Perhaps you should try some spelling variations:
"so sach ky thuat co khi" » "so sach ky thuat do khi", "so sach ky thuat o khi", "so sanh ky thuat co khi", "co sach ky thuat co khi", "so sac ky thuat co khi", "so sach y thuat co khi", "so sach ty thuat co khi"
"bo sach ky thuat co khi" » "bo sach ky thuat do khi", "bo sach ky thuat o khi", "bo sac ky thuat co khi", "bo sach y thuat co khi", "bo sach ty thuat co khi", "co sach ky thuat co khi"
"hoc sach ky thuat co khi" » "hoc sach ky thuat do khi", "hoc sach ky thuat o khi", "hoc sinh ky thuat co khi", "hoc cac ky thuat co khi", "hoc anh ky thuat co khi", "hoc sac ky thuat co khi", "hoc sach y thuat co khi", "hoc sach ty thuat co khi"

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("so sach ky thuat co khi") or ((("bo sach ky thuat co khi") OR ("hoc sach ky thuat co khi"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("so sach ky thuat co khi") OR ((("bo sach ky thuat co khi") OR ("hoc sach ky thuat co khi")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"so sach ky thuat co khi\") or (((\"bo sach ky thuat co khi\") OR (\"hoc sach ky thuat co khi\"))))".
• Removing quotes may allow a broader search: (( so sach ky thuat co khi ) or ((( bo sach ky thuat co khi ) OR ( hoc sach ky thuat co khi )))).
• Adding a wildcard symbol may retrieve word variants: (("so sach ky thuat co khi") or ((("bo sach ky thuat co khi") OR ("hoc sach ky thuat co khi"))))*.