一微米是一毫米的千分之一。
这些线可能仅有千分之一毫米那么粗，所以要用这些线进行编织是很麻烦的，并且费用也相当昂贵。
But the weaving of these yarns, which may be only one-thousandth of a millimetre thick, is complicated and expensive.
在极端情况下，科学家估计浮尘的放射性在个人的骨骼中的积累可以达到每年18毫雷姆(千分之一雷姆，衡量电离辐射剂量的单位)。
At one extreme, the scientists estimated fly ash radiation in individuals' bones at around 18 millirems (thousandths of a rem, a unit for measuring doses of ionizing radiation) a year.
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