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71.
Michael D. Ludden Christopher G. P. Taylor Max B. Tipping Jennifer S. Train Nicholas H. Williams Jack C. Dorrat Kellie L. Tuck Michael D. Ward 《Chemical science》2021,12(44):14781
An octanuclear M8L12 coordination cage catalyses the Kemp elimination reaction of 5-nitro-1,2-benzisoxazole (NBI) with hydroxide to give 2-cyano-4-nitrophenolate (CNP) as the product. In contrast to the previously-reported very efficient catalysis of the Kemp elimination reaction of unsubstituted benzisoxazole, which involves the substrate binding inside the cage cavity, the catalysed reaction of NBI with hydroxide is slower and occurs at the external surface of the cage, even though NBI can bind inside the cage cavity. The rate of the catalysed reaction is sensitive to the presence of added anions, which bind to the 16+ cage surface, displacing the hydroxide ions from around the cage which are essential reaction partners in the Kemp elimination. Thus we can observe different binding affinities of anions to the surface of the cationic cage in aqueous solution by the extent to which they displace hydroxide and thereby inhibit the catalysed Kemp elimination and slow down the appearance of CNP. For anions with a −1 charge the observed affinity order for binding to the cage surface is consistent with their ease of desolvation and their ordering in the Hofmeister series. With anions that are significantly basic (fluoride, hydrogen carbonate, carboxylates) the accumulation of the anion around the cage surface accelerates the Kemp elimination compared to the background reaction with hydroxide, which we ascribe to the ability of these anions to participate directly in the Kemp elimination. This work provides valuable mechanistic insights into the role of the cage in co-locating the substrate and the anionic reaction partners in a cage-catalysed reaction.A cage-catalysed Kemp elimination reaction of 5-nitro-1,2-benzisoxazole (NBI) with hydroxide to give 2-cyano-4-nitrophenolate (CNP) as the product is sensitive to binding of different types of anion to the cage surface. 相似文献
72.
John Tuck und W. Joung 《Fresenius' Journal of Analytical Chemistry》1865,4(1):486-487
Ohne Zusammenfassung 相似文献
73.
A mathematical model describing the coupling of electrical,optical and thermal effects in semiconductor lasers is introduced.Numerical and asymptotic solutions are derived, including expressionsfor key physical quantities such as the initial time delay,the frequency of spike oscillation and the temperature rise,together with its influence on the photon density, the electronconcentration and the threshold current. The consequences ofthermal effects in reducing efficiency are thus quantified. 相似文献
74.
Megan K. Thorson Phuc Ung Franklin M. Leaver Teresa S. Corbin Kellie L. Tuck Bim Graham Amy M. Barrios 《Analytica chimica acta》2015
A series of lanthanide-based, azide-appended complexes were investigated as hydrogen sulfide-sensitive probes. Europium complex 1 and Tb complex 3 both displayed a sulfide-dependent increase in luminescence, while Tb complex 2 displayed a decrease in luminescence upon exposure to NaHS. The utility of the complexes for monitoring sulfide levels in industrial oil and water samples was investigated. Complex 3 provided a sensitive measure of sulfide levels in petrochemical water samples (detection limit ∼ 250 nM), while complex 1 was capable of monitoring μM levels of sulfide in partially refined crude oil. 相似文献
75.
Andrea Ambrosi Katarzyna A. Piechowicz Tyler A. Tuck Di Xu Haiming Zhang Francis Gosselin 《Helvetica chimica acta》2023,106(8):e202300023
A six-step, stereoselective synthesis of cyclin-dependent kinase 2 (CDK2) inhibitor GNE-140 was developed. The key bonds were assembled through palladium-catalyzed Negishi cross-coupling and Buchwald–Hartwig C−N coupling steps. The stereodiad was established through a single-step, CuH-catalyzed enone reduction proceeding in >99 : 1 er and 89 : 11 dr. GNE-140 was obtained in 25 % overall yield with 98.6 A% HPLC purity. 相似文献
76.
Dr Brian Tuck 《Contemporary Physics》2013,54(3):261-263
A review of Diflusion in Crystalline Solids, edited by G. E. Murch and A. S. Nowick. (New York: Academic Press Inc.) [Pp. xv + 484.] $73.00; £51.50. 相似文献
77.
The electrochemical oxidation of cadmium metal in the presence of methyl or ethyl iodide leads to the formation of unstable RCdI. These, and related species, can be stabilised with neutral ligands, and a series of adducts of alkylaryl- and perfluoroaryl-cadmium halides have been prepared. The oxidation apparently involves a free radical mechanism. The results support previous studies of solution equilibria involving R2Cd and CdX2 species. 相似文献
78.
J D Lovin G E Wesbey B L Engelstad G Sosnovsky M Moseley D L Tuck R C Brasch 《Magnetic resonance imaging》1985,3(1):73-81
We examined the magnetic resonance properties of 12 paramagnetic piperidinyl nitroxyls in water and plasma solutions. Paramagnetic contributions to proton relaxation times were measured using 10.7 and 100 MHz spectrometers. Proton relaxation enhancement from nitroxyls increased with ascending molecular weight, in plasma solutions versus equimolar aqueous solutions, and with measurements at 10.7 MHz compared to 100 MHz. Relaxation rates were observed to approximately double at 10.7 MHz compared to 100 MHz and from water to plasma solutions. The data indicate that proton spin-lattice relaxation enhancement is magnetic field-dependent, and increases using nitroxyls of large molecular weight and with chemical substitutents that increase the microviscosity of solvent water molecules. The development of nitroxyls for diagnostic MRI will be aided by understanding these in vitro physical characteristics and trends. 相似文献
79.
80.
The kinetics of the polymerization of cyclopentene by WCl6/AliBu3 catalysts have been studied and the factors controlling the reproducibility of the rate of polymerization have been ascertained. A significant dependence of the rate of polymerization on the time between the additions of WCl6 and AliBu3 was observed. The dependence of the catalyst activity r,i this time delay suggested that WCl6 reacted with cyclopentene to produce an unstable species (W1) that could react with AliBu3 to produce a catalytically active species (W11) or that could react further with cyclopentene to produce another species W2 that in turn would react with AliBu3 to produce a much less active catalyst W21. The detailed study of the kinetics of polymerization under controlled conditions suggested a kinetic chain mechanism initiated by two catalyst species; mechanism of polymerization based on the carbene system is suggested. 相似文献