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31.
Ragnarsson U Grehn L Koppel J Loog O Tsubrik O Bredikhin A Mäeorg U Koppel I 《The Journal of organic chemistry》2005,70(15):5916-5921
The pK(a) values in DMSO for 22 di- and triprotected hydrazine NH acids and two monosubstituted hydrazines have been determined using potentiometric titration. The results of density functional theory calculations at the B3LYP/6-311+G level of gas-phase acidities of a representative selection of mono-, di-, and trisubstituted hydrazines are compared with both the relevant published and novel experimental titration data. In the course of this work, a rough estimation of the pK(a) value of hydrazine in DMSO (ca. 38.0) has been deduced. For typical triprotected compounds of this kind containing moderately electron-withdrawing carbamate and imidodicarbonate or arenesulfonylcarbamate functions the pK(a) values fall in the range 15.1-17.3, whereas for N,N'-diprotected hydrazines with a carbamate and an aromatic sulfonyl group the corresponding values are 12.7-14.5. Several of these triprotected derivatives have recently been applied preparatively in stepwise synthesis of substituted hydrazines using alkyl halides as electrophiles in the presence of a phase transfer catalyst, and a few of them, with varying success, have been examined in model experiments with benzyl alcohol, triphenylphosphine, and diethyl azodicarboxylate in the Mitsunobu reaction. The dependence of the reactivity on the intrinsic acidity of the hydrazines in this reaction is highlighted. Furthermore, the regioselective alkylation of an N,N'-diprotected hydrazine can be rationalized on the basis of the presented data. 相似文献
32.
33.
G. Denigès H. B. Merrill V. Lenher I. Koppel J. Štěrba-Böhmund J. Vostřebal Dorothy Hall A. E. Stoppel Ch. F. Sidener P. H. M. P. Brinton E. Färber W. F. Murray Ch. H. Cramer S. Little J. R. Camp J. W. Marden C. M. Johnson E. Montignie N. N. Tananaeff G. Tkatschenko 《Analytical and bioanalytical chemistry》1931,86(9-10):382-391
34.
L. Medicus K. Richter J. Eggert M von Laue R. von Mises R. Zsigmondy E. Schoenberg P. Seliger A. Wegener N. Bjerrum P. Pringsheim G. Kirsch K. W. F. Kohlrausch E. Pietsch H. Kallmann H. Mark E. Friederich H. Bongards Th. von Fellenberg J. Koppel W. A. Roth H. G. Grimm H. v. Euler K. Myrbäck O. Hammarsten J. E. Johansson K. Oppenheimer E. Schmitz F. Wrede A. Schleede F. Röhmann A. Pütter 《Analytical and bioanalytical chemistry》1927,70(9):347-349
35.
S. L. Malowan J. Koppel P. Jannasch O. Laubi Leiste und Wasowicz 《Fresenius' Journal of Analytical Chemistry》1921,60(12):463-470
Ohne Zusammenfassung 相似文献
36.
Ohne Zusammenfassung 相似文献
37.
Roman A. Kunetskiy Dr. Svetlana M. Polyakova Jiří Vavřík Dr. Ivana Císařová Jaan Saame Eva Roos Nerut Dr. Ivar Koppel Prof. Ilmar A. Koppel Dr. Agnes Kütt Prof. Ivo Leito Dr. Ilya M. Lyapkalo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(12):3621-3630
A series of stable organosuperbases, N‐alkyl‐ and N‐aryl‐1,3‐dialkyl‐4,5‐dimethylimidazol‐2‐ylidene amines, were efficiently synthesized from N,N′‐dialkylthioureas and 3‐hydroxy‐2‐butanone and their basicities were measured in acetonitrile. The derivatives with tert‐alkyl groups on the imino nitrogen were found to be more basic than the tBu P1 (pyrr) phosphazene base in acetonitrile. The origin of the high basicity of these compounds is discussed. In acetonitrile and in the gas phase, the basicity of the alkylimino derivatives depends on the size of the substituent at the imino group, which influences the degree of aromatization of the imidazole ring, as measured by 13C NMR chemical shifts or by the calculated ΔNICS(1) aromaticity parameters, as well as on solvation effects. If a wider range of imino‐substituents, including electron‐acceptor substituents, is treated in the analysis then the influence of aromatization is less predominant and the gas‐phase basicity becomes more dependent on the field‐inductive effect, polarizability, and resonance effects of the substituent. 相似文献
38.
