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排序方式: 共有1926条查询结果,搜索用时 100 毫秒
971.
J. Van Keirsbilck M. Cannie C. Robrechts T. de Ravel S. Dymarkowski T. Van den Bosch D. Van Schoubroeck 《黑龙江环境通报》2006,26(8):684-688
We present a case of sirenomelia diagnosed on a first trimester ultrasound at 10 weeks' gestation and confirmed on 3D-ultrasound and MRI. The pregnancy was terminated at 15 gestational weeks and the post-mortem examination, including RX and microscopy, is presented. The sirenomelia sequence is a rare and lethal anomaly characterized by fusion, rotation, hypotrophy or atrophy of the lower limbs and severe urogenital abnormalities leading to oligohydramnios in the second half of pregnancy. Our case illustrates that the diagnosis of sirenomelia can be reliably made in the first trimester. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
972.
973.
We investigated the fledging probability of oystercatcher, Haematopus ostralegus, chicks as a function of hatching order, brood size, territory quality and food availability. Sibling dominance was related
to the hatching order in both low- (’leapfrogs’) and high-quality (’residents’) territories. Differences in hatchling mass
might have aided the establishment of a dominance hierarchy, since breeders produced small late eggs and hatchlings. These
mass differences were most pronounced in leapfrogs, and in large broods in years with lower food availability (’poor’ years).
Late hatchlings fledged less often and with lower body masses compared to early hatchlings in all situations. Leapfrogs produced
smaller broods and hatched their broods more asynchronously in poor years than leapfrogs breeding in years with more available
food (’good’ years) and residents breeding in both poor and good years. Large brood sizes resulted in lower survival of hatchlings
in poor years. These results favour the ’brood reduction’ hypothesis. However, contrary to the expectations of this hypothesis,
hatching order also affected fledging success in residents. Moreover, large brood size resulted in higher survival of hatchlings
in good years, particularly in residents. Thus, although large broods experienced losses due to sibling competition in some
years, they nevertheless consistently produced more fledglings per brood in all years, both as leapfrogs and residents. We
believe this effect is due to parental quality correlating with initial brood size. Most leapfrogs, at best, fledged one chick
successfully each year, losing chicks due to starvation. Nevertheless, leapfrog broods were reduced in size after hatching
significantly less quickly than resident broods. These results suggest that breeders lay and hatch insurance eggs to compensate
for unpredictable losses due to the high predation rates on both nests (ca 50%) and chicks (ca 90%), in accordance with the
’nest failure’ hypothesis.
Received: 14 February 2000 / Revised: 27 September 2000 / Accepted: 10 June 2000 相似文献
974.
J.M.N. van Kasteren M.J.P. Slapak 《Journal of Material Cycles and Waste Management》2001,3(2):114-117
This study is concerned with the influence of additives on the steam gasification of polyvinyl chloride (PVC) waste. Three
types of PVC waste, namely pipe waste, cable waste, and flooring, were tested. The presence of additives proved to have a
profound effect on the carbon-to-gas conversion. Plasticizers and other organic additives caused an increase in carbon-to-gas
conversion. Inorganic additives, especially calcium, caused a decrease in carbon-to-gas conversion, resulting in an overall
decrease in the yield of syngas for all three types of waste. This decrease is probably caused by the deposition of Ca on
the surface of the alumina bed material. In addition, calcium reacts with the HCl formed to give CaCl2. This results in a decrease in the recovery of hydrochloric acid.
Received: July 19, 2000 / Accepted: October 9, 2000 相似文献
975.
976.
Theresa M. Marteau Irma Nippert Sue Hall Caroline Limbert Margaret Reid Martin Bobrow Alan Cameron Martina Cornel Mariet van Diem Bernd Eiben Sixto García-Miñaur Janine Goujard Donna Kirwan Karen McIntosh Peter Soothill Corien Verschuuren-Bemelmans Catherine de Vigan Stephen Walkinshaw Lenore Abramsky Frank Louwen Peter Miny Jürgen Horst 《黑龙江环境通报》2002,22(7):562-566
977.
A W G Van der Wurff S A E Kools M E Y Boivin P J Van den Brink H H M Van Megen J A G Riksen A Doroszuk J E Kammenga 《Ecological applications》2007,17(1):190-202
This study aims to reveal whether complexity, namely, community and trophic structure, of chronically stressed soil systems is at increased risk or remains stable when confronted with a subsequent disturbance. Therefore, we focused on a grassland with a history of four centuries of patchy contamination. Nematodes were used as model organisms because they are an abundant and trophically diverse group and representative of the soil food web and ecosystem complexity. In a field survey, a relationship between contaminants and community structures was established. Following, two groups of soil mesocosms from the field that differed in contamination level were exposed to different disturbance regimes, namely, to the contaminant zinc and a heat shock. The zinc treatment revealed that community structure is stable, irrespective of soil contamination levels. This implies that centuries of exposure to contamination led to adaptation of the soil nematode community irrespective of the patchy distribution of contaminants. In contrast, the heat shock had adverse effects on species richness in the highly contaminated soils only. The total nematode biomass was lower in the highly contaminated field samples; however, the biomass was not affected by zinc and heat treatments of the mesocosms. This means that density compensation occurred rapidly, i.e., tolerant species quickly replaced sensitive species. Our results support the hypothesis that the history of contamination and the type of disturbance determine the response of communities. Despite that ecosystems may be exposed for centuries to contamination and communities show adaptation, biodiversity in highly contaminated sites is at increased risk when exposed to a different disturbance regime. We discuss how the loss of higher trophic levels from the entire system, such as represented by carnivorous nematodes after the heat shock, accompanied by local biodiversity loss at highly contaminated sites, may result in detrimental effects on ecosystem functions. 相似文献
978.
979.
Management of Wetlands 总被引:1,自引:1,他引:0
980.
Female (SD) rats were fed diets containing 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153) in various concentrations for three months. PCB 153 had no significant effect on the body weight gain when given alone or in combination with TCDD. The increases in relative liver weights were additive. For thymic atrophy no interactive effects became apparent. PCB 153 had no effect on the EROD induction by TCDD. PROD induction by PCB 153 was diminished in the presence of TCDD. The level of TCDD in the liver was decreased by PCB 153. Increasing TCDD dosage led to an increase in PCB 153 levels. 相似文献