at the same time, meanwhile，还有 meantime，in the meanwhile，in the meanwhile，都是副词用法，意为“与此同时”。在句中作时间状语，基本没有区别，可以换用。例如：

At the same time, we must do a good job in transport and communications. 

In the meantime, we must do a good job in transport and communications.

In the meanwhile, we must do a good job in transport and communications.

Meanwhile, we must do a good job in transport and communications. 

Meantime, we must do a good job in transport and communications. 

同时，我们要搞好交通运输工作。