A few years ago, the University of Bielfeld set up a search engine to search the scientific content of repositories and other databases. More than 2 million documents are available, indexed in more than 8000 data sources, ranging from repositories to commercial providers of scholarly works. It is estimated that more than 60 % of all indexed works are available in open or open access.
The web address of this interesting information tool is at https://www.base-search.net.
