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排序方式: 共有137条查询结果,搜索用时 15 毫秒
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The reaction of PPh2Cl with orthomanganated acetophenone, 2′-CH3C(O)C6H4Mn(CO)4, gives Mn2(μ-η1,η1-Ph2PPPh2)(μ-Cl)2(CO)6. An X-ray structure determination [triclinic, space group P1 , a = 10.908(4) Å, b = 11.756(3) Å, c = 12.186(3) Å, α = 96.20(2)°, β = 99.51(2)°, γ = 96.52(2)°] shows two Mn(CO)3 groups held together by two bridging Cl ligands, and further bridged by a Ph2P? PPh2 group prepared in situ. 相似文献
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Do Kim Tiung N. A. Lebedev Nguyen Quang Main V. A. Khalkin 《Journal of Radioanalytical and Nuclear Chemistry》1976,30(2):353-360
The nuclear reactions of (p, xn)-type, Ep=100–120 MeV, on Gd and Nd have been used to produce highly radioactive preparations of Tb and Pm enriched with neutron-deficient isotopes. Under comparable conditions the yields of practically all isotopes are considerably higher than in Tb and Gd spallation reactions at Ep=660 MeV. The radioactivity of screened154Tb and156Tb isotopes has been increased more than 40 times. Tb and Pm were separated from gram amounts of the target-elements by the extraction chromatography technique with undiluted di-(2-ethylhexyl) phosphoric acid as stationary phase. The radiochemical method developed was also applied to separate the radiochemically pure preparation of161Tb from Gd oxide irradiated with thermal neutrons. 相似文献
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J. Main A. Holle G. Wiebusch K. H. Welge 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1987,6(4):295-302
Three-dimensional “regular” quasi-Landau resonances, recently discovered experimentally in the Balmer spectrum of the highly excited hydrogen atom around the ionization limit in external static homogeneous magnetic fields, are investigated theoretically by extending previous classical trajectory calculations to semi-classically. Employing the EBK-method for multidimensional non-separable systems, closed trajectories of the excited electron with the proton as origin are quantized by numerical quadrature of the two-dimensional EBK-integral in cylindrical coordinates. The results are resonances with quantum numbersn=1, 2,... for each closed classical trajectory as functions of both the excitation energyE and field strengthB. The calculations include in particular also the classically chaotic region around the ionization limit with experimentally accessible fields, just the region which has so far defied exact quantum mechanical solution. Based on simple physical arguments for the motion of the highly excited electron, an analytic relation is derived for the (E, B)-dependence of the regular three-dimensional resonances which fits quantitatively the numerical EBK-results. 相似文献
68.
Mortensen GK Main KM Andersson AM Leffers H Skakkebaek NE 《Analytical and bioanalytical chemistry》2005,382(4):1084-1092
Daily exposure of humans to phthalates may be a health risk because animal experiments have shown these compounds can affect the differentiation and function of the reproductive system. Because milk is the main source of nutrition for infants, knowledge of phthalate levels is important for exposure and risk assessment. Here we describe the development and validation of a quantitative analytical procedure for determination of phthalate metabolites in human milk. The phthalate monoesters investigated were: monomethyl phthalate (mMP), monoethyl phthalate (mEP), mono-n-butyl phthalate (mBP), monobenzyl phthalate (mBzP), mono-(2-ethylhexyl) phthalate (mEHP), and monoisononyl phthalate (mNP). The method is based on liquid extraction with a mixture of ethyl acetate and cyclohexane (95:5) followed by two-step solid-phase extraction (SPE). Detection and quantification of the phthalate monoesters were accomplished by high-pressure liquid chromatography using a Betasil phenyl column (100 mm×2.1 mm×3 m) and triple tandem mass spectrometry (LC–MS–MS). Detection limits were in the range 0.01 to 0.5 g L–1 and method variation was from 5 to 15%. Analysis of 36 milk samples showed that all these phthalates were present, albeit at different concentrations. Median values (g L–1) obtained were 0.11 (mMP), 0.95 (mEP), 3.5 (mBP), 0.8 (mBzP), 9.5 (mEHP), and 101 (mNP). We also analysed seven samples of consumer milk and ten samples of infant formula. Only mBP and mEHP were detected in these samples, in the ranges 0.6–3.9 g L–1 (mBP) and 5.6–9.9 g L–1 (mEHP). 相似文献
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Peter Main 《Journal of Chemical Sciences》1983,92(4-5):385-396
The properties and previous use of the double Patterson function in x-ray crystallography are briefly reviewed followed by
an account of a new iterative technique, based on the double Patterson, which is being developed by the author. The technique
starts with an approximation to the double Patterson which does not require phases, then improves the approximation by making
it conform to the known projections and known magnitudes of the Fourier coefficients. The latter are 3-phase structure invariants
and estimating their phases is an important step in the direct determination of structure factor phases. Tests carried out
on one-dimensional centro-symmetric structures show that the technique is successful. At best, it determines correct phases
for all 3-phase invariants. At worst, it fails to improve on the estimate of all phases being zero. It consistently does very
much better than the B3, 0 formula which is also based on the double Patterson. Further development is necessary to apply the technique to non-centrosymmetric
structures and to real structures in three dimensions. 相似文献
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