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51.
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53.
Y.P. Yadava D.A. Landinez Tellez M.T. de Melo J.M. Ferreira J. Albino Aguiar 《Applied Physics A: Materials Science & Processing》1998,66(4):455-458
2 ZrO5.5 has been synthesized by solid-state reaction. Structural ordering in this material has been studied by X-ray diffraction
(XRD). The XRD spectra reveal that DyBa2ZrO5.5 has an ordered complex cubic perovskite structure. The presence of superstructure reflections in the XRD spectra is characteristic
of A2BB’O6-type crystalline structure. The chemical stability of DyBa2ZrO5.5 with YBa2CuO7-δ (YBCO) superconductors has been studied by XRD and electrical resistivity measurements. These studies show that DyBa2ZrO5.5 is chemically stable with YBCO and there is no degradation in the superconducting transition temperature Tc of YBCO even when mixed up to 1:1 vol%, with DyBa2ZrO5.5 in YBCO. Detailed study of the superconducting transition region shows that Tc(onset) and Tc(0) values of pure YBCO and YBCO–DyBa2ZrO5.5 composites are similar in both cases. The implications are discussed.
Accepted: 13 October 1997 相似文献
54.
55.
The peak algebra
is a unital subalgebra of the symmetric group algebra, linearly spanned by sums of permutations with a common set of peaks.
By exploiting the combinatorics of sparse subsets of [n−1] (and of certain classes of compositions of n called almost-odd and thin), we construct three new linear bases of
. We discuss two peak analogs of the first Eulerian idempotent and construct a basis of semi-idempotent elements for the peak
algebra. We use these bases to describe the Jacobson radical of
and to characterize the elements of
in terms of the canonical action of the symmetric groups on the tensor algebra of a vector space. We define a chain of ideals
of
, j = 0,...,
, such that
is the linear span of sums of permutations with a common set of interior peaks and
is the peak algebra. We extend the above results to
, generalizing results of Schocker (the case j = 0).
Aguiar supported in part by NSF grant DMS-0302423
Orellana supported in part by the Wilson Foundation 相似文献
56.
J. Barba-Ortega Edson Sardella J. Albino Aguiar 《Physica C: Superconductivity and its Applications》2010,470(21):1964-1967
Nonlinear time-dependent Ginzburg–Landau (TDGL) equations were solved in the present work using the link variables method. Vortex configurations were investigated in a superconducting circular sector immersed in an external magnetic field applied perpendicular to its plane. Magnetization and free energy were calculated as a function of the applied magnetic field at several temperatures. This paper illustrates how the vortices moved around at the transition fields before they become accommodated into an equilibrium configuration. A linear dependence of the magnetization dependence on temperature has been found for a certain magnetic field. 相似文献
57.
L. De Los Santos Valladares A. Bustamante Dominguez J. Albino Aguiar R. M. Reeve T. Mitrelias R. M. Langford Y. Azuma C. H. W. Barnes Y. Majima 《Brazilian Journal of Physics》2013,43(4):209-213
In this work, we report the mechanical reorientation of thiolated ferromagnetic microspheres bridging a pair of gold electrodes under an external magnetic field. When an external magnetic field (7 kG) is applied during the measurement of the current–voltage characteristics of a carboxyl ferromagnetic microsphere (4 μm diameter) attached to two gold electrodes by self-assembled monolayers (SAMs) of octane dithiol (C8H18S2), the current signal is distorted. Rather than due to magnetoresistance, this effect is caused by a mechanical reorientation of the ferromagnetic sphere, which alters the number of SAMs between the sphere and the electrodes and therefore affects conduction. To study the physical reorientation of the ferromagnetic particles, we measure their hysteresis loops while suspended in a liquid solution. 相似文献
58.
