Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
tu sach » thu sach, su sach, te sach
tang xa » trang xa, tang ma, lang xa
van cau » van dau, van hau, van chat
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cuu tre, cua triet
co viet » so viet, o viet, hoc viet
y tang » ky tang, 6 tang, 7 tang
cau tu » dau tu, cau truc

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach y tang xa hoi. hieu van cau tu va hanh vi ((cua tre) or (co viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y tang xa hoi. hieu van cau tu va hanh vi ((cua tre) OR (co viet)).
• Adding a wildcard symbol may retrieve word variants: tu sach y tang xa hoi. hieu van cau tu va hanh vi ((cua tre) or (co viet))*.