"only"倒装句的基本用法如下：
当"only"后跟的是主语时，句子不需要倒装。例如：
Only he is responsible for the mistake.
当"only"后跟的是副词、介词短语或从句等状语时，主句需要倒装。例如：
Only in this way can you learn English.
Only when the war was over in 1918 was he able to get back to work.
Only by shouting was he able to make himself heard.
如果"only"所强调的状语为状语从句，该状语从句不倒装，只对主句进行倒装。例如：
Only if you work hard can you succeed.
"only"倒装句通常用于强调某个特定的条件、方式、时间或地点。例如：
Only in this way, can we realize our dream.
Only then did I understand what she meant.
总结：
"only"后跟主语时，不倒装。
"only"后跟副词、介词短语或从句等状语时，主句需要倒装。
强调状语从句时，状语从句不倒装，主句倒装。