单词：source of neutrons
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Science and Technolgy. 科技。 Modern alchemy. 现代炼金术。 Turning a line. 进入新的一行。 The race to extend the periodic table continues. 扩展元素周期表的比赛仍在继续。 ONE of the first inklings that chemistry has an u
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By Kari Barber Dakar 21 March 2008 In many African countries, few people have access to computers and the Internet. Experts say this is hindering development and preventing students from being able to compete for jobs. At a conference in Dakar this w
VOA标准英语2008年（三月）
Some people of Italian ancestry, like me, might have a surprise in the family treea man of east Asian descent, who was living and working 2,000 years ago in the boondocks near the heel of the Italian boot. The discovery is the first good evidence of
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Questions 12-20 The elements other than hydrogen and helium exist In such small quantities that it is accurate to say that the universe somewhat more than 25 percent helium by weight and somewhat less than 25 percent hydrogen. Astronomers have measur
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This involved bombarding samples with neutrons in a small nuclear reactor and carefully counting the gamma rays that were emitted; 这项技术包括在一个小型核反应堆里用中子轰击样品，仔细计算释放出来的射线。 it was ext
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