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31.
The rate of intramolecular migration of the triphenylstannyl group in 3,6-ditert-butyl-2(triphenylstannyl) oxyphenoxyl decreases with increasing viscosity of the medium. A linear relationship ex=·c is observed between the characteristic time of stannotropy ex and the correlation time for reorientational motions of the radical c within a range of temperature variation no greater than 30°C. The parameter depends on the medium; this is explained by the possibility of complexation of the radical with the solvent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 781–786, April, 1990. 相似文献
32.
Alexander V Lebedev Marina V Ivanova Alexander A Timoshin Enno K Ruuge 《Chemphyschem》2007,8(12):1863-1869
The unexpected effects of Ca(2+) on the free-radical chain reactions of dopamine, norepinephrine, isoproterenol, and pyrocatechol oxidation are studied using oxygen consumption measurements, EPR-spectroscopy, UV/VIS spectrophotometry, and by potentiometric titration. It is found that the formation of Ca(2+)-catecholate complexes is accompanied by an increase in the dissociation constants (K(ai) ) of their phenolic hydroxyls. At pH>pK(ai) and in the presence of alkaline-earth metal cations, the rate of catecholate oxidation increases (Ca(2+), Mg(2+)> Sr(2+), Ba(2+)), whereas on addition of Zn ions the rate decreases. The effects of Group II metal cations on catecholate autoxidation are concomitant with a transient increase of the EPR signal for metal-semiquinonate complexes. Therefore, the effects of Ca(2+) and other alkaline-earth metal cations on catecholate autoxidation can be defined as 1) additional deprotonation of catechol OH-groups involved in the formation of M(2+)-catecholate complexes, the latter exceeding catechols in the susceptibility to dioxygen-induced oxidation and 2) formation of relatively stable free-radical intermediates responsible for chain propagation. 相似文献
33.
The destruction ofB-polyfluorosubstitutedo-carboranes by the action of ethanolic alkali and amines was studied. The destraction of trifluoro-o-carborane was found to occur regioselectively. The nature of the amine was shown to affect the stereochemistry of the destruction of trifluoro-o-carborane. The intermediate of the reaction of tetrafiuoro-o-carborane with diethylamine was detected.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1141–1145, June, 1995. 相似文献
34.
Zabolotskii V. I. Manzanares J. A. Mafe S. Nikonenko V. V. Lebedev K. A. 《Russian Journal of Electrochemistry》2002,38(8):819-827
A relatively simple mathematical model based on the Poisson equation is considered. The model is intended for modeling transport through multilayered ion-exchange membranes operating at overlimiting currents. The boundary-value problem is solved by a numerical method of parallel shooting and by an approximate method based on the assumption that the charge density is distributed quasi-uniformly. Concentration profiles in diffusion layers and membranes, current–voltage curves, and dependences of effective transport numbers on the current density are examined. 相似文献
35.
E. A. Chernyshev O. V. Kuz'min A. V. Lebedev V. G. Zaikin A. I. Mikaya 《Russian Chemical Bulletin》1986,35(4):821-824
Conclusions The main products of the pyrolysis of 8,8-dimethyl-8-sila-2,3,4,5-tetrathiabicycIo-[4.3.0]nonane at 400 are 1,1-dimethylsilacyclopent-3-ene and 1,1-dimethyl-1-sila-2-thiacyclo-hexa-3, 5-diene, and at 600 carbon disulfide and thiophene; silacyclopentene is the sole reaction product, characteristic for the mass-spectrometric decomposition of the initial tetrasulfide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No, 4, pp. 902–905, April, 1986. 相似文献
36.
The temperature dependences of the heat capacities of crystalline tetraphenyltetrahydroxycyclotetrasiloxane, octaphenyltetrahydroxytricyclooctasiloxane, and octaphenylpentacyclosilsesquioxane and of glassy polyphenylsilsesquioxane were measured in the range 6-300 K with an adiabatic vacuum calorimeter, with an accuracy of 0.3%. From these data, the thermodynamic functions C
0
p
(T), H
0(T) - H
0(0), S
0(T) - S
0(0), and G
0(T) - H
0(0) of these substances were calculated for the range 0-300 K. The standard entropies of their formation from elements at 298.15 K,
f
S
0, and the entropies of mutual transformations of these substances in the range 0-298.15 K were calculated. 相似文献
37.
V. P. Lebedev V. V. Chironov A. N. Kizin I. F. Falyahov I. Sh. Saifullin O. R. Klyuchnikov Yu. D. Orlov Yu. A. Lebedev 《Russian Chemical Bulletin》1995,44(4):639-641
The enthalpies of combustion of some pyridine derivatives in the solid state have been measured by precision bomb calorimetry, and their enthalpies of formation have been calculated. The enthalpies of sublimation of these compounds have been determined from the experimental temperature dependences of saturated vapor pressure using the Clausius-Clapeyron equation. The enthalpies of combustion, formation, and sublimation are the following (kJ mol–1): -3360.9±2.1, -0.5±2.1, and 79.1±1.3, respectively, for 4-methylpyridine 1-oxide; -2551.0±1.7, 11.7±1.7, and 89.1±2.5, respectively, for 4-nitropyridine 1-oxide;-2355.6±1.3, 102.1±1.3, and 106.3±2.9 for 2,4,6-trinitropyridine 1-oxide; and -2287.6±1.3, 34.3±1.3, and 101.7±2.9 for 2,4,6-trinitropyridine. The enthalpies of formation in the solid state and the enthalpies of sublimation of pyridine derivatives obtained together with the literature data allowed the energies of dissociation of the donor-acceptor N—O bonds in pyridine 1-oxides to be calculated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 660–662, April, 1995. 相似文献
38.
39.
We consider a certain combinatorial game on a digraph for two cases of the price function. For one case the game in question extends the cyclical game studied in Ehrenfeucht and Mycielski (1979) and Gurvitch, Karzanov and Khachiyan (1988) which, in its turn, is a generalization of the well-known problem of finding a minimum mean cycle in an edge-weighted digraph. We prove the existence of optimal uniform stationary strategies for both cases and give algorithms to find such strategies.This work was partially supported by Chaire municipale, Mairie de Grenoble. 相似文献
40.
1. | The rate constant for the destruction of radical pairs decreases with increase in the distance between the traps of the H atom. |
2. | A mechanism was proposed for the destruction of radical pairs, according to which the main channel for hydrogen transfer during annealing does not coincide with the channel for phototransfer when the RP are formed. |
3. | Based on a formally kinetic analysis for a stepwise rate, distribution parameters based on the activation energies were found for the deuterated and undeuterated samples. A superficial estimate was made of the change in the activation energy when the distance between the unpaired electrons in the radical pairs is changed by one unit of length. |