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31.
We consider two limiting regimes, the large-spin and the mean-field limit, for the dynamical evolution of quantum spin systems. We prove that, in these limits, the time evolution of a class of quantum spin systems is determined by a corresponding Hamiltonian dynamics of classical spins. This result can be viewed as a Egorov-type theorem. We extend our results to the thermodynamic limit of lattice spin systems and continuum domains of infinite size, and we study the time evolution of coherent spin states in these limiting regimes. 相似文献
32.
Laura Äkäslompolo Ana M. Sánchez Qi Hang Qin Antti Hakola Timo Kajava Sebastiaan van Dijken 《Applied Physics A: Materials Science & Processing》2013,110(4):889-894
We report on the growth of all-oxide SrRuO3/CoFe2O4/La2/3Sr1/3MnO3 and La2/3Sr1/3MnO3/CoFe2O4/SrRuO3 heterostuctures on SrTiO3(001) and MgO(001) substrates by pulsed laser deposition. Structural analyses by X-ray diffraction and transmission electron microscopy clearly indicate the preservation of epitaxial relations when the La2/3Sr1/3MnO3 layer is grown first, whereas trilayers with SrRuO3 at the bottom are more disordered. Both the substrate material and the deposition sequence strongly influence the formation of various structural defects such as interfacial dislocations and sub-grain structures, and this is clearly reflected by a reduction of the saturation magnetization in the top electrode. When the substrate material and the deposition sequence are correctly chosen, however, the magnetic moments of the La2/3Sr1/3MnO3 and SrRuO3 layers reverse independently, and the La2/3Sr1/3MnO3 layer retains bulk-like magnetic properties. 相似文献
33.
Dmitri Kuzmin Antti Hannukainen Sergey Korotov 《Journal of Computational and Applied Mathematics》2008
A new a posteriori error estimate is derived for the stationary convection–reaction–diffusion equation. In order to estimate the approximation error in the usual energy norm, the underlying bilinear form is decomposed into a computable integral and two other terms which can be estimated from above using elementary tools of functional analysis. Two auxiliary parameter-functions are introduced to construct such a splitting and tune the resulting bound. If these functions are chosen in an optimal way, the exact energy norm of the error is recovered, which proves that the estimate is sharp. The presented methodology is completely independent of the numerical technique used to compute the approximate solution. In particular, it is applicable to approximations which fail to satisfy the Galerkin orthogonality, e.g. due to an inconsistent stabilization, flux limiting, low-order quadrature rules, round-off and iteration errors, etc. Moreover, the only constant that appears in the proposed error estimate is global and stems from the Friedrichs–Poincaré inequality. Numerical experiments illustrate the potential of the proposed error estimation technique. 相似文献
34.
Timo J. Tolmunen Antti V. Räisänen 《International Journal of Infrared and Millimeter Waves》1989,10(4):505-518
The multiplication efficiency of a millimeter-wave Schottky-varactor quintupler with fixed idler terminations was studied. The highest efficiency measured was 4.2% at 168 GHz with 10 mW input power and 3.3% with 40 mW input power. Over the range from 165 GHz to 170 GHz the output power was 0.7–1.3 mW withp
in
=40 mW. 相似文献
35.
36.
We consider Hermitian and symmetric random band matrices H in d ≥ 1 dimensions. The matrix elements H xy , indexed by \({x,y \in \Lambda \subset \mathbb{Z}^d}\), are independent, uniformly distributed random variables if \({\lvert{x-y}\rvert}\) is less than the band width W, and zero otherwise. We prove that the time evolution of a quantum particle subject to the Hamiltonian H is diffusive on time scales \({t\ll W^{d/3}}\). We also show that the localization length of the eigenvectors of H is larger than a factor W d/6 times the band width. All results are uniform in the size \({\lvert{\Lambda}\rvert}\) of the matrix. 相似文献
37.
We consider the adjacency operator of the Linial‐Meshulam model for random simplicial complexes on n vertices, where each d‐cell is added independently with probability p to the complete ‐skeleton. Under the assumption , we prove that the spectral gap between the smallest eigenvalues and the remaining eigenvalues is with high probability. This estimate follows from a more general result on eigenvalue confinement. In addition, we prove that the global distribution of the eigenvalues is asymptotically given by the semicircle law. The main ingredient of the proof is a Füredi‐Komlós‐type argument for random simplicial complexes, which may be regarded as sparse random matrix models with dependent entries. © 2017 Wiley Periodicals, Inc. Random Struct. Alg., 51, 506–537, 2017 相似文献
38.
Virginia P. Silva Nykänen Mervi A. Puska Antti Nykänen Janne Ruokolainen 《Journal of Polymer Science.Polymer Physics》2013,51(17):1318-1327
This work presents the synthesis of polyphosphazenes bearing L ‐proline methyl ester (ProOMe) and 4‐hydroxy‐l ‐proline methyl ester (HypOMe), aiming for new bioactive polymers for bone repair. The polymers were characterized by 1H and 31P NMR, FTIR, DSC, and TGA. Electrospun fibers were prepared using poly[bis(l ‐proline methyl ester)phosphazene] (PProP), and their potential for biomimetic mineralization, as well as the bulk material, were tested in simulated body fluid (1×SBF). Samples were analyzed between 24 h and 3 weeks of incubation using SEM/EDS and FTIR. After 24 h, spherical and flower‐like shapes of calcium phosphates (CaP) were crystallized on the bulk samples. The nanofibers presented spherical CaP crystals attached to them after 48 h of incubation. The Ca/P molar ratio of the crystals varied from 1.5 to 1.6. According to this study, PProP presents bioactivity in vitro, and its fibers offer sites for CaP nucleation like the collagen fibers in bone. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1318–1327 相似文献
39.
40.
Pekka Tiikkainen Antti Poso Olli Kallioniemi 《Journal of computer-aided molecular design》2009,23(4):227-239
In this work, we calculated the pair wise chemical similarity for a subset of small molecules screened against the NCI60 cancer
cell line panel. Four different compound similarity calculation methods were used: Brutus, GRIND, Daylight and UNITY. The
chemical similarity scores of each method were related to the biological similarity data set. The same was done also for combinations
of methods. In the end, we had an estimate of biological similarity for a given chemical similarity score or combinations
thereof. The data from above was used to identify chemical similarity ranges where combining two or more methods (data fusion)
led to synergy. The results were also applied in ligand-based virtual screening using the DUD data set. In respect to their
ability to enrich biologically similar compound pairs, the ranking of the four methods in descending performance is UNITY,
Daylight, Brutus and GRIND. Combining methods resulted always in positive synergy within a restricted range of chemical similarity
scores. We observed no negative synergy. We also noted that combining three or four methods had only limited added advantage
compared to combining just two. In the virtual screening, using the estimated biological similarity for ranking compounds
produced more consistent results than using the methods in isolation. 相似文献