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101.
Wilson JN Josowicz M Wang Y Bunz UH 《Chemical communications (Cambridge, England)》2003,(24):2962-2963
The cruciform pentamers 3a-g were synthesized by a combined Horner-Sonogashira approach; their band gaps vary significantly with emission varying from blue to red depending upon their substituent pattern. 相似文献
102.
Summary Purine derivative drugs, aminophylline, theophylline, xantinolnicotinate, 6-mercaptopurine, 6-thyoguanine, azathioprine, 1-methylxantine, 3-methylxantine, 1-methyluric acid, 1,3-dimethyluric acid, 6-thioxantine, 2-amino-6-methylmercaptopurine, were separated by thin-layer chromatography on rice starch and cellulose by three different solvent systems. Conditions for quantitative fluorodensitometric determination of purine derivatives drugs were investigated. 相似文献
103.
Peré-Trepat E Petrovic M Barceló D Tauler R 《Analytical and bioanalytical chemistry》2004,378(3):642-654
Identification, resolution and distribution of main microcontaminant sources of endocrine disruptors in Spanish harbours, coastal waters and sediments are investigated using chemometric methods. We investigated eighteen different endocrine disruptor chemical compounds, including non-ionic surfactants, their degradation products and linear alkylbenzene sulfonates, found in a total number of 74 samples (35 water samples and 39 sediment samples) over a period of 16 months from March 1999 to July 2000, and in 32 different geographical sites along the Spanish Mediterranean Coast (e.g. Barcelona, Tarragona, Almeria Harbour, Malaga and the Bay of Cadiz). Main environmental contamination sources of these endocrine disruptor compounds were investigated and interpreted according to their chemical composition and according to their resolved geographical distribution profiles.An erratum to this article can be found at 相似文献
104.
Recent advances in the mass spectrometric analysis related to endocrine disrupting compounds in aquatic environmental samples 总被引:1,自引:0,他引:1
An overview of mass spectrometric methods used for the determination of endocrine disrupting compounds (EDCs) in environmental samples is presented. Among the EDCs we have selected five groups of compounds that are of priority within European Union and US research activities: alkylphenols, polychlorinated compounds (dioxins, furans and biphenyls), polybrominated diphenyl ethers, phthalates and steroid sex hormones. Various aspects of current LC-MS and GC-MS methodology, including sample preparation, are discussed. 相似文献
105.
A method to quantify the linearity and dynamic range of terahertz detectors is reported and used to show that terahertz time-domain-spectrometers exhibit a nonlinear amplitude response at frequencies below 1.5 THz. 相似文献
106.
We show that for every n > 0 there is a planar topological disk A0 and n translates A1, A2, ..., An of A0 such that the interiors of A0, ..., An are pairwise disjoint, but with each Ai touching A0 for 1 ≤ i ≤ n. 相似文献
107.
A criterion used for the determination of first- and second-order magnetic phase transitions from purely magnetic methods is applied to manganese perovskites of formula La2/3(Ca1−xSrx)1/3MnO3. A crossover from first- to second-order character at a tolerance factor t=0.92 is found, which also brings about several variations in other physical properties. At t=0.92 a change from orthorhombic to rhombohedral symmetry also takes place. The impossibility of establishing static cooperative Jahn–Teller distortions in the rhombohedral symmetry is suggested as being responsible for the observed behaviour. 相似文献
108.
To gain an initial understanding of the copper-based catalysts in commercially important chemical reactions such as the oxygen-assisted water-gas shift reaction, we performed density-functional theory calculations, investigating the interaction of oxygen and copper, focusing on the relative stability of surface oxides and oxide surfaces of the O/Cu system. By employing the technique of “ab initio atomistic thermodynamics”, we show that surface oxides are only metastable at relevant pressures and temperatures of technical catalysis, with no stable chemisorption phase observed even at very low coverage. Although exhibiting only metastability, these surface oxides resemble the bulk oxide material both geometrically and electronically, and may serve as a precursor phase before onset of the bulk oxide phase. Having identified the bulk oxide as the most stable phase under realistic catalytic conditions, we show that a Cu2O(1 1 1) surface with Cu vacancies has a lower free energy than the stoichiometric surface for the considered range of oxygen chemical potential and could be catalytically relevant. 相似文献
109.
[reaction: see text] HOF.CH(3)CN, a very efficient oxygen-transfer agent, made readily from F(2), H(2)O, and CH(3)CN, was reacted with various 1,10-phenanthroline derivatives to form the corresponding N,N'-dioxides in good yields and short reaction times. 相似文献
110.
Mira J Rivadulla F Rivas J Fondado A Guidi T Caciuffo R Carsughi F Radaelli PG Goodenough JB 《Physical review letters》2003,90(9):097203
MnAs exhibits a first-order phase transition from a ferromagnetic, high-spin metal hexagonal phase to a paramagnetic, lower-spin insulator orthorhombic phase at T(C)=313 K. Here, we report the results of neutron diffraction experiments showing that an external magnetic field, B, stabilizes the hexagonal phase above T(C). The phase transformation is reversible and constitutes the first demonstration of a bond-breaking transition induced by a magnetic field. The field-induced phase transition is accompanied by an enhanced magnetoresistance of about 17% at 310 K. The phenomenon appears to be similar to that of the colossal magnetoresistance response observed in the Mn [corrected] perovskite family. 相似文献