RT Journal Article SR Electronic T1 Covert pharmaceutical promotion in free medical journals JF Canadian Medical Association Journal JO CMAJ FD Canadian Medical Association SP 534 OP 535 DO 10.1503/cmaj.110156 VO 183 IS 5 A1 Aaron S. Kesselheim YR 2011 UL http://www.cmaj.ca/content/183/5/534.abstract