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71.
Sawka-Dobrowolska W Bator G Sobczyk L Pawlukojć A Ptasiewicz-Bak H Rundlöf H Krawczyk J Nowina-Konopka M Jagielski P Janik JA Prager M Steinsvoll O Grech E Nowicka-Scheibe J 《The Journal of chemical physics》2005,123(12):124305
The 1:1 hexamethylbenzene (HMB)-tetracyanoquinodimethane (TCNQ) complex shows a first-order phase transition at 230/218 K (heating/cooling) with no change of the space group. The neutron-diffraction studies reveal that this transition is related to a freezing of the rotation of methyl groups. The results for 100 K enabled precise determination of configuration of HMB.TCNQ complexes. The planes of HMB and TCNQ molecules from small angle (6 degrees) so that the dicyanomethylene group approaches the HMB molecule to a distance of 3.34 angstroms. The conformation of methyl groups was exactly determined. The quasielastic neutron-scattering spectra can be interpreted in terms of 120 degrees jumps with different activation barrier in low- and high-temperature phases, equal to 3.7 and 1.8 kJ/mol, respectively. These values are lower than that for neat HMB (6 kJ/mol). The conclusion can be drawn that the methyl groups can reorient more freely in the complex. This conclusion is in agreement with the results of inelastic neutron-scattering studies of low-frequency modes assigned to torsional vibrations of methyl groups. These frequencies are lower than those for neat HMB. The analyzed increase of frequencies of these modes as compared with free molecules can be interpreted as due to formation of unconventional C-H...Y hydrogen bonds which are more pronounced in crystals of neat HMB than in those of HMB.TCNQ. The low-frequency librational modes can be treated as a sensitive measure of unconventional hydrogen bonds formed by the CH3 groups. 相似文献
72.
Nozirov F Szczesniak E Fojud Z Dobrzynski P Klinowski J Jurga S 《Solid state nuclear magnetic resonance》2002,22(1):19-28
Copolymers of glycolide and epsilon-caprolactone were studied using differential scanning calorimetry and solid-state NMR. The variation of the T1 relaxation time with temperature reflects local disorder and can be quantified in terms of the distribution of correlation times predicted by the Davidson-Cole model. T, relaxation is dominated by trans-gauche isomerisation, with an activation energy of 34-35 kJ mol(-1). 相似文献
73.
Leszek Czuchajowski Matthew Morra Eugeniusz Kubaszewski Tadeusz Malinski 《Journal of heterocyclic chemistry》1992,29(6):1417-1422
The title compound, a mixture of two isomers differing in the position of a methoxy substituent in one benzene ring, was obtained in a Ni-templated synthesis directly as a water soluble dihydrochloride of the free base. The cyclic voltametry study indicated that in a neutral solution the reduction and oxidation are irreversible one electron processes, the latter leading to cation radical undergoing polymerization, a process followed by deposition of a film on the electrode. In 1,2-dichloroethane the cation radical is oxidized to a dication, both species being much less stable than those originating from meso-tetraphenylporphyrin. The title compoud at 2.5 × 10?5 M in Tris buffer showed a 50% inhibition of the growth of malignant melanoma cells as compared to a 44% inhibition shown by a water soluble meso-monomethoxy-tris(N-methylpyridinium)porphyrin. The exposure to light for 30 minutes at 2.5 times smaller concentration increased the inhibition caused by the pseudo-porphyrin from 9% to 49%. 相似文献
74.
Bo?ena Bittner Ewa Janus Eugeniusz Milchert 《Central European Journal of Chemistry》2011,9(1):192-198
A comparative study of the Diels-Alder reactions between cyclopentadiene (1) and dienophiles (2 a–c) in N-hexylpyridinium
bis(trifluoromethylsulfonyl)imide in a temperature range of 20–45°C is reported. The reaction rate constants and activation
energies were calculated. Moreover, the catalytic systems based on N-hexylpyridinium bis(trifluoromethylsulfonyl)imide and
Lewis acids were tested as a reaction media to perform the Diels-Alder reaction. Yb, Y, Mg, Zn triflates and chlorides (0.005
to 0.1 mmol) were used as catalysts. The recycling of catalytic system consisted of YCl3 and ionic liquid was performed.
相似文献
75.
