这个词是什么意思？
Substances that comprise all matter. Each element is made up of atoms that are identical in number of electrons and protons and in nuclear charge but may differ in mass or number of neutrons.
中文名称索引；定义为 MeSH 英文原文，尚未逐条译审。MESH:D004602 · MeSH 2026。
Courtesy of the U.S. National Library of Medicine. Annual snapshot; later updates may not be reflected. NLM does not endorse this service.