Perhaps you should try some spelling variations:
cach thoi » cac thoi, cach thuc, cach noi
cua viet » ca viet, hoa viet, cua vat
sach hoi » sach doi, sach moi, hoach hoi
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
hieu va » lieu va, hieu qua
nang ma » tang ma, sang ma, nang cao
hanh di » hanh vi, hanh de, hang di
ma hoi » mai hoi, xa hoi, ma hoa
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: tu ((sach hoi) OR (cach thoi)) nang 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: tu ((sach hoi) OR (cach thoi)) nang ma hoi. ((hieu van) OR (hieu va)) nam thuc dan hanh di cua viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach hoi) OR (cach thoi)) nang ma hoi. ((hieu van) or (hieu va)) nam thuc dan hanh di cua viet".
• Adding a wildcard symbol may retrieve word variants: tu ((sach hoi) OR (cach thoi)) nang ma hoi. ((hieu van) or (hieu va)) nam thuc dan hanh di cua viet*.