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31.
P. H. Chavanis 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(3):413-433
We discuss the distribution of the gravitational force
created by a Poissonian distribution of field sources (stars,
galaxies,...) in different dimensions of space d. In d = 3, when
the particle number N →+∞, it is given by a Lévy
law called the Holtsmark distribution. It presents an algebraic
tail for large fluctuations due to the contribution of the nearest
neighbor. In d = 2, for large but finite values of N, it is given
by a marginal Gaussian distribution intermediate between Gaussian
and Lévy laws. It presents a Gaussian core and an algebraic
tail. In d = 1, it is exactly given by the Bernouilli distribution
(for any particle number N) which becomes Gaussian for N ≫
1. Therefore, the dimension d = 2 is critical regarding the
statistics of the gravitational force. We generalize these results
for inhomogeneous systems with arbitrary power-law density profile
and arbitrary power-law force in a d-dimensional universe. 相似文献
32.
Tobias Frank Johannes CM Schlachetzki Bettina G?ricke Katrin Meuer Gundula Rohde Gunnar PH Dietz Mathias B?hr Armin Schneider Jochen H Weishaupt 《BMC neuroscience》2009,10(1):49-10
Background
The hematopoietic Granulocyte-Colony Stimulating Factor (G-CSF) plays a crucial role in controlling the number of neutrophil progenitor cells. Its function is mediated via the G-CSF receptor, which was recently found to be expressed also in the central nervous system. In addition, G-CSF provided neuroprotection in models of neuronal cell death. Here we used the retinal ganglion cell (RGC) axotomy model to compare effects of local and systemic application of neuroprotective molecules. 相似文献33.
Monchaux R Cortet PP Chavanis PH Chiffaudel A Daviaud F Diribarne P Dubrulle B 《Physical review letters》2008,101(17):174502
We experimentally characterize the fluctuations of the nonhomogeneous nonisotropic turbulence in an axisymmetric von Kármán flow. We show that these fluctuations satisfy relations, issued from the Euler equation, which are analogous to classical fluctuation-dissipation relations in statistical mechanics. We use these relations to estimate statistical temperatures of turbulence. 相似文献
34.
Bare G. Jacques PH. Hubert J. B. Rikir R. Thonart PH. 《Applied biochemistry and biotechnology》1991,28(1):445-456
Applied Biochemistry and Biotechnology - The ability of the yeastSaccharomyces cerevisiae to bioconvert stereo-selectively octyl-4-chloroacetoacetate (OCA) into the corresponding chiral alcohol,... 相似文献
35.
J. Bystricky P. Chaumette J. Deregel J. Fabre F. Lehar A. De Lesquen L. Van Rossum J.M. Fontaine J. Gosset F. Perrot C.A. Whitten J. Ball PH. Chesny C.R. Newsom J. Yonnet T. Niinikoski M. Rieubland A. Michalowicz S. Dalla Torre-Colautti 《Nuclear Physics B》1985,262(4):727-743
The spin correlation parameter Aoonn and the analyzing powers Aoono and Aooon were measured simultaneously, in the energy range 0.5–0.8 GeV and in the angular region 40°–80° CM. The experiment used the polarized proton beam of SATURNE II and the Saclay frozen spin polarized target. 相似文献
36.
37.
When considering the hydrodynamics of Brownian particles, one is confronted to a difficult closure problem. One possibility to close the hierarchy of hydrodynamic equations is to consider a strong friction limit. This leads to the Smoluchowski equation that reduces to the ordinary diffusion equation in the absence of external forces. Unfortunately, this equation has infinite propagation speed leading to some difficulties. Another possibility is to make a Local Thermodynamic Equilibrium (L.T.E) assumption. This leads to the damped Euler equation with an isothermal equation of state. However, this approach is purely phenomenological. In this paper, we provide a preliminary discussion of the validity of the L.T.E assumption. To that purpose, we consider the case of free Brownian particles and harmonically bound Brownian particles for which exact analytical results can be obtained [S. Chandrasekhar, Rev. Mod. Phys. 15, 1 (1943)]. For these systems, we find that the L.T.E. assumption is not unreasonable and that it can be improved by introducing a time dependent kinetic temperature Tkin(t)=γ(t)T instead of the bath temperature T. We also compare hydrodynamic equations and generalized diffusion equations with time dependent diffusion coefficients. 相似文献
38.
Two recent methods (Shanno, 1978; Toint, 1980) for revisingestimates of sparse second derivative matrices in quasi-Newtonoptimization algorithms reduce to variable metric formulae whenthere are no sparsity conditions. It is proved that these methodsare equivalent. Further, some examples are given to show thatthe procedure may make the second derivative approximationsworse when the objective function is quadratic. Therefore theconvergence properties of the procedure are sometimes less goodthan the convergence properties of other published methods forrevising sparse second derivative approximations. 相似文献
39.
Chavanis Pierre-Henri 《The European Physical Journal B - Condensed Matter and Complex Systems》2022,95(3):1-6
The European Physical Journal B - A two-cluster system with a bistable potential is constructed in one-dimensional channels. Using molecular dynamics and Monte Carlo methods, we study the... 相似文献
40.
X. -Q. Ding E. L. Bominaar E. Bill H. Winkler A. X. Trautwein S. Drüeke PH. Chaudhuri K. Wieghardt 《Hyperfine Interactions》1990,53(1-4):311-315
In this paper, we briefly summarize the main conclusions of the Mössbauer analysis of [L2Fe2(-OH)3] (ClO4)2·2CH3OH·2H2O with L=N,N',N"-trimethyl-1,4,7-triazacyclononane, a novel dimeric iron compound, which possesses a central exchange-coupled delocalized-valence Fe(II/III) unit. The complete delocalization of the excess electron in the dimeric iron center is concluded from the indistinguishability of the two iron sites in Mössbauer spectroscopy. The magnetic Mössbauer spectra imply a system spinS
t=9/2 for the dimer in its ground state. The values for hyperfine and spin-Hamiltonian parameters, obtained from simulations of the Mössbauer spectra, are =0.74 mms–1, E
Q=–2.14 mms–1,A
=–10.6 T,A
=–13.5 T andD=1.8 cm–1. The system spinS
t=9/2 is interpreted to be a consequence of double-exchange coupling. 相似文献