Google Scholar is a freely accessible web search engine. Its index includes most peer-reviewed online academic journals and books, conference papers, theses and dissertations, preprints, abstracts, technical reports, and other scholarly literature, including court opinions and patents SciVerse Scopus is the largest abstracts and citations database of Elsevier’s SciVerse, that integrates the familiar–trusted content from SciVerse Scopus, peer-reviewed literature, SciVerse ScienceDirect full-text articles and the Web