Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
thuc dan » hoc dan, thuc vat
ky lang » ky dang, ky tang, tay lang
hieu va » lieu va, hieu qua
cuu tre » cua tre, cau tren, cau treo
ha hoi » hoa hoi, ha noi, xa hoi
dan va » doan va, dan ca, ban va
va cuu » va cau, va chu, va huu
va am » va lam, va cam

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 ((ky lang) or (ky nang)) ha hoi. hieu va am ((thuc dan) OR (thuc hanh)) dan va cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky lang) OR (ky nang)) ha hoi. hieu va am ((thuc dan) OR (thuc hanh)) dan va cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ky lang) or (ky nang)) ha hoi. hieu va am ((thuc dan) OR (thuc hanh)) dan va cuu tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky lang) or (ky nang)) ha hoi. hieu va am ((thuc dan) OR (thuc hanh)) dan va cuu tre*.