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 va » lieu va, hieu qua
va pham » van pham, va phat, va phap
dinh di » dinh vi, danh di, dinh da
dinh du » dinh duc, dinh cu, dinh tu
cua tre » cua te, cuu tre, cua triet

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 va pham duc va ((dinh di) OR (dinh du)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach tu ((nang x) OR (nang ma)) hoi. hieu va pham duc va ((dinh di) OR (dinh du)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach tu ((nang x) or (nang ma)) hoi. hieu va pham duc va ((dinh di) OR (dinh du)) cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach tu ((nang x) or (nang ma)) hoi. hieu va pham duc va ((dinh di) OR (dinh du)) cua tre*.