Rosiana Aguiar Dmitry Logvinovich Anke Weidenkaff Armin Reller Stefan G. Ebbinghaus 《Thermochimica Acta》2008,471(1-2):55-60
Oxynitride perovskites with bright and variable colour have the potential to be employed as non-toxic pigments, and to substitute colourants that contain harmful heavy metals. For this application it is extremely important to have a precise knowledge about the materials stability. The thermal stability of oxynitride perovskites in different atmospheres was measured by thermogravimetry in combination with mass spectroscopy (MS). The studied compounds, namely LaTiO2N, SrNbO2N and SrTaO2N, were heated up to 1200 °C in argon–oxygen mixtures with varying oxygen contents. It was found that the thermal behaviour of the studied oxynitrides changes drastically with the oxygen concentration. When heated up in pure argon the oxynitrides transform to oxides containing transition metals of lower oxidation state and/or binary nitrides. For oxygen contents between 0.5% and 20% the samples were completely oxidised. The oxidation rate increases with oxygen content. MS analysis of the gaseous products (including N2, NO and NO2) reveals a complex reaction mechanism, which is strongly modified by the composition of the atmosphere. 相似文献
59.
Katz MJ Michaelis VK Aguiar PM Yson R Lu H Kaluarachchi H Batchelor RJ Schreckenbach G Kroeker S Patterson HH Leznoff DB 《Inorganic chemistry》2008,47(14):6353-6363
The reaction of Pb(ClO4)2 x xH2O, an ancillary ligand L, and two equivalents of Au(CN)2(-) gave a series of crystalline coordination polymers, which were structurally characterized. The ligands were chosen to represent a range of increasing basicity, to influence the stereochemical activity (i.e., p-orbital character) of the Pb(II) lone pair. The Pb(II) center in [Pb(1,10-phenanthroline)2][Au(CN)2]2 (1) is 8-coordinate, with a stereochemically inactive lone pair; all 8 Pb-N bonds are similar. The Au(CN)2(-) units propagate a 2-D brick-wall structure. In [Pb(2,2'-bipyridine)2][Au(CN)2]2 (2), the 8-coordinate Pb(II) center has asymmetric Pb-N bond lengths, indicating moderate lone pair stereochemical activity; the supramolecular structure forms a 1-D chain/ribbon motif. For [Pb(ethylenediamine)][Au(CN)2]2 (3), the Pb(II) is only 5-coordinate and extremely asymmetric, with Pb-N bond lengths from 2.123(7) to 3.035(9) A; a rare Pb-Au contact of 3.5494(5) A is also observed. The Au(CN)2(-) units connect the Pb(ethylenediamine) centers to form 1-D zigzag chains which stack via Au-Au interactions of 3.3221(5) A to yield a 2-D sheet. (207)Pb MAS NMR of the polymers indicates an increase in both the chemical shielding span and isotropic chemical shift with increasing Pb(II) coordination sphere anisotropy (from delta iso = -2970 and Omega = 740 for 1 to delta iso = -448 and Omega = 3980 for 3). The shielding anisotropy is positively correlated with Pb(II) p-character, and reflects a direct connection between the NMR parameters and lone-pair activity. Solid-state variable-temperature luminescence measurements indicate that the emission bands at 520 and 494 nm, for 1 and 2, respectively, can be attributed to Pb --> L transitions, by comparison with simple [Pb(L)2](ClO4)2 salts. In contrast, two emission bands for 3 at 408 and 440 nm are assignable to Au-Au and Pb-Au-based transitions, respectively, as supported by single-point density-functional theory calculations on models of 3. 相似文献
60.
Fabio da Silva Bortoli Carlos Frajuca Sergio Turano de Sousa Arlette de Waard Nadja Simao Magalhaes Odylio Denys de Aguiar 《Brazilian Journal of Physics》2016,46(3):308-315
SCHENBERG is a resonant-mass gravitational wave detector built in Brazil. Its spherical antenna, weighting 1.15 t, is connected to the outside world by a suspension system whose main function is to attenuate the external seismic noise. In this work, we report how the system was modeled using finite elements method. The model was validated on experimental data. The simulation showed that the attenuation obtained is of the order of 260 dB, which is sufficient for decreasing the seismic noise below the level of the thermal noise of the detector operating at 50 mK. 相似文献