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1.
Laser excited S1→S0 fluorescence spectra are obtained from p-fluorotoluene in a supersonic jet in order to probe internal rotational-vibrational
coupling. Resolved fluorescence spectra after selective excitation of S1 levels with high quanta states of the CH3 internal rotation contain evidence of extensive interactions with isoenergetic vibrational levels. Analogous spectra from
states without excitation of the internal rotor show little or no interactions. The results are consistent with a recently
developed theory of the intramolecular collisional transfer of rotor energy to the vibrational field. 相似文献
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Individual rovibronic transitions are isolated at high resolution from a crowded absorption feature with a fluorescence excitation technique which is based on detection of fluorescence from one and only one rovibronic level. The method is illustrated by resolving four rovibronic transitions from the single rotational line-like feature in the 0, 0 band of the (S1 ← S0) absorption of glyoxal vapor. The rotational structure of the 510 fluorescence band is studied as a function of tuning a narrow-band laser line (linewidth < 10?4 cm?1) to various positions in and near this absorption feature. The fluorescence structure proves an extremely sensitive tool for detecting small absorptions, with emission from 12 rovibronic levels being identified. One of the spectra so obtained is a close approximation of true single rotational level fluorescence. 相似文献
5.
Dr. David E. Clarke Dr. Christopher D. J. Parmenter Prof. Oren A. Scherman 《Angewandte Chemie (International ed. in English)》2018,57(26):7709-7713
Oligopeptide‐based supramolecular hydrogels hold promise in a range of applications. The gelation of these systems is hard to control, with minor alterations in the peptide sequence significantly influencing the self‐assembly process. We explored three pentapeptide sequences with different charge distributions and discovered that they formed robust, pH‐responsive hydrogels. By altering the concentration and charge distribution of the peptide sequence, the stiffness of the hydrogels could be tuned across two orders of magnitude (2–200 kPa). Also, through reassembly of the β‐sheet interactions the hydrogels could self‐heal and they demonstrated shear‐thin behavior. Using spectroscopic and cryo‐imaging techniques, we investigated the relationship between peptide sequence and molecular structure, and how these influence the mechanical properties of the hydrogel. These pentapeptide hydrogels with tunable morphology and mechanical properties have promise in tissue engineering, injectable delivery vectors, and 3D printing applications. 相似文献
6.
The yields, lifetimes and spectra of singlet 1Au (S1) and triplet 3Au (T1) emissions from glyoxal vapor (0.003 to 10 torr) have been measured after initially pumping levels about 1000 cm?1 above the S1 zero-point level with the 4358 A Hg line and with flash excitation centered at 4345 A. Only S1 emission is observed at the lowest pressures. The singlet fluorescence contains appreciable structure from the zero-point level even when the hard sphere collision interval exceeds the radiative lifetime calculated from the absorption coefficient. Implications of long lifetimes (due to S1 - T1 vibronic interactions) are not confirmed by pulsed excitation studies. Both S1 and T1 emissions are observed at pressures above about 0.1 tert and both are self-quenched. However, added gases such as cyclohexane, argon, and helium selectively quench only S1 emission. This quenching is collision-induced S1→T1 intersystem crossing with cross sections of order 0.1 hard sphere for transitions from the S1 zero-point level. The triplet yield in 0.2 torr of pure glyoxal is probably near unity, and the subsequent crossing T1 → S0, if it occurs, lies in the statistical limit. Indications of fast nonradiative decay from high triplet vibrational levels are seen in the phosphorescence yields. Self-quenching of the triplet state appears to be associated with the photochemical activity of glyoxal. 相似文献
7.
The system consisting of three identical harmonic oscillators impulsively coupled can be described by the four-dimensional triple-twist map. This map is capable of generating a uniform stochastic web, periodic in all four dimensions. Some properties of this web are studied. 相似文献
8.
Quantum mechanical equations of motion are obtained for a system consisting of a very large number of three types of interacting bosons. Under suitable choice of parameters of the Hamiltonian of the system, the equations of motion are those describing three Josephson junctions in a superconducting loop. It is shown numerically that this system is capable of exhibiting deterministic chaos (extreme sensitivity to initial conditions). 相似文献
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Intensity perturbations in forbidden radiative transitions due to cubic anharmonic mixing involving the inducing mode and a totally symmetric progression-forming mode are discussed. It is shown that such mixing will lead to deviations from mirror symmetry of the absorption and fluorescence structure because the destructive-constructive interference pattern which prevails in absorption is different to that in emission. This analysis is applied to intensities in the 2600 Å system of benzene. Moderate cubic coupling energies (ca. 10 cm-1) have marked effects on intensity distributions even when the interacting levels are 200 cm-1 apart. The splitting of the progressions 10 n 61 2 and 1 n 062 1 into two sub-progressions (l=0, 2) is linearly dependent on the extent of vibronic excitation in the a 1g mode v 1. These effects are amenable to experimental detection. 相似文献