Book and Periodical Databases

Agricola
agricola.nal.usda.gov
Provides access to the National Agricultural Library's (NAL) online catalog and article database. Search by keyword or browse by title, author, subject and NAL call number.

MEDLINE/PubMed
www.ncbi.nlm.nih.gov/entrez/query.fcgi
Biomedical/health database from the National Library of Medicine. MEDLINE/PubMed includes over 16 million journal article citations from the 1950's to present. International in scope. Appropriate for locating articles on medicinal plant research.

Biodiversity Heritage Library
archive.org/details/biodiversity
Provides access to biodiversity literature. 

Google Scholar
https://scholar.google.com/schhp?hl=en&as_sdt=0,44
Google Scholar is a search engine that searches scholarly literature and academic resources.