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61.
A. A. Levin T. Leisegang R. Forker M. Koch D. C. Meyer T. Fritz 《Crystal Research and Technology》2010,45(4):439-448
3,4:9,10‐Perylenetetracarboxylic dianhydride (PTCDA) powder obtained from Sigma‐Aldrich was purified by three cycles of temperature gradient sublimation in an evacuated quartz glass tube providing variable conditions. By means of X‐ray diffraction (XRD) analysis, a crystallographic characterization of the powders obtained during the sublimation process and selected single crystals was carried out evidencing the presence of a major α‐ and a minor β‐PTCDA component in all samples. Lattice parameters of high precision were obtained for α‐PTCDA (a = 3.73283(4) Å, b = 12.0328(6) Å, c = 17.3998(4) Å, β = 98.689(2)°, V = 772.57(4) Å3 and d102 = 3.219(3) Å) by whole‐X‐ray‐powder‐pattern‐fitting of the experimental XRD pattern using the Le Bail approach. Employing a (001) KCl wafer as substrate for the material purification results in formation of single phase α‐PTCDA accompanied by a decrease in the size of the crystallites which is attributed to the presumed lower temperature of the KCl wafers. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
62.
Dr. Andrew J. Bordner 《Chemphyschem》2012,13(17):3981-3988
The density functional version of symmetry‐adapted perturbation theory, SAPT(DFT), is a computationally efficient method for calculating intermolecular interaction energies. We evaluate its accuracy by comparison with experimentally determined noble gas interaction potentials and sublimation enthalpies, most of which have not been previously calculated using this method. In order to compare the results with wavefunction methods, we also calculate these quantities using MP2 and, for noble gas dimers, using CCSD(T). For the crystal lattice energy calculations, we include corrections to the dispersion, electrostatic, and induction energies that account for the finite interaction distance cutoff and higher‐order induction contributions. Overall, the energy values extrapolated to the complete basis set limit show that SAPT(DFT) achieves significantly better agreement with experiment than MP2. 相似文献
63.
Vladimir N. Emel’yanenko 《The Journal of chemical thermodynamics》2008,40(12):1661-1665
Molar enthalpies of sublimation of two crystal forms of caffeine were obtained from the temperature dependence of the vapour pressure measured by the transpiration method. A large number of primary experimental results on the temperature dependences of vapour pressure and phase transitions have been collected from the literature and have been treated in a uniform manner in order to derive sublimation enthalpies of caffeine at T = 298.15 K. This collection together with the new experimental results reported here has helped to resolve contradictions in the available sublimation enthalpies data and to recommend a consistent and reliable set of sublimation and formation enthalpies for both crystal forms under study. Ab initio calculations of the gaseous molar enthalpy of formation of caffeine have been performed using the G3MP2 method and the results are in excellent agreement with the selected experimental data. 相似文献
64.
S. H. J. De Beukeleer J. F. Janssens H. O. Desseyn 《Journal of Thermal Analysis and Calorimetry》1997,48(2):225-231
The influence of intermolecular hydrogen bonding on some physical constants is clearly shown by comparing some thermal data for simple oxamides and thiooxamides.S. De Beukeleer wishes to thank N. F. W. O. for financial support. G. Thijs is thanked for technical assistance. 相似文献
65.
Dr. Vojtěch Štejfa Václav Pokorný Carlos F. P. Miranda Óscar O. P. Fernandes Prof. Luís M. N. B. F. Santos 《Chemphyschem》2020,21(9):938-951
This work presents a new Knudsen effusion apparatus employing continuous monitoring of sample deposition using a quartz-crystal microbalance sensor with internal calibration by gravimetric determination of the sample mass loss. The apparatus was tested with anthracene and 1,3,5-triphenylbenzene and subsequently used for the study of sublimation behavior of several proteinogenic amino acids. Their low volatility and thermal instability strongly limit possibilities of studying their sublimation behavior and available literature data. The results presented in this work are unique in their temperature range and low uncertainty required for benchmarking theoretical studies of sublimation behavior of molecular crystals. The possibility of dimerization in the gas phase that would invalidate the effusion experiments is addressed and disproved by theoretical calculations. The enthalpy of sublimation of each amino acid is analyzed based on the contributions in two hypothetical sublimation paths involving the proton transfer in the solid and in the gas phase. 相似文献
66.
