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21.
Piet F. M. Verdonschot 《Hydrobiologia》1992,232(2):111-132
A survey was carried out at 157 sites, situated in pools and small lakes in the province of Overijssel (The Netherlands), to describe the macro-invertebrate community and their environment. A total of 61 environmental viriables was measured at each sampling site. The main aim was to described a regional ecological typology of ponds and small lakes. Multivariate analysis techniques are appropriate in data analysis for typological purposes. Different multivariate analysis techniques (FLEXCLUS, NODES, DCCA, PCA) were used in combination with ecological information on individual taxa to derive and describe site groups in terms of taxon composition and mean environmental conditions. The resulting site groups were termed cenotypes. Nine cenotypes were distinguished among the ponds and small lakes. The main differences between the cenotypes were related to duration of drought, acidity, morphology and nutrient load. In particular, the four cenotypes within the group of stagnant, pH-neutral ponds/lakes showed an overlap in taxon composition. These cenotypes represent a web-shaped continuum dominated by dimensions (relation of width to depth), nutrient load, and bottom composition (especially mesotrophic peat). The most important anthropogenic processes are acidification, eutrophication, and changes in the original hydrology. 相似文献
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23.
Inge Santman-Berends Saskia Luttikholt René Van den Brom Gerdien Van Schaik Maaike Gonggrijp Han Hage Piet Vellema 《PloS one》2014,9(8)
The aim of this study was to estimate the quantity of antibiotics and classes of antibiotics used in the small ruminant industry in the Netherlands in 2011 and 2012. Twelve large veterinary practices, located throughout the Netherlands were selected for this study. All small ruminant farms associated with these practices that had complete records on the quantity of antibiotics prescribed were included. The veterinary practices provided data on all antibiotics prescribed, and the estimated animal used daily dose of antibiotics per year (AUDD/Y) was calculated for each farm. The median AUDD/Y in small ruminant farms was zero in both years (mean 0.60 in 2011, and 0.62 in 2012). The largest quantity of antibiotic use was observed in the professional goat industry (herds of ≥32 goats) with a median AUDD/Y of 1.22 in 2011 and 0.73 in 2012. In the professional sheep industry (flocks of ≥32 sheep), the median AUDD/Y was 0 in 2011 and 0.10 in 2012. In the small scale industry (flocks or herds of <32 sheep or goats), the median AUDD/Y never exceeded 0. The most frequently prescribed antibiotics in the small scale industry and professional sheep farms belonged to the penicillin class. In professional goat farms, antibiotics of the aminoglycoside class were most frequently prescribed. This study provides the first assessment on the quantity of antibiotic use in the small ruminant industry. Given a comparable attitude towards antibiotic use, these results might be valid for small ruminant populations in other north-western European countries as well. The antibiotic use in the small ruminant industry appeared to be low, and is expected to play a minor role in the development of antibiotic resistance. Nevertheless, several major zoonotic bacterial pathogens are associated with the small ruminant industry, and it remains important that antibiotics are used in a prudent way. 相似文献
24.
Marijn Bauters Sofie Meeus Matti Barthel Piet Stoffelen Hannes P. T. De Deurwaerder Flicien Meunier Travis W. Drake Quentin Ponette Jerme Ebuy Pieter Vermeir Hans Beeckman Francis wyffels Samuel Bod Hans Verbeeck Filip Vandelook Pascal Boeckx 《Global Change Biology》2020,26(8):4449-4461
Forests exhibit leaf‐ and ecosystem‐level responses to environmental changes. Specifically, rising carbon dioxide (CO2) levels over the past century are expected to have increased the intrinsic water‐use efficiency (iWUE) of tropical trees while the ecosystem is gradually pushed into progressive nutrient limitation. Due to the long‐term character of these changes, however, observational datasets to validate both paradigms are limited in space and time. In this study, we used a unique herbarium record to go back nearly a century and show that despite the rise in CO2 concentrations, iWUE has decreased in central African tropical trees in the Congo Basin. Although we find evidence that points to leaf‐level adaptation to increasing CO2—that is, increasing photosynthesis‐related nutrients and decreasing maximum stomatal conductance, a decrease in leaf δ13C clearly indicates a decreasing iWUE over time. Additionally, the stoichiometric carbon to nitrogen and nitrogen to phosphorus ratios in the leaves show no sign of progressive nutrient limitation as they have remained constant since 1938, which suggests that nutrients have not increasingly limited productivity in this biome. Altogether, the data suggest that other environmental factors, such as increasing temperature, might have negatively affected net photosynthesis and consequently downregulated the iWUE. Results from this study reveal that the second largest tropical forest on Earth has responded differently to recent environmental changes than expected, highlighting the need for further on‐ground monitoring in the Congo Basin. 相似文献
25.
Abstract An enantioselective approach towards the synthesis of optically pure cyclohexene nucleosides 3 has been developed starting from (R)-carvone. The key steps are the regio- and stereoselective hydroboration of an exo double bond, the selective reduction of an enone intermediate and introduction of a base moiety by Mitsunobu reaction. Conformational analysis showed that the adenine base adopts predominantly in a pseudo-axial position. 相似文献
26.
Erik De Clercq Arthur Van Aerschot Piet Herdewijn Masanori Baba Rudi Pauwels Jan Balzarini 《Nucleosides, nucleotides & nucleic acids》2013,32(5-6):659-671
Abstract Among the purine and pyrimidine 2′,3′-dideoxynucleosides, 2′,3′-didehydro-2′,3′-dideoxynucleosides, 3′-azido-2′,3′-dideoxynucleosides and 3′-fluoro-2′,3′-dideoxynucleosides, several congeners have been identified which achieve a potent and selective inhibition of HIV-1 replication in vitro. 相似文献
27.
André B. P. van Kuilenburg Heinz-Josef Klumpen Anneke M. Westermann Lida Zoetekouw Piet J. M. Bakker Henk-Jan Guchelaar 《Nucleosides, nucleotides & nucleic acids》2013,32(6-7):726-732
Dihydropyrimidine dehydrogenase (DPD) plays a pivotal role in the metabolism of 5-fluorouracil (5FU). In patients treated with capecitabine or 5FU combined with other chemotherapeutic drugs, DPD activity in peripheral blood mononuclear cells was increased in patients experiencing grade I/II neutropenia. In contrast, decreased DPD activity proved to be associated with grade I/II dermatological toxicity, including hand-foot syndrome. Thus, patients with a low-normal or high-normal DPD activity proved to be at risk of developing mild toxicity upon treatment with 5FU-based chemotherapy, demonstrating the important role of DPD in the etiology of toxicity associated with 5FU and the catabolites of 5FU. 相似文献
28.
Ilse Verheggen Arthur Van Aerschot Jef Rozenski Gerard Janssen Erik De Clercq Piet Herdewijn 《Nucleosides, nucleotides & nucleic acids》2013,32(1-3):325-335
Abstract 1,5-Anhydrohexitol congeners of AZT, D4T and DDC were synthesized. These compounds did not show anti-HIV activity. 相似文献
29.
Sergey N. Mikhailov Erik De Clercq Piet Herdewijn 《Nucleosides, nucleotides & nucleic acids》2013,32(7-8):1323-1334
Abstract The previously developed method for the preparation of 2′-O-D-ribofuranosyl-nucleosides is extended to ribosylation of 2′-deoxynucleosides. The scope and limitations of this reaction are discussed. 相似文献
30.