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81.
Adsorption of phospholipid vesicles on titanium dioxide was studied by a combination of quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy techniques. Vesicle size, concentration in solution, and bilayer composition were systematically varied. A strong dependence of the QCM-D response (magnitude of the frequency and dissipation factor shifts) on the vesicle concentration in solution was observed. QCM-D data were compared with a linear viscoelastic model based on the Voight element to determine layer thickness, density, elastic modulus, and viscosity. Based on the results of this comparison, it is proposed that (i) layer thickness and density, as sensed by QCM-D, saturate much earlier (in time) than the actual surface coverage of the vesicles (number of vesicles per unit area); (ii) changes in surface coverage that occur after the density and thickness, as sensed by QCM-D, have saturated, are interpreted by the model as changes in the layer's viscoelastic properties. This is caused by the replacement of the viscous media (water) between the vesicles by viscoelastic media of similar density (vesicles); (iii) viscoelastic properties of layers formed at different vesicle concentrations differ significantly, while the vesicle surface coverage in those layers does not. Based on the comparison between the atomic force microscopy images and QCM-D data acquired at various vesicle concentrations it is proposed that QCM-D response is not directly related to the surface coverage of the vesicles. 相似文献
82.
Castagnola M Rossetti DV Inzitari R Vitali A Lupi A Zuppi C Cabras T Fadda MB Podda I Petruzzelli R Giardina B Messana I 《Electrophoresis》2003,24(10):1612-1619
Binding of Zn(2+) to bacitracin A(1) was studied by capillary electrophoresis in water/2,2,2-trifluoroethanol (70/30 v/v) at different apparent pH values in order to estimate the association constant of metal, the acidic dissociation constants and the Stokes radii of both free and bounded peptide in apolar environment. The Stokes radii of the free peptide species were compared with those in aqueous solution, as obtained in a recent study performed by our group, indicating that apolar environment stabilizes bacitracin A(1) in a conformational structure with the lateral chain of apolar amino acids exposed on the external surface. This conformation of the macrocyclic dodecapeptide is ready to interact with Zn(2+) ion, as pointed out by the strong increase of the association constant measured in water/2,2,2-trifluoroethanol with respect to the value obtained in aqueous solution. In addition, whereas Zn(2+) ion binding in aqueous solution provides a sensible reduction of peptide Stokes radius, no sensible variations following to ion binding were observed in hydro-organic solution. The present results suggest that the apolar environment, rather than the metal ion binding, could be responsible for the conformational transition that brings bacitracin A(1) towards its biologically active structure.* 相似文献
83.
Mattia Rossetti Paolo Bardella Ivo Montrosset 《Optical and Quantum Electronics》2008,40(14-15):1129-1134
We present the results of a one-dimensional (1D) numerical model for the simulation of quantum dot (QD) multi-section superluminescent diodes (SLD) using a rate equation approach. A comparison between experimental and simulated P–I characteristics of a single section SLD is provided in order to validate the model parameters. Using these parameters we analyzed more complicated structures with non-uniform injection and waveguide cross section. The purpose has been to investigate how to increase power at the broad-band emission condition (equal power emission from ground state and excited state) and to tune this condition in a wide range of power. We found that applying a non uniform injection in the two sections no improvement in the maximum output power is achieved at the broad bandwidth condition in devices with uniform waveguide. On the contrary, when a tapered section is introduced, the use of two electrodes and non-uniform current injection allows to obtain larger output power and tunability range respect to the case with uniform injection. 相似文献
84.
E. Marinari G. Parisi D. Rossetti 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):495-500
We study the dynamical behavior of the Sherrington Kirkpatrick model. Thanks to the APE supercomputer we are able to analyze
large lattice volumes, and to investigate the low T region. We present a new and precise determination of the remnant magnetization and of its time decay exponent, of the energy
time decay exponent, and we discuss aging phenomena in the model. We exclude validity of naive aging, and propose different
options that fit the numerical data.
Received: 14 August 1997 / Revised: 2 December 1997 / Accepted: 30 January 1998 相似文献
85.
A novel micro force balance (MFB) is used to investigate the rupture energy of a silicon oil liquid bridge formed in water between two glass particles of either the same or dissimilar surface energy. Rupture energies are integrated from force curves and compared with the models proposed by Simons et al. (Chem. Eng. Sci. 49 (1994) 2331) and Pitois et al. (Eur. Phys. J. B 23 (2001) 79). The latter showed slightly better agreement to the experimental data. Glass ballotini ( approximately 100 microm diameter) are either silanized, in order to increase their wettability toward the oil binder, or kept untreated. Results showed how the interaction between the binder and the particle influences the geometry, the capillary pressure, the force, and the rupture energy of the liquid bridge. Higher values of force and liquid bridge energy were measured between particles characterized by higher interaction (silanized-silanized configuration). A thermodynamic approach to the evaluation of the energy stored in a liquid bridge is also proposed. The mechanical work done to stretch apart the liquid bridge is evaluated as the difference of internal and hysteresis energy between the initial and the rupture configuration of the bridge. This approach showed good agreement with the experimental data only for liquid bridges formed between silanized and untreated glass particles. 相似文献
86.
87.
The vibroluminescence of N2O excited by activated nitrogen is studied under high resolution using a SISAM spectrometer in the 4.7 μ region. For the first time a Treanor-type distribution is applied to the vibrational population of the ν3 mode which shows a non-Boltzmann distribution. 相似文献
88.
Emission spectra of CO2 vibrationally excited by a dc electric discharge were recorded under Doppler-limited resolution, using the high information interferometer of Laboratoire d'Infrarouge Orsay, France, in the spectral region 4–5 μm. Sixteen bands with Δv3 = 1 of 12C16O2 involving the Fermi dyads (100v3, 020v3)I and II and (111v3, 031v3)I and II have been studied. The band centers and the spectroscopic constants for all the vibrational levels involved are given. They reproduce the experimental wavenumbers with a rms of the order of 4 × 10?5 cm?1 for the best vibrational transition and always less than 3 × 10?4 cm?1 for the others. These results are compared with laser measurements for the (1000, 0200) dyad. 相似文献
89.
Emission spectra of six isotopic species of CO2 excited by dc discharge were recorded under Doppler limited resolution using the Fourier transform spectrometer of the Laboratoire d'Infrarouge in the 4.5-μm region. In this paper, the results concerning 12C16O18O are given. The band centers and the spectroscopic constants for 19 levels involved in vibrational transitions Δv3 = 1 are reported. They reproduce 853 experimental wavenumbers with a RMS of the order of 2 × 10?5 cm?1 for the best vibrational transition, less than 1 × 10?4 cm?1 for most of the others. From experimental wavenumbers, to determine molecular parameters, it is shown that it is impossible to include in the same fit all the transitions Σ-Σ until v3 = 10 using a polynomial representation of the rovibrational energy, the responsible phenomenon being the small Fermi resonance which occurs on Σ levels. Nevertheless, the 321 wavenumbers belonging to the first four vibrational transitions are satisfactorily reproduced by the model. 相似文献
90.
In this paper we determine all five-dimensional compact flat Riemannian manifolds with holonomy group Z
2Z
2. The classification is achieved by classifying their fundamental groups up to isomorphism. The Betti numbers of all these manifolds are also computed. 相似文献