近年来国际上兴起的样品分析前处理新技术 – 简便、快速、无溶剂，集“采样、萃取、浓缩、 进样”于一体 1990年－加拿大 Arhturhe和 Pawliszyn首创 1993年－美国 Supelco公司商品化固相微萃取装置 1994年－获美国匹兹堡分析仪器会议大奖

1.耗费时间长 2.效率不高 3.溶剂消耗量较大，成本较高 4.难于实现自动化 5.不够“绿色

Principle of Virtual Displacements Consider a body in equilibrium. We know that the stress field must satisfy the differential equations of equilibrium. Multiply the differential equations of equilibrium by an \arbitrary\displacement field T

一、微波能介绍 二、微波化学的发展历程

Extend definition to material bodies: total work is the addition of the work done on all particles by forces distributed over the volume W by forces distributed over the surface t·udS

会计要素，是指按照交易或者事项的经济特征所作的 基本分类，分为反映企业财务状况的会计要素和反映企 业经营成果的会计要素。它既是会计确认和计量的依据， 也是确定财务报表结构和内容的基础。 我国物业管理企业会计要素按照其性质分为资产、负 债、所有者权益、收入、费用和利润，其中，资产、负 债和所有者权益要素侧重于反映企业的财务状况，收入、 费用和利润要素侧重于反映企业的经营成果

The following stress-strain curves were obtained for dif- ferent materials subjecting the specimen to the loading path(a, b, c, d ). Which one(s) of them correspond to elas- tic material(s)

For the uniform state of plane strain shown in the fig ure,which one(s) of the following statement(s) is(are valid?(Assume Poisson's ratio v+0)

Concept Question Consider the following simple displacement field

We seek to characterize the local state of deformation of the material in a neighborhood of a point P. Consider two points P and Q in the undeformed