Perhaps you should try some spelling variations:
thuat sach » thuat lanh, thuat san
hieu van » hieu va, thien van, lieu va
nam tuc » nam thuc, nam truc, nam tu
xa tinh » va tinh, ha tinh, ca tinh
tinh ve » trinh ve, tinh ven, dinh ve
cuu tre » cua tre, cau tren, cau treo
7 tang » 6 tang
ma hoi » mai hoi, xa hoi, ma hoa
y tang » ky tang, 6 tang, 5 tang
cua tu » cua tuc, cua su, cua cu

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

• Performing a fuzzy search may retrieve terms with similar spellings: thuat sach ((y tang) OR (7 tang)) ma hoi. hieu van nam tuc xa tinh ve ((cua tu) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thuat sach ((y tang) OR (7 tang)) ma hoi. hieu van nam tuc xa tinh ve ((cua tu) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "thuat sach ((y tang) OR (7 tang)) ma hoi. hieu van nam tuc xa tinh ve ((cua tu) or (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: thuat sach ((y tang) OR (7 tang)) ma hoi. hieu van nam tuc xa tinh ve ((cua tu) or (cuu tre))*.