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一种黑色普通角闪石玉的宝石学特征 被引量:3
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作者 罗跃平 《宝石和宝石学杂志》 CAS 2007年第4期59-62,共4页
传统意义上的墨玉是指黑色软玉,其颜色由内部石墨包裹体造成。软玉市场上常出现一种被称为"墨玉"的玉石,为黑色,有白色点状区域,折射率为1.63(点测),密度为3.09g/cm3,与软玉的折射率(1.61)和密度(3.00g/cm3)相近。通过研究该... 传统意义上的墨玉是指黑色软玉,其颜色由内部石墨包裹体造成。软玉市场上常出现一种被称为"墨玉"的玉石,为黑色,有白色点状区域,折射率为1.63(点测),密度为3.09g/cm3,与软玉的折射率(1.61)和密度(3.00g/cm3)相近。通过研究该玉石发现,其黑色不是由于含有石墨造成,其主要成分为深绿色的普通角闪石。因此,该玉石不应称为墨玉,而应命名为普通角闪石玉或角闪石玉。 展开更多
关键词 “墨玉” 普通角闪石 宝石学特征
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Liberalization of Staple Crops: Lessons from the Mexican Experience in Maize
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作者 A. Yunez-Naude V. Serrano 《Journal of Agricultural Science and Technology》 2010年第3期95-101,共7页
In this paper the authors inquire why, after more than 25 years of domestic agricultural reforms in Mexico and 15 years of trade liberalization of maize under the North American Free Trade Agreement (NAFTA), the dom... In this paper the authors inquire why, after more than 25 years of domestic agricultural reforms in Mexico and 15 years of trade liberalization of maize under the North American Free Trade Agreement (NAFTA), the domestic production of maize, a non-competitive crop and the major staple in Mexico, has increased. The authors present new empirical evidence showing that, as expected, maize prices in Mexico dropped until 2006 and have experienced a process of convergence with USA prices, and maize imports from the USA have increased. However, despite lower prices, maize production in Mexico has trended upward since 1992, two years before the beginning of NAFTA's implementation. Based on the heterogeneity of maize production in Mexico, three possible explanations are proposed to explain this unexpected outcome: government supports to big commercial farmers in the agriculturally rich North of Mexico; the persistence of maize production by subsistence farmers; and to a lesser degree, increasing yields on some irrigated maize farms. We finish the paper by drawing lessons from the experience of Mexico for other Less Developed Countries. 展开更多
关键词 Domestic and trade liberalization price convergence structural change
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