Perhaps you should try some spelling variations:
doanh van » doanh va, doanh ban, doanh nhan
toc sach » hoc sach, doc sach, thuoc sach
doan van » doan va, hoang van, luan van
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
tang ma » tang van
cua tre » cua te, cuu tre, cua triet
ve cac » va cac, vien cac
cac tu » cac thu, cach tu, cac du

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach ky ((tang ma) OR (mang may)) hoa. hieu ve cac tu va ((doanh van) or (doan van)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky ((tang ma) OR (mang may)) hoa. hieu ve cac tu va ((doanh van) OR (doan van)) cua tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky ((tang ma) OR (mang may)) hoa. hieu ve cac tu va ((doanh van) or (doan van)) cua tre*".