List of academic databases and search engines

This article contains a representative list of notable databases and search engines useful in an academic setting for finding and accessing articles in academic journals, institutional repositories, archives, or other collections of scientific and other articles. Databases and search engines differ substantially in terms of coverage and retrieval qualities. Users need to account for qualities and limitations of databases and search engines, especially those searching systematically for records such as in systematic reviews or meta-analyses. As the distinction between a database and a search engine is unclear for these complex document retrieval systems, see: the general list of search engines for all-purpose search engines that can be used for academic purposes the article about bibliographic databases for information about databases giving bibliographic information about finding books and journal articles. The terms "free", "subscription", and "free & subscription" will refer to the availability of the website as well as the journal articles used. Furthermore, some programs are only partly free (for example, accessing abstracts or a small number of items), whereas complete access is prohibited (login or institutional subscription required). The "Size" column denotes the number of documents (articles, publications, datasets, preprints) rather than the number of citations or references. The database itself should be the primary source of statistics, and if it is not accessible, the independent estimates released as journal papers should be. Notably, Google Scholar does not offer such detail, but the database's size has been calculated.