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101.
Valeriy Brytik Maarten V. de Hoop Mikko Salo 《Journal of Fourier Analysis and Applications》2010,16(4):544-589
Earthquakes, viewed as passive sources, or controlled sources, like explosions, excite seismic body waves in the earth. One
detects these waves at seismic stations distributed over the earth’s surface. Wave-equation tomography is derived from cross
correlating, at each station, data simulated in a reference model with the observed data, for a (large) set of seismic events.
The times corresponding with the maxima of these cross correlations replace the notion of residual travel times used as data
in traditional tomography. Using first-order perturbation, we develop an analysis of the mapping from a wavespeed contrast
(between the “true” and reference models) to these maxima. We develop a construction using curvelets, while establishing a
connection with the geodesic X-ray transform. We then introduce the adjoint mapping, which defines the imaging of wavespeed
variations from “finite-frequency travel time” residuals. The key underlying component is the construction of the Fréchet
derivative of the solution to the seismic Cauchy initial value problem in wavespeed models of limited smoothness. The construction
developed in this paper essentially clarifies how a wavespeed model is probed by the method of wave-equation tomography. 相似文献
102.
Linnolahti M Kinnunen NM Pakkanen TA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):218-224
Structural preferences of single-walled and coordinatively saturated spherical and tubular nanostructures of silica have been determined by ab initio calculations. Two families of spherical (SiO2)n clusters derived from Platonic solids and Archimedean polyhedra are depicted, with n ranging from 4-120. The analogue of a truncated icosidodecahedron, Ih-symmetric Si120O240, is favored in energy, closely followed by the Ih-symmetric Si60O120-truncated icosahedron. The silica nanotubes derived from spherical clusters are capped by Si2O2 rings, whereas the tubular section consists of single oxygen bridges. Periodic studies performed with open-ended silica nanotubes and the alpha-quartz polymorph of silica, along with a comparisons to fullerenes and carbon nanotubes, suggest that tubes with diameters of approximately 1 nm should be chemically stable. 相似文献
103.
Murtola T Falck E Patra M Karttunen M Vattulainen I 《The Journal of chemical physics》2004,121(18):9156-9165
We construct a coarse-grained (CG) model for dipalmitoylphosphatidylcholine (DPPC)/cholesterol bilayers and apply it to large-scale simulation studies of lipid membranes. Our CG model is a two-dimensional representation of the membrane, where the individual lipid and sterol molecules are described by pointlike particles. The effective intermolecular interactions used in the model are systematically derived from detailed atomic-scale molecular dynamics simulations using the Inverse Monte Carlo technique, which guarantees that the radial distribution properties of the CG model are consistent with those given by the corresponding atomistic system. We find that the coarse-grained model for the DPPC/cholesterol bilayer is substantially more efficient than atomistic models, providing a speedup of approximately eight orders of magnitude. The results are in favor of formation of cholesterol-rich and cholesterol-poor domains at intermediate cholesterol concentrations, in agreement with the experimental phase diagram of the system. We also explore the limits of the coarse-grained model, and discuss the general validity and applicability of the present approach. 相似文献
104.
Jarkko Ihanus Eric Lambers Paul H. Holloway Mikko Ritala Markku Leskel 《Journal of Crystal Growth》2004,260(3-4):440-446
SrS1−xSex and ZnS1−xSex thin films were deposited by the atomic layer deposition (ALD) technique using elemental selenium as the Se source, thus avoiding use of H2Se or organometallic selenium compounds. X-ray diffraction (XRD) analysis showed that the films were solid solutions and X-ray photoelectron spectroscopy (XPS) data showed that the surface of both ZnS1−xSex and SrS1−xSex were covered with an oxide and carbon-containing contaminants from exposure to air. The oxidation of SrS1−xSex extended into the film and peak shifts from sulfate were found on the surface. Luminance measurements showed that emission intensity of the ZnS1−xSex:Mn alternating current thin film electroluminescent (ACTFEL) devices at fixed voltage was almost the same as that of the ZnS:Mn device, while emission intensity of the SrS1−xSex:Ce devices decreased markedly as compared to the SrS:Ce device. Emission colors of the devices were altered only slightly due to selenium addition. 相似文献
105.
