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101.
102.
D-p-hydroxyphenylglycine (D-HPG) is prepared from racemic HPG via salicylaldehyde mediated resolution-racemization of the corresponding D-3-bromocamphor-8-sulfonate salt in acetic acid. After slurry purification to improve the de to >99.9%, the crystallized salt is neutralized to produce D-HPG in 92% overall yield and 99.9% ee. 相似文献
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105.
Foster CE Krämer T Wait AF Parkin A Jennings DP Happe T McGrady JE Armstrong FA 《Journal of the American Chemical Society》2012,134(17):7553-7557
Formaldehyde-a rapid and reversible inhibitor of hydrogen evolution by [FeFe]-hydrogenases-binds with a strong potential dependence that is almost complementary to that of CO. Whereas exogenous CO binds tightly to the oxidized state known as H(ox) but very weakly to a state two electrons more reduced, formaldehyde interacts most strongly with the latter. Formaldehyde thus intercepts increasingly reduced states of the catalytic cycle, and density functional theory calculations support the proposal that it reacts with the H-cluster directly, most likely targeting an otherwise elusive and highly reactive Fe-hydrido (Fe-H) intermediate. 相似文献
106.
Carina M.L. Delpiccolo Sebastián A. Testero Federico N. Leyes Dora B. Boggián Cristián M. Camacho Ernesto G. Mata 《Tetrahedron》2012,68(52):10780-10786
A straightforward solid phase-based strategy for the rapid generation of two small libraries of trans 3-alkyl-substituted β-lactams is described. For the glycine-derived library, a controlled excess of nonactivated acid chlorides was used to prevent oxazinone formation. The second library involved the attachment of Fmoc-protected p-aminophenol to Wang resin for the preparation of structurally-closed analogues of known cholesterol absorption inhibitors. This strategy allowed us to introduce diversity in the three variable positions of the β-lactam ring. 相似文献
107.
Virginia Puccia Carina Luengo Marcelo Avena 《Colloids and surfaces. A, Physicochemical and engineering aspects》2009,348(1-3):221-227
The kinetics of the arsenate-induced desorption of phosphate from goethite has been studied with a batch reactor system and ATR-FTIR spectroscopy. The effects of arsenate concentration, adsorbed phosphate, pH and temperature between 10 and 45 °C were investigated. Arsenate is able to promote phosphate desorption because both oxoanions compete for the same surface sites of goethite. The desorption occurs in two steps: a fast step that takes place in less than 5 min and a slow step that lasts several hours. In the slow step, arsenate ions exchange adsorbed phosphate ions in a 1:1 stoichiometry. The reaction is first order with respect to arsenate concentration and is independent of adsorbed phosphate under the experimental conditions of this work. The rate law is then r = kr[As], where r is the desorption rate, kr is the rate constant and [As] is the arsenate concentration in solution. The values of kr at pH 7 are 1.87 × 10−5 L m−2 min−1 at 25 °C and 7.95 × 10−5 L m−2 min−1 at 45 °C. The apparent activation energy of the desorption process is 51 kJ mol−1. Data suggest that the rate-controlling process is intraparticle diffusion of As species, probably As diffusion in pores. ATR-FTIR spectroscopy suggests that adsorbed phosphate species at pH 7 are mainly bidentate inner-sphere surface complexes. The identity of these complexes does not change during desorption, and there is no evidence for the formation of intermediate species during the reaction. 相似文献
108.
A crystal structural model for the orthorhombic compound V2.38Nb10.7O32.7, which is known as “V2Nb9O27.5”, was developed by means of selected area electron diffraction (SAED), Rietveld refinement and high resolution electron microscopy (HREM). The metastable compound is obtained by thermal decomposition of freeze-dried precursors as chain-like agglomerated nanoparticles or by reaction of V2O5 with fresh-precipitated Nb2O5 as more compact micro-scaled crystals. With the latter, it was possible to identify its structure for the first time (space group Cmmm). The tetragonal tungsten bronze (TTB)-type structure shows high potential for ionic intercalation, since easily reducible [V5+2O2−] units are implemented in the tunnels of a rigid niobium oxide framework. 相似文献
109.
An efficient one pot asymmetric synthesis of tetrahydropyrano[2,3-c]pyrazoles has been developed. This class of biologically active heterocycles can be obtained via a secondary amine catalyzed asymmetric Michael/Wittig/oxa-Michael reaction sequence. Remarkably, the title compounds were accessible in good to very good yields and very good to excellent enantioselectivities after a single purification step. 相似文献
110.
Bäcktorp C Wass JR Panas I Sköld M Börje A Nyman G 《The journal of physical chemistry. A》2006,110(44):12204-12212
This study concerns the autoxidation of one of the most used fragrances in daily life, linalool (3,7-dimethyl-1,6-octadien-3-ol). It reacts with O2 to form hydroperoxides, which are known to be important contact allergens. Pathways for hydroperoxide formation are investigated by means of quantum mechanical electronic structure calculations. Optimized molecular geometries and harmonic vibrational frequencies are determined using density functional theory (DFT). Insight into how the addition of O2 to linalool occurs is obtained by establishing a theoretical framework and systematically investigating three smaller systems: propene, 2-methyl-2-butene, and 2-methyl-2-pentene. 2-Methyl-2-pentene was chosen as a model system and used to compare with linalool. This theoretical study characterizes the linalool-O2 biradical intermediate state, which constitutes a branching point for the further oxidation reactions pathways. Thus, the observed linalool oxidation product spectrum is discussed in terms of a direct reaction path, the ene-type mechanism, and the radical mechanism. The major hydroperoxide found in experiments is 7-hydroperoxy-3,7-dimethyl-octa-1,5-diene-3-ol, and the calculated results support this finding. 相似文献