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Eccentric exercise has been associated with an increase in serial sarcomere number in some studies,1 but not in others.2 Similarly,increasing excursion of muscles resulted in sarcomerogenesis in some studies using growing animals,3 but not in others using skeletally mature animals.4 However,chronic elongation and chronic shortening appears to be a strong regulator of sarcomere number increase5,6 and decrease,5,7 respectively,in animal models.Despite an abundance of research on the regulation of sarcomerogenesis under a variety of conditions,the mechanisms underlying in series sarcomere number adaptations in skeletal muscles remain a puzzle,especially in non-invasive human studies where measurements of sarcomerogenesis following interventions have not been possible to date.  相似文献   
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Obesity is a disease that has become an epidemic in economically developed countries,and manifests itself at increasing rates in economically developing countries.Obesity is associated with a variety of comorbidities,such as metabolic disease,diabetes,cardiovascular diseases,and musculoskeletal disorders,all resulting in tremendous costs to health care systems around the world,a reduced capacity for work,and reduced quality of life for people with obesity,coupled with physical inactivity,thereby producing a vicious circle of inactivity-induced diseases that enhances obesity.  相似文献   
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Background:Osteoarthritis is one of the leading causes of pain and disability worldwide,and a large percentage of patients with osteoarthritis are individuals who are also obese.In recent years,a series of animal models have demonstrated that obesity-inducing diets can result in synovial joint damage(both with and without the superimposition of trauma),which may be related to changes in percentage of body fat and a series of low-level systemic inflammatory mediators.Of note,there is a disparity between whether the dietary challenges commence at weaning,representing a weanling onset,or at skeletal maturity,representing an adult onset of obesity.We wished to evaluate the effect ofthe dietary exposure time and the age at which animals are exposed to a high-fat and high-sucrose(HFS) diet to determine whether these factors may result in disparate outcomes,as there is evidence suggesting that these factors result in differential metabolic disturbances.Based on dietary exposure time,we hypothesized that rats fed an HFS diet for 14 weeks from weaning(HFS Weanling) would demonstrate an increase in knee joint damage scores,whereas rats exposed to the HFS diet for 4 weeks,starting at 12 weeks of age(HFS Adult) and rats exposed to a standard chow diet(Chow)would not display an increase in knee joint damage scores.Methods:Male Sprague-Dawley rats were fed either an HFS diet for 14 weeks from weaning(HFS Weanling) or an HFS diet for 4 weeks,starting at 12 weeks of age(HFS Adult).At sacrifice,joints were scored using the modified Mankin Criteria,and serum was analyzed for a defined subset of inflammatory markers(Interleukin-6,leptin,monocyte chemoattractant protein-1,and tumor necrosis factorα).Results:When the HFS Weanling and HFS Adult groups were compared,both groups had a similar percent of body fat,although the HFS Weanling group had a significantly greater body mass than the HFS Adult group.The HFS Weanling and HFS Adult animals had a significant increase in body mass and percentage of body fat when compared to the Chow group.Although knee joint damage scores were low in all 3 groups,we found,contrary to our hypothesis,that the HFS Adult group had statistically significant greater knee joint damage scores than the Chow and HFS Weanling groups.Furthermore,we observed that the HFS Weanling group did not have significant differences in knee joint damage scores relative to the Chow group.Conclusion:These findings indicate that the HFS Weanling animals were better able to cope with the dietary challenge of an HFS diet than the HFS Adult group.Interestingly,when assessing various serum proinflammatory markers,no significant differences were detected between the HTS Adult and HFS Weanling groups.Although details regarding the mechanisms underlying an increase in knee joint damage scores in the HFS Adult group remain to be elucidated,these findings indicate that dietary exposure time maybe less important than the age at which an HFS diet is introduced.Moreover,increases in serum proinflammatory mediators do not appear to be directly linked to knee joint damage scores in the HFS Weanling group animals but may be partially responsible for the observed knee joint damage in the adults over the very short time of exposure to the HFS diet.  相似文献   
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This study employed a national sample of college students who initially aspired to be, or later became, physicians to determine the influence of precollege characteristics, college origins, and the academic and social experience of college on the likelihood of becoming a physician. Estimates of a 14-variable causal model indicated that the major direct effects on attainment were attributable to college characteristics and the academic experience of college. Net of other causes, the selectivity/prestige of the undergraduate institution attended, collegiate academic achievement, and majoring in the physical or life sciences each had significant direct effects on becoming a physician. The direct positive influence of college quality, however, was partially counterbalanced by its negative indirect effect. Moreover, the greatest advantage in attending an elite institution accrued to those students with relatively high levels of academic performance. As academic performance declined, so did the positive effect of college quality. The effects of precollege characteristics on becoming a physician were largely indirect, mediated by the student's college experience. Net of other factors, women were no less likely than men to become physicians, but being female had a significant negative indirect effect. Conversely, secondary school achievement did not directly influence attainment but did have a large positive indirect influence.An earlier version of this paper was presented at the annual meeting of the Association for the Study of Higher Education, San Diego, February, 1987.  相似文献   
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In this quasi-experimental study various strategies are developed and empirically tested for an approach to physics instruction that should improve girls' and boys' attitudes toward and achievements in physics. Strategies include opportunities to integrate different pre-existing knowledge and the variation of teaching methods to enhance co-operation and communication in the classroom. The core of this study is an intervention in 31 classes of public schools in Switzerland. The intervention, one unit in optics and one in motion (velocity/acceleration), includes the first 40 lessons of the first physics course that all students have to attend at the upper secondary level. Data sources are various student and teacher questionnaires, tests and semi-structured interviews with teachers. Results of the entrance and final survey are presented. The focus will be on some of the applied strategies. Implications for the teaching and learning of physics and for teacher education are discussed.  相似文献   
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Flexural and torsional rigidity are important properties of skis. However, the flexural and torsional rigidity that lead to optimal performance remain to be established. In the present study, four pairs of slalom skis that differed in flexural and torsional rigidity were tested by advanced and expert skiers. Using a 10-item questionnaire, different aspects of the skis' performance were rated on a 9-point scale. For each pair of skis, physical measurements were compared with the ratings of the two groups of skiers. Correlations (Spearman) were then determined between (i) different mechanical properties of the skis (static and dynamic), (ii) subjective assessments of the participants, and (iii) properties of the skis and the participants' assessments. The latter showed that expert skiers rate the aspects of the skis more accurately than advanced skiers. Most importantly, expert skiers are particularly sensitive to torsion of the skis. These results suggest that such highly rated elements should be addressed in future ski designs.  相似文献   
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