Perhaps you should try some spelling variations:
hieu phan » phieu phan, lieu phan, hieu pham
phan dau » phan tu, hang dau
dau luan » dan luan, dat luan, khau luan
cua viet » ca viet, hoa viet, cua vat
su sach » so sach, vu sach
hang co » hang cho, hang ca, nang co
luan va » luan van, luat va
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cuu tre, cua triet
y hang » ly hang, ty hang, yu hang
co hoi » co hoc, co loi

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 y hang co hoi. hieu phan dau luan va hanh vi ((cua tre) or (cua viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y hang co hoi. hieu phan dau luan va hanh vi ((cua tre) OR (cua viet)).
• Adding a wildcard symbol may retrieve word variants: su sach y hang co hoi. hieu phan dau luan va hanh vi ((cua tre) or (cua viet))*.