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排序方式: 共有451条查询结果,搜索用时 31 毫秒
71.
Leszek Plaskota 《Journal of Approximation Theory》1998,93(3):501-515
We consider the average caseL∞-approximation of functions fromCr([0, 1]) with respect to ther-fold Wiener measure. An approximation is based onnfunction evaluations in the presence of Gaussian noise with varianceσ2>0. We show that the n th minimal average error is of ordern−(2r+1)/(4r+4) ln1/2 n, and that it can be attained either by the piecewise polynomial approximation using repetitive observations, or by the smoothing spline approximation using non-repetitive observations. This completes the already known results forLq-approximation withq<∞ andσ0, and forL∞-approximation withσ=0. 相似文献
72.
Silica mesoporous materials modified with manganese and iron were obtained by the hydrothermal method. Gold was introduced
to pure and modified silica materials by the direct hydrothermal and impregnation methods. Nitrogen adsorption/desorption
studies evidenced formation of the materials with large total surface area and mesoporous structure. Unmodified silica materials
showed regular pore arrangement. The uniform porous structure was distorted in the iron or manganese containing samples. XRD,
UV-Vis/DRS spectroscopy and temperature programmed reduction studies revealed changes of the nature of transition metal oxide
and gold species on the different preparation stages. The oxide species after drying were strongly dispersed and partially
incorporated to the silica framework. High temperature treatment led to the formation of extraframework Mn and Fe oxide species.
Complex processes of gold deposition were observed during hydrothermal synthesis and impregnation of modified silica materials.
The increase of the size of gold species was observed during calcination. The presence of transition metal oxides decreased
sintering of gold crystallites. 相似文献
73.
Dzwolak W Loksztejn A Galinska-Rakoczy A Adachi R Goto Y Rupnicki L 《Journal of the American Chemical Society》2007,129(24):7517-7522
Unlike folding, protein aggregation is a multipathway, kinetically controlled process yielding different conformations of fibrils. The dynamics and determinism/indeterminism boundaries of misfolded conformations remain obscure. Here we show that, upon vortexing, insulin forms two distinct types of fibrils with opposite local chiral preferences, which manifest in the opposite twists of bound dye, thioflavin T. Occurrence of either type of fibrils in a test tube is only stochastically determined. By acting through an autocatalytic, "chiral amplification"-like mechanism, a random conformational fluctuation triggers conversion of the macroscopic amount of insulin into aggregates with uniformly biased chiral moieties, which bind and twist likewise the achiral dye. Although a convection-driven chiral amplification in achiral systems, which results in randomly distributed excesses of optically active forms, is known, observation of such a phenomenon in misfolded protein built of l-amino acids is unprecedented. The two optical variants of insulin fibrils show distinct morphologies and can propagate their chiral biases upon seeding to nonagitated insulin solutions. Our findings point to a new aspect of topological complexity of protein fibrils: a chiral feature of hierarchically assembled polypeptides, which is partly emancipated from the innate left-handedness of amino acids. Because altering chirality of a molecule changes dramatically its biological activity, the finding may have important ramifications in the context of the structural basis of "amyloid strains". 相似文献
74.
The Simha and Somcynsky (S‐S) lattice‐hole theory has been shown to represent accurately the pressure‐volume‐temperature (PVT) surface of chain molecular melts and their mixtures. Proceeding beyond its original intent, it has led to correlations with other properties and extension into the steady state and relaxing glass. The equilibrium results appear as the solutions of two coupled equations, involving the variables of state and the hole fraction, h = h (V, T) – a kind of free volume quantity. These are to be solved numerically. Notwithstanding the theory's quantitative success, its implicit form has on some occasions been a practical limitation. We remedy this situation by fitting the scaled and thus general solutions of the coupled equations to accurate algebraic equations, V = V (T, P) and h = hV, T). In this manner, explicit analytical expressions for configurational thermodynamic functions and their derivatives are now available. The new expressions for V and h are simple to employ; the convergence of the non‐linear least‐squares fit is obtained in seconds. The numerical values of the scaling parameters so derived are nearly identical to those computed from the original coupled equations. Having h and V from the original theory, the cohesive energy density [CED = δ2V, T)] was also considered. The results are again well represented by a simple algebraic expression. An expression for the reduced solubility parameter δ = δ (T, P) is also given. The usefulness of these solutions is further illustrated by an application to the PVT surfaces of polystyrene and polyphenylene ether blends. 相似文献
75.