Ruthenium, palladium and platinum complexes of 2,2,6,6-tetramethyl-3,5-heptanedione (thd) and ruthenium tris acetylacetonate
(acac) were synthetized and studied with TG, DTA, DSC and MS methods. Thermal properties of ruthenocene were also studied.
The platinum thd complex has the highest volatility despite the second highest molecular mass of the complex. All the complexes
sublimed under reduced pressure. Ru(acac)3 decomposed during sublimation under atmospheric pressure of nitrogen whereas the
other compounds studied sublimed also under these conditions. Pd(thd)2 reduced under atmospheric pressure of H2 /N2 (5% H2 ) whereas the ruthenium complexes were not reduced. The field desorption mass spectra of complexes showed only the molecular
peaks and no fragmentation occurred.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
67.
We investigated the early nucleation stages of evaporated gold submonolayers on different carbon surfaces (pristine HOPG, argon-ion irradiated HOPG and amorphous carbon). Gold core-level and valence band spectra were measured by monochromatised X-ray photoelectron spectroscopy (MXPS). The Au 4f spectra for the lowest coverages (0.1 Å equivalent thickness) on irradiated HOPG and amorphous carbon surprisingly exhibited two well-separated doublets. We attribute this phenomenon to a bimodal particle size distribution caused by gold atom pinning at carbon defect sites. Deposition at elevated temperatures (on irradiated HOPG) opens a possibility to grow particles preferentially on defect sites. The influence of carbon surface defects on the cluster morphology was checked by SEM imaging. These results are interesting for future applications as they help to improve control over metal nanodots growth. 相似文献
68.
J Schnadt J SchiesslingJ.N O’Shea S.M GrayL Patthey M.K.-J JohanssonM Shi J KrempaskýJ Åhlund P.G KarlssonP Persson N Mårtensson P.A Brühwiler 《Surface science》2003,540(1):39-54
X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy (STM) have been used to study the absorption of monolayers of the pyridinecarboxylic acid monomers (isonicotinic acid, nicotinic acid, and picolinic acid) and benzoic acid on a rutile TiO2(1 1 0) surface. We find that the pyridine and phenyl rings are oriented with their planes largely perpendicular to the surface. The azimuthal orientations are strongly influenced by adsorbate-adsorbate interactions, which in each case leads to at least two different molecular species. In order to reach this conclusion a detailed strategy has been developed for the interpretation of angle-dependent XAS data, which does not rely on any curve fitting procedures. 相似文献
69.
70.
Manuel A.V. Ribeiro da Silva Ana I.M.C. Lobo Ferreira Álvaro Cimas 《The Journal of chemical thermodynamics》2011,43(12):1857-1864
This paper reports a combined experimental and computational thermochemical study of 4-benzyloxyphenol. Static bomb combustion calorimetry and Knudsen mass-loss effusion technique were used to determine the standard (p° = 0.1 MPa) molar enthalpy of combustion, , and of sublimation, , respectively, from which the standard (p° = 0.1 MPa) molar enthalpy of formation, in the gaseous phase, at T = 298.15 K, were derived.For comparison purposes, the gas-phase enthalpy of formation of this compound was estimated by G3(MP2)//B3LYP calculations, using a set of gas-phase working reactions; the results are in excellent agreement with experimental data. G3(MP2)//B3LYP computations were also extended to the calculation of the gas-phase enthalpies of formation of the 2- and 3-benzyloxyphenol isomers. Furthermore, this composite approach was also used to obtain information about the gas-phase acidities, gas-phase basicities, proton and electron affinities, adiabatic ionization enthalpies and, finally, O–H bond dissociation enthalpies. 相似文献