单词：cesium carbonate
[医] 碳酸铯
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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(158) / 评论(0)
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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
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日常生活中，意外伤害很难避免。如果我们不及时救治或者操作不当的话，很可能会对自身或者他人的身体造成伤害，所以，掌握一些急救常识非常必要。下面我们来看一段关于学习急救的对
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英语口语