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publishers/providers full-text pdf publisher of information in url subscription/membership/fee required Atypon
aggregators free resource full-text online preference Europe PubMed Central
aggregators full-text online subscription/membership/fee required Ingenta plc
aggregators full-text online subscription/membership/fee required Ovid Technologies, Inc.
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clinical trials free resource ClinicalTrials.gov
free resource Hazardous Substances Data Bank
consumer health free resource MedlinePlus Health Information
institutional repository free resource full-text pdf Spiral, Imperial College Digital Repository