防震减灾三大体系 Three systems for earthquake prevention and disaster mitigation
乐亭完善三大科技体系 Hebei Agricultural Science and Technology
三是界定其内涵结构，确立三大体系，以完整地描述并构造电子政务网络结构。
The third is to determine its connotative structure and establish three big systems to describe and constructs a perfect electronic government affairs network.
阐述了农业节水灌溉的三大体系，并指出节水必须遵循经济规律同时要考虑综合效益。
The water saving irrigation in the three systems, and that water must follow the economic laws at the same time take into account the benefits.
解决这两大难题的关键是催化剂的选择，文中也简单介绍了目前由丙烷选择氧化制丙烯酸反应的三大体系催化剂。
The choosing of catalysts was the key to the reaction. The three main system catalysts of the reaction were introduced briefly.
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