"IRSpy maintains a registry of information retrieval targets supporting the standard IR protocol ANSI/NISO Z39.50 (ISO 23950) and the SRU/SRW web services. Each registry entry consists of both database level information, such as the indexes supported for searching and the record syntax and schemas supported for retrieval, and record level metadata such as titles, authors and descriptions."
it supports explain and searchRetrieve, with mods and dc schemas. should page through records just fine, i think, if you pass it the correct params. lots of other suggested things are not supported (esp. no diagnostics, yet).