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1.
I. Sajó und Frau B. Sipos 《Fresenius' Journal of Analytical Chemistry》1966,222(1):23-50
Summary A novel method has been developed for the rapid analysis of silicates. Each component is determined from the temperature variation of the solution resulting from the addition to the test solution of a selectively reacting reagent. By suitable construction of the instrument the concentration of the component to be determined can be read directly in per cent. The determination of a component takes usually 4 to 8 minutes.In the test solution a temperature change proportional to the concentration of the component to be determined has been produced by the following reagents: sulphuric acid for barium, ammonium peroxodisulphate for iron, hydrogen peroxide for titanium, hydrofluoric acid for silicic acid, potassium permanganate for sulphur, ammonium molybdate and hydrogen peroxide for phosphate, potassium permanganate for manganese, potassium oxalate for calcium, diammonium hydrogenphosphate for magnesium, ascorbic acid for chromium. The above components can be determined without any separations. Only in the case of aluminium a separation of silicic acid from aluminium by dehydrating with perchloric acid in necessary. Thereafter the aluminium can be determined with hydrofluoric acid.The precision of the determinations is practically identical with the precision of the usual plant methods. 相似文献
2.
Summary Electrostatic and structural properties of a set of -lactam, -lactam and nonlactam compounds have been analyzed and compared with those of a model of the natural substrate d-alanyl-d-alanine for the carboxy- and transpeptidase enzymes. This first comparison of the electrostatic properties has been based on a distributed multipole analysis of high-quality ab initio wave functions of the substrate and potential antibiotics. The electrostatic similarity of the substrate and active compounds is apparent, and contrasts with the electrostatic properties of the noninhibitors. This has been quantified to give a reasonable correlation with the MIC (Minimum Concentration for Inhibition) and with kinetic data (k2/K) in accordance with the model for interaction of the lactam compounds with dd-peptidase. These correlations provide a better prediction of antibacterial activity than purely structural criteria. 相似文献
3.
Zusammenfassung Die Verfasser bestimmten mit Hilfe ihres Dampfraumanalysenverfahrens die Alkoholtension über Äthanol-Wasser-Zinkchlorid-Lösungen. Auch die Viskosität der flüssigen Phase wurde gemessen. Die Meß-ergebnisse werden mit den beim Calciumchlorid in einer früheren Arbeit erhaltenen verglichen.
Summary With the aid of their vapor space analytical procedure the authors determined the alcohol tension above ethanol-water-zinc chloride solutions. The viscosity of the liquid phase was also measured. The findings were compared with those obtained with calcium chloride in a previous study.
Résumé Les auteurs ont déterminé la tension de vapeur de l'alcool sur des solutions éthanol-eau-chlorure de zinc par leur méthode d'analyse à chambre de vaporisation. Ils ont également déterminé la viscosité de la phase liquide. Les résultats des mesures sont comparés à ceux qui ont été obtenus antérieurement avec le chlorure de calcium.相似文献
4.
Vijayakumar Uppar Sandeep Chandrashekharappa Chandan Shivamallu Sushma P Shiva Prasad Kollur Joaquín Ortega-Castro Juan Frau Norma Flores-Holguín Atiyaparveen I. Basarikatti Mallikarjun Chougala Mrudula Mohan M Govindappa Banuprakash Jayadev Katharigatta N. Venugopala Belakatte P. Nandeshwarappa Ravindra Veerapur Abdulaziz A. Al-Kheraif Abdallah M. Elgorban Asad Syed Kiran K. Mudnakudu-Nagaraju Basavaraj Padmashali Daniel Glossman-Mitnik 《Molecules (Basel, Switzerland)》2021,26(9)
5.
Juan Frau Josefa Donoso Francisco Muoz Bartolom Vilanova Francisco García-Blanco 《Helvetica chimica acta》1997,80(3):739-747
A comprehensive study of the alkaline hydrolysis of the β-lactam ring of azetidin-2-one was carried out using ab initio molecular-orbital calculations at the RHF/6-31 + G* level. The influence of the solvent on this reaction was investigated by using the reaction field method (SCRF); the solvent was found to suppress the interference of some gas-phase reactions and allow the presence of a transition state to be detected as the nucleophile approaches the β-lactam ring. The transition state corresponds to a structure where the OH? group lies at a distance of 1.927 Å from the C?O group of the β-lactam ring and exhibits a potential barrier of 13.6 kcal/mol. 相似文献
6.
