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mdpi is a publisher of peer-reviewed, open access journals since its establishment in 1996.

sistema de información científica redalyc. red de revistas científicas. acceso abierto sin fines de lucro propiedad de la academia. modelo de acceso abierto diamante.

elsevier’s scopus, the largest abstract and citation database of peer-reviewed literature. search and access research from the science, technology, medicine, social sciences and arts and humanities fields.

sci-hub website. get free access to academic journals. download research papers for free from sciencedirect, ieee, wiley, springer, nature and others

ministerio de ciencia, innovación y universidades

semantic scholar uses groundbreaking ai and engineering to understand the semantics of scientific literature to help scholars discover relevant research.

the world’s largest collection of open access research papers

internet archive is a non-profit digital library offering free universal access to books, movies & music, as well as 624 billion archived web pages.