IEEE: Institute of Electrical and Electronics Engineers
NTIS: National Technical Information Service database
NIST: National Institute of Standards and Technology
DTIC: Access to all unclassified, unlimited citations to documents in the Defense Technical Information Center (DTIC) Scientific and Technical Information Network
NASA Technical Reports: includes research reports, journal articles, conference and meeting papers, technical videos, etc.
PubMed: Access to over 12 million MEDLINE citations back to the mid-1960's and additional life science journals
