Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
lang mai » lang dai, lang hai, lang man
nam truc » nam truoc, nam thuc, nam trung
hieu van » thien van, lieu va, hieu ve
nang mai » nang ma, nang tai, nang cai
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
truc va » thuc va, thuc vat, trung va
va hanh » van hanh, va thanh, va danh
su sach » so sach, vu sach
vi cau » va cau, ve cau, di cau

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach ky ((nang mai) or (lang mai)) hoi. ((hieu van) OR (hieu va)) nam truc va hanh vi cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky ((nang mai) OR (lang mai)) hoi. ((hieu van) OR (hieu va)) nam truc va hanh vi cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky ((nang mai) or (lang mai)) hoi. ((hieu van) OR (hieu va)) nam truc va hanh vi cau tren".
• Adding a wildcard symbol may retrieve word variants: su sach ky ((nang mai) or (lang mai)) hoi. ((hieu van) OR (hieu va)) nam truc va hanh vi cau tren*.