When searching for technical reports in specific subject areas, keep in mind these tips:
Technical report literature forms a significant portion of the information that engineers and scientists may find useful. Even so, different disciplines place varying amounts of emphasis on technical report literature. Some subject areas provide good indexes to this material while others may not. Reports prepared at academic institutions may be well indexed within the institution but not generally known outside it. And technical reports prepared by for-profit companies and organizations may be completely proprietary and remain essentially invisible to anyone outside the organization.
The resources below offer several ways to search for technical reports in a fairly comprehensive manner.