Danuta Kaczmarek Damian Wojcieszak Jaroslaw Domaradzki Eugeniusz Prociow Frank Placido Steffen Lapp Rafal Dylewicz 《Central European Journal of Physics》2011,9(2):349-353
In this work, the influence of Tb-doping on structure, and especially hardness of nanocrystalline TiO2 thin films, has been described. Thin films were formed by a high-energy reactive magnetron sputtering process in a pure oxygen
atmosphere. Undoped TiO2-matrix and TiO2:Tb (2 at. % and 2.6 at. %) thin films, had rutile structure with crystallite sizes below 10 nm. The high-energy process produces
nanocrystalline, homogenous films with a dense and close packed structure, that were confirmed by X-ray diffraction patterns
and micrographs from a scanning electron microscope. Investigation of thin film hardness was performed with the aid of a nanoindentation
technique. Results of measurements have shown that the hardness of all manufactured nanocrystalline films is above 10 GPa.
In the case of undoped TiO2 matrix, the highest hardness value was obtained (14.3 GPa), while doping with terbium results in hardness decreasing down
to 12.7 GPa and 10.8 GPa for TiO2:(2 at. % Tb) and TiO2:(2.6 at. % Tb) thin films, respectively. Incorporation of terbium into TiO2-matrix also allows modification of the elastic properties of the films. 相似文献
76.
Karolina Sieradzka Danuta Kaczmarek Jarosław Domaradzki Eugeniusz Prociów Michał Mazur Barbara Górnicka 《Central European Journal of Physics》2011,9(2):313-318
Electrical and optical properties of TiO2:Pd thin films deposited from Ti-Pd mosaic targets sputtered in reactive oxygen plasma have been studied. The properties were
investigated for thin films with the Pd amount of 5.5 at. %, 8.4 at. % and 23 at. %. Based on resistivity measurements a drop
from 103 down to almost 10−3Ωcm has been recorded when the Pd amount was varied from 5.5 at. % to 23 at. %, respectively. Moreover, it was shown that
doping with different amounts of Pd results in the possibility of obtaining both types of electrical conduction: n-type for
the TiO2 with 5.5 at. % and 8.4 at. % of Pd and p-type for the TiO2 with 23 at. % of Pd thin films. From optical measurements it has been found that as the Pd amount was increased the transmission
through the thin films was reduced and position of the fundamental absorption edge was shifted toward a longer wavelength
range of up to 600 nm. The optical band gap was calculated for direct and indirect transitions from optical absorption spectra.
Structural properties were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The XRD patterns displayed
occurrence of the crystalline, TiO2-rutile for lower Pd amounts (5.5 at. %, 8.4 at. %), while the TiO2:Pd (23 at. %) thin films displayed XRD-amorphous behaviour. Images obtained from AFM displayed dense, nanocrystalline structure
with homogenous distribution of crystallites. Additionally performed secondary ion mass spectroscopy investigation confirmed
homogenous distribution of Pd in the whole thickness of the prepared thin films. 相似文献
77.
Damian Wojcieszak Danuta Kaczmarek Jaroslaw Domaradzki Eugeniusz L. Prociow Antoni W. Morawski Magdalena Janus 《Central European Journal of Physics》2011,9(2):354-359
In this work photocatalytic properties of TiO2 thin films doped with different amount of Tb have been described. Thin films were prepared by high energy reactive magnetron
sputtering process. Comparable photocatalytic activity has been found for all doped TiO2 thin films, while different amounts of Tb dopant (0.4 and 2.6 at. %) results in either an anatase or rutile structure. It
was found that the terbium dopant incorporated into TiO2 was also responsible for the amount of hydroxyl groups and water particles adsorbed on the thin film surfaces and thus photocatalytic
activity was few times higher in comparison with results collected for undoped TiO2 thin films. 相似文献
78.
Raw powders of BaHfO3:Ce were prepared with modified Pechini process and were calcined in the 650–1700 °C range of temperatures, at different atmospheres – air, vacuum and nitrogen–hydrogen mixture. The powders were converted into sintered ceramics by vacuum sintering. The materials were characterized by XRD, TEM, photoluminescence and radioluminescence spectroscopy. UV-VUV excitation spectra were recorded using synchrotron radiation. Excitation spectra proved that atmosphere of preparation significantly influences the host-to-activator energy transfer, which is the most efficient for materials made in reducing conditions. Also radioluminescence efficacy was found to be superior for materials prepared in such conditions. 相似文献
79.