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排序方式: 共有196条查询结果,搜索用时 15 毫秒
191.
192.
Frederick W. Kutz Donald G. Barnes Erich W. Bretthauer David P. Bottimore Helmut Greim 《毒物与环境化学》2013,95(1-4):99-109
The International Toxicity Equivalency Factor (I‐TEF) method of risk assessment is a revised interim procedure for assessing the risks associated with exposures to complex mixtures of chlorinated dibenzo‐p‐dioxins and dibenzofurans (CDDs and CDFs). This updated scheme was developed by a working group of the North Atlantic Treaty Organization's Committee on the Challenges of Modern Society and has been officially adopted by the U.S. Environmental Protection Agency (EPA), Canada, Ontario Ministry of the Environment, the Nordic countries, the Netherlands, and the United Kingdom. Prior to the development of the I‐TEF method, at least ten slightly different schemes had been used throughout the world which complicated communication among scientists and regulatory agencies concerning the toxicological significance of complex mixtures of CDDs and CDFs. The I‐TEF approach facilitates risk communication internationally by reducing large volumes of analytical data into a single number‐International Toxicity Equivalents (I‐TEQ). As a result, the I‐TEF method represents an improvement in an already useful risk assessment/regulatory tool. 相似文献
193.
194.
Summary. Summary. Oilseed rape, Brassica napus L. (cv Express),
plants were grown under three different sulphur regimes:
sulphur-free (S0), normal sulphur (Sn, normal field concentration)
and a sulphur-rich (S+, 2 × concentration of Sn). We
performed dual choice oviposition assays with the diamondback
moth, Plutella xylostella, using real plants and,
for the first time with this insect, artificial leaves sprayed
with methanolic leaf-surface extracts. The results mirrored
those of a separate study of preferences for whole plants.
Females laid more eggs on surrogate leaves that were
treated with Sn extracts than on S0 plants, while only a
slight, not significant, difference was observed between
extracts of normal and sulphur-rich plants. This shows
that chemical compounds on the leaf surface mediate the
oviposition preference and that the female insect can
perceive the quality of the host-plants in terms of their
fertilisation status.Since leaf volatiles are known to be oviposition stimulants,
we investigated the effects of leaf-surface extracts on
insect olfactory responses using electroantennograms
(EAGs). In agreement with the behavioural data, we found
that extracts of sulphur-treated plants yielded higher EAG
amplitudes than the S0 extracts. Since the leaf content of the
volatiles isothiocyanates is influenced by sulphur nutrition,
we analysed the extracts for these compounds. Above the
detection threshold of our GC-MS system, no isothiocyanates
were found. Thus, other compounds present in the
surface extracts must be perceived by the antenna.However, the HPLC analysis revealed 11 different
glucosinolates. Progoitrin (2-Hydroxy-3-butenyl) and
gluconapoleiferin (2-Hydroxy-4-pentenyl), which belong to
the hydroxy-alkene class of glucosinolates, were the most
abundant compounds. The total glucosinolate content
sharply increased from S0 to Sn plants, whereas it was slightly
lower in n versus S+ plants. Since it is known that glucosinolates
can stimulate oviposition, it seems likely that the
increased content we observed was influencing the insect
preference in this study too. 相似文献
195.
The Science of Nature - 相似文献
196.
Erich M. G. Fitzgerald Matthew T. Carrano Timothy Holland Barbara E. Wagstaff David Pickering Thomas H. Rich Patricia Vickers-Rich 《Die Naturwissenschaften》2012,99(5):397-405
The basal theropod dinosaur clade Ceratosauria, and its subclade Abelisauroidea, is characteristic of late Mesozoic terrestrial vertebrate faunas in western Gondwana (South America, Africa, Madagascar, and India) and Europe. Yet unambiguous records of ceratosaurs have hitherto been absent from Australia, where the theropod assemblage appears to include several typically Laurasian clades. Here, we report the first evidence of ceratosaurs (and potentially abelisauroids) from eastern Gondwana––a diagnostic astragalocalcaneum from the Aptian (121–125?Ma) of Victoria, Australia. Ceratosauria thus occurred in both western and eastern Gondwana during the Early Cretaceous. This fossil adds to the poorly known dinosaur fauna of Australia, a major clade of basal theropods, emphasising that its mid-Cretaceous theropod diversity was surprisingly cosmopolitan despite relative geographic isolation, including clades that have been thought to be typical of both Gondwana and Laurasia––Ceratosauria, Spinosauridae, Carcharodontosauria, Tyrannosauroidea, and Deinonychosauria. Such a contemporaneous association of theropod clades is unknown from other Gondwanan continents and questions the views that the late Mesozoic dinosaur fauna of Australia was dominated by Gondwanan or Laurasian elements, extreme isolation, relictualism, and/or novelty as a ‘centre of origin’. The cosmopolitan theropod fauna of Australia probably reflects the global distribution of these clades early in their history, prior to significant continental breakup. 相似文献