Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
vat hanh » vat thanh, van hanh, va hanh
nang ma » tang ma, sang ma, nang cao
ca tren » cau tren, cu tren, la tren
ve nam » he nam, va nam, te nam
le nam » ly nam, he nam, le na
vi ca » vit ca, li ca, va ca

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 ma) or (nang x)) hoi. hieu ((ve nam) or (le nam)) thuc vat hanh vi ca tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach y ((nang ma) OR (nang x)) hoi. hieu ((ve nam) OR (le nam)) thuc vat hanh vi ca tren.
• Adding a wildcard symbol may retrieve word variants: toc sach y ((nang ma) or (nang x)) hoi. hieu ((ve nam) or (le nam)) thuc vat hanh vi ca tren*.