of all studies, and of randomized or controlled clinical trials, are subsequently published as peer-reviewed journal articles."¹
From the Plain Language Summary of: Scherer RW, Langenberg P, von Elm E. Full publication of results initially presented in abstracts. Cochrane Database of Systematic Reviews 2007, Issue 2. Art. No.: MR000005. DOI: 10.1002/14651858.MR000005.pub3.
Many conference proceedings, meeting abstracts, and symposia are published in journal supplements. These supplements are generally not indexed in PubMed so you need to search other places to find them.
The links below provide instructions on where and how to find abstracts and proceedings online.