academia.edu
arxiv.org
cambridge.org/core/publications/open-access
core.ac.uk
doaj.org
doabooks.org
scholar.google.com
archive.org
v2.sherpa.ac.uk/opendoar
jstor.org
direct.mit.edu/journals
oaister.on.worldcat.org/discovery
oalib.com
oapen.org
oro.open.ac.uk
citeseerx.ist.psu.edu
researchgate.net
springeropen.com
loc.gov/collections
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