Perhaps you should try some spelling variations:
"so sach ky thuat co khi" » "so sach ky thuat o khi", "so sanh ky thuat co khi", "bo sach 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"
"su dai ky thuat do khi" » "su dai ky thuat o khi", "sau dai ky thuat do khi", "si dai ky thuat do khi", "su tai ky thuat do khi", "su dan ky thuat do khi", "su sai ky thuat do khi", "su dai ky thuat doi khi", "su dai ky thuat do thi", "su dai ky thuat bo khi"
"su dai ly thuat do khi" » "su dai ly thuat o khi", "su dai my thuat do khi", "su dai ly thuyet do khi", "su dai kxy thuat do khi", "sau dai ly thuat do khi", "si dai ly thuat do khi", "su tai ly thuat do khi", "su dai ly thuat doi khi", "su dai ly thuat do thi", "su dai ly thuat bo 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 ((("su dai ky thuat do khi") OR ("su dai ly thuat do khi"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("so sach ky thuat co khi") OR ((("su dai ky thuat do khi") OR ("su dai ly thuat do khi")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"so sach ky thuat co khi\") or (((\"su dai ky thuat do khi\") OR (\"su dai ly thuat do khi\"))))".
• Removing quotes may allow a broader search: (( so sach ky thuat co khi ) or ((( su dai ky thuat do khi ) OR ( su dai ly thuat do khi )))).
• Adding a wildcard symbol may retrieve word variants: (("so sach ky thuat co khi") or ((("su dai ky thuat do khi") OR ("su dai ly thuat do khi"))))*.