1. Index Copernicus

2. CrossRef (included in 2016)

3. Google Scholar

4. WorldCat

5. Directory of Open Access Journals (DOAJ)

6. 1findr

7. Ulrich's Periodicals Directory

8. Neliti

9. ResearchBib

10. BASE

11. Directory of Open Access scholarly Resources (ROAD)

12. Semantic Scholar

13. CORE (COnnecting REpositories)

14. MIAR

15. JournalTOCs

16. WorldWideScience.org

17. OpenAIRE

18. Zeitschriftendatenbank (ZDB)

19. Scilit

20. Dimensions

21. Соционет

22. Scholarly Citation Index Analytics (SCIA)

23. Hinari