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31.
Density gradient ultracentrifugation (DGU) and fluorescence spectroscopy are used to probe the limiting behaviors of the dynamic response of surfactant structure at the single-walled carbon nanotube (SWNT) surface to reorganizing forces, including changes in surfactant concentration and electrolyte screening. DGU results indicate that, as surfactant (sodium dodecyl sulfate, SDS) concentration is increased, SDS adsorbed on metallic SWNTs becomes limited in its ability to reorganize before SDS adsorbed on semiconducting species. A diameter-dependent enhancement is observed in photoluminescence intensities from semiconducting SWNTS upon initial titration with NaCl. This response to electrostatic screening diminishes as SDS concentration is increased. The results are understood as a saturation of the surfactant structural response, defined as both a loss in ability to increase SDS loading at the SWNT surface and a loss in ability to reorient surface structure in response to a reorganizing force. Saturation of response is found to be reversible and also occurs as a result of restricting SDS mobility. These results confirm several aspects of recent molecular dynamics simulations of SDS behavior on SWNTs and have important implications for tunability of density-based separation approaches using cosurfactant systems that include SDS. 相似文献
32.
5-Methoxy-3H-naphtho[2,1,8-mna]xanthen-3-one (musafluorone, 1), the only naphthoxanthenone reported so far from Musaceae, was synthesized starting from 2-naphthol in nine steps and resulted in an overall yield of 3%. Grignard addition of phenylmagnesium bromide to 4-methoxyperinaphthenone afforded the corresponding 4-methoxy-9-phenylphenalenone which, after epoxidation and methyl transposition, was subjected to a photochemical cyclization procedure to furnish 1. 相似文献
33.
Seven new diterpene glycosides, pseudopterosins P (1), Q (2), R (3), S (4), T (5), U (6) and V (7) along with two known compounds PsG and PsK have been isolated from the methanol/dichloromethane extract of the gorgonian octocoral Pseudopterogorgia elisabethae collected off Providencia Island, Colombian Caribbean. The structures of the new metabolites, including their relative and absolute configuration, were established by MS and NMR spectroscopic studies as well as their conversion to known compounds. 相似文献
34.
Ayats C Camps P Duque MD Font-Bardia M Muñoz MR Solans X Vázquez S 《The Journal of organic chemistry》2003,68(22):8715-8718
Two alternative syntheses of the new D2d symmetric tetramethyl tricyclo[3.3.0.0(3,7)]octane-1,3,5,7-tetracarboxylate from the known dimethyl 3,7-dioxo-cis-bicyclo[3.3.0]octane-1,5-dicarboxylate and 1,5-(2,2'-biphenylene)-cis-bicyclo[3.3.0]octane-3,7-dione are described. 相似文献
35.
We present here molecular-dynamics simulation results of the vapor-liquid coexistence curve, surface tension, and self-diffusion coefficients of sulfur hexafluoride. Sulfur hexafluoride is modeled as a rigid molecule, following the model proposed by Pawley [Mol. Phys. 43, 1321 (1981)]. Vapor-liquid coexistence curve and surface tension are obtained through direct molecular-dynamic simulations in the NVT ensemble. Simulation results are able to reproduce the qualitative shape of the vapor-liquid envelope. However, lower densities, a higher critical temperature, and an overestimated surface tension are obtained here. Those deviations are explained on the basis of the rigidity of the molecular model used. Self-diffusion coefficients are calculated from simulations in the NVE ensemble for different gas states at atmospheric pressure. The rigid model performs better for dynamical properties since simulation results provide very good agreement with available experimental data in this case. 相似文献
36.
Julio Duque Hctor Novoa de Armas Ramn Poms Hernndez Margarita Surez Navarro Estael Ochoa Rodríguez Esperanza Salfrn Yamila Verdecia Reyes Norbert. M Blaton Oswald M. Peeters Camiel J. De Ranter 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(11):1346-1347
In the title compound, C28H38N4O6, the 4‐aryl substituent occupies a pseudo‐axial position approximately orthogonal to the plane of the dihydropyridine ring [88.1 (3)°]. The dihydropyridine ring adopts a flattened boat conformation. The H atom on the pyridine N atom is involved in a bifurcated intramolecular hydrogen bond, the acceptors being the N atoms of the two piperidylmethyl groups [N?N 2.629 (4) and 2.695 (4) Å]. 相似文献
37.
38.
Origin of the Enantioselectivity in Organocatalytic Michael Additions of β‐Ketoamides to α,β‐Unsaturated Carbonyls: A Combined Experimental,Spectroscopic and Theoretical Study
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Dr. Adrien Quintard Dr. Diana Cheshmedzhieva Dr. Maria del Mar Sanchez Duque Dr. Anouk Gaudel‐Siri Dr. Jean‐Valère Naubron Dr. Yves Génisson Dr. Jean‐Christophe Plaquevent Dr. Xavier Bugaut Prof. Jean Rodriguez Prof. Thierry Constantieux 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):778-790
The organocatalytic enantioselective conjugate addition of secondary β‐ketoamides to α,β‐unsaturated carbonyl compounds is reported. Use of bifunctional Takemoto’s thiourea catalyst allows enantiocontrol of the reaction leading either to simple Michael adducts or spirocyclic aminals in up to 99 % ee. The origin of the enantioselectivity has been rationalised based on combined DFT calculations and kinetic analysis. This study provides a deeper understanding of the reaction mechanism, which involves a predominant role of the secondary amide proton, and clarifies the complex interactions occurring between substrates and the catalyst. 相似文献
39.
R. N. Kreidel M. D. Duque C. H. R. Serra M. V. R. Velasco A. R. Baby T. M. Kaneko 《Journal of Dispersion Science and Technology》2013,34(9):1354-1359
The solid dispersion approach is an alternative to increase drug solubility. Many carriers have been studied, but there is few information about poloxamer 407 (P407). Consequently, the objective of this study was to evaluate P407 as a carrier for nimodipine solid dispersions and to compare its solubility and dissolution rates with those from polyethylene glycol (PEG 6000). The solid dispersions were prepared by the hot melting and solvent methods and they were characterized by FTIR, DSC, solubility, and dissolution tests. The results indicated a three-fold increase in solid dispersions solubility in the presence with P407 than those prepared with PEG. 相似文献
40.
C. A. Duque M. E. Mora-Ramos E. Kasapoglu H. Sari I. Sökmen 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,81(4):441-449
In this work are studied the intense laser effects on the impurity states in GaAs-Ga1−
x
Al
x
As quantum wells under applied electric and magnetic fields. The electric field is taken oriented along the growth direction
of the quantum well whereas the magnetic field is considered to be in-plane. The calculations are made within the effective
mass and parabolic band approximations. The intense laser effects have been included through the Floquet method by modifying
the confinement potential associated to the heterostructure. The results are presented for several configurations of the dimensions
of the quantum well, the position of the impurity atom, the applied electric and magnetic fields, and the incident intense
laser radiation. The results suggest that for fixed geometry setups in the system, the binding energy is a decreasing function
of the electric field intensity while a dual monotonic behavior is detected when it varies with the magnitude of an applied
magnetic field, according to the intensity of the laser field radiation. 相似文献