To export annotated XML or RDF data for a particular PMID from GoPubMed, use these:
http://www.gopubmed.org/GoMeshPubMed/gomeshpubmed/Search/Xml?q={$pmid}[PMID]
http://www.gopubmed.org/GoMeshPubMed/gomeshpubmed/Search/RDF?q={$pmid}[PMID]
eg 17989695
The 'q' parameter is a standard PubMed search, so you can fetch multiple items at once (up to 100).
Other types available include 'BibTex', 'Endnote' and 'PlainText'.