entropy change of 3.99 Jkg?1K?1 and refrigeration capacity of 90 Jkg?1 was obtained at a 2?T magnetic field. 相似文献
104.
An effective-field theory study of hexagonal Ising nanowire: Thermal and magnetic properties
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By means of the effective-field theory (EFT) with correlations, the thermodynamic and magnetic quantities (such as magnetization, susceptibility, internal energy, specific heat, free energy, hysteresis curves, and compensation behaviors) of the spin-l/2 hexagonal Ising nanowire (HIN) system with core/shell structure have been presented. The hysteresis curves are obtained for different values of the system parameters, in both ferromagnetic and antiferromagnetic cases. It has been shown that the system only undergoes a second-order phase transition. Moreover, from the thermal variations of the total magnetization, the five compensation types can be found under certain conditions, namely the Q-, R-, S-, P-, and N-types. 相似文献
105.
Yurtsever U 《Physical review letters》2003,91(4):041302
I show how the holographic entropy bound can be derived from elementary flat-spacetime quantum field theory when the total energy of Fock states is constrained gravitationally. This energy constraint makes the Fock space dimension (whose logarithm is the maximum entropy) finite for both bosons and fermions. Despite the elementary nature of my analysis, it results in an upper limit on entropy in remarkable agreement with the holographic bound, and also provides a microscopic deviation of a more general entropy bound recently introduced by Gour. 相似文献
106.
107.
F. Calvo E. Yurtsever 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):81-91
Finite-size effects on the static and thermodynamical
properties of small three-dimensional clusters of identical charged
particles confined by an harmonic trap are investigated using global
optimization and numerical simulations. The relative stabilities of
clusters containing up to 100 particles are estimated from the
second energy derivatives, as well as from the energy gap between
the two lowest-energy structures at a given size. We also provide a
lower bound for the number of permutationally independent minima, as
a function of size, up to n=75. Molecular dynamics and exchange
Monte Carlo simulations are performed to get insight into the finite
temperature behaviour of these clusters. By focusing on specific
sizes, we illustrate the interplay between the stable structures,
the possible competition between different isomers, and the melting
point. In particular, we find that the orientational melting
phenomenon known in two-dimensional clusters has an equivalent form
in some three-dimensional clusters. The vibrational spectra,
computed for all sizes up to 100, shows an increasing number of
low-frequency modes, but comparing to hydrodynamical theory reveals
strong correlation effects. Finally, we investigate the effects
of the trap anisotropy on the general shape of Coulomb clusters, and
on the melting point of a selected case. 相似文献
108.
109.
Bodo E Sebastianelli F Gianturco FA Yurtsever E Yurtsever M 《The Journal of chemical physics》2004,120(19):9160-9166
The potential energy surface (PES) for the interaction between Li2(1Sigmag+) and 4He has been computed using an accurate, post-Hartree-Fock quantum calculation for its ground electronic state. The orientational anisotropy of the forces and the interplay between repulsive and attractive effects within the PES are analyzed to extract information on the possible existence of bound states in the triatomic system. The structures of a few of the Li2(He)n small clusters are examined by comparing a classical approach with a full quantum one to generate bound configurations and to extract information on the possible spatial arrangements of the smaller clusters via à vis the location of the Li2 dopant. Some significant consequences on the Li2 behavior in larger clusters and droplets are drawn from the above findings. 相似文献
110.