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