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111.
Christopher T. Clarke 《Restoration Ecology》1997,5(3):256-264
No guidelines are currently available that advise which soil properties of arable land can be used to suggest suitable locations for heathland reconstruction. This paper reviews studies comparing soil properties of heathland or semi-natural grassland with those of adjacent arable fields, investigations in the autecology of the dominant heathland plant, Calluna vulgaris (common heather), and long-term experiments of fertilizer inputs on arable soils. Three properties must be assessed before the suitability of a field can be determined: extractable phosphorus, exchangeable calcium, and pH. A number of other nutrients may also be important, but evidence is currently insufficient to substantiate this. Natural changes in levels of extractable phosphorus, exchangeable calcium, and pH appear to be very slow, so nutrient stripping and acidification will be necessary where recommended levels are exceeded to successfully restore heathland vegetation. 相似文献
112.
OBJECTIVE--To examine the relation between bone density and indices of calcium metabolism including parathyroid hormone and 25-hydroxyvitamin D concentrations in middle aged women. DESIGN--A cross sectional study. SETTING AND SUBJECTS--138 women volunteers aged 45-65 with no known osteoporosis and unselected for disease status recruited for a dietary assessment study from the community using general practice registers. Volunteer rate was 20%. MAIN OUTCOME MEASURE--Bone mineral density measured with dual energy x ray absorptiometry. RESULTS--Bone density at the lumbar spine and neck and trochanteric regions of the femur was inversely related to serum intact parathyroid hormone concentrations and positively related to serum 25-hydroxyvitamin D concentrations. These associations were independent of possible confounding factors, including age, body mass index, cigarette smoking habit, menopausal status, and use of diuretics and postmenopausal hormone replacement therapy. These associations were apparent throughout the whole distribution of bone density and 25-hydroxyvitamin D and parathyroid hormone concentrations within the normal range, suggesting a physiological relation. CONCLUSIONS--The findings are consistent with the hypothesis that parathyroid hormone and 25-hydroxyvitamin D concentrations influence bone density in middle aged women. Findings from this study together with other work suggest that the role of vitamin D in osteoporosis should not be neglected. The associations with parathyroid hormone also indicate plausible biological mechanisms. The roughly 5-10% difference in bone density between top and bottom tertiles of serum 25-hydroxyvitamin D concentrations, though not large in magnitude, may have considerable public health implications in terms of prevention of osteoporosis and its sequelae, fractures. 相似文献
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Vinogradov Michael E.; Shushkina Elvira A.; Nezlin Nikolay P.; Arnautov Genrikh N. 《Journal of plankton research》1998,20(1):85-103
Zooplankton data collected during September 1995 in the NorthWest Atlantic at 4139'N, 4958'W (the location of the siteof the Titanic wreck) were analysed. The regioninvestigated was characterized by a very sharp frontal zonebetween the Gulf Stream and the main stream of the LabradorCurrent. The total plankton biomass in the water column wasvery high. The macroplankton biomass values below the 600 mlayer were significantly higher as compared with the similarvalues measured before in other productive boreal regions ofthe Atlantic and Pacific oceans. A lot of dead mesoplanktonanimals occurred in the deep layers. The reason was that thecold-water mesoplankton advected by the Labrador Current diedoff intensively within the deep layers of the frontal zone andwere used as a food resource by the macroplankton carnivoresand scavengers that were very abundant there. 相似文献
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M R Chandler 《Perspectives in biology and medicine》1991,35(1):105-115
Over the past 10 years the AIDS crisis has produced a large volume of writing. Much of this is documentary. Dozens of studies of AIDS from various clinical and political perspectives have been complemented by just as many published diaries, autobiographies, novels, plays, and poems. A few of these works have risen to the surface not only as extraordinarily valuable testimonies to the changes AIDS has wrought in individual and collective life but also as first-rate literary works, worth reading because beyond their immediate purposes they articulate with extraordinary lucidity and compassion some deep truths about the human--and the modern--condition. Paul Monette's Borrowed Time is among the most distinctive of those. It speaks not only for the community of people with AIDS and those who support them but for a generation. 相似文献
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