Perhaps you should try some spelling variations:
toc sach » doc sach, thuoc sach, nuoc sach
hieu van » hieu va, thien van, lieu va
tinh tai » trinh tai, tinh thai, tinh hai
thuc dan » thuc hanh, hoc dan, thuc vat
hoc sach » hoc sinh, hoc cac, hoc anh
cau tren » cu tren, dau tren, ca tren
van lam » van nam
thuc va » thuc vat, thuc day
tai cau » tai cac, tai cao
x hoi » xa hoi, o hoi, x ho

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) or (hoc sach)) ky nang x hoi. hieu van lam ((thuc va) OR (thuc dan)) tinh tai cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc sach)) ky nang x hoi. hieu van lam ((thuc va) OR (thuc dan)) tinh tai cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) or (hoc sach)) ky nang x hoi. hieu van lam ((thuc va) OR (thuc dan)) tinh tai cau tren".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (hoc sach)) ky nang x hoi. hieu van lam ((thuc va) OR (thuc dan)) tinh tai cau tren*.