Perhaps you should try some spelling variations:
sach hoc » cach hoc, sach hoi, mach hoc
cuu cong » cua cong, thu cong, cac cong
cong luc » dong luc, cong suc, cong duc
luc hang » luc sang, duc thang, duc hoang
hang hoa » hang khoa, thanh hoa, hang va
tu sach » thu sach, su sach, te sach
hai tan » hai van, hai quan
hoc xa » hoc ma
ha van » hoa van, nha van, va van

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach hoc tap, nghien cuu cong luc hang hoa hoc xa ((ha van) or (hai tan)) pham van~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach hoc tap, nghien cuu cong luc hang hoa hoc xa ((ha van) OR (hai tan)) pham van.
• Adding a wildcard symbol may retrieve word variants: tu sach hoc tap, nghien cuu cong luc hang hoa hoc xa ((ha van) or (hai tan)) pham van*.