Online toegang naar http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V98-%203SX7FNR2&_user=457046&_coverDate=03%2F31%2F1998&_rdoc=1&_fmt=high&_orig=%20gateway&_origin=gateway&_sort=d&_docanchor=&view=c&_acct=C000021878&_version=%201&_urlVersion=0&_userid=457046&md5=dc33857997c251c1d26a4ca56dea26c3&searchtyp%20e=a
