Perhaps you should try some spelling variations:
hanh gian » thanh gian, thanh giang, dan gian
so sach » so sanh, bo sach, co sach
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
nang ma » sang ma, nang cao, mang may
tang ma » mang may, tang van
bao bo » bac bo, ban bo, nao bo
va bao » va bai
bo va » bao va, do va, so va

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach ky ((nang ma) OR (tang ma)) hoi. hieu va bao bo va ((hanh gian) or (manh giang)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ky ((nang ma) OR (tang ma)) hoi. hieu va bao bo va ((hanh gian) OR (manh giang)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach ky ((nang ma) OR (tang ma)) hoi. hieu va bao bo va ((hanh gian) or (manh giang)) cua tre".
• Adding a wildcard symbol may retrieve word variants: so sach ky ((nang ma) OR (tang ma)) hoi. hieu va bao bo va ((hanh gian) or (manh giang)) cua tre*.