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71.
The function of photosystem (PS)II during desiccation and exposure to high photon flux density (PFD) was investigated via analysis of chlorophyll fluorescence in the desert resurrection plant Selaginella lepidophylla (Hook. and Grev.) Spring. Exposure of hydrated, physiologically competent stems to 2000 mol · m–2 · s–1 PFD caused significant reductions in both intrinsic fluorescence yield (FO) and photochemical efficiency of PSII (FV/FM) but recovery to pre-exposure values was rapid under low PFD. Desiccation under low PFD also affected fluorescence characteristics. Both FV/FM and photochemical fluorescence quenching remained high until about 40% relative water content and both then decreased rapidly as plants approached 0% relative water content. In contrast, the maximum fluorescence yield (FM) decreased and non-photochemical fluorescence quenching increased early during desiccation. In plants dried at high PFD, the decrease in FV/FM was accentuated and FO was reduced, however, fluorescence characteristics returned to near pre-exposure values after 24-h of rehydration and recovery at low PFD. Pretreatment of stems with dithiothreitol, an inhibitor of zeaxanthin synthesis, accelerated the decline in FV/FM and significantly increased FO relative to controls at 925 mol · m–2 · s–1 PFD, and the differences persisted over a 3-h low-PFD recovery period. Pretreatment with dithiothreitol also significantly decreased non-photochemical fluorescence quenching, increased the reduction state of QA, the primary electron acceptor of PSII, and prevented the synthesis of zeaxanthin relative to controls when stems were exposed to PFDs in excess of 250 mol · m–2 · s–1. These results indicate that a zeaxanthin-associated mechanism of photoprotection exists in this desert pteridophyte that may help to prevent photoinhibitory damage in the fully hydrated state and which may play an additional role in protecting PSII as thylakoid membranes undergo water loss.Abbreviations and Symbols DTT
dithiothreitol
- EPS
epoxidation state
- FO
yield of instantaneous fluorescence at open PSII centers
- FM
maximum yield of fluorescence at closed PSII centers induced by saturating light
- FM
FM determined during actinic illumination
- FV
yield of variable fluorescence (FM-FO)
- FV/FM
photochemical efficiency of PSII
- qP
photochemical fluorescence quenching
- qNP
non-photochemical fluorescence quenching of Schreiber et al. (1986)
- NPQ
non-photochemical fluorescence quenching from the Stern-Volmer equation
- PFD
photon flux density
- RWC
relative water content
This paper is based on research done while W.G.E. was on leave of absence at Duke University during the fall of 1990. We would like to thank Dan Yakir, John Skillman, Steve Grace, and Suchandra Balachandran and many others at Duke University for their help and input with this research. Dr. Barbara Demmig-Adams provided zeaxanthin for standard-curve purposes. 相似文献
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Beta-carboxylation during photosynthesis in Atriplex 总被引:2,自引:0,他引:2
C B Osmond 《Biochimica et biophysica acta》1967,141(1):197-199
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The reasons why mortality is higher in the poorer areas of Britain are largely unknown. Thus how to reduce inequalities in health is a matter of conjecture. In three neighbouring towns in northern England the rates of death from all causes differ greatly. Socioeconomic conditions in the towns are similar though below average for England and Wales. The pattern of disease specific rates was analysed and related to past differences in infant mortality. It is suggested that past differences in maternal health and physique and in the postnatal environment, particularly infant feeding, housing, and overcrowding, may be determinants of current differences in adult mortality. 相似文献
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The occurrence of appendicectomy in three national samples of British children was analysed in relation to household amenities, crowding in the home, and social class. The risk of having the operation depended on the amenities present in the home, in particular whether or not there was a bathroom. This risk was independent of social class.The findings support a relation between acute appendicitis and Western hygiene, which would explain the geographical distribution of the disease and its changing incidence over time. In the developing world, where children grow up in conditions of poor hygiene, there may be outbreaks of appendicitis when housing improves. 相似文献