单词：antimony-cesium photocathode
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The most popular toys this holiday season, as you know, if you're a parent, are zhu zhu pets. They're little robot hamsters that move around or something and there're people going crazy for them. Zhu zhu pets are manufactured in China, and over the w
访谈录2009
[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
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
Scientific American(八)月