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