Perhaps you should try some spelling variations:
su sach » so sach, vu sach
sach tu » sach thu, cach tu, sach ty
nang ma » tang ma, sang ma, nang cao
hieu ve » hieu va, hieu van
ve pham » vi pham, v pham, ve phan
va dinh » van dinh, va kinh, va tinh
dinh vi » dinh ve, dinh viet, dinh tri
cua tre » cuu tre, cua triet, dua tren
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: su sach tu ((nang x) or (nang ma)) hoi. hieu ve pham duc va dinh vi ((cua tre) OR (cua te))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach tu ((nang x) OR (nang ma)) hoi. hieu ve pham duc va dinh vi ((cua tre) OR (cua te)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach tu ((nang x) or (nang ma)) hoi. hieu ve pham duc va dinh vi ((cua tre) OR (cua te))".
• Adding a wildcard symbol may retrieve word variants: su sach tu ((nang x) or (nang ma)) hoi. hieu ve pham duc va dinh vi ((cua tre) OR (cua te))*.