Please consider the following sites and projects:

UNESCO Global Open Access Portal - resources by area, language, location

http://www.unesco.org/new/en/communication-and-information/portals-and-platforms/goap/

Social Science Open Access Repository - http://www.ssoar.info/en/home.html

The German Initiative 'Open Access net' - repositories in various areas incl. social science; economics, political science, history, education and psychology are separate fields

http://open-access.net/ch_en/open_access_in_individual_disciplines/social_sciences/

Humanities and Social Sciences Online Resources (freely avaialable) - links provided by INASP

http://www.inasp.info/en/training-resources/open-access-resources/subject-specific-resources/humanities-and-social-sciences/

Depending on indexing criteria, you might find social science resources under various categories (e.g. some social sciences may be indexed in the humanities; sometimes social science is not very broad just as in the German site above; education may be separated as a field, etc.)

I would also suggest to have a look at MERLOT http://www.merlot.org/merlot/index.htm

They cover many fields and you can search for learning materials by multiple criteria:

http://www.merlot.org/merlot/advSearchMaterials.htm

@Hristina Petrova: Thanks for these links. I have added them in my list. You did great contirbution

@Peter Suber Thanks for your contribution. Added in the list.

@Peter Suber - It looks like a wikipedia. I am in search of those open access databases where research papers and articles could be found easily.

Dear Hassan, don't underestimate educational wikis. They are edited by scientists, not just by anyone. If you want to go directly to the ''research papers'',

see their page on data repositories

http://oad.simmons.edu/oadwiki/Data_repositories

and disciplinary repositories http://oad.simmons.edu/oadwiki/Disciplinary_repositories

but I advise you to look at other lists too, e.g. on courses, books and their list of research wikis http://oad.simmons.edu/oadwiki/Research_wikis

By the way, Peter is an expert (one of the most quoted ones if not the most quoted) in the field of open access to science and education.

Some resources may not be indexed in the above lists, e.g. resources for reviews and student works.

Sites where you can find reviews:

Dissertation Reviews which has a focus on Asia; very useful for finding resources in a specific area and information about archives, libraries and research centers http://dissertationreviews.org/

H-Net - various websites in the humanities and social sciences and reviews https://www.h-net.org/reviews/home.php

Platforms where students and scientists can submit/upload their published and unpublished term papers, essays, theses, books:

GRIN http://www.grin.com/en/catalog/

The Undergraduate Journals and Conferences Directory http://wordpress.mercyhurst.edu/upd/

Berkeley Press Selected Works - http://works.bepress.com/authors.html

The Scientific Electronic Library Online - SciELO is an electronic library covering a selected collection of Brazilian scientific journals

http://www.scielo.br/