Besides NTIS, available via Engineering Village/Elsevier, Princeton University now has access to NTRL (National Technical Reports Library) (1800+) from the U.S. Government.
It provides indexing and access to a collection of more than 2,000,000 historical and current unclassified government technical reports archived by the National Technical Information Service. Over 500,000 documents are available in full-text from departments such as Department of Energy, NASA, and the Environmental Protection Agency.
NTRS differs from NTIS in that it covers more years, mainly from 1960, but as far back as 1800. The database is updated daily and there is full text for about 25% of the reports.
Source: P.U.‘s Engineering Library and Database Management Group