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51.
A.-L. Barra G. Chouteau A. Stepanov A. Rougier C. Delmas 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):551-562
compounds have a layered structure made of alternating Ni-O and Li-O slabs. An amount z of extra divalent Ni ions is always present in the Li-O layers. We show, using high field magnetisation, static and dynamic
susceptibility and high frequency ESR, that the magnetic properties are driven by the z parameter. The compounds can be described as ferromagnetic Ni-O layers, bridged by clusters possessing a net ferromagnetic
moment.
Received: 24 July 1998 / Revised and Accepted: 23 September 1998 相似文献
52.
We express the cohomology of the complement of a real subspace arrangement of diagonal linear subspaces in terms of the Betti numbers of a minimal free resolution. This leads to formulas for the cohomology in some cases, and also to a cohomology vanishing theorem valid for all arrangements. 相似文献
53.
S.?de?BrionEmail author G.?Storch G.?Chouteau A.?Janossy W.?Prellier E.?Rauwel Buzin 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(4):413-418
Compressed
Pr0.5Ca0.5MnO3
films (250 nm) deposited on LaAlO3 have
been studied by Electron Spin Resonance technique under high
frequency and high magnetic field. We show evidences for the
presence of a ferromagnetic phase (FM) embedded in the
charge-order phase (CO), in form of thin layers which size
depends on the strength and orientation of the magnetic field
(parallel or perpendicular to the substrate plane). This FM
phase presents an easy plane magnetic anisotropy with an
anisotropy constant 100 times bigger than typical bulk values.
When the magnetic field is applied perpendicular to the
substrate plane, the FM phase is strongly coupled to the CO
phase whereas for the parallel orientation it keeps an
independent ferromagnetic resonance even when the CO phase
becomes antiferromagnetic. 相似文献
54.
János D. Pintér 《Annals of Operations Research》2001,104(1-4):213-230
The well-balanced distribution of points over the surface of a sphere is of significant interest in various fields of science. The quality of point configurations is typically expressed by criterion functions that have many local optima. A general global optimization framework is suggested to solve such problems. To illustrate the viability of this approach, the model development and solver system LGO is applied to four different model versions. Numerical results – including the visual representation of criterion functions in these models – are presented. The global optimization approach can be tailored to specific problem settings, and it is also applicable to a large variety of other model forms. 相似文献
55.
Ruth Charney 《Transactions of the American Mathematical Society》2004,356(10):3881-3897
This paper concerns the homotopy type of hyperplane arrangements associated to infinite Coxeter groups acting as reflection groups on . A long-standing conjecture states that the complement of such an arrangement should be aspherical. Some partial results on this conjecture were previously obtained by the author and M. Davis. In this paper, we extend those results to another class of Coxeter groups. The key technical result is that the spherical Deligne complex for the 4-strand braid group is CAT(1).
56.
Some improvements for two-sided bounds on the inverse of diagonally dominant tridiagonal matrices 总被引:2,自引:0,他引:2
In this paper, we obtain lower and upper bounds for the entries of the inverses of diagonally dominant tridiagonal matrices. First of all we derive the bounds for off-diagonal elements of the inverse as a function of the diagonal ones, then we improve the two-sided bounds for the diagonal entries obtaining sharper lower and upper bounds for all the elements of the inverse. 相似文献
57.
58.
F. Semadeni A. Amato B. Roessli P. Böni C. Baines T. Masuda K. Uchinokura G. Shirane 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):307-311
The temperature-concentration phase diagram of the Si-doped spin-Peierls compound CuGeO3 is investigated by means of neutron scattering and muon spin rotation spectroscopy in order to determine the microscopic
distribution of the magnetic and lattice dimerised regions as a function of doping. The analysis of the zero-field muon spectra
has confirmed the spatial inhomogeneity of the staggered magnetisation that characterises the antiferromagnetic superlattice
peaks observed with neutrons. In addition, the variation of the macroscopic order parameter with doping can be understood
by considering the evolution of the local magnetic moment as well as of the various regions contributing to the muon signal.
Received 6 September 2000 and Received in final form 29 January 2001 相似文献
59.
N. El Khayati R. Cherkaoui El Moursli J. Rodríguez-Carvajal G. André N. Blanchard F. Bourée G. Collin T. Roisnel 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(4):429-442
We have studied in detail the crystal and magnetic structures of the oxyphosphates MFePO5 (M: divalent transition metal) using neutron powder diffraction as a function of temperature. All of them are isomorphic
to the mixed valence compound α-Fe2PO5 with space-group Pnma. No disorder exists between the two metallic sites. The M2+O6 octahedra share edges between them and faces with Fe3+O6 octahedra building zigzag chains running parallel to the b-axis that are connected by PO4 tetrahedra. The topology of this structure gives rise to a complex pattern of super-exchange interactions responsible of
the observed antiferromagnetic order. The magnetic structures are all collinear with the spin directed along the b-axis except for M = Co. The experimental magnetic moments of Cu+2 and Ni2+ correspond to the expected ionic value, on the contrary the magnetic moment of Fe3+ is reduced, probably due to covalence effects, and that of Co2+ is greater than the spin-only value indicating a non negligible orbital contribution. Using numerical calculations we have
established a magnetic phase diagram adapted for this type of crystal structure and determined the constraints to be satisfied
by the values of the exchange interactions in order to obtain the observed magnetic structure as the ground state.
Received 15 December 2000 and Received in final form 25 June 2001 相似文献
60.
O. Moze J.M. Cadogan Y. Janssen F.R. de Boer K.H.J. Buschow S.J. Kennedy 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(1):29-36
The magnetic structure of RFe6Ga6 intermetallic compounds with R = Y, Ho have been determined by neutron powder diffraction, 57Fe M?ssbauer spectroscopy, AC susceptibility, TGA (Thermo-Gravimetric Analysis) and magnetization measurements. Both compounds
crystallize in the tetragonal ThMn12 structure (space group I4/mmm) with the magnetic structure of YFe6Ga6 consisting of a simple ferromagnetic alignment of Fe moments in the basal plane with a Curie temperature of 475(5) K. Gallium
atoms are found to fully occupy the 8i site, with Fe and Ga atoms equally distributed over the 8j site, whilst Fe atoms fully
occupy the 8f site. The average Fe moments are 1.68(10)
and 1.46(10)
at 15 and 293 K, respectively. The average room temperature Fe magnetic moments determined by neutron diffraction are in
overall agreement with the average Fe moment deduced from M?ssbauer spectroscopy and bulk magnetization measurements on this
compound. The magnetic anisotropy of the compound HoFe6Ga6 is also planar in the temperature range 6-290 K, with Ho magnetic moments of 9.28(20)
and 2.50(20)
at 6 K and 290 K, respectively, coupled anti-ferromagnetically to the Fe sublattice and a Curie temperature of 460(10) K.
The magneto-crystalline anisotropies of both compounds are comparable at low temperatures.
Received 8 March 2001 and Received in final form 18 June 2001 相似文献