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1.
The method of laser photoelectron emission from metals in electrolyte solutions has been used to measure the rate constants w3 for the electrochemical reduction of simple organic radicals R to carbanions R–. The following empirical rule has been established: the changes in the standard redox potential E° for R–/R in series of organic radicals are equal to the changes in the potential corresponding to individual values of w3. On the basis of this rule and the value of E° for CH3
–/CH3 E° values were obtained for C2H5, n-C3H7, n-C4H9, CH2OH, CH3CHOH, (CH3)2COH, CH2Cl, CHF2, CHFCl, CHCl2, CF2Cl, CFCl2, CF3, CCl3, C6H5, C6Cl5, and a scale of pK for the CH acids conjugate to R–. Consideration is given to the nature of the changes in E° and pK on passing from aqueous solutions to solutions in water-dioxane mixtures and in acetonitrile.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1508–1514, July, 1990. 相似文献
2.
3.
E. Ya. Misochko V. A. Benderskii A. U. Goldshleger A. V. Akimov A. V. Benderskii C. A. Wight 《Russian Chemical Bulletin》1997,46(4):678-686
The products of UV photolysis of ternary Ar?CH4(CD4)?F2 mixtures (1:c:c 0,c, c 0=0.001–0.01) at 13–16 K were identified by ESR and FTIR spectroscopy. These products are?CH3 (?CD3) radicals of typesI andII and molecular CH3F?HF complexes. The latter were characterized by the IR bands of the stretching C?F (1003 cm?1) and H?F (3774 cm?1) vibrations. The ESR spectra of radicalsI are asymmetric. The anisotropy of theg-factor (Δg~10?3) of radicalI indicates that the structure of the radicals is nonplanar. The ESR spectrum of the typeII radical is identical to that of matrix-isolated?CH3 (?CD3) radicals with the planar structure (Δg<5·10?5). Under the experimental conditions, the amount of complexes formed in the photolysis is equal to 0.022·c. When the photolysis is ceased, radicalI disappears after ≈103 s and radicalII is stabilized. The limiting concentrations of the stabilized?CH3 and?CD3 radicals are equal to 2·10?2·c and 2·10?3·c, respectively. A mechanism of the formation of the products is suggested. It is based on the assumption that both matrix-isolated CH4 and F2 and their heterodimers CH4?F2 are present in the samples and it takes into account the long-range migration of translationally excited flourine atoms. The CH3F?HF complexes and radicalsI are generated by the photolysis of the CH4?F2 heterodimers. The decay of radicalsI is caused by geminate recombination of proximate F...CH3 pairs. RadicalsII are formed in the reaction of translationally excited fluorine atoms with isolated CH4 (CD4) molecules. 相似文献
4.
E. Ya. Misochko V. A. Benderskii A. U. Goldshleger A. V. Akimov A. V. Benderskii C. A. Wight 《Russian Chemical Bulletin》1997,46(4):687-692
The products of reactions of dopant CH4 molecules with F atoms diffusing in solid argon at 20–30 K were identified by ESR and FTIR spectroscopy. The F atoms stabilized in the matrix were generated by UV photolysis of Ar?CH4(CD4)?F (1000∶1∶1) samples at 13 K. Subsequent heating above 20 K results in thawing off diffusion of the F atoms and formation of products of their reaction with CH4: radical-molecular complexes·CH3?HF (·CD3?DF) and radicals·CH3 (·CD3). The ESR spectra of the radicala are similar to those observed for matrix-isolated·CH3. The·CH3?HF complexes are characterized by the IR band of HF stetching vibration at 3764 cm?1. Two additional splittings on the H (a H·=2 G) and F(a F=16G) nuclei of the HF molecule appeal in the ESR spectrum of the complex. The latter splitting is retained in the·CD3?DF complex, whereA D· <0.3G The rate constant of the reaction CH4+F→·CH3+HF is equal to ?10?25 cm3s?1 at 20 K. Its activation energy (1.7±0.2 kcal mol?1) is ?0.5 kcal mol?1 greater than that in the gas phase. The collinear C3v-configuration of the·CH3?HF complex, which is similar to the configuration of the reagents in the transition state of the reaction considered, was established by the comparison of the exprrimental constants of hyperfine coupling with the results of the quantum-chemical calculation. 相似文献
5.
