Perhaps you should try some spelling variations:
nam thuc » nam thuoc, am thuc, nam thu
hoi nang » hoi lang, ho nang, hoa nang
dan hanh » dang hanh, dan khanh, dan thanh
hieu van » thien van, lieu va, hieu ve
thuc dan » thuc hanh, hoc dan, thuc vat
sach hoi » sach doi, sach moi, cach thoi
tu sach » thu sach, su sach, te sach
hieu va » lieu va, hieu qua
nang ma » tang ma, sang ma, nang cao
ma hoi » mai hoi, xa hoi, ma hoa
di cua » doi cua, de cua, do 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 nang ma hoi. ((hieu van) or (hieu va)) nam thuc dan hanh ((di cua) OR (dai cua)) viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach hoi nang ma hoi. ((hieu van) OR (hieu va)) nam thuc dan hanh ((di cua) OR (dai cua)) viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach hoi nang ma hoi. ((hieu van) or (hieu va)) nam thuc dan hanh ((di cua) OR (dai cua)) viet".
• Adding a wildcard symbol may retrieve word variants: tu sach hoi nang ma hoi. ((hieu van) or (hieu va)) nam thuc dan hanh ((di cua) OR (dai cua)) viet*.