Milan Randic Xiaofeng Guo T. Oxley H. K. Krishnapriyan L. Naylor 361-367 1994 34 Journal of Chemical Information and Computer Sciences 2 http://pubs.acs.org/cgi-bin/archive.cgi/jcisd8/1994/34/i02/f-pdf/f_ci00018a022.pdf db/journals/jcisd/jcisd34.html#RandicGOKN94