6.
The change in the supramolecular structure upon drying (solvent removal) of colloidal solutions of fluoroalkyl oligomers at atmospheric pressure has been studied using atomic force microscopy. In an initial colloidal solution, micrometer-sized particles of the dense phase consist of randomly oriented oligomers in the form of rigid rods of a 3–5 nm length forming a porous framework filled with solvent molecules, which solvate the oligomer chains. The drying-induced capillary pressure, which in nanosized pores is of the same order of magnitude as the solvation energy, leads to framework deformation, collapse of the pores, and the formation of lamellar and dendritic structures on a 50–100 nm scale. The ordering of these structures (formation of blocks of parallel oriented fibers typical of a fluoroplastic) increases as the heat-treatment temperature and the drying rate are increased, increasing the roughness of the surface (ratio of real to smooth surface area) and its hydrophobicity. 相似文献
7.
Aerogels of the tetrafluoroethylene radical polymerization products H(C2F4)nR, where R is the radical formed by the abstraction of a hydrogen atom from a solvent molecule, have been obtained by replacing the solvent with supercritical CO2 and its subsequent rapid evaporation. According to the data of scanning electron and atomic force microscopy, the aerogel consists of loosely bound particles of 1–3 μm in diameter, which is two to three times that of colloid particles in the initial solution, where the particles consist of an oligomer framework filled with solvent molecules. The internal structure of the framework is manifested in the surface topography with a roughness coefficient of 1.6–1.8. High roughness leads to the formation of ultrahydrophobic coatings with contact angles of >160°. A model of supercritical drying in which the solvent is removed from the colloidal particles without alteration of the supramolecular structure is discussed. 相似文献
8.
A quantum dynamical problem has been analytically solved for a two-level system where localized states L
0 and R
0 are strongly coupled with reservoirs of local oscillations {L
n
} and {R
n
}. It is additionally assumed that the spectra of reservoirs are equidistant and the coupling constants are the same. It has
been shown that the evolution of states L
0 and R
0 in recurrence cycles depends on three independent factors, which characterize exchange with the two-level system, exchange
of L
0 with {L
n
} (R
0 with {R
n
}) and the phonon-induced decay of {L
n
} and {R
n
}. In addition to coherent oscillations with the frequency of the two-level system, Δ, and dissipative tunneling with a rate
Δ2/πC
2 (where C is the matrix element of the coupling of L
0 and R
0 with L
n
and R
n
), a new regime appears where L-R transitions are induced by the partial recovery of the populations of L
0 and R
0 in each recurrence cycle due to synchronous transitions from reservoirs. These transitions induce repeating changes in the
populations of the states of the two-level system (Loschmidt echo). The number and width of the echo components increase with
the cycle number. Evolution becomes irregular because of the mixing of the contributions from pulses of the neighboring cycles,
when the cycle number k exceeds the critical value k
c = π2
C
2. Unlike the populations, their cycle-average values remain regular at k ≫ k
c. When Δ ≪ πC
2, the cycle-average populations oscillate with a frequency of ΔΩ/πC
2 irrespective of mixing. The frequency of oscillations of the populations of the states {L
n
} and {R
n
} is approximately nΩ(Δ/2πC
2)2, where Ω is the spacing between the neighboring levels of the reservoir and nΩ is the difference between the energies of the states L
0 and L
n
. The appearance of the mentioned low-frequency oscillations is due to the formation of collective states of the two-level
system that are “dressed” by the reservoir. The predicted oscillations can be detected by femtosecond spectroscopy methods. 相似文献
9.
10.
V.A. Benderskii V.Kh. Brikenstein V.L. Broude A.G. Lavrushko 《Solid State Communications》1974,15(8):1235-1237
Measurement of temperature pulses with time resolution less than 5 nsec based, on the high-speed registration of the Debye-Waller factor in the fluourescence spectrum of an impurity layer deposited on a sample, has been achieved. In anthracene single crystals, the velocity of heat propagation was found to be equal to 0.7?1.0.105 cm/sec, approaching that sound; the mean free path of phonons was found to exceed 30 μm. 相似文献