| 单词 | helium |
| 释义 | Word Frequency helium(ˈhiːlɪəm) noun a very light nonflammable colourless odourless element that is an inert gas, occurring in certain natural gases: used in balloons and in cryogenic research. Symbol: He; atomic no: 2; atomic wt: 4.002602; density: 0.1785 kg/m3; at normal pressures it is liquid down to absolute zero; melting pt: below –272.2°C; boiling pt: –268.90°C See also alpha particle Word origin C19: New Latin, from helio- + -ium; named from its having first been detected in the solar spectrum |
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