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21.
Doklady Mathematics - The dynamics of systems in a potential field is considered in the case where kinetic energy can be represented in conformal form. In the case of two degrees of freedom,... 相似文献
22.
S. B. Denisova E. G. Galkin V. T. Danilov Yu. I. Murinov 《Chemistry of Natural Compounds》2003,39(3):237-239
Simple sugars were isolated from the ethanol extract of Glycyrrhiza glabra L. root. The component composition of the carbohydrate fraction was established using GC-MS (gas-chromatographic separation and mass-spectrometric analysis). 相似文献
23.
S. A. Denisova O. S. Kudryashova A. E. Lesnov E. A. Sazonova 《Russian Journal of General Chemistry》2007,77(11):1855-1858
Solubility isotherms of the antipirin-pyrocatechol-water ternary system at 25 and 50°C were constructed. A field where two liquid phases are present in equilibrium which results from the protolytic interaction between the components was revealed. The various-composition chemical compounds that formed were isolated preparatively. Interphase distribution of a series of metal ions was studied. The half-extraction pHs of rare-earth metals were found to be linearly related to their ionic radii. 相似文献
24.
The O-H bond dissociation energies (D O-H) in five alcohols and six acids have been determined from experimental data (rate constants of radical reactions). The ratio of the rate constants of the reactions R1O˙+RH→R1OH+R˙ and R i O˙+RH→R i OH+R˙ and the intersecting parabolas method are used in the estimation procedure. The D O-H values are used to calculate the activation energies and rate constants for hydrogen abstraction from 2-methylbutane, butene-1, and cumene by alkoxyl and carboxyl radicals. The geometric parameters of the transition state are calculated for these reactions. 相似文献
25.
Sheiman B. M. Yuzefovich L. Yu. Denisova L. Ya. Filippova T. M. Mairanovskii V. G. Berezovakii V. M. 《Chemistry of Heterocyclic Compounds》1977,13(5):511-515
The constants and thermodynamic parameters of the ring-chain tautomeric equilibrium of p-substituted (benzene ring) 2,3,3-trimethyl-1-aryl-2-hydroxy-5-pyrrolidones in aqueous pyridine solution were determined by PMR spectroscopy. Conversion of the ring tautomer to the open form is accompanied by an increase in the enthalpy and entropy. The AH value decreases by a factor of 2.8 kcal/mole on passing from electron-donor substituents to electron-acceptor substituants, whereas the AS value remains approximately constant and decreases by 2–4 eu only for strong electron acceptors (COOCH3, CN, and NO2). The correlation between the free energies and the a substituent constants in the benzene ring is discussed.See [1] for communication XII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 634–638, May, 1977. 相似文献
26.
Conclusions The parallel formation of hydroperoxide, lactone, and acids in the initial period of the initiated oxidation of cyclohexanone was established. The reaction RO2 + cyclohexanone RO+lactone, RO acid, explaining this fact, was proposed.Translated from Izvestiya Akademii Nauk SSSR, Setiya Khimicheskaya, No. 6, pp. 1108–1110, June, 1964 相似文献
27.
B. B. Troitskii L. V. Khokhlova A. N. Konev V. N. Denisova M. A. Novikova M. A. Lopatin 《Russian Journal of Applied Chemistry》2005,78(6):1018-1022
Wariation of the concentration of fullerenes C60 and C70 in poly(methyl methacrylate) films under UV exposure in atmospheric oxygen was studied. The mechanism of the influence exerted by addition of some photostabilizing polymers and xanthene dyes on the photooxidative degradation of fullerene in the polymer matrix was analyzed.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005, pp. 1038–1042.Original Russian Text Copyright © 2005 by Troitskii, Khokhlova, Konev, Denisova, Novikova, Lopatin. 相似文献
28.
The parabolic model of radical abstraction reactions is used to analyze experimental data on monomolecular hydrogen-atom transfer in the reactionsRC.H(CH2)
n
CH2R1 RCH2(CH2)
n
C.HR1(n= 2, 3, 4)RCH(O.)(CH2)2CH2R1 RCH(OH)(CH2)2C.HR1
RCH(OO.)(CH2)
n
CH2R1 RCH(OOH)(CH2)
n
C.HR1(n= 1, 2).The activation energies and rate constants that specify each class of these reactions are calculated. Alkyl radical isomerization is characterized by the following activation energies of a thermally neutral reaction depending on the cycle size in the transition state (nis the number of atoms in a cycle): E
e
, 0(kJ/mol) = 46.6 (n= 6), 59.4 (n= 5), and 57.1 (n= 7). Alkoxy radicals isomerize with E
e
, 0(kJ/mol) = 53.4 (n= 6), whereas peroxy radicals isomerize with E
e
, 0(kJ/mol) = 53.2 (n= 6) and E
e
, 0(kJ/mol) = 54.8 (n= 7). The E
e
, 0value varies with changes in the cycle size and the strain energy in cycloparaffin C
n
H2n
in the same manner. The activation energies E
e
, 0for the intra- and intermolecular H-atom abstractions are compared. It is found that E
e
, 0(isomerization) < E
e
, 0(R.+ R1H) for alkyl radicals and that E
e
, 0(isomerization) E
e
, 0(RO.(RO.) + R1H) for alkoxy and peroxy radicals. 相似文献
29.
30.
Dr. Dmitry B. Eremin Ekaterina A. Denisova Dr. Alexander Yu. Kostyukovich Dr. Jonathan Martens Dr. Giel Berden Prof. Dr. Jos Oomens Prof. Dr. Victor N. Khrustalev Prof. Dr. Victor M. Chernyshev Prof. Dr. Valentine P. Ananikov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(72):16564-16572
N-Heterocyclic carbene (NHC) ligands are ubiquitously utilized in catalysis. A common catalyst design model assumes strong M–NHC binding in this metal–ligand framework. In contrast to this common assumption, we demonstrate here that lability and controlled cleavage of the M−NHC bond (rather than its stabilization) could be more important for high-performance catalysis at low catalyst concentrations. The present study reveals a dynamic stabilization mechanism with labile metal–NHC binding and [PdX3]−[NHC-R]+ ion pair formation. Access to reactive anionic palladium intermediates formed by dissociation of the NHC ligands and plausible stabilization of the molecular catalyst in solution by interaction with the [NHC-R]+ azolium ion is of particular importance for an efficient and recyclable catalyst. These ionic Pd/NHC complexes allowed for the first time the recycling of the complex in a well-defined form with isolation at each cycle. Computational investigation of the reaction mechanism confirms a facile formation of NHC-free anionic Pd in polar media through either Ph–NHC coupling or reversible H–NHC coupling. The present study formulates novel ideas for M/NHC catalyst design. 相似文献