Oh, this is interesting. filetype:pdf is now working in Google Scholar. It used to be ignored. Using it seems to filter out citation-only records. Results are still cluttered with paywall Springer / Oxford / Sage / Muse etc results — those services will happily send a PDF which will always fail to open on a home connection, presumably due to encryption — but the results are noticeably different and give a better chance of obtaining full-text articles.