Perhaps you should try some spelling variations:
thuat sach » thuat lanh, thuat san
hieu van » hieu va, thien van, lieu va
nam duoc » nam thuoc, da duoc, dat duoc
duoc may » duoc ma, duoc ly, hoc may
tinh dan » trinh dan, tinh da, binh dan
sach ky » sac ky, sach y, sach ty
sang ma » tang ma, nang ma, sang tao
cu tren » tu tren, dua tren
dan cu » dan cua, dan ca, dan su

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

• If you are trying to use Boolean operators, they must be ALL CAPS: thuat sach ky ((mang may) OR (sang ma)) hoi. hieu van nam duoc may tinh dan cu tren~.
• Adding a wildcard symbol may retrieve word variants: thuat sach ky ((mang may) or (sang ma)) hoi. hieu van nam duoc may tinh dan cu tren*.