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431.
432.
The synthesis of a conformationally restricted analog of the anti-migraine drug sumatriptan 总被引:3,自引:0,他引:3
The synthesis of 5-N-Methylaminosulfonylmethyl-3-(N-methylpyrrolidin-2-ylmethyl)indole (1), a conformationally restricted analog of the anti-migraine drug, sumatriptan, is described. To incorporate our novel stereogenic replacement for the aminoethyl sidechain in sumatriptan, a convergent synthesis of the 3,5-disubstituted indole (1) was employed which utilized an intramolecular Heck reaction as the cornerstone reaction. 相似文献
433.
A quantitative method for determination of low levels (0.05%, w/w) of nitrilotriacetic and ethylenediaminetetraacetic acids in diethylenetriaminepentaacetic acid is described. Palmitic acid is added to the chelator as an internal standard before esterification with methanol containing 2%(v/v)H2SO4. The methyl esters of palmitic, nitrilotriacetic, and ethylenediaminetetraacetic acids are first separated from diethylenetriaminepentaacetate by silicic acid column chromatography and are subsequently quantitated by gas-liquid chromatography. The method is both accurate and reproducible with less than 10% relative error. Thin-layer chromatographic separations of the methyl esters, and quantitation at the 1% level, are also described. 相似文献
434.
The dynamics of a series of 1-acylaminoanthraquinones with varying degrees of excited-state intramolecular proton transfer are studied in acetonitrile and dichloromethane. Events are followed via changes in the third-order intermolecular Raman response as a function of time after resonant excitation of the chromophore. Compared to electronically resonant probes of the solute, measuring the ultrafast dynamics using the nonresonant solvent response offers a new and complementary perspective on the events that accompany excitation and proton transfer. Experimentally observed changes in the nuclear polarizability of the solvent follow dynamic changes in the solvent-solute interactions. Reorganization of the solvent in response to the significant changes in the intermolecular interactions upon proton transfer is found to play an important role in the reaction dynamics. With transfer of the proton taking place rapidly, the solvent controls the dynamics via the time-dependent evolution of the free energy surface, even on subpicosecond time scales. In addition, the solvent response probes the effects of intermolecular energy transfer as energy released during the reactive event is rapidly transferred to the local solvent environment and then dissipates to the bulk solvent on about a 10 ps time scale. A brief initial account of a portion of this work has appeared previously, J. Am. Chem. Soc. 2004, 126, 8620-8621. 相似文献
435.
Vadim G. Kessler Gerald I. Spijksma Gulaim A. Seisenbaeva Sebastian Håkansson Dave H. A. Blank Henny J. M. Bouwmeester 《Journal of Sol-Gel Science and Technology》2006,40(2-3):163-179
This paper summarizes recent literature data and presents new experimental data on the mechanisms of chemical modification,
hydrolysis and polycondensation of the alkoxides and demonstrates possibilities to approach new classes of materials, exploiting
these mechanisms. Low reactivity of silicon alkoxides is improved by either basic catalysis exploiting an SN2 mechanism or acidic catalysis facilitating a proton-assisted SN1 mechanism as well as by modification with chelating ligands. Metal alkoxides are much stronger Lewis bases compared to silicon
alkoxides and the acidity of water is strong enough to achieve their rapid hydrolysis via proton-assisted SN1 pathway even in the absence of additional catalysts. Introduction of the modifying chelating ligands is leading generally
to increased charge distribution in the precursor molecules. Modifying chelating ligands are also appreciably smaller than
the alkoxide ligands they replace. The modification with chelating ligands is thus facilitating the kinetics of hydrolysis
and polycondensation. The size and shape of the primary particles formed in sol-gel treatment of metal alkoxides are defined
not by kinetic factors in their hydrolysis and polycondensation but by the interactions on the phase boundary, which is in
its turn directed by the ligand properties. The products of the fast hydrolysis and condensation sequence consist of micelles
templated by self-assembly of ligands (mainly oxo-species). This concept provides explanations for commonly observed material
properties and allows for the development of new strategies for the preparation of materials. We discuss the formation of
inverted micelles, obtained by the appropriate choice of solvents, which allows for the formation of hollow spheres. The modifying
β-diketonate ligands act as the surfactant and form an interface between the hollow sphere and the solvent. Retention of ligands
inside the gel particles is possible only if ligands possessing both chelating and bridging properties are applied. Application
of such ligands, for example, diethanolamine, permits to prepare new transition metal oxide based microporous membranes. 相似文献
436.
W. G. Leighton M. Francis P. Saffert W. Wustrow G. F. Liebig E. W. Blank K. Hauschild H. Flood J. A. Patterson jun G. E. Le Worthy H. B. Brooks A. W. Spinks R. Links W. Geyger W. Schmidts K. Peters L. G. C. Warne R. A. J. Boschart J. van den Berg M. Plaut R. E. Dunbar H. A. J. Pieters 《Analytical and bioanalytical chemistry》1935,100(1-2):36-40
437.
438.
Electron spin resonance microscopy (ESRM) is an imaging method aiming at the observation of stable free radicals in small samples with a spatial resolution of about 1 micrometer. One of the challenges associated with the useof ESRM in conjunction with small biological samples (e.g., single cells) is containing these samples in a manner that will minimize the effect on the quality factor of the resonator but yet enable easy handling and simultaneous optical and ESR observation. Here we present a new type of flat samples that provide an adequate answer to this challenge. The samples are made of thin glass coverslips, manufactured by photolithography techniques. Details of the manufacturing process as well as the expected improvements in sensitivity and resolution are provided. 相似文献
439.
Refraction and ultra‐small‐angle scattering of X‐rays in a single‐crystal diamond compound refractive lens
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S. Gasilov A. Mittone T. dos Santos Rolo S. Polyakov S. Zholudev S. Terentyev V. Blank A. Bravin T. Baumbach 《Journal of synchrotron radiation》2017,24(6):1137-1145
In this work a double‐crystal setup is employed to study compound refractive lenses made of single‐crystal diamond. The point spread function of the lens is calculated taking into account the lens transmission, the wavefront aberrations, and the ultra‐small‐angle broadening of the X‐ray beam. It is shown that, similarly to the wavefront aberrations, the ultra‐small‐angle scattering effects can significantly reduce the intensity gain and increase the focal spot size. The suggested approach can be particularly useful for the characterization of refractive X‐ray lenses composed of many tens of unit lenses. 相似文献
440.
New metal-nanocarbon composites were obtained by high-energy (ball milling) pre-treatment of the powder mixture followed by high-pressure/high-temperature treatment. Acoustic microscopy was used to study elastic properties and bulk irregularities of the samples. 相似文献