Perhaps you should try some spelling variations:
vat thanh » dat thanh, gat thanh, tat thanh
nhan thuc » nhan luc, dan thuc, toan thuc
toc sach » hoc sach, doc sach, thuoc sach
ky tang » ky nang, ky dang, kho tang
van hoi » van hoa, van hoc, van hoe
hieu ve » hieu va, hieu van
ve nhan » ve nha, de nhan, va nhan
vai cua » dai cua, hai cua, lai cua
y tang » 6 tang, 7 tang, 5 tang
vi 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: toc sach ((y tang) OR (ky tang)) van hoi. hieu ve nhan thuc vat thanh ((vi cua) or (vai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((y tang) OR (ky tang)) van hoi. hieu ve nhan thuc vat thanh ((vi cua) OR (vai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((y tang) OR (ky tang)) van hoi. hieu ve nhan thuc vat thanh ((vi cua) or (vai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ((y tang) OR (ky tang)) van hoi. hieu ve nhan thuc vat thanh ((vi cua) or (vai cua)) tre*.