Perhaps you should try some spelling variations:
hoc sach » hoc sinh, hoc cac, hoc anh
mang mai » lang mai, mang lai, mang mam
nam thuc » nam thuoc, am thuc, nam thu
thuc dan » thuc hanh, hoc dan, thuc vat
danh vi » hanh vi, dinh vi, danh va
danh di » danh du, xanh di, danh dien
hieu he » hieu ve, hiem he, hieu le
sach ky » sac ky, sach y, sach ty
he nam » ha nam, nghe nam

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 ((mang mai) or (mang may)) hoi. hieu he nam thuc dan ((danh vi) OR (danh di)) hoa viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc sach ky ((mang mai) OR (mang may)) hoi. hieu he nam thuc dan ((danh vi) OR (danh di)) hoa viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc sach ky ((mang mai) or (mang may)) hoi. hieu he nam thuc dan ((danh vi) OR (danh di)) hoa viet".
• Adding a wildcard symbol may retrieve word variants: hoc sach ky ((mang mai) or (mang may)) hoi. hieu he nam thuc dan ((danh vi) OR (danh di)) hoa viet*.