Google Scholar primarily searches the following: academic publisher websites, Google books, institutional repositories and .edu sites, .gov sites
SocArXiv is a repository of articles that have been made available by authors (often referred to as pre-print, post-print, or author accepted). SocArXiv has content across multiple disciplines, and includes a social work specific category.
PsycArXiv is also a disciplinary repository. PsycArXiv includes clinical psychology, developmental psychology and other related areas.
PubMed is a federally supported database of health-sciences related articles, including psychology, psychiatry, and public health. PubMed Central is a subset of PubMed and is composed of all open access articles.
ERIC is a federally supported database of education-related articles.