Perhaps you should try some spelling variations:
thanh phan » thanh pho, thanh san, thanh toan
hieu van » hieu va, thien van, lieu va
phan cua » nhan cua, than cua, phat cua
thuc van » thuc vat, thuc dan, thuc hanh
thuc va » thuc vat, thuc dan, thuc day
sach ty » sach y, sach thu, xach tay
nang xa » nang x, lang xa, nang ma
sach tu » sach thu, cach tu, sach uu
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: so ((sach ty) or (sach tu)) nang xa hoi. hieu van nam ((thuc van) OR (thuc va)) thanh phan cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so ((sach ty) OR (sach tu)) nang xa hoi. hieu van nam ((thuc van) OR (thuc va)) thanh phan cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so ((sach ty) or (sach tu)) nang xa hoi. hieu van nam ((thuc van) OR (thuc va)) thanh phan cua tre".
• Adding a wildcard symbol may retrieve word variants: so ((sach ty) or (sach tu)) nang xa hoi. hieu van nam ((thuc van) OR (thuc va)) thanh phan cua tre*.