4. virtual resources
This is the most searched British META-OPAC. It contains the online catalogue of 22 of the largest university research libraries in the UK and Ireland, plus the British Library catalogue.
NUKAT offers a search of Polish academic and research libraries; one difficulty, though, is that many libraries have electronically catalogued only more recent acquisitions, usually post-1989, while some older materials are yet to be included. Thus, a trip to the library card indexes might be necessary.