Motores de busca especializados

1Findr - Search 110+ million scholarly journal articles | all disciplines, all languages, all over the world
Base - Bielefeld Academic Search Engine | one of the world's most voluminous search engines especially for academic web resources
CiteSeerX - Scientific literature digital library and search engine
Google Académico (Google Scholar)
MedNar - Free, medically-focused web search engine
Microsoft  Academic - Semantic search engine
Open Science Directory - Global search tool for all open access and special programs journal titles
RefSeek - Web search engine for students and researchers
RePec - Research Papers in Economics
Smantic Scholar - Academic search engine from the Allen Institute for AI
Wolfram|Alfa - Expert-level knowledge and capabilities to the broadest possible range of people
WorldWideScience - Global science gateway