Perhaps you should try some spelling variations:
va doanh » van doanh, vay doanh, va danh
te sach » toc sach
cua tre » cuu tre, cua triet, dua tren
cac tac » cac toc, cac bac, cac dac
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
ky dang » ky nang, ky danh
ve cac » va cac, vien cac
tac va » tac da, tac xa, tuc va
ma hoi » mai hoi, ma hoa, me hoi
cua te » cua tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: te sach ky dang ((ma hoi) or (xa hoi)). hieu ve cac tac va doanh tai ((cua tre) OR (cua te))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sach ky dang ((ma hoi) OR (xa hoi)). hieu ve cac tac va doanh tai ((cua tre) OR (cua te)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "te sach ky dang ((ma hoi) or (xa hoi)). hieu ve cac tac va doanh tai ((cua tre) OR (cua te))".
• Adding a wildcard symbol may retrieve word variants: te sach ky dang ((ma hoi) or (xa hoi)). hieu ve cac tac va doanh tai ((cua tre) OR (cua te))*.