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11.
[reaction: see text] Various factors that influence the rate of the intramolecular Diels-Alder reaction of amidofurans were investigated with density functional theory calculations using the Becke3LYP/6-31G* model. Conformational effects imposed by the placement of a carbonyl group within the tether, combined with a rotational bias about the C(2)-N bond, account for the observed rate differences in the thermal chemistry of these amidofurans. 相似文献
12.
M. Hartmanová V. Navrátil V. Buršíková F. Kundracik C. Mansilla 《Russian Journal of Electrochemistry》2011,47(5):505-516
Electrical conductivity, dielectric permittivity and mechanical hardness of the polycrystalline CeO2 + xSm2O3 (x = 0, 10.9–15.9 mol %) films prepared by Electron Beam Physical Vapour Deposition (EB-PVD) and Ionic Beam Assisted Deposition,
(IBAD), techniques were investigated in dependence on their structure and microstructure influenced by the deposition conditions,
namely composition, deposition temperature and Ar+ ion bombardment. The electrical conductivity of doped ceria prepared without Ar+ ion bombardment and investigated by the impedance spectroscopy, IS, was found to be predominantly ionic one under the oxidizing
atmosphere/low-temperature conditions and the higher amounts of Sm2O3 (>10 mol %) used. The bulk conductivity as a part of total measured conductivity was a subject of interest because the grain
boundary conductivity was found to be ∼3 orders of magnitude lower than the corresponding bulk conductivity. Ar+ ion bombardment acted as a reducer (Ce4+ → Ce3+) resulting in the development of electronic conductivity. Dielectric permittivity determined from the bulk parallel capacitance
measured at room temperature and the frequency of 1 MHz, similarly as the mechanical hardness measured by indentation (classical
Vickers and Depth Sensing Indentation-DSI) techniques were also found to be dependent on the deposition conditions. The approximative
value of hardness for the investigated films deposited on the substrate was estimated using a simple phenomenological model
described by the power function HV = HV
0 + aP
b
and compared with the so-called apparent hardness (substrate + investigated film) determined by the classical Vickers formula.
Results obtained are analyzed and discussed. 相似文献
13.
Hein JE Burés J Lam YH Hughes M Houk KN Armstrong A Blackmond DG 《Organic letters》2011,13(20):5644-5647
Experimental and computational studies probing the nature of intermediates in the α-amination of aldehydes catalyzed by prolinate salts support an enamine carboxylate intermediate in the stereodetermining step. 相似文献
14.
15.
Pavel?Bro?Email author Jir?í?Bur?ík Zdeňka?Stará 《Monatshefte für Chemie / Chemical Monthly》2005,136(11):1915-1920
Summary. Multicomponent Ni-base alloys exhibit good mechanical properties even at elevated temperatures and they are widely used for
industrial production of exertion-resistive parts of engines. These properties are mainly determined by the coexistence of
a disordered γ matrix with a face centred cubic lattice and cuboidal domains of its ordered γ′ structure. Therefore it is
useful to study phase equilibria in Ni-base systems, namely in the regions involving both mentioned phases. One of the conclusions
of our recent work on Ni–Al–Cr–W system was a necessity of modification of selected thermodynamic parameters of the ternary
Ni–Al–W subsystem in order to achieve a better agreement of our experimental observations with theoretical modelling. This
involves new measurements of the microstructure of selected samples of the Ni–Al–W system at 900°C and the comparison of the
results with existing literature data in order to confirm our conclusions on higher order system investigated before. It is
a first step on the way to an assessment of the Ni–Al–W system, which has not been done before. 相似文献
16.
Asaula V. M. Shvets O. V. Pariiska O. O. Bur’yanov V. V. Ryabukhin S. V. Volochnyuk D. M. Kolotilov S. V. 《Theoretical and Experimental Chemistry》2020,56(4):261-267
Theoretical and Experimental Chemistry - It is shown that a composite containing nickel nanoparticles and carboneous multi-layer graphene-like particles on aerosil, prepared by pyrolysis of... 相似文献
17.
As N-sulfenyl imines (e.g., RR'C=N-SAr) can be readily transformed to their N-sulfinyl imines (RR'C=N-SOAr), N-sulfonyl imines (RR'C=N-SO2Ar), and N-sulfonyl oxaziridines, the very mild procedure developed to convert ketoximes and secondary nitro derivatives to N-arenesulfenyl ketimines constitutes a new and efficient route to all these series of compounds. The configuration of the alpha-stereocenters is retained. 相似文献
18.
19.
Oefner C Binggeli A Breu V Bur D Clozel JP D'Arcy A Dorn A Fischli W Grüninger F Güller R Hirth G Märki H Mathews S M ller M Ridley RG Stadler H Vieira E Wilhelm M Winkler F Wostl W 《Chemistry & biology》1999,6(3):127-131
BACKGROUND: The aspartic proteinase renin catalyses the first and rate-limiting step in the conversion of angiotensinogen to the hormone angiotensin II, and therefore plays an important physiological role in the regulation of blood pressure. Numerous potent peptidomimetic inhibitors of this important drug target have been developed, but none of these compounds have progressed past clinical phase II trials. Limited oral bioavailability or excessive production costs have prevented these inhibitors from becoming new antihypertensive drugs. We were interested in developing new nonpeptidomimetic renin inhibitors. RESULTS: High-throughput screening of the Roche compound library identified a simple 3, 4-disubstituted piperidine lead compound. We determined the crystal structures of recombinant human renin complexed with two representatives of this new class. Binding of these substituted piperidine derivatives is accompanied by major induced-fit adaptations around the enzyme's active site. CONCLUSIONS: The efficient optimisation of the piperidine inhibitors was facilitated by structural analysis of the renin active site in two renin-inhibitor complexes (some of the piperidine derivatives have picomolar affinities for renin). These structural changes provide the basis for a novel paradigm for inhibition of monomeric aspartic proteinases. 相似文献
20.
Amanda M. Franey Nina D. Serratore Noah A. Setterholm Scott K. Bur 《Tetrahedron letters》2012,53(2):179-181
Increasing the size of the silyl group on 2-trialkylsilyloxyfurans reduces the rate of Diels–Alder reactions with maleic acid derivatives. While the exo-adduct resulted from the reaction between 2-silyloxyfurans and maleic anhydride, endo-adducts resulted from the reactions with maleate esters. Analysis of transition state structures for the cycloaddition, calculated at the B3LYP/6-31G1 level of theory, revealed significant stretch-mode asynchronicity in the forming bonds, with selectivity arising from steric interactions that affect torsional strain about the shorter of the forming bonds. 相似文献