Kunetskiy RA Polyakova SM Vavřík J Císařová I Saame J Nerut ER Koppel I Koppel IA Kütt A Leito I Lyapkalo IM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(12):3621-3630
A series of stable organosuperbases, N-alkyl- and N-aryl-1,3-dialkyl-4,5-dimethylimidazol-2-ylidene amines, were efficiently synthesized from N,N'-dialkylthioureas and 3-hydroxy-2-butanone and their basicities were measured in acetonitrile. The derivatives with tert-alkyl groups on the imino nitrogen were found to be more basic than the tBuP(1) (pyrr) phosphazene base in acetonitrile. The origin of the high basicity of these compounds is discussed. In acetonitrile and in the gas phase, the basicity of the alkylimino derivatives depends on the size of the substituent at the imino group, which influences the degree of aromatization of the imidazole ring, as measured by (13)C?NMR chemical shifts or by the calculated ΔNICS(1) aromaticity parameters, as well as on solvation effects. If a wider range of imino-substituents, including electron-acceptor substituents, is treated in the analysis then the influence of aromatization is less predominant and the gas-phase basicity becomes more dependent on the field-inductive effect, polarizability, and resonance effects of the substituent. 相似文献
39.
Vilve Nummert Mare Piirsalu Ilmar A. Koppel 《Journal of Physical Organic Chemistry》2010,23(6):497-504
The second‐order rate constants k (dm3 mol?1 s?1) for the alkaline hydrolysis of phenyl esters of meta‐, para‐ and ortho‐substituted benzoic acids in aqueous 5.3 M NaClO4 and 1.0 M Bu4NBr were measured by UV/Vis spectrophotometry at 25 °C. The variations in the ortho inductive, ortho resonance, as well as meta and para polar effects with solvent parameters were studied using data for the alkaline hydrolysis of phenyl esters of substituted benzoic acids in various media. The dependence of the ortho substituent effect on solvent can be precisely described with the following equation: Δlog kortho = log kortho ? log kH = 0.059 + 2.19σI + 0.304σ°R + 2.79E ? 0.016ΔEσI ? 0.085ΔEσ°R, where ΔE is the solvent electrophilicity, ΔE = ES ? EH2O, characterizing the hydrogen‐bond donating power of the solvent. The increase in the meta and para polar substituent effects with decrease in the solvent hydrogen‐bond donor capacity (electrophilicity) was approximately to the same extent (?0.068ΔEσ°m,p) as the resonance term for the ortho substituents. The steric term of ortho substituents was independent of the solvent parameters. The variations in the ortho inductive, ortho resonance, as well as meta and para polar substituent effects with the solvent electrophilicity were to the same extent as in phenyl benzoates containing the substituents in the phenyl part. The substituent effects in the alkaline hydrolysis of ethyl benzoates appeared to vary with the solvent electrophilicity nearly to the same extent as in the alkaline hydrolysis of substituted phenyl esters of benzoic acids. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
40.
Vilve Nummert Mare Piirsalu Ilmar A. Koppel 《Central European Journal of Chemistry》2013,11(12):1964-1975
The second-order rate constants k for the alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C6H4CO2C6H5, in aqueous 50.9% acetonitrile have been measured spectrophotometrically at 25°C. The log k values for meta and para derivatives correlated well with the Hammett σm,p substituent constants. The log k values for ortho-substituted phenyl benzoates showed good correlations with the Charton equation, containing the inductive, σI, resonance, σ○ R, and steric, E s B, and Charton υ substituent constants. For ortho derivatives the predicted (log k X)calc values were calculated with equation (log k ortho)calc = (log k H AN)exp + 0.059 + 2.19σI + 0.304σ○ R + 2.79E s B ? 0.0164ΔEσI — 0.0854ΔEσ○ R, where DE is the solvent electrophilicity, ΔE = E AN — E H20 = ?5.84 for aqueous 50.9% acetonitrile. The predicted (log k X)calc values for phenyl ortho-, meta- and para-substituted benzoates in aqueous 50.9% acetonitrile at 25°C precisely coincided with the experimental log k values determined in the present work. The substituent effects from the benzoyl moiety and aryl moiety were compared by correlating the log k values for the alkaline hydrolysis of phenyl esters of substituted benzoic acids, X-C6H4CO2C6H5, in various media with the corresponding log k values for substituted phenyl benzoates, C6H5CO2C6H4-X. 相似文献