Perhaps you should try some spelling variations:
dua tren » dung tren
hieu van » hieu va, thien van, lieu va
so sach » bo sach, co sach, hoc sach
so sanh » do sanh
nang ma » tang ma, sang ma, nang cao
van cau » van dau, van hau, van chat
cau tuc » cau truc, cau tu, cau luc
dan hai » doan hai, dang hai, dan khai
hai dua » hai cua, dai dua, hai qua
su sach » vu sach
y nang » ky nang, ly nang, v nang
ma hoi » mai hoi, xa hoi, ma hoa
tuc va » thuc va, truc va, tuc xa
va dan » ca dan, va dao, va dau

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) or (((so sach) OR (so sanh)))) y nang ma hoi. hieu van cau tuc va dan hai dua tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (((so sach) OR (so sanh)))) y nang ma hoi. hieu van cau tuc va dan hai dua tren*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) or (((so sach) OR (so sanh)))) y nang ma hoi. hieu van cau tuc va dan hai dua tren*".