Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
thuc dan » thuc hanh, hoc dan, thuc vat
dan dan » dang dan, ban dan, dao dan
hieu va » lieu va, hieu qua
ky lang » ky dang, ky tang, tay lang
ha hoi » hoa hoi, ha noi, xa hoi
va cuu » va cau, va huu
va chu » va che, va cau, va chi
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 dan ((va cuu) OR (va chu)) 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 dan ((va cuu) OR (va chu)) 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 dan ((va cuu) OR (va chu)) tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky lang) or (ky nang)) ha hoi. hieu va am thuc dan dan ((va cuu) OR (va chu)) tre*.