Terminal cretaceous extinctions in the hell creek area, montana: compatible with catastrophic extinction     

Smit J  VAN DER Kaars S 《Science (New York, N.Y.)》1984,223(4641):1177-1179

Inaccurate stratigraphic correlations in the Hell Creek area, Montana, have led to the assumption that transitional vertebrate faunas (Bug Creek Anthills) exist in the latest Cretaceous, refuting a catastrophic turnover at the Cretaceous-Tertiary boundary. Establishment of the transitional faunas in Paleocene channels that cut down through the Cretaceous-Tertiary boundary renders the terrestrial faunal record compatible with the marine record and with catastrophic extinction.  相似文献   

转PEPC基因水稻接种固氮菌的效应   总被引：1，自引：1，他引：1  

严建民  闫春玲  林敏  张保明  陈炳松  焦德茂 《江苏农业学报》2003,19(2):65-69

利用~(15)N-同位素技术研究转PEPC基因水稻及无PEPC基因水稻在接种不同固氮菌后的光合特性、产量性状和固氮能力的变化。结果表明:接种水稻联合固氮工程菌处理与未接种固氮菌处理相比,转PEPC基因水稻的PEPC活性、PS Ⅱ光化学效率(Fv/Fm)、净光合速率均明显提高,生物学产量和经济产量也相应增加了38.08％和26.86％;与无PEPC基因水稻相比,转PEPC基因水稻能明显提高水稻联合固氮工程菌的固氮效率。这种水稻光合与固氮相互促进的机理值得深入研究。  相似文献   

Magnetotactic bacteria at the geomagnetic equator     

Frankel RB  Blakemore RP  DE Araujo FF  Esquivel DM  Danon J 《Science (New York, N.Y.)》1981,212(4500):1269-1270

Magnetotactic bacteria are present in fresh water and marine sediments of Fortaleza, Brazil, situated close to the geomagnetic equator. Both South-seeking and North-seeking bacteria are present in roughly equal numbers in the same samples. This observation is consistent with the hypothesis that the vertical component of the geomagnetic field selects the predominant polarity type among magnetotactic bacteria in natural environments.  相似文献   

PHYSIOLOGY OF THE AMINO ACIDS     

VAN Slyke DD 《Science (New York, N.Y.)》1942,95(2463):259-263

We have followed the amino acids from their entrance into the alimentary tract in the form of food proteins through the successive steps of digestion, absorption into the blood stream and passage from the blood stream into the tissues, where they are concentrated by some unknown mechanism to many times their concentration in the blood plasma. We have seen something of the way in which certain of the amino acids can be transformed into one another in the body or synthesized from ammonia and keto acids. However, we have had to admit that our bodies can form in such ways only about half of the different amino acids that are required, and that the other half must be made for us by plants, bacteria or other organisms which have greater synthetic powers than we. And finally we have seen something of the manifold fates of the amino acids after they have entered our tissues; how they may be destroyed and their nitrogenous parts turned into urea in the liver before it is possible to put them to their more specialized uses, how their carbon fractions can be used to form glucose, how they may sacrifice themselves to protect us from toxic products, how they can serve as source material for certain vitamins, hormones and other compounds with physiological functions still to be identified, and how finally those amino acids which are not deflected to these various fates may enter into the proteins of the tissues and become for a time parts of our living structures.  相似文献   

Oceanic Residence Times of Dissolved Beryllium and Aluminum Deduced from Cosmogenic Tracers 10Be and 26Al     

Yokoyama Y  Guichard F  Reyss JL  VAN NH 《Science (New York, N.Y.)》1978,201(4360):1016-1017

The residence times of the soluble fractions of beryllium and aluminum in seawater are estimated to be 1500 years or more. These residence times are estimated from a comparison of the annual deposition rates of cosmogenic beryllium-10 and aluminum-26 with the concentrations of beryllium-10 and aluminum-26 in seawater estimated from the specific activities of these radionuclides in an authigenic mineral assembly such as a manganese nodule. These residence times are greater by an order of magnitude than the mean residence times of beryllium and aluminum estimated from the geochemical balance.  相似文献   

NUTRITIVE VALUE OF THE MEXICAN TORTILLA     

Cravioto RO  Anderson RK  Lockhart EE  DE P Miranda F  Harris RS 《Science (New York, N.Y.)》1945,102(2639):91-93

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A homolog of Drosophila grainy head is essential for epidermal integrity in mice   总被引：1，自引：0，他引：1  

Ting SB  Caddy J  Hislop N  Wilanowski T  Auden A  Zhao LL  Ellis S  Kaur P  Uchida Y  Holleran WM  Elias PM  Cunningham JM  Jane SM 《Science (New York, N.Y.)》2005,308(5720):411-413

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A NORTHERN MICHIGAN BASELEVEL     

VAN Hise CR 《Science (New York, N.Y.)》1896,4(86):217-220

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The Name of America     

DE St Bris T 《Science (New York, N.Y.)》1888,12(283):12

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THE GEOLOGY OF ORE DEPOSITS. II     

VAN Hise CR 《Science (New York, N.Y.)》1901,14(360):785-793

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