Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hanh vai » hanh vi, hanh tai, hanh van
nam thuc » nam thuoc, am thuc, nam thu
cau tren » cu tren, dau tren, ca tren
hieu ve » hieu va, hieu van
thuc va » thuc vat, thuc dan, thuc day
hanh va » hang va, hanh vi
ve nam » he nam, va nam, le nam

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach y ((nang cao) or (nang x)) hoi. hieu ve nam thuc va ((hanh vai) OR (hanh va)) cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach y ((nang cao) OR (nang x)) hoi. hieu ve nam thuc va ((hanh vai) OR (hanh va)) cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach y ((nang cao) or (nang x)) hoi. hieu ve nam thuc va ((hanh vai) OR (hanh va)) cau tren".
• Adding a wildcard symbol may retrieve word variants: toc sach y ((nang cao) or (nang x)) hoi. hieu ve nam thuc va ((hanh vai) OR (hanh va)) cau tren*.