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41.
Adams MR Aïd S Anthony PL Averill DA Baker MD Baller BR Banerjee A Bhatti AA Bratzler U Braun HM Breidung H Busza W Carroll TJ Clark HL Conrad JM Davisson R Derado I Dhawan SK Dietrich FS Dougherty W Dreyer T Eckardt V Ecker U Erdmann M Faller F Fang GY Figiel J Finlay RW Gebauer HJ Geesaman DF Griffioen KA Guo RS Haas J Halliwell C Hantke D Hicks KH Hughes VW Jackson HE Jancso G Jansen DM Jin Z Kaufman S Kennedy RD Kinney ER Kirk T Kobrak HG Kotwal AV Kunori S Lancaster S Lord JJ Lubatti HJ 《Physical review letters》1995,74(9):1525-1529
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We prove the existence of uncountably many nonisomorphic topological projective planes, each universal in the sense that it contains an isomorphic copy of every pseudoline arrangement. 相似文献
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Chromatography has been an important tool in marine laboratories. Since the 1960s, marine laboratories have been involved in the analysis of polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), and brominated flame retardants (BFRs). Column chromatography and liquid chromatography (LC) techniques have been used, mainly in the clean-up phase, while gas chromatography (GC) has been used extensively in the final determination of these contaminants. Developments have been observed from the use of packed GC columns, via capillary columns to the use of heart-cut multi-dimensional GC and comprehensive multi-dimensional GC. The progress made in interlaboratory studies and the availability of certified reference materials are discussed. 相似文献
47.
John A. Montgomery James R. Piper Robert D. Elliott Eugene C. Roberts Carroll Temple Y. Fulmer Shealy 《Journal of heterocyclic chemistry》1979,16(3):537-539
Eighteen derivatives of 2,4-diamino-6-methylpteridine related to methotrexate and aminopterin have been prepared from 6-(bromomethyl)-2,4-pteridinediamine by nucleophilic displacement reactions. None of these compounds showed any antileukemic acitivity. 相似文献
48.
A new two-step four-component synthesis of highly functionalized cyclohexenols by sequential nickel-catalyzed couplings 总被引:1,自引:0,他引:1
A new two-step procedure for the synthesis of cyclohexenols has been developed. A nickel-catalyzed three-component addition of an enal, alkyne, and acetylenic tin affords substituted hept-4-en-6-ynals. The products of this first step then undergo a second nickel-catalyzed reaction with organozincs or organoboranes to afford densely functionalized cyclohexenols. Variation in each of the four components is tolerated to provide access to a wide range of versatile building blocks. 相似文献
49.
The defect rock-salt type materials Zr1?xS, Sc1?xS, and Lu1?xS have been shown to exhibit a complex variety of ordered superstructures. These superstructures are reviewed within the context of Landau's theory of symmetry and phase transitions, and it is concluded that there is a significant similarity in the transitions when they are considered from the point of view of reciprocal space. 相似文献
50.
John A. Montgomery Anita T. Shortnacy Sarah D. Clayton 《Journal of heterocyclic chemistry》1977,14(2):195-197
The reaction of the trimethylsilyl derivative of 4,6-dichloroimidazo[4,5-c]pyridine with 2,3,5-tri-O-benzoyl- D -ribofuranosyl bromide gave four nucleosides-the α- and β-anomers of the 1-isomer and the α- and β-anomers of the 3-isomer (3.9:2.7:1.5:1). In contrast, the fusion reaction of 4,6-dichloroimidazo[4,5-c ]pyridine with 1,2,3,5-tetra-O-acetyl-β- D -ribofuranose gave a high yield of the 1-β-isomer, which was converted to the known 3-deazaadenosine (4-amino-l-β- D -ribofuranosylimidazo[4,5-c]pyridine). 相似文献