Answer Last Updated: Jul 29, 2016 Views: 42
According to Google, they "index research articles and abstracts from most major academic publishers and repositories worldwide, including both free and subscription sources." Google does not provide names of specific databases, indexes, publishers or repositories.
Having searched Google Scholar on a wide range of topics, I have noticed results from the following databases:
If you are interested in finding a specific journal, use the advanced search options to search for a publication. For example, Lancet.