7.
Miquel Adrover Juan Frau Catalina Caldés Bartolomé Vilanova Josefa Donoso Francisco Muñoz 《Journal of photochemistry and photobiology. A, Chemistry》2010,209(1):19-26
4-Aminomethylpyridine (4-PAM) has been widely used as a model compound to elucidate the mechanisms of biological and biomedical action of the amino derivatives of vitamin B6. By virtue of the presence of two ionizable groups (viz. a pyridine nitrogen and an amino function) in its structure, 4-PAM in solution occurs as various ionic and tautomeric forms in equilibrium. In this work, we optimized the geometries of such forms and found the protonation status of the ionizable groups in 4-PAM to affect the molecular geometry and frontier orbitals. In addition, we determined the experimental electronic excitation energies for each molecular species of 4-PAM from deconvoluted UV–vis spectra. The results thus obtained were compared with their theoretical counterparts as determined from TD-DFT calculations. Based on the outcome, the theoretical methodology used affords correct simulation of electronic excitation energies. The theoretical and experimental results showed that the deprotonation of the pyridine nitrogen has no effect on the energy of the first electronic transition, however it affects its intensity. Additionally, the deprotonation of both pyridine nitrogen and methylamino group increases the number of bands, by increasing the n–π* transitions. 相似文献
8.
Rodrigo Casasnovas David Fernández Joaquín Ortega-Castro Juan Frau Josefa Donoso Francisco Muñoz 《Theoretical chemistry accounts》2011,130(1):1-13
CBS-QB3, two simplified and less computationally demanding versions of CBS-QB3, DFT-B3LYP, and HF quantum chemistry methods
have been used in conjunction with the CPCM continuum solvent model to calculate the free energies of proton exchange reactions
in water solution following an isodesmic reaction approach. According to our results, the precision of the predicted pK
a values when compared to experiment is equivalent to that of the thermodynamic cycles that combine gas-phase and solution-phase
calculations. However, in the aqueous isodesmic reaction schema, the accuracy of the results is less sensitive to the presence
of explicit water molecules and to the global charges of the involved species since the free energies of solvation are not
required. In addition, this procedure makes easier the prediction of pK
a values for molecules that undergo large conformational changes in solvation process and makes possible the pK
a prediction of unstable species in gas-phase such as some zwitterionic tautomers. The successive pK
a values of few amino acids corresponding to the ionization of the α-carboxylic acid and α-amine groups, which is one of the
problematic cases for thermodynamic cycles, were successfully calculated by employing the aqueous isodesmic reaction yielding
mean absolute deviations of 0.22 and 0.19 pK
a units for the first and second ionization processes, respectively. 相似文献
9.
A theoretical study of the gas-phase alkaline hydrolysis of penicillin G on the assumption of a BAC2 mechanism is reported. Various semiempirical methods were used to determine the influence of different parameterizations on the process. Among the most salient results obtained, the standard AM1 method predicted opening of the thiazolidine ring to yield the corresponding imine and enamine structures. 相似文献
10.
Kasture S Pawar A Kasture A Foddis C Frau MA Maxia A 《Natural product research》2011,25(20):1950-1954
In the traditional system of medicine in Sardinia, Rubia peregrina (RP) is reported as an aphrodisiac herb. Since aphrodisiacs may also have dopaminergic activity, and there can be a reciprocal relationship between dopaminergic and serotonergic functions in the central nervous system, the aim here was to study the effect of the ethanolic extract of the aerial parts of R. peregrina on monoamine-mediated behaviour. The RP (100 and 200?mg?kg(-1) intraperitoneally) significantly inhibited haloperidol (1?mg?kg(-1) i.p.) induced catalepsy in mice (p?0.01, dopamine-mediated response) lithium sulphate induced head twitches in rats (serotonin-mediated response) and was without effect on clonidine-induced hypothermia in rats (noradrenaline-mediated response). The study concludes that R. peregrina improves the dopaminergic function, diminishes the serotonin-mediated function and is devoid of any effect on the noradrenergic function. The study suggests that we should carry out further experiments to investigate the psychopharmacological profile of R. peregrina. 相似文献