单词：cesium tetraiodide
四碘化铯
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[00:06.37]The United States has a new official clock. [00:10.95]The clock began operating late last year in the American city of Boulder,Colorado. [00:18.39]Experts say the new clock is so exact that it will neither gain nor lose so much as one secon
发表于:2018-12-26 / 阅读(199) / 评论(0)
美国英语听力80篇
美国英语听力80篇
Youve given some thought to oxygen, carbon, uranium. But youve probably never mused about the element ytterbium, symbol Yb. A new study by scientists at the National Institute of Standards and Technology, or NIST, says that ytterbium could find a rol
发表于:2019-01-08 / 阅读(177) / 评论(0)
Scientific American(八)月
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