One way of identifying a substance without resorting to fiddly chemical methods is to determine its density.
其中一种不用高精度的化学方法验证物质的办法就是确定它的密度。
One way to identify a substance without resorting to fiddly chemical methods is to determine its density.
要分辨一种物质,可以用密度测量法。而无须借助费事繁琐的化学分析法。
Or a radioactive substance may be disintegrating at a known rate and we may be required to determine the amount of material present after a given time.
又如,某种放射性物质可能正在以已知的速度进行衰变,需要我们确定在给定的时间后遗留物质的总量。
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