什么是马雅人
Maya
Group of Mesoamerican Indians who between AD 250 and 900 developed one of the Western Hemisphere's greatest civilizations. By AD 200 they had developed cities containing palaces, temples, plazas, and ball courts. They used stone tools to quarry the immense quantities of stone needed for those structures; their sculpture and relief carving were also highly developed. Mayan hieroglyphic writing survives in books and inscriptions. Mayan mathematics featured positional notation and the use of the zero; Mayan astronomy featured an accurately determined solar year and precise tables of the positions of Venus and the moon. Calendrical accuracy was important for the elaborate rituals and ceremonies of the Mayan religion, which was based on a pantheon of gods. Ritual bloodletting, torture, and human sacrifice were employed to propitiate the gods, ensure fertility, and stave off cosmic chaos. At the height of its Classic period, Mayan civilization included more than 40 cities of 5,000-50,000 people. After 900 the civilization declined rapidly for unknown reasons. Descendants of the Maya are now subsistence farmers in southern Mexico and Guatemala. See also Chichén Itzá, Copán, Lacandon, Maya codices, Mayan languages, Quiche, Tikal, Tzeltal, Tzotzil, Uxmal.
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乙醇与钠反应
乙醇与金属钠反应的化学方程式:2C2H5OH+2Na→2C2H5ONa+H2↑醇跟钠反应的通式为:2ROH+2Na→2RONa+H2↑乙醇钠由金属钠与无水乙醇作用蒸干乙醇制得,乙醇与与金属钠反应生成乙醇钠和氢气,断开羟基上的氢氧键,生成氢气。乙醇钠为白色或微黄色吸湿性粉末,在空气中易分解,贮...
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望远镜倍数怎么理解10*50
望远镜10x50的意思是:口径是50mm,放大倍率是10倍。望远镜的第一个作用是放大远处物体的张角,使人眼能看清角距更小的细节。望远镜第二个作用是把物镜收集到的比瞳孔直径(最大8毫米)粗得多的光束,送入人眼,使观测者能看到原来看不到的暗弱物体。常见参数1、放大倍...
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按生产要素分配的类型有
一、我国按生产要素分配的三种分配类型1、以劳动作为生产要素分配;2、劳动以外的生产要素所有者参与分配;3、管理和知识产权类的生产要素参与分配。二、生产要素分配形式生产要素主要包括资本、技术、土地、劳动力等,按生产要素分配,这是凭借资本、技术、土地、劳...
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龙战于野是什么意思?
意思是:群龙在郭野大战。比喻群雄争天下成语名字:龙战于野成语发音:lóngzhànyúyě成语解释:群龙在郭野大战。比喻群雄争天下成语出处:《周易·坤卦》:“龙战于野,其血玄黄。”成语繁体:龍戰于野感情色彩:中性成语成语用法:作宾语、定语;用于比喻句成语结构:补充式成语产...