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Rates of morphological evolution documented in laboratory selection experiments, historical colonization events, and the fossil record are inversely related to the interval of time over which they are measured. This inverse relationship is an artifact of comparing a narrow range of morphological variation over a wide range of time intervals, and it is also a product of time averaging. Rates measured over different intervals of time must be scaled against interval length before they can be compared.  相似文献   
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新春祝辞     
值此农历乙酉年新春佳节之际,我谨代表中国兽医药品监察所,向工作在全国兽药科研、生产、检验、销售一线的全体同仁,以及所有关心、支持和帮助我们工作的各位领导和朋友们拜年,并致以新春的祝贺!衷心地祝愿大家在新的一年里,工作顺利,身体健康,阖家幸福,万事如意!  相似文献   
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Total intravenous feeding was accomplished for 5 clinically normal calves and for 1 calf with atresia coli. During the trials, which lasted 8 to 14 days (mean of 12 days), calves were not permitted to ingest any food or water. Body weight and state of hydration remained essentially constant. Plasma protein content decreased, but there were only minor changes in other physiologic measures. Calves were clinically normal at the conclusion of the trials.  相似文献   
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Commercial white leghorn egg layer flocks being used to produce fertile eggs for human vaccine production exhibited dramatically low peaks in egg production, two to four times higher than normal weekly mortality, and high numbers of cull, nonlaying birds after the onset of sexual maturity. These lower production characteristics could not be associated with management-related problems. Gross lesions of cull and fresh dead birds necropsied showed approximately 60% lacked ovarian activity and had lesions of a bacterial bursitis or synovitis, whereas the other 40% had tumors of the viscera but not of the bursa of Fabricius. Histologic examination of tumor-containing tissues showed lesions typical of myelocytomatosis. The diagnosis of myeloid leukosis was confirmed by the isolation of a recombinant avian leukosis virus (ALV) containing the LTR of subgroup J and the envelope of subgroup B ALV. A positive polymerase chain reaction with primers specific for the 3' untranslated region LTR confirmed the presence of LTR of ALV-J. The source of infection with this recombinant ALV was not determined; however, it is likely that commingling of the day-old egg-type chicks with ALV-J-infected meat-type chicks in a common hatchery had contributed to this outbreak.  相似文献   
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Objective To provide information on changes in the social and educational backgrounds of veterinary students over a 10 year period in an effort to determine the extent to which they are representative of the community.
Methods Questionnaires were completed by first-year veterinary students at The University of Queensland in 1985 and 1986 (152 students), and 1995 and 1996 (154), and the data were analysed using the SAS System for Windows.
Results The gender ratio of first-year veterinary students was 50:50 (male:female) in 1985 and 1986 but 10 years later it had changed to 38:62. In 1985 and 1986 77% had come directly from school, with 43% of the total coming from government schools, 17% from Catholic schools and 34% from other private (Independent) schools. A decade later the percentage coming directly from school had decreased to 40%, that from Independent schools increased to 45% and that from cities increased from 53% to 64%. The educational backgrounds of parents varied widely though a high percentage had university degrees; mothers had received less formal education than fathers, and the educational attainments of both parents were higher at the beginning than at the end of the study. More than half (57% initially; 67% 10 years later) the fathers were in professional or managerial occupations, and a similar number (50% initially; 48% 10 years later) of mothers were teachers, nurses or clerks. The number of males from country areas decreased from 26 to 16 over this period.
Conclusion These veterinary students differed from the community generally in that progressively more were female, more were from Independent schools, their parents had more formal education and more of their parents were in professional, managerial or clerical occupations.  相似文献   
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The preatmospheric mass of the Tagish Lake meteoroid was about 200,000 kilograms. Its calculated orbit indicates affinity to the Apollo asteroids with a semimajor axis in the middle of the asteroid belt, consistent with a linkage to low-albedo C, D, and P type asteroids. The mineralogy, oxygen isotope, and bulk chemical composition of recovered samples of the Tagish Lake meteorite are intermediate between CM and CI meteorites. These data suggest that the Tagish Lake meteorite may be one of the most primitive solar system materials yet studied.  相似文献   
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Genetically engineered (GE) animals are likely to have an important role in the future in meeting the food demand of a burgeoning global population. There have already been many notable achievements using this technology in livestock, poultry and aquatic species. In particular, the use of RNA interference (RNAi) to produce virus‐resistant animals is a rapidly‐developing area of research. However, despite the promise of this technology, very few GE animals have been commercialised. This review aims to provide information so that veterinarians and animal health scientists are better able to participate in the debate on GE animals.  相似文献   
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