Perhaps you should try some spelling variations:
thanh doi » thanh loi, thanh moi, thanh do
day thanh » dao thanh, dat thanh, da thanh
hoc sach » hoc sinh, hoc cac, hoc anh
hieu van » hieu va, thien van, lieu va
cua viet » hoa viet, cua vat, cua dieu
thuc day » thuc dan, thuc vat
nam thuc » nam thuoc, am thuc, nam thu
sach ky » sac ky, sach y, sach ty
lang xa » lang ha, dang xay, lang van
nang xa » nang x, nang ma, mang xa
ca viet » va viet, co viet, hoa viet

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

• Performing a fuzzy search may retrieve terms with similar spellings: hoc sach ky ((nang xa) or (lang xa)) hoi. hieu van nam thuc day thanh doi ((cua viet) or (ca viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc sach ky ((nang xa) OR (lang xa)) hoi. hieu van nam thuc day thanh doi ((cua viet) OR (ca viet)).
• Adding a wildcard symbol may retrieve word variants: hoc sach ky ((nang xa) or (lang xa)) hoi. hieu van nam thuc day thanh doi ((cua viet) or (ca viet))*.