Analysis:

"Four searches" refer to engineering index (Ei), scientific citation index (SCI), scientific conference proceedings index (ISTP) and scientific review index (ISR). Ei, SCI and ISTP can be searched under the "Literature Search" column of the library homepage.

Four major reports in the United States: PB report, AD report, NASA report and DOE report.

PB is the abbreviation of the publishing bureau of the US Department of Commerce. The content has gradually shifted from military science to civilian use, and now it mainly focuses on civil engineering technology, urban planning, environmental pollution, biomedicine and so on.

AD report is a report of scientific research institutions of the United States Army, Navy and Air Force, including the research results of companies, enterprises, foreign scientific research institutions and international organizations, as well as some documents translated from the former Soviet Union and other countries. Its content soon includes military aspects, but also involves many civilian technologies, including aviation, military, electronics, communications, agriculture and other 22 fields.

National Aeronautics and Space Administration is the abbreviation of National Aeronautics and Space Administration. The contents of NASA's report focus on aviation and aerospace technology, involving many basic and technical disciplines.

DOE, also known as DE, is the abbreviation of US Department of Energy. DOE is a report on atomic energy and energy management system.