There is a command in org-ref-pubmed that will download a bibtex entry from a pmid: pubmed-insert-bibtex-from-pmid. There is also the commands: pubmed-simple-search which will prompt for a query and open the search in pubmed, the command "pubmed" which just opens the pubmed site, and "pubmed-advanced" which opens the advances search page.
There isn't however, anything as sophisticated as you want for pubmed. You would have to use it to get the DOIs, and then use the doi-add-bibtex-entry function to get the bibtex entry and (if it knows how) the pdf.