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Using Library of Congress subject headings can help narrow or broaden your search as well as identify specific key words that will be using conducting your research. Move from a broad to a specific topic. Review the "Subject of Works" for historical/foundational resources.
Science Direct includes a topical index which separates topics by field. Each entry includes excerpts from scholarly articles, books, books chapters, encyclopedias, and other resources produced by Elsevier. If you locate a pertinent resource, search for the title on the ZSR library website. If needed, request access to the resource using interlibrary loan.