青年在网络社区的危险行为 (2)
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科学60秒:树木造就的现代河流
Rivers today have high muddy banks, sandbars and bends. But they didn’t always look that way. Because it wasn’t until the of tree-like plants, some 330 million years ago, that rivers were corr...
价格的定义
价格的定义The Definition of "Price" Prices determine how resources are to be used. They are also the means by which products and services that are in limited supply are rationed ...
美科学家发现猛犸象化石 (2)
Harris; ZedHarris is chief curator at the Page Museum, which houses treasures from the tar pits. He says only partial remains of mammoths were found at this site before, and Zed is thelargest eve...
异形蚊子(2)
科学家正在进行异形蚊子在抵御疟疾病流行的研究Marcelo Jacobs-Lorena is with the Malaria Research Institute at Johns Hopkins University in Baltimore, Maryland. Jacobs-Lorena says investigators creat...