Perhaps you should try some spelling variations:
tinh doi » trinh doc, trinh do, tinh hoc
su sach » so sach, vu sach
sach tu » sach thu, cach tu, sach ty
hieu ve » hieu va, hieu van
ve pham » vi pham, v pham, ve phan
tinh di » trinh di, tinh da, tin di
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 cao)) hoi. hieu ve pham duc va ((tinh di) OR (tinh doi)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach tu ((nang x) OR (nang cao)) hoi. hieu ve pham duc va ((tinh di) OR (tinh doi)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach tu ((nang x) or (nang cao)) hoi. hieu ve pham duc va ((tinh di) OR (tinh doi)) cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach tu ((nang x) or (nang cao)) hoi. hieu ve pham duc va ((tinh di) OR (tinh doi)) cua tre*.