Perhaps you should try some spelling variations:
doanh thuong » anh thuong, dinh thuong, dong thuong
nghien thu » nghiem thuc, nghiep thuc, nghien cuu
sach hoc » cach hoc, sach hoi, mach hoc
thu hang » thi hang, thuc hanh, thu huong
hang hoa » hang khoa, thanh hoa, hang va
tai toan » bai toan, tap toan, tai tuan
toan ban » van ban
su sach » so sach, vu sach
hoc tai » hoc dai, hoc tap, hoc bai
ma hoc » va hoc, ma hoa, mo hoc

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach hoc tai, nghien thu hang hoa ((doanh thuong) or (doan phuong)) hoc ma hoc tai toan ban~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach hoc tai, nghien thu hang hoa ((doanh thuong) OR (doan phuong)) hoc ma hoc tai toan ban.
• Adding a wildcard symbol may retrieve word variants: su sach hoc tai, nghien thu hang hoa ((doanh thuong) or (doan phuong)) hoc ma hoc tai toan ban*.