Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
danh xay » dang xay, manh xay, anh xay
va hanh » van hanh, va thanh, va danh
dau luc » cau luc, dau luan, dau nuoc
tu sach » thu sach, su sach, te sach
xay hoi » xa hoi, tay hoi, cay phoi
ky danh » ky anh, ky dang
hieu va » hieu qua
luc va » duc va, tuc va, loc va
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: ((tu sach) or (thu hoach)) ky danh xay hoi. ((hieu va) OR (lieu va)) dau luc va hanh vi cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (thu hoach)) ky danh xay hoi. ((hieu va) OR (lieu va)) dau luc va hanh vi cau tren*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (thu hoach)) ky danh xay hoi. ((hieu va) OR (lieu va)) dau luc va hanh vi cau tren*".