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排序方式: 共有249条查询结果,搜索用时 15 毫秒
1.
Estimation in linear models with censored data 总被引:1,自引:0,他引:1
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Excitation-Contraction Coupling in Crayfish 总被引:8,自引:0,他引:8
REUBEN JOHN P.; BRANDT PHILIP W.; GARCIA HORACIO; GRUNDFEST HARRY 《Integrative and comparative biology》1967,7(3):623-645
High-sensitivity recording techniques demonstrate a continuousrelation between the onset and magnitude ot tension and themembrane depolarization that is induced by increasing K in thebathing medium or by intracellularly applied outward currents.This finding is not consistent with the mechanism of signallinge-c coupling by electrotonic spread of a "critical" depolarizationinward along the membrane of the transverse tubular system.It is in accord, however, with the channelled current mechanismthat is based on the known anion-permselectivity of the membranein the terminals of the TTS. The channelled-current model alsopredicts a direct role of Cl and a possible interaction betweenCa and CI in e-c coupling. The initiation and maintenance oftension as well as its magnitude, are in fact dependent uponthe concentrations of Ca and Cl in the medium. Thus, both thesignalling to, and the activation of, the contractile systemappear to be performed by a flow of current in the loop: cellmembrane cell interior TTS membrane TTS channels exterior, as is envisaged in the channelled-currentmodel of e-c coupling. 相似文献
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HAROLD K. SCHNEIDER 《American anthropologist》1977,79(1):9-25
Employing genetic theory as an analog, the paper argues that when the concept of culture is separated from the concept of society, anthropology can be shown to have depended for culture-change theory on a genetic model, which predicts pre-Columbian contact between the Old and New World, a prediction which is supported by a growing list of cultural parallels . [prehistoric transpacific contact, culture, society, culture change, scientific explanation] 相似文献
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HORACIO ZAGARESE CRAIG WILLIAMSON TIMOTHY VAIL OLAF OLSEN & CLAUDIA QUEIMALIÑOS 《The Plant journal : for cell and molecular biology》2004,37(1):99-106
1. The freshwater calanoid copepod Boeckella gibbosa is typical of high elevation lakes and ponds in Patagonia (Argentina). Previous studies have shown that this species is highly tolerant to short-term exposure to natural and artificial UVB radiation, and that its tolerance is due to photoreactivation by longer wavelength radiation. In this study, we investigate the potential sublethal effects of solar radiation after prolonged exposure.
2. We incubated B. gibbosa at 1 m depth in oligotrophic Lake Toncek for 24 days. The incubation chambers were 1.2 l acrylic cylinders covered with appropriate filters in order to obtain three radiation treatments: visible radiation only, visible radiation + UVA and visible radiation + UVA + UVB.
3. The three treatments did not differ significantly in variables considered as indicators of survival (number of individuals), reproduction (proportion of ovigerous females, clutch size) and development (instar composition). Although resistance to solar UVB radiation is certainly a requisite to live in transparent high elevation habitats, the fact of being effectively exposed to natural levels of UVB radiation does not seem to have measurable consequences on an already adapted species, such as B. gibbosa 相似文献
2. We incubated B. gibbosa at 1 m depth in oligotrophic Lake Toncek for 24 days. The incubation chambers were 1.2 l acrylic cylinders covered with appropriate filters in order to obtain three radiation treatments: visible radiation only, visible radiation + UVA and visible radiation + UVA + UVB.
3. The three treatments did not differ significantly in variables considered as indicators of survival (number of individuals), reproduction (proportion of ovigerous females, clutch size) and development (instar composition). Although resistance to solar UVB radiation is certainly a requisite to live in transparent high elevation habitats, the fact of being effectively exposed to natural levels of UVB radiation does not seem to have measurable consequences on an already adapted species, such as B. gibbosa 相似文献