共查询到20条相似文献,搜索用时 15 毫秒
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Hydrogen ions in precipitation are correlated much more closely with sulfate than with nitrate, whereas ammonium ions are correlated more closely with nitrate than with sulfate. Target loadings of 14 to 16 kilograms of wet sulfate deposition per hectare per year, instead of 20 as suggested hitherto, are probably necessary to produce average pH values of 4.6 to 4.7, the approximate boundary levels for damage to aquatic ecosystems. Cluster analysis reveals that there are three linked groups of ions related to air pollution, agriculture, and sea spray. 相似文献
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Trustworthy eco-labels provide consumers with valuable information on environmentally friendly products and thus promote green consumerism. But what makes an eco-label trustworthy and what can government do to increase consumer confidence? The scant existing literature indicates that low governmental involvement increases confidence. This suggests that government should just provide the basic legal framework for eco-labeling and leave the rest to non-governmental organizations. However, the empirical underpinning of this conclusion is insufficient. This paper analyses consumer confidence in different organic food labeling regimes with varying degrees of governmental involvement. Using unique and detailed survey data from the US, United Kingdom, Denmark, and Sweden, the analysis shows that confidence is highest in countries with substantial state involvement. This suggests that governments can increase green consumerism through active and substantial involvement in eco-labeling. 相似文献
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E A Nadelmann 《Science (New York, N.Y.)》1989,245(4921):939-947
"Drug legalization" increasingly merits serious consideration as both an analytical model and a policy option for addressing the "drug problem." Criminal justice approaches to the drug problem have proven limited in their capacity to curtail drug abuse. They also have proven increasingly costly and counterproductive. Drug legalization policies that are wisely implemented can minimize the risks of legalization, dramatically reduce the costs of current policies, and directly address the problems of drug abuse. 相似文献
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Fertility in the United States 总被引:1,自引:0,他引:1
C F Westoff 《Science (New York, N.Y.)》1986,234(4776):554-559
From the postwar high of 3.8 births per woman at the peak of the baby boom, the total fertility rate in the United States has fallen to 1.8, where it has remained unchanged for nearly a decade. This below-replacement level of fertility has, in recent decades, characterized most Western countries, some of which have shown declines to well below 1.5 births per woman. Were it not for the continued infusion of immigrants, the U.S. population, which already shows the aging characteristic of low fertility, would stop growing and begin to decline before the middle of the next century. The low fertility in the United States has been accomplished by a postponement of marriage and by the widespread use of contraception, with heavy reliance on surgical sterilization as a contraceptive method. Judging from the experience of other Western countries and from our own historical experience of two centuries of fertility decline interrupted only by the baby boom, as well as from the absence of social trends that would counteract those contributing to that decline, the prognosis is for a continued low level of fertility in the United States. 相似文献
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Dermer OC 《Science (New York, N.Y.)》1988,239(4844):1184-1185
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Perry H 《Science (New York, N.Y.)》1983,222(4622):377-384
Historical trends in U.S. coal production, transportation and utilization and their causes are analyzed. The changing structure of the coal industry and its possible future direction, as it is driven by the effects of the oil embargo and world oil prices, are examined. National policies in the United States to increase coal use from indigenous sources in order to diversify and increase reliability of supply raise questions as to availability of coal supply and potential markets. Possible constraints on U.S. coal production, transportation, and utilization are appraised and it is concluded that increased coal consumption is "demand constrained." The causes and potential means of removal of these limitations are examined. 相似文献
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Leukemia mortality: downturn rates in the United States 总被引:3,自引:0,他引:3
A decline, the first ever observed, has recently occurred in leukemia mortality rates for the white population of the United States between the ages of 1 and 74. Possible explanations include diminished exposure to medical x-rays following the release in the United States and Great Britain in 1956 of widely publicized reports on the biologic effects of ionizing radiation. 相似文献
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根据美国农业部农业经济局、美国劳工部劳工统计局和美国商业部国情普查局3家官方分别调查公布的数据看,美国在1910~1970年农业人口锐减,人口结构完成了由农业人口向工业人口的转型.但是官方的统计数据中也存在很多纰漏,主要包括“农业服务”工人、流动农业人口、非法移民、童工这4类直接或间接从事农业生产的劳动力人口并没有被统计入美国农业人口数据.美国官方出于夸大农业劳动生产率,掩盖剥削,统计方法局限,情况复杂等原因,导致农业人口统计数字差异大,绝对数量不准确等数据问题. 相似文献
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