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Summary TIMSS promises to be the educational study of the 1990s, yielding valuable data not only for curriculum developers, mathematics and science educators, and educational researchers, but also for policy-makers, and those charged with the responsibility of resource allocation. In a complex undertaking such as TIMSS the challenges are many, but the potential of such international efforts are of an equal scale.  相似文献   
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Few works serve as solid a framework for the field of health sciences librarianship or provide as many insights and detailed knowledge as Introduction to Reference Sources in the Health Sciences. Now in its fourth edition, the book's editors and contributors represent an impressive range of experience, expertise, and subject knowledge appreciated by practicing librarians in a variety of settings and by students of health sciences librarianship. Jo Anne Boorkman, Jeffrey T. Huber, and Fred W. Roper answered a series of questions about the latest edition of this seminal work, and offered opinions about reference works, services, and librarians.  相似文献   
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We provide a wide-ranging review of health-related physical activity in children and adolescents using a behavioural epidemiology framework. In contrast to many other reviews, we highlight issues associated with true sedentary behaviours alongside physically active behaviours. Specifically, we review the evidence concerning the links between physical activity and cardiovascular disease, overweight and obesity, psychosocial measures, type II diabetes, and skeletal health. Although the evidence is unconvincing at times, several factors lead to the conclusion that promoting physical activity in youth is desirable. A review of the prevalence of physical activity and sedentary behaviours shows that many young people are active, but this declines with age. A substantial number are not adequately active for health benefits and current trends in juvenile obesity are a cause for concern. Prevalence data on sedentary behaviours are less extensive but suggest that total media use by young people has not changed greatly in recent years. Most children and adolescents do not exceed recommended daily hours of TV viewing. Physical activity is unrelated to TV viewing. We also identified the key determinants of physical activity in this age group, highlighting demographic, biological, psychological, behavioural, social and environmental determinants. Interventions were considered for school, family and community environments. Finally, policy recommendations are offered for the education, governmental, sport and recreation, health, and mass media sectors.  相似文献   
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Clark S 《Endeavour》2007,31(3):104-109
An explosion on the Sun in 1859, serendipitously witnessed by amateur astronomer Richard Carrington, plunged telegraphic communications into chaos and bathed two thirds of the Earth's skies in aurorae. Explaining what happened to the Sun and how it could affect Earth, 93 million miles away, helped change the direction of astronomy. From being concerned principally with charting the stars to aid navigation, astronomers became increasingly concerned with what the celestial objects were, how they behaved and how they might affect life on Earth.  相似文献   
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