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排序方式: 共有257条查询结果,搜索用时 383 毫秒
221.
Nuclear shell model calculations based on a modified harmonic-oscillator potential result in amazingly stable triaxial nuclear shapes. Major gaps in the single-particle energy spectra at proton number 71 and neutron number 94 combine constructively at low and intermediate rotational frequencies. At high frequencies, gaps at proton number 72 and neutron number 97 combine in an equally favourable way. The sizes of the gaps may be as large as 35% of the values for the gaps at the classical magic numbers 50 and 82 at spherical shape. The dependence on the positions of the intruder levels in forming the gaps is discussed. Experimentally observed rotational bands in lutetium (Z = 71) and hafnium (Z = 72) appear in isotopes and frequency ranges, which are consistent with the gaps in the theoretical single-particle energy spectra. 相似文献
222.
223.
Aihara H Alston-Garnjost M Avery RE Barbaro-Galtieri A Barker AR Barnes AV Barnett BA Bauer DA Bengtsson H Bintinger DL Bobbink GJ Bolognese TS Bross AD Buchanan CD Buijs A Caldwell DO Clark AR Cowan GD Crane DA Dahl OI Derby KA Eastman JJ Eberhard PH Edberg TK Eisner AM Enomoto R Erné FC Fujii T Gary JW Gorn W Hauptman JM Hofmann W Huth JE Hylen J Kamae T Kaye HS Kees KH Kenney RW Kerth LT Ko W Koda RI Kofler RR Kwong KK Lander RL Langeveld WG Layter JG Linde FL Lindsey CS Loken SC Lu A Lu X 《Physical review letters》1987,59(7):751-754
224.
Aihara H Alston-Garnjost M Avery RE Barbaro-Galtieri A Barker AR Barnes AV Barnett BA Bauer DA Bengtsson H Bintinger DL Blumenfeld BJ Bobbink GJ Bross AD Buchanan CD Buijs A Cain MP Caldwell DO Chamberlain O Chien C Clark AR Cowan GD Crane DA Dahl OI Derby KA Eastman JJ Eberhard PH Eisner AM Enomoto R Erné FC Fujii T Gabioud B Gary JW Gorn W Hauptman JM Hofmann W Huth JE Hylen J Joshi UP Kamae T Kaye HS Kees KH Kenney RW Kerth LT Ko W Koda RI Kofler RR Kwong KK Lander RL Langeveld WG Layter JG 《Physical review letters》1986,57(4):404-407
225.
Ducros VM Tarling CA Zechel DL Brzozowski AM Frandsen TP von Ossowski I Schülein M Withers SG Davies GJ 《Chemistry & biology》2003,10(7):619-628
The formation of glycoconjugates and oligosaccharides remains one of the most challenging chemical syntheses. Chemo-enzymatic routes using retaining glycosidases have been successfully harnessed but require tight kinetic or thermodynamic control. "Glycosynthases," specifically engineered glycosidases that catalyze the formation of glycosidic bonds from glycosyl donor and acceptor alcohol, are an emerging range of synthetic tools in which catalytic nucleophile mutants are harnessed together with glycosyl fluoride donors to generate powerful and versatile catalysts. Here we present the structural and kinetic dissection of the Humicola insolens Cel7B glycosynthases in which the nucleophile of the wild-type enzyme is mutated to alanine and serine (E197A and E197S). 3-D structures reveal the acceptor and donor subsites and the basis for substrate inhibition. Kinetic analysis shows that the E197S mutant is considerably more active than the corresponding alanine mutant due to a 40-fold increase in k(cat). 相似文献
226.
Michael MecklenburgJuraj Svitel Fredrik WinquistJin Gang Katharina OrnsteinEstera Dey Xie BinEva Hedborg Ragnar NorrbyHans Arwin Ingemar LundströmBengt Danielsson 《Analytica chimica acta》2002,459(1):25-31
Bacterial infection and inflammation result in massive changes in serum glycoproteins. These changes were investigated by the interaction of the saccharide glycoprotein moiety with lectins. A panel of eight lectins (Canavalia ensiformis, Bandeiraea simplicifolia BS-I, Arachis hypogaea, Phytolacca americana, Phaseolus vulgaris, Artocarpus integrifolia, Triticum vulgaris and Pisum sativum) was used to differentiate human serum glycoproteins obtained from patients with various bacterial infections. Lectin functionalised sensing layers were created on gold-coated wafers and lectin-glycoprotein interactions were monitored by surface plasmon resonance. The interaction of the lectin panel with serum glycoproteins produces unique patterns. Principal component analysis (PCA) was used to analyse the patterns. The actual panel of eight lectins enabled discrimination between sera obtained from patients sick with bacterial infection and healthy patients. Extended lectin panels have the potential to distinguish between types of bacterial infection and identify specific disease state. 相似文献
227.
Metal ions (Cu2+, Co2+, Cd2+, Ni2+, Pb2+, Zn2+) were concentrated quantitatively and isolated from the sample matrix by a colum 相似文献
228.
G. B. Bengtsson A. I. Bortun V. V. Strelko 《Journal of Radioanalytical and Nuclear Chemistry》1996,204(1):75-82
A comparison of strontium sorption on synthetic inorganic ion exchangers and zeolites from 0.01M CaCl2 solution, sea water and an artificial foodstuff fluid has been carried out in batch and column experiments. It was found that some adsorbents among the groups manganese dioxides, mixed titanium-manganese oxides, antimony-based materials and synthetic zeolites had the highest selectivity to strontium (K
d
>1000). These adsorbents are interesting for further investigation concerning their use for radiostrontium decontamination of foodstuffs (if nontoxic), as well as for analytical purposes. 相似文献
229.
Brånalt J Kvarnström I Classon B Samuelsson B 《The Journal of organic chemistry》1996,61(11):3611-3615
The synthesis of [4,5-bis(hydroxymethyl)-1,3-dithiolan-2-yl]nucleosides is described. (2S,3S)-1,2:3,4-Diepoxybutane (13) was reacted with potassium thiocyanate to give (2R,3R)-1,2:3,4-diepithiobutane (14). Thiiranering opening with acetate followed by deacetylation gave (2R,3R)-2,3-dithiothreitol (19) which was silylated and treated with trimethyl orthoformate to give the 2-methoxy-1,3-dithiolane 20. Condensation of 20 with silylated thymine, uracil, N(4)-benzoylcytosine and 6-chloropurine using a modified Vorbrüggen procedure, followed by deprotection, gave the nucleoside analogues. Compounds 26, 28, and 30 were found to be inactive when tested for anti-HIV activity in vitro. 相似文献
230.
An ion formed by loss of 56 mass units from the molecular ion is often seen in mass spectra of trimethylsilyl ethers of C19 and C21 steroids having a 3β-hydroxy-Δ5 structure and an oxo group at C-17 or C-20. The nature of this fragment was investigated by the use of perdeuteriotrimethylsilyl ether derivatives and of [4-14C], [3-18O], [4,4-2H2] and [2,2,4,4-2H] labelled derivatives of 3β-hydroxy-5-androsten-17-one and 3β-hydroxy-5-pregnen-20-one. Evidence is presented to show that the neutral fragment of mass 56 is composed of carbon atoms 1, 2 and 3, the oxygen at C-3 and four hydrogen atoms. During the fragmentation process, the trimethylsilyl group and one of the hydrogens at C-2 are transferred to the fragment that carries the charge. 相似文献