curl --parallel --parallel-immediate -k -L -C - -o local_file ftp_file
--parallel --parallel-immediate 开启多线程：
--parallel Perform transfers in parallel
--parallel-immediate Do not wait for multiplexing (with --parallel)
--parallel-max Maximum concurrency for parallel transfers
-C - 开启断点续传：
-C, --continue-at <offset> Resumed transfer offset
-o指定输出文件名称：
-o, --output <file> Write to file instead of stdout
失败重新自动提交：
--retry <num> Retry request if transient problems occur
--retry-all-errors Retry all errors (use with --retry)
--retry-connrefused Retry on connection refused (use with --retry)
--retry-delay <seconds> Wait time between retries
--retry-max-time <seconds> Retry only within this period