Perhaps you should try some spelling variations:
nam thuc » nam thuoc, am thuc, nam thu
doi hoac » doi hoa, doi hoat, doi thoai
day hanh » day nhanh, day thanh, dao hanh
hieu van » thien van, lieu va, hieu ve
thuc day » thuc dan, thuc vat
tu sach » thu sach, su sach, te sach
sach lo » sach dao, sach doi, sach hoi
hieu va » lieu va, hieu qua
nang ma » tang ma, sang ma, nang cao
lo nang » ho nang, ly nang, loai nang
ma hoi » mai hoi, xa hoi, ma hoa
di hoa » dai hoa, doi hoa, do hoa

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