Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
dan hanh » dang hanh, dan khanh, dan thanh
thuc dan » thuc hanh, hoc dan, thuc vat
nam thuc » nam thuoc, am thuc, nam thu
sach hoi » sach doi, sach moi, cach thoi
hieu van » thien van, lieu va, hieu ve
cua viet » ca viet, hoa viet, cua vat
tang ma » mang may, tang van
hieu va » lieu va, hieu qua
nang ma » sang ma, nang cao, mang may
hanh di » hanh vi, hanh de, hang di
di cua » dai cua, doi cua, de cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach hoi ((nang ma) or (tang ma)) hoi. ((hieu van) or (hieu va)) nam thuc dan hanh di cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach hoi ((nang ma) OR (tang ma)) hoi. ((hieu van) OR (hieu va)) nam thuc dan hanh di cua viet.
• Adding a wildcard symbol may retrieve word variants: thu sach hoi ((nang ma) or (tang ma)) hoi. ((hieu van) or (hieu va)) nam thuc dan hanh di cua viet*.