Barabasi和Bonabeau可能是最早使用这个词的。
对于network，scale是指节点的连接数。
Scale-free networks are noteworthy because many empirically observed networks appear to be scale-free, including the protein networks, citation networks, and some social networks.
http://en.wikipedia.org/wiki/Scale-free_network#cite_note-0Albert R. and Barabási A.-L., "Statistical mechanics of complex networks", Rev. Mod. Phys. 74, 47–97 (2002).