A citation index is a kind of bibliographic index, an index of citations between publications, allowing the user to easily establish which later documents cite which earlier documents. A form of citation index is first found in 12th-century Hebrew religious literature. Legal citation indexes are found in the 18th century and were made popular by citators such as Shepard's Citations (1873). In 1960, Eugene Garfield's Institute for Scientific Information (ISI) introduced the first citation index for papers published in academic journals, first the Science Citation Index (SCI), and later the Social Sciences Citation Index (SSCI) and the Arts and Humanities Citation Index (AHCI). The first automated citation indexing was done by CiteSeer in 1997. Other sources for such data include Google Scholar and Elsevier's Scopus.
Major citation indexing services
Major citation indexing services
General-purpose, subscription-based academic citation indexes include:
- Web of Science by Clarivate Analytics (previously the Intellectual Property and Science business of Thomson Reuters)
- Scopus by Elsevier, available online only, which similarly combines subject searching with citation browsing and tracking in the sciences and social sciences.
Each of these offer an index of citations between publications and a mechanism to establish which documents cite which other documents. They are not open-access and differ widely in cost: Web of Science and Scopus are available by subscription (generally to libraries).
In addition, CiteSeer and Google Scholar are freely available online.
Several open-access, subject-specific citation indexing services also exist, such as:
- INSPIRE-HEP which covers high energy physics,
- PubMed, which covers life sciences and biomedical topics, and
- Astrophysics Data System which covers astronomy and physics.