人们发现，在一些保存着太阳系原始化学成分的陨石中，铱元素的含量很高。
Ir is found in high concentrations in some meteorites, in which the solar system's original chemical composition is preserved.
每一种样式代表一种不同的化学元素，所以光谱线的不同集合或模式意味着这颗恒星有不同的化学成分。
Each pattern stands for a distinct chemical element, and so different sets or patterns of spectral lines mean that the star has a different chemical composition.
文章从铸铁的化学成分、微量元素、孕育处理及金属型的热交换方面叙述了产生白口的原理及防白口的有效方法。
From the chemical composition, trace element, inoculation and thermal exchange of metal mold casting, the principle of chill formation and the effective methods for preventing chill were studied.
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