共查询到20条相似文献,搜索用时 9 毫秒
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D P Addy 《BMJ (Clinical research ed.)》1984,289(6456):1457-1458
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J S Robertson 《BMJ (Clinical research ed.)》1977,1(6057):375-376
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Regional variations in need for and provision and use of child health services in England and Wales.
An analysis of indicators of the need for and provision and use of child health services in the 15 pre- 1974 hospital board regions in England and Wales showed that need and provisions were badly matched. There was a high degree of correlation between the indices within each of the three groups, indicating that a region with a small provision in one area of child health services would tend to have few resources in other areas also. Statistics on the use of services relate more to the provision of those services than to the need for them. Regions with large resources will justify these resources by claiming that their use statistics indicate needs, whereas they really indicate met demands. It is more important to identify demands and needs that are not being met. 相似文献
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A D Milner 《BMJ (Clinical research ed.)》1984,288(6420):811-812
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《BMJ (Clinical research ed.)》1977,1(6057):338-339
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BACKGROUND AND AIMS: In dioecious species male and female plants experience different selective pressures and often incur different reproductive costs. An increase in reproductive investment habitually results in a reduction of the resources available to other demands, such as vegetative growth. Tree-ring growth is an integrative measure that tracks vegetative investment through the plant's entire life span. This allows the study of gender-specific vegetative allocation strategies in dioecious tree species thoughout their life stages. METHODS: Standard dendrochronological procedures were used to measure tree-ring width. Analyses of time-series were made by means of General Mixed Models with correction of autocorrelated values by the use of an autoregressive covariance structure of order one. Bootstrapped correlation functions were used to study the relationship between climate and tree-ring width. KEY RESULTS: Male and female trees invest a similar amount of resources to ring growth during the early life stages of Juniperus thurifera. However, after reaching sexual maturity, tree-ring growth is reduced for both sexes. Furthermore, females experience a significantly stronger reduction in growth than males, which indicates a lower vegetative allocation in females. In addition, growth was positively correlated with precipitation from the current winter and spring in male trees but only to current spring precipitation in females. CONCLUSIONS: Once sexual maturity is achieved, tree rings grow proportionally more in males than in females. Differences in tree-ring growth between the genders could be a strategy to respond to different reproductive demands. Therefore, and responding to the questions of when, how and how much asked in the title, it is shown that male trees invest more resources to growth than female trees only after reaching sexual maturity, and they use these resources in a different temporal way. 相似文献
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In recent years, a number of studies have been performed to evaluate the possible health benefits of an increased intake of folic acid (FA) on human health. However, the only well-documented benefit emerging from randomized controlled trials, nonrandomized interventions trials, and observational studies is the risk reduction of neural tube defects (NTDs). NTDs are congenital malformations that include anencephaly, encephalocele, and spina bifida caused by the failure of fusion of the neural tube that normally closes between 22nd and 28th day since conception (on an average 40-42th day after the first day of last menstrual period). The occurrence of NTDs varies among population between 0.8 and 3 per 1,000, and it is estimated that 324,000 pregnancies are affected every year worldwide. More FA can decrease the NTDs risk up to 0.6 per 1,000 births. Other malformations as congenital heart defects, cleft lip, and limb deficiencies can be most probably also reduced. To decrease the NTDs risk, it is recommended that all women capable of becoming pregnant should have more FA. The goal is that every woman could start her pregnancy with an optimal folate status, estimated today to be as more than 906 nmol/L of red blood cell folate concentration. More FA can be obtained through a strict Mediterranean pattern of nutrition and healthy life style, fortified food, supplements. Women and health authorities can choose the most appropriate strategy. Monitoring folate status of women during the periconceptional period is an essential way to evaluate the success of the preferred strategy. 相似文献
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H A Mason 《BMJ (Clinical research ed.)》1980,280(6209):248-249
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Polar auxin transport: controlling where and how much. 总被引:12,自引:0,他引:12
Auxin is transported through plant tissues, moving from cell to cell in a unique polar manner. Polar auxin transport controls important growth and developmental processes in higher plants. Recent studies have identified several proteins that mediate polar auxin transport and have shown that some of these proteins are asymmetrically localized, paving the way for studies of the mechanisms that regulate auxin transport. New data indicate that reversible protein phosphorylation can control the amount of auxin transport, whereas protein secretion through Golgi-derived vesicles and interactions with the actin cytoskeleton might regulate the localization of auxin efflux complexes. 相似文献