排序方式: 共有32条查询结果,搜索用时 15 毫秒
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Hahn CN Chong CE Carmichael CL Wilkins EJ Brautigan PJ Li XC Babic M Lin M Carmagnac A Lee YK Kok CH Gagliardi L Friend KL Ekert PG Butcher CM Brown AL Lewis ID To LB Timms AE Storek J Moore S Altree M Escher R Bardy PG Suthers GK D'Andrea RJ Horwitz MS Scott HS 《Nature genetics》2011,43(10):1012-1017
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D E Humphries G W Wong D S Friend M F Gurish W T Qiu C Huang A H Sharpe R L Stevens 《Nature》1999,400(6746):769-772
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J P Friend 《Experientia》1979,35(12):1577-1578
Pituitary cells increase their numbers more than 3-fold during the 1st 10 days of life while maintaining the same cell size ratios. In the 25-day-old animal, the rate of cell division slows and there is a slight increase in the number of large cells. An increase in adult weight is attributed to hyperplasia and a shift to a population of larger cells. 相似文献
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Cell size and cell division of the anterior pituitary: Time course in the growing rat 总被引:1,自引:0,他引:1
J. P. Friend 《Cellular and molecular life sciences : CMLS》1979,35(12):1577-1578
Summary Pituitary cells increase their numbers more than 3-fold during the 1st 10 days of life while maintaining the same cell size ratios. In the 25-day-old animal, the rate of cell division slows and there is a slight increase in the number of larger cells. An increase in adult weight is attributed to hyperplasia and a shift to a population of larger cells.Supported by NIH grant HD08844. 相似文献
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Europe-wide reduction in primary productivity caused by the heat and drought in 2003 总被引:22,自引:0,他引:22
Ciais P Reichstein M Viovy N Granier A Ogée J Allard V Aubinet M Buchmann N Bernhofer C Carrara A Chevallier F De Noblet N Friend AD Friedlingstein P Grünwald T Heinesch B Keronen P Knohl A Krinner G Loustau D Manca G Matteucci G Miglietta F Ourcival JM Papale D Pilegaard K Rambal S Seufert G Soussana JF Sanz MJ Schulze ED Vesala T Valentini R 《Nature》2005,437(7058):529-533
Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate, their impact on terrestrial carbon cycling is unclear. Here we report measurements of ecosystem carbon dioxide fluxes, remotely sensed radiation absorbed by plants, and country-level crop yields taken during the European heatwave in 2003. We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003, and their consequences for the net carbon balance. We estimate a 30 per cent reduction in gross primary productivity over Europe, which resulted in a strong anomalous net source of carbon dioxide (0.5 Pg C yr(-1)) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration. Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat, respectively. We also find that ecosystem respiration decreased together with gross primary productivity, rather than accelerating with the temperature rise. Model results, corroborated by historical records of crop yields, suggest that such a reduction in Europe's primary productivity is unprecedented during the last century. An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes. 相似文献
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Interventionism analyses causal influence in terms of correlations of changes under a distribution of interventions. But the correspondence between correlated changes and causal influence is not obvious. I probe its plausibility with a problem-case involving variables related as time derivative (velocity) to integral (position), such that the latter variable must change given an intervention on the former unless dependencies are introduced among the testing and controlling interventions. Under the orthodox criteria such interventions will fail to be appropriate for causal analysis. I consider various alternatives, including permitting control interventions to be chancy, restricting the available models and mitigating variation of off-path variables. None of these work. I then present a fourth suggestion which modifies the interventionist criteria in order to permit interventions which can influence other variables than just their own targets. The correspondence between correlated changes and causal influence can thereby saved when dependencies are introduced among such interventions. This modification and the required dependencies, I argue, are perfectly in line with practice and may also assist in a wider class of cases. 相似文献
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Spin-dependent exciton formation in pi-conjugated compounds. 总被引:1,自引:0,他引:1
The efficiency of light-emitting diodes (LEDs) made from organic semiconductors is determined by the fraction of injected electrons and holes that recombine to form emissive spin-singlet states rather than non-emissive spin-triplet states. If the process by which these states form is spin-independent, the maximum efficiency of organic LEDs will be limited to 25 per cent. But recent reports have indicated fractions of emissive singlet states ranging from 22 to 63 per cent, and the reason for this variation remains unclear. Here we determine the absolute fraction of singlet states generated in a platinum-containing conjugated polymer and its corresponding monomer. The spin-orbit coupling introduced by the platinum atom allows triplet-state emission, so optically and electrically generated luminescence from both singlet and triplet states can be compared directly. We find an average singlet generation fraction of 22 +/- 1 per cent for the monomer, but 57 +/- 4 per cent for the polymer. This suggests that recombination is spin-independent for the monomer, but that a spin-dependent process, favouring singlet formation, is effective in the polymer. We suggest that this process is a consequence of the exchange interaction, which will operate on overlapping electron and hole wavefunctions on the same polymer chain at their capture radius. 相似文献
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