- Directory of Open Access Journals (DOAJ)
- Moraref
- Crossref
- Academic Microsoft
- Portal Garuda
- Google Scholar
- Bielefeld Academic Search Engine (BASE)
- PKP Index
- Dimension
- CORE
- Hardvard Library
- Worldcat
- Leiden University Libraries
- Gent Univesity Library
- Boston University Library
- The University of Sheffield
- University of Saskatchewan Library
- Columbia University Libraries
