机械密封是依靠固定于轴上的转环和固定在泵壳上的静环两者平滑端面之间的紧密接触来达到密封。
参考答案:对
For nearly ten years, the Unified Modeling Language (UML) has been the industry standard for visualizing, specifying, constructing, and documenting the (26) of a software-intensive system. As the (27) standard modeling language, the UML facilitates communication and reduces confusion among project (28) The recent standardization of UML 2.0 has further extended the language’s scope and viability.Its inherent expressiveness allows users to (29) everything from enterprise information systems and distributed Web-based applications to real-time embedded systems. The UML is not limited to modeling software. In fact, it is expressive enough to model (30) systems, such as workflow in the legal system, the structure and behavior of a patient healthcare system, software engineering in aircraft combat systems, and the design of hardware. To understand the UML, you need to form a conceptual model of the language, and this requires learning three major elements: the UML’s basic building blocks, the rules that dictate how those building blocks may be put together, and some common mechanisms that apply throughout the UML.
A.investors
B.developers
C.designers
D.stakeholders
保安武装守护的治安保卫重点单位和要害部位的特点是()
A.目标固定、部署分散、隶属关系多
B.不便联系协同、情况复杂
C.技术性强、安全要求高
D.责任重大、难以控制
E.任务繁重