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• OAI-PMH : Open Archives Initiative Protocol for Metadata Harvesting
  

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• OAIster

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• OAPEN : Open Access Publishing in European Networks
  

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• OATD : Open Access Theses and Dissertations
  

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• Obra huérfana
  

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• Oceanic Abstratcs
  

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• OCR : Optical Character Recognition
  

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• OCLC : Online Computer Library Center
  

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• OCW : OpenCourseWare
  

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• Offsetting
  

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• OJS : Open Journal System
  

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• OPAC : Catálogo Público de Acceso en Línea
  

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• OpenDOAR
  

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• OpenGrey
  

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• ORCID : Open Research and Contributor ID
  

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• Osiris