Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
tuc thai » thuc thai, toc thai, tuc hai
thuc tap » tuc tap, thuc thai, thuc vat
toan cua » than cua, tan cua, doanh cua
ky lang » ky nang, ky tang, tay lang
ky dang » ky nang, ky danh
cua te » cua tu

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 dang)) xa hoi. hieu van nam ((tuc thai) or (thuc tap)) tinh toan cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky lang) OR (ky dang)) xa hoi. hieu van nam ((tuc thai) OR (thuc tap)) tinh toan cua te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ky lang) OR (ky dang)) xa hoi. hieu van nam ((tuc thai) or (thuc tap)) tinh toan cua te".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky lang) OR (ky dang)) xa hoi. hieu van nam ((tuc thai) or (thuc tap)) tinh toan cua te*.