You can search for research documents with the search machine Google Scholar. The search is free-of-charge. The hits include Open Access full texts as well as chargeable documents. Google Scholar works on the one hand like a specialist portal that lists all hits for a particular search, but on the other hand, it is the world’s largest Open Access search machine, because it links the best freely accessible version of a hit in the right-hand column. This means that Google Scholar is suitable for searching for and in repositories.
Using a public access feature, the profiles of researchers are, in part, freely available in Google Scholar, showing how many of their research works are subject to an Open Access mandate from funding organisations. This gives researchers an overview of which of their publications they may still need to make freely available in repositories (an upload to Google Drive, as suggested there, is not recommended under Open Access perspectives). The feature does not function perfectly however, and shows some weaknesses in the social sciences, for example.