Rantala A Utriainen M Kaushik N Virta M Välimaa AL Karp M 《Analytical and bioanalytical chemistry》2011,400(4):1041-1049
A bacterial biosensor method for the selective determination of a bioavailable organomercurial compound, methylmercury, is
presented. A recombinant luminescent whole-cell bacterial strain responding to total mercury content in samples was used.
The bacterial cells were freeze-dried and used as robust, reagent-like compounds, without batch-to-batch variations. In this
bacteria-based sensing method, luciferase is used as a reporter, which requires no substrate additions, therefore allowing
homogenous, real-time monitoring of the reporter gene expression. A noninducible, constitutively light-producing control bacterial
strain was included in parallel for determining the overall cytotoxicity of the samples. The specificity of the total mercury
sensor Escherichia coli MC1061 (pmerRBlux) bacterial resistance system toward methylmercury is due to a coexpressed specific enzyme, organomercurial lyase. This enzyme
mediates the cleavage of the carbon–mercury bond of methylmercury to yield mercury ions, which induce the reporter genes and
produce a self-luminescent cell. The selective analysis of methylmercury with the total mercury strain is achieved by specifically
chelating the inorganic mercury species from the sample using an optimized concentration of EDTA as a chelating agent. After
the treatment with the chelating agent, a cross-reactivity of 0.2% with ionic mercury was observed at nonphysiological ionic
mercury concentrations (100 nM). The assay was optimized to be performed in 3 h but results can already be read after 1 h
incubation. Total mercury strain E. coli MC1061 (pmerRBlux) has been shown to be highly sensitive and capable of determining methylmercury at a subnanomolar level in optimized assay
conditions with a very high dynamic range of two decades. The limit of detection of 75 ng/l (300 pM) allows measurement of
methylmercury even from natural samples. 相似文献
106.
We have numerically investigated the effect of lowered T on the performance of the Coulomb blockade thermometer, which has been demostrated to yield primary thermometry in the high T limit where thermal excitations compete with the Coulomb blockade. The thermometer is formed by an array of tunnel junctions whose differentiated IV—curve is used to determine the temperature. The IV—curves were calculated by computer simulations and we have obtained corrections to the analytic high T behaviour due to the lowered temperature. 相似文献
107.
108.
Dioxomolybdenum(VI) complex [MoO2Cl2(dmso)2] reacts with a series of tetradentate O3N-type aminoalcohol–bisphenol ligands to form oxomolybdenum(VI) complexes of type [MoOCl(Ln)]. The reaction of H3L1 produces [MoOCl(L1)] as two separable isomers, whereas the reaction of H3L2 or H3L3 yields a single product. The X-ray analyses of cis- and trans-[MoOCl(L1)] reveal that the complexes are formed of monomeric molecules. The ligands have tetradentate coordination through three oxygen donors and one nitrogen donor, which is located trans to the terminal oxo group. The sixth coordination site is occupied by a chloro ligand. 相似文献
109.
Mikko Parviainen 《Journal of Differential Equations》2009,246(2):512-540
We show that weak solutions to a singular parabolic partial differential equation globally belong to a higher Sobolev space than assumed a priori. To this end, we prove that the gradients satisfy a reverse Hölder inequality near the boundary. The results extend to singular parabolic systems as well. Motivation for studying reverse Hölder inequalities comes partly from applications to regularity theory. 相似文献
110.
In this article we compare different force fields that are widely used (Gromacs, Charmm-22/x-Plor, Charmm-27, Amber-1999, OPLS-AA) in biophysical simulations containing aqueous NaCl. We show that the uncertainties of the microscopic parameters of, in particular, sodium, and, to a lesser extent, chloride, translate into large differences in the computed radial-distribution functions. This uncertainty reflect the incomplete experimental knowledge of the structural properties of ionic aqueous solutions at finite molarity. We discuss possible implications on the computation of potential of mean force and effective potentials. 相似文献