Perhaps you should try some spelling variations:
sach doi » sach hoi, sach moi, sach dao
doi nang » dai nang, hoi nang, voi nang
dan hanh » dang hanh, dan khanh, dan thanh
thuc dan » thuc hanh, hoc dan, thuc vat
nam thuc » nam thuoc, am thuc, nam thu
hieu van » thien van, lieu va, hieu ve
tu sach » thu sach, su sach, te sach
hanh di » hanh vi, hanh de, hang di
ca viet » va viet, co viet, hoa viet
hieu va » lieu va, hieu qua
ma hoi » mai hoi, xa hoi, ma hoa
di ca » di cau, di cua, doi ca

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 doi nang ((ma hoi) or (dai hoc)). ((hieu van) or (hieu va)) nam thuc dan hanh di ca viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach doi nang ((ma hoi) OR (dai hoc)). ((hieu van) OR (hieu va)) nam thuc dan hanh di ca viet.
• Adding a wildcard symbol may retrieve word variants: tu sach doi nang ((ma hoi) or (dai hoc)). ((hieu van) or (hieu va)) nam thuc dan hanh di ca viet*.