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71.
Intra‐ and Intermolecular Dispersion Interactions in [n]Cycloparaphenylenes: Do They Influence Their Structural and Electronic Properties?
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José‐Vicente Climent‐Medina Prof. Ángel‐José Pérez‐Jiménez Dr. Mónica Moral Prof. Emilio San‐Fabián Prof. Juan‐Carlos Sancho‐García 《Chemphyschem》2015,16(7):1520-1528
Cycloparaphenylenes (CPPs) are nanosized structures with unique isolated and bulk properties, and are synthetic targets for the template‐driven bottom‐up synthesis of carbon nanotubes. Thus, a systematic understanding of the supramolecular order at the nanoscale is of utmost relevance for molecular engineering. In this study, it is found that intramolecular noncovalent (dispersion) interactions must be taken into account for obtaining accurate estimates of the structural and optoelectronic properties of [n]CPP compounds, and their influence as the number of repeat units increases from n=4 to n=12 is also analyzed, both in the gas phase and in solution. The supramolecular self‐assembly, for which both intra‐ and intermolecular noncovalent interactions are relevant, of [6]CPP is also investigated by calculating the binding energies of dimers taken along several crystal directions. These are also used to estimate the cohesive energy of the crystal, which is compared to the value obtained by means of dispersion‐corrected DFT calculations using periodic boundary conditions. The reasonable agreement between both computational strategies points towards a first estimate of the [6]CPP cohesive energy of around 50 kcal mol?1. 相似文献
72.
Solvent effects on oxygen-17 chemical shifts in methyl formate: linear solvation shift relationships
de Kowalewski DG Kowalewski VJ Contreras RH Díez E Casanueva J San Fabián J Esteban AL Galache MP 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,148(1):1-10
A multiple linear regression analysis has been carried out using the Kamlet-Abboud-Taft solvatochromic parameters in order to quantify the solvent effects on the (17)O chemical shifts of methyl formate (MF). The influence of the solvents upon the carbonyl oxygen chemical shifts is smaller for MF than for N-methylformamide (NMF). The influence (in parts per million) of the solvent polarity-polarizability reduces from -21.9pi* in amides to -9.6pi* in MF. The influence of the solvent hydrogen-bond-donor acidities reduces from -42.0alpha in formamides to -16.9alpha in MF. The solvent effects upon the dicoordinated oxygen chemical shifts of MF are smaller in magnitude and opposite in direction, i.e., 4.8pi* and 2.6alpha, than those for the carbonyl oxygen. (17)O hydration shifts have been calculated for the NMF + (H(2)O)(6) and MF + (H(2)O)(5) complexes by the ab initio GIAO method at the 6-311 + G** level. The hydration shifts calculated for the carbonyl oxygens of NMF and MF and for the dicoordinated oxygen of MF, -102.4, -64.7, and 17.6 ppm, respectively, show the same trend as the corresponding empirical hydration shifts, -101.7, -42.0, and 14.2 ppm. 相似文献
73.
74.
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75.
Espinosa-Solares T Morales-Contreras M Robles-Martínez F García-Nazariega M Lobato-Calleros C 《Applied biochemistry and biotechnology》2008,147(1-3):133-142
Agro-food industrial processes produce a large amount of residues, most of which are organic. One of the possible solutions
for the treatment of these residues is anaerobic digestion in bioreactors. A novel 18-L bioreactor for treating waste water
was designed based on pneumatic agitation and semispherical baffles. Flow patterns were visualized using the particle tracer
technique. Circulation times were measured with the particle tracer and the thermal technique, while mixing times were measured
using the thermal technique. Newtonian fluid and two non-Newtonian fluids were used to simulate the operational conditions.
The results showed that the change from Newtonian to non-Newtonian properties reduces mixed zones and increases circulation
and mixing times. Circulation time was similar when evaluated with the thermal and the tracer particle methods. It was possible
to predict dimensionless mixing time (θ
m) using an equivalent Froude number (Fr
eq). 相似文献
76.
