难点

Basing on the Graf′s addition theorem, two expessions, interior and exterior expression, are deduced and the suitable problems for them are discussed. It has been found that the interior expression is the main point for sovling the scattering problem of circular inclusion in half-space. It also has been found that the exterior expression is the key for the scattering problem of circular arc canyon and circular arc alluvial valley, and is one of the main points for scattering problem of circular arc hill as well.

从Graf原有加法公式出发，本文给出了其内域型和外域型两种表达形式并讨论了这两种表达的适用范围，同时指出：内域型表达是求解半空间内含夹塞区出平面散射问题的要点，而外域型表达是解决任意圆弧型凹陷地形和任意圆弧型沉积盆地出平面散射问题中求解难点的关键，同时也是克服任意圆弧型凸起地形出平面散射问题求解困难的要点之一。

The core issue of nutrient control was focused and the dynamic studies on phosphorus pollution of the whole watershed were conduced: 1 to highlight the non-point source pollution control, which is the difficulties research subject of water resource protection; 2 to perfect the calculation method for phosphate input and output, providing important basis on decision making for nutrient control; 3 to establish database and water quality model, to predict the water quality response after different phosphorus control schemes realized; 4 to determine admissible phosphorus loading and control standard according to the quantitative relationship between the external force function (mainly the exotic nutrient salt concentration or loading) and internal nutrient state response, and to work out the effective and practical techniques for eutrophication control.

围绕营养盐控制的核心问题，进行全流域范围磷污染的动态研究：1）突出了目前我国水资源保护研究难点—非点源污染控制；2）完善了流域水库磷盐收支计算方法，为流域营养盐控制决策提供了重要依据；3）建立数据库和水质模型，预测了在实施不同磷削减控制方案后流域供水水质的响应情况；4）根据湖泊外力函数（主要是外来营养盐浓度或负荷）与湖库内营养状态响应间的定量关系，确定了磷允许负荷量及控制标准，提出了有效的富营养化控制实用技术。

The synchronization problem of the receiver is one of the difficulties in designing the ADSL on-line test system.

在ADSL在线测试系统设计中，接收器的同步问题是设计的难点之一。

In the teaching Chinese as a foreign language, the adverb is not only important but also difficult.

在对外汉语教学中，副词一直是教学的重点，也是令许多留学生头疼的难点。

These methods give solutions of adversarial problems by focusing on different points of view, and are of great advantage to adversarial problems solving.

这些方法从不同的角度对对抗性问题的难点问题提供了解决方案，有利于对抗性问题的求解。

Aerodynamical parameters in longitudinal model of a certain type of helicopter are identified in the paper.

直升机气动参数辨识是气动参数辨识研究的热点和难点之一。

The ground effect is one of the main difficulties in road vehicle aerodynamics.

地面效应是汽车空气动力学研究的主要难点之一。

According to the difficulties of designing and molding aerofoil blades, a application program which can be used to exactly draw profile curve of blade section is developed with VBA, which is based on the analysis of calculation method for designing and molding aerofoil blades and adopts OLE provided by CAD software SolidWorks.

在分析翼型叶片造型计算方法的基础上，针对翼型叶片造型的难点，利用三维 CAD 软件 SolidWorks 提供的 OLE 应用编程接口，使用 VBA 开发了准确绘制叶片截面轮廓曲线的应用程序，并给出了叶轮三维建模的方法和步骤。

In part Three, on the basis of the theory of Chomsky "principle parameters", we compare the syntactic similarities and differences of passive voices among English, French and Chinese. The passives in all these three languages comply with the following principles. 1 Affectedness of entity.