Perhaps you should try some spelling variations:
thuat sach » thuat lanh, thuat san
van hanh » van thanh, ban hanh, van anh
van cac » van cau, van bac, dan cac
van hac » van hoc, van ha, van hai
dat van » dao van, dat va, dam van
y tang » ky tang, 6 tang, 5 tang
7 tang » 6 tang
ma hoi » mai hoi, xa hoi, ma hoa
vi cua » vai cua, di cua

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 cac) or (van hac)) dat van hanh vi cua vat~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thuat sach ((y tang) OR (7 tang)) ma hoi. hieu ((van cac) OR (van hac)) dat van hanh vi cua vat.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thuat sach ((y tang) OR (7 tang)) ma hoi. hieu ((van cac) or (van hac)) dat van hanh vi cua vat".
• Adding a wildcard symbol may retrieve word variants: thuat sach ((y tang) OR (7 tang)) ma hoi. hieu ((van cac) or (van hac)) dat van hanh vi cua vat*.