Theoretical models of the interfacial tension coefficient in polymer blends, v12, were evaluated. A new working relation was derived that makes it possible to compute v12 from the chemical structure of two polymers. The calculations involve determination of the dispersive, polar and hydrogen-bonding parts of the solubility parameter from the tabulated group and bond contributions. The computed values of v12 for 46 blends were found to follow the experimental ones with a reasonable scatter of ± 36%. Next, the experimental methods of v12-measurements were critically examined. Although many have been developed for low viscosity Newtonian fluids, most are irrelevant to industrial polymeric systems. For the present studies two were selected. Values of v12 were measured using the so-called “capillary breakup method,” and a newly developed method based on the retraction rate of deformed drop. 相似文献
76.
Joanna Korec Karol A. Stasiewicz Katarzyna Garbat Leszek R. Jaroszewicz 《Molecules (Basel, Switzerland)》2021,26(24)
This paper is a continuation of previous work and shows the enhancement of the surface plasmon resonance effect in a tapered optical fiber device. The study investigated liquid crystal cells containing a tapered optical fiber covered with a silver nanolayer, surrounded by a low refractive index liquid crystal in terms of the properties of light propagation in the taper structure. Silver films with a thickness of d = 10 nm were deposited on the tapered waist area. Measurements were performed at room temperature; liquid crystal steering voltage U from 0 to 200 V, with and without any amplitude modulation with a frequency of f = 5 Hz, and the wavelength λ ranged from 550 to 1200 nm. A significant influence of the initial arrangement of liquid crystals molecules on light propagation was observed. Three types of liquid crystal cells—orthogonal, parallel, and twist—were considered. During the measurements, resonant peaks were obtained—the position of which can also be controlled by the type of liquid crystal cells and the steering voltage. Based on the obtained results, the best parameters, such as highest peak’s width reduction, and the highest SNR value were received for twisted cells. In addition, the present work was compared with the previous work and showed the possibility of improving properties of the manufactured probes, and consequently, the surface plasmon resonance effect. In the presented paper, the novelty is mainly focused on the used materials as well as suitable changes in applied technological parameters. In contrast to gold, silver is characterized by different optic and dielectric properties, e.g., refractive index, extension coefficient, and permittivity, which results in changes in the light propagation and the SPR wavelengths. 相似文献
77.
In this paper we prove the existence of solutions for a hyperbolic hemivariationalinequality of the form u″ + Bu + ∂j (u) ∋ f where B is a linear elliptic operator and ∂j is the Clarke subdifferential of a locally Lipschitz function j. Our result is based on the parabolic regularization method. 相似文献
78.
Dariusz Bieliński Leszek Pysklo Jan Dul Ludomir Ślusarski Grażyna Janowska Grażyna Lewandowicz 《Macromolecular Symposia》2003,194(1):233-240
Characterization of the surface layer of starch powder, originated from potato or maize, was carried out applying various experimental techniques: Fourier-transformed infrared internal reflection spectroscopy (FTIR-IRS), inverse gas chromatography (IGC) and scanning electron microscopy (SEM). The main kinds of starch were studied as potential fillers for rubber and results discussed in terms of factors requiring modification to improve starch miscibility and activity towards rubber. Starch of high amylopectine content shows surface enrichment with amylose what makes crystallinity of the surface layer higher than in bulk of the material. Particles of the both kinds of starch have very smooth surface (morphological index, Im = 0.995), highly resistant to its geometrical development. Dispersive component of the surface energy of starch was found to be similar to that of low energy polymers (γsd = 32.5 mJ/m2 at 23°C) and its surface to be of electron-donor character. 相似文献
79.
80.
Leszek Plaskota Grzegorz W. Wasilkowski 《Journal of Fixed Point Theory and Applications》2009,6(2):227-248
This is an overview of recent results on complexity and optimality of adaptive algorithms for integrating and approximating
scalar piecewise r-smooth functions with unknown singular points. We provide adaptive algorithms that use at most n function samples and have the worst case errors proportional to n−r for functions with at most one unknown singularity. This is a tremendous improvement over nonadaptive algorithms whose worst case errors are at best proportional to n−1 for integration and n−1/p for the Lp approximation problem. For functions with multiple singular points the adaptive algorithms cease to dominate the nonadaptive
ones in the worst case setting. Fortunately, they regain their superiority in the asymptotic setting. Indeed, they yield convergence of order n−r for piecewise r-smooth functions with an arbitrary (unknown but finite) number of singularities. None of these results hold for the L∞ approximation. However, they hold for the Skorohodmetric, which we argue to be more appropriate than L∞ for dealing with discontinuous functions. Numerical test results and possible extensions are also discussed. 相似文献