Velardez GF Lemke HT Breiby DW Nielsen MM Møller KB Henriksen NE 《The journal of physical chemistry. A》2008,112(35):8179-8187
The structures of the ground and excimer states of perylene pairs are calculated [using density functional theory (DFT) and time-dependent DFT techniques] in a free as well as a crystal environment, and their spectroscopic properties are studied for the most stable configurations. The vertical transition energies for the absorption and emission bands are obtained, and they are in good agreement with experimental data. In these calculations, up to six excited states are considered. With the calculated structures of the ground and excimer states, the scattering factors are analyzed as a function of the concentration of excimers in a crystal. The intensity of the 110, 005, and 0 10 0 reflections are found to be fairly sensitive to the presence of excimers in the crystal. The finite (nanosecond) lifetime of the excimer may make it possible to observe this state using time-resolved X-ray diffraction techniques. 相似文献
77.
Fabián Flores-Bazán Nicolas Hadjisavvas Cristián Vera 《Journal of Global Optimization》2007,37(2):229-243
Given a closed convex cone P with nonempty interior in a locally convex vector space, and a set
, we provide various equivalences to the implication
among them, to the pointedness of cone(A + int P). This allows us to establish an optimal alternative theorem, suitable for vector optimization problems. In addition, we
present an optimal alternative theorem which characterizes two-dimensional spaces in the sense that it is valid if, and only
if, the space is at most two-dimensional. Applications to characterizing weakly efficient solutions through scalarization;
the zero (Lagrangian) duality gap; the Fritz–John optimality conditions for a class of nonconvex nonsmooth minimization problems,
are also presented. 相似文献
78.
Gustavo C. Buscaglia Enzo A. Dari J. Ezequiel Martín Daniela L. Arnica Fabián J. Bonetto 《International Journal of Computational Fluid Dynamics》2013,27(5):355-365
A finite element simulation of flow and heat transfer in the moderator cell of a cold-neutron source (CNS), in which liquid deuterium subject to internal heat generation is flowing, is reported. The numerical scheme consists of a stabilized equal-order method. A time-accurate approach is adopted to resolve the large-scale eddies of the flow, with a Smagorinsky's model for the subgrid-scale effects. The thermal coupling follows a staggered strategy, with SUPG-type upwinding. A specific wall-law is developed that accounts for the correct partition of the heat deposited at the wall by radiation between the liquid deuterium and the helium gas flowing at the outer side of the wall. The average flow and thermal structure are presented. The turbulent fluctuations are both illustrated in physical space and decomposed into spectral components. The wavenumber spectrum suggests that adequate resolution of the large-scale eddies has been attained with just 200,000 nodes, while a DNS analysis would have required at least 1010 nodes. Usefulness of the approach in the design process of the CNS is highlighted. 相似文献
79.
Suardíaz R Crespo-Otero R Pérez C San Fabián J García de la Vega JM 《The Journal of chemical physics》2011,134(6):061101
Quantitative side-chain torsion angle χ(1) determinations of phenylalanine residues in Desulfovibrio vulgaris flavodoxin are carried out using exclusively the correlation between the experimental vicinal coupling constants and theoretically determined Karplus equations. Karplus coefficients for nine vicinal coupling related with the torsion angle χ(1) were calculated using the B3LYP functional and basis sets of different size. Optimized χ(1) angles are in outstanding agreement with those previously reported by employing x ray and NMR measurements. 相似文献
80.
Besnard M Cabaço MI Chávez FV Pinaud N Sebastião PJ Coutinho JA Danten Y 《Chemical communications (Cambridge, England)》2012,48(9):1245-1247
The formation of 1-butyl-3-methylimidazolium-2-carboxylate in the mixture of CO(2) with 1-butyl-3-methylimidazolium acetate under mild conditions (298 K, 0.1 MPa) has been put in evidence in the liquid phase using Raman and infrared spectroscopy complemented by DFT calculations and NMR ((1)H, (13)C, (15)N) spectroscopy. 相似文献