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排序方式: 共有594条查询结果,搜索用时 15 毫秒
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Halogen contents similar to those in meteorites are reported in Apollo 11 samples. Concentrations of 0.6 to 13 parts mercury, 0.2 to 0.8 part uranium, 1 to 17 parts lithium, and 1 to 800 parts osmium per million and 0.5 to 1 percent chromium oxide by weight have been measured. In contrast to meteorites and terrestrial rocks a large mercury release below 110 degrees C is observed. Some implications of these results are presented. Fluorapatite, quartz, tridymite, fayalite, and iron-rich, manganese-poor pyroxmangite, previously unreported, have been identified. The small amount of fluorapatite found does not account for the fluorine contents. 相似文献
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Adenylyl cyclase amino acid sequence: possible channel- or transporter-like structure 总被引:47,自引:0,他引:47
J Krupinski F Coussen H A Bakalyar W J Tang P G Feinstein K Orth C Slaughter R R Reed A G Gilman 《Science (New York, N.Y.)》1989,244(4912):1558-1564
Complementary DNA's that encode an adenylyl cyclase were isolated from a bovine brain library. Most of the deduced amino acid sequence of 1134 residues is divisible into two alternating sets of hydrophobic and hydrophilic domains. Each of the two large hydrophobic domains appears to contain six transmembrane spans. Each of the two large hydrophilic domains contains a sequence that is homologous to a single cytoplasmic domain of several guanylyl cyclases; these sequences may represent nucleotide binding sites. An unexpected topographical resemblance between adenylyl cyclase and various plasma membrane channels and transporters was observed. This structural complexity suggests possible, unappreciated functions for this important enzyme. 相似文献
47.
Infants' discrimination of the duration of a rapid spectrum change in nonspeech signals 总被引:1,自引:0,他引:1
Two-month-old infants discriminated complex sinusoidal patterns that varied in the duration of their initial frequency transitions. Discrimination of these nonspeech sinusoidal patterns was a function of both the duration of the transitions and the total duration of the stimulus pattern. This contextual effect was observed even though the information specifying stimulus duration occurred after the transitional information. These findings parallel those observed with infants for perception of synthetic speech stimuli. Specialized speech processing capacities are thus not required to account for infants' sensitivity to contextual effects in acoustic signals, whether speech or nonspeech. 相似文献
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Lopatto D Alvarez C Barnard D Chandrasekaran C Chung HM Du C Eckdahl T Goodman AL Hauser C Jones CJ Kopp OR Kuleck GA McNeil G Morris R Myka JL Nagengast A Overvoorde PJ Poet JL Reed K Regisford G Revie D Rosenwald A Saville K Shaw M Skuse GR Smith C Smith M Spratt M Stamm J Thompson JS Wilson BA Witkowski C Youngblom J Leung W Shaffer CD Buhler J Mardis E Elgin SC 《Science (New York, N.Y.)》2008,322(5902):684-685
49.
The crystal structure of the tri-isopropyl silyl species, i-Pr(3)Si(Br(6)-CB(11)H(6)), where the brominated carborane Br(6)-CB(11) H(6)(-) is perhaps the least nucleophilic anion presently known, has revealed the highest degree of silylium cation character (R(3)Si(+)) yet observed. The average C-Si-C angle is 117 degrees , only 3 degrees short of the planarity expected of a pure silylium ion(120 degrees ). This value compares to 114 degrees recently reported for a toluene-solvated silyl cation, [Et(3)Si(toluene)](+) by Lambert and co-workers. The greater silylium ion character of i-Pr(3)Si(Br(6)-CB(11)H(6)) versus [i-Pr(3)Si(toluene)](+) is also reflected in the larger downfield shift of the silicon-29 nuclear magnetic resonance, 109.8 versus =94.0 parts per million. The unusual bonding of toluene to R(3)Si(+) in Lambert's compound is reinterpreted as a significant covalent pi interaction. 相似文献
50.
Burlingame AL Calvin M Han J Henderson W Reed W Simoneit BR 《Science (New York, N.Y.)》1970,167(3918):751-752
The carbon concentration in Apollo 11 lunar fine material is of the order of 200 ppm. By far the largest single amount of this carbon appears to be in carbon monoxide. Some of this seems to be in the form of gas bubbles in the glass spheres, but most of it could be in some complex form other than gas. This result would be consistent with the idea that most of the fines passed through a high temperature and that the carbon was oxidized by mineral oxides at that time. 相似文献