University library "St. Kliment Ohridski"

Multidisciplinary

Bulgarian Portal for Open Science – Consists of dissertations, scientific publications and papers from bulgarian scientists and conferences.

Oxford University Research Archive (ORA) – Consists of journals, books, dissertations, conference papers and other scientific works with open access.

Highwire Press – Stanford University – Consists over 2 million open access articles.

European Patent Office – Consists of over 110 million patents from all over the world.

SpringerOpen – Full-text access to peer-review journals in various science fields.

Journals for Free – Offers open access to over 17 000 scientific journals.

The Directory of Open Access Journals – Consists of nearly 4 million articles published in more than 15 000 journals from all over the world.

The Digital Commons Network – Offers open access to more than 3 million articles from more that 590 institutions.

Index Copernicus – Indexes more than 2500 journals from all over the world selected by certain criteria.

Paperity – Consists of over 1.5 million full-text articles published in more than 4200 journals. There is a full-text search for most of them.

CiteSeerX – Consists of more than 750 000 full-text resources.

SciELO – Offers access to more than 985 full-text journals.

arXiv – Repository of e-preprints and articles.

CogPrints: Cognitive Sciences Eprint Archives – E-archive where authors present their scientific publications.

OMICS International – Offers access to more than 700 leading peer-review journals.

MDPI  – Indexes more than 240 peer-review open access journals in all science fields.

Scientific Research Publishing  (SCIRP) – Offers open access to more than 200 academic journals.

Russian Science Citation Index – Bibliographic database which offers reference search. Some of the resources are full-text.

SCIndeks – Serbian Citation Index – Offers access to more than 250 journals published in the Republic of Serbia.

Научная электронная библиотека „КиберЛенинка” – A scientific digital library which consists of more than 2 million articles in Russian.

ReroDoc – Consists of over 79 000 articles, books, dissertations, theses, maps and periodicals.