The compounds have the connecting ring structures of piperazine or piperidine, have notable antitumor activity, and provide a new choice for preparing antitumor drugs in clinical practice.

该类化合于具有哌嗪或哌啶的连接环结构，且具有显著的抗肿瘤活性，为临床上制备抗肿瘤药物提供了新的选择。

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The ring road connecting the main cities, the symbol of reconstruction, became perilous.

联系各主要城市的环城公路是重建的象征，也变得岌岌可危。

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Generally, do not remove components (including valve, connector, rubber, plastic ring and copper cap) before the tubing for connecting indoor, outdoor units are prepared.

一般地，如果没有准备好连接室内、外机组的配管，请勿拆卸部件(阀门、接头、橡胶、塑料圈及铜帽等元件)。

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