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排序方式: 共有467条查询结果,搜索用时 31 毫秒
81.
Karel Žák Martin Košťák Otakar Man Victor A. Zakharov Mikhail A. Rogov Petr Pruner Jan Rohovec Oksana S. Dzyuba Martin Mazuch 《Palaeogeography, Palaeoclimatology, Palaeoecology》2011,299(1-2):83-96
Carbon and oxygen stable isotope records were compared for Jurassic/Cretaceous (J/K) boundary sections located in the Tethyan Realm (Brodno, Western Slovakia, and Puerto Escaño, Southern Spain; bulk limestones), and the Boreal Realm (Nordvik Peninsula, Northern Siberia, belemnites). Since a detailed biostratigraphic correlation of these Tethyan and Boreal sections is impossible due to different faunal assemblages, correlation of the isotope records was based on paleomagnetic data. This novel approach can improve our understanding of the synchroneity of individual isotope excursions in sections where detailed biostratigraphic correlation is impossible. No significant excursions in either the carbon or oxygen isotope records to be used for future Boreal/Tethyan correlations were found around the J/K boundary (the upper Tithonian and lower Berriasian; magnetozones M20n to M18n) in the studied sections. At the Nordvik section, where a much longer section (middle Oxfordian–basal Boreal Berriasian) was documented, the transition from the middle Oxfordian to the Kimmeridgian and further to the Volgian is characterized by a decrease in belemnite δ18O values (from δ18O values up to + 1.6‰ vs. V-PDB in the Oxfordian to values between + 0.3 and ? 0.8‰ in the late Volgian and earliest Boreal Berriasian). This trend, which has previously been reported from the Russian Platform and Tethyan Realm sections, corresponds either to gradual warming or a decrease in seawater δ18O. Supposing that the oxygen isotope compositions of seawater in the Arctic/Boreal and Tethyan Realms were similar, then the differences between oxygen isotope datasets for these records indicate differences in temperature. The Boreal/Tethyan temperature difference of 7–9 °C in the middle and late Oxfordian decreases towards the J/K boundary, indicating a significant decrease in latitudinal climatic gradients during the Late Jurassic. Two positive carbon isotope excursions recorded for the middle Oxfordian and upper Kimmeridgian in the Nordvik section can be correlated with a similar excursion described earlier for the Russian Platform. Minor influence of biofractionation at the carbon isotopes, and the influence of migration of belemnites to deeper, slightly cooler water at the oxygen isotopes, cannot be excluded for the obtained belemnite data. 相似文献
82.
83.
Jiří Luštinec Fatima Cvrčková Jana Čížková Jaroslav Doležel Miroslav Kamínek Viktor Žárský 《Acta Physiologiae Plantarum》2014,36(8):1981-1991
We describe complex multiple concentration dependencies for the response of isolated pith tissues to plant biologically active substances. Kale and tobacco stem pith explants were cultured on agar media containing combinations of sucrose, cytokinin [kinetin or benzyladenine (BA)] and auxin [indole-3-acetic acid (IAA) or naphthaleneacetic acid (NAA)]. Absorption of these components by explants and their effects on explant mass, contents of soluble proteins, starch and sugars, and activity of ADP-glucose pyrophosphorylase (AGPase) were studied in relation to their concentration. Up to ten pronounced statistically significant maxima (peaks or waves) were repeatedly detected in the dose–response curves over a concentration range of several logarithmic orders. Slight maxima were observed in the corresponding absorption curves. Pronounced maxima of sucrose absorption were induced by IAA and BA, and those of NAA absorption were induced by sucrose. Both types of multiple maxima (in dose–response and absorption curves) may be due to changes in concentration of intracellular solutes (sugars, auxins and cytokinins), thereby affecting metabolic processes that act as sinks for external solutes and elicit feedback appearance of maxima in absorption curves. Good correspondence between external concentrations at which maxima of different compared curves occur in addition to statistical significance of individual maxima and repeatability of experimental results supports the conclusion that the multiple maxima exhibited are genuine. We consider it possibile that the multiple maxima are associated with endopolyploidy or mixoploidy and/or epigenomic diversity of pith cells that show different sensitivities to biologically active solutes. 相似文献
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86.
Anna Chrtková-Žertová 《Folia Geobotanica》1971,6(2):215-216
Four new taxa in the variable speciesLotus corniculatus L. has been described: var.alandicus Chrtková-?ertová, var.norvegicus Chrtková-?ertová, var.fallax Chrtková-?ertová and var.posoniensis Chrtková-?ertová. 相似文献
87.
88.
Jar KŘíŽenecký 《Development genes and evolution》1913,36(3):294-341
Ohne Zusammenfassung 相似文献
89.
Jar KŘíŽenecký 《Development genes and evolution》1913,37(4):629-634
Ohne Zusammenfassung 相似文献
90.
Søren Lykke-Andersen Kristina Žumer Ewa Šmidová Molska Jérôme O. Rouvière Guifen Wu Carina Demel Björn Schwalb Manfred Schmid Patrick Cramer Torben Heick Jensen 《Molecular cell》2021,81(3):514-529.e6
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