Perhaps you should try some spelling variations:
sach thu » sach thue, sach thieu, sach tham
hieu van » hieu va, thien van, lieu va
van pham » san pham, van phan, van phat
su sach » so sach, vu sach
nang xa » lang xa, nang ma, mang xa
hanh va » hanh vi
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 thu ((nang xa) or (nang x)) hoi. hieu van pham duc tan ((hanh va) OR (hang va)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach thu ((nang xa) OR (nang x)) hoi. hieu van pham duc tan ((hanh va) OR (hang va)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach thu ((nang xa) or (nang x)) hoi. hieu van pham duc tan ((hanh va) OR (hang va)) cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach thu ((nang xa) or (nang x)) hoi. hieu van pham duc tan ((hanh va) OR (hang va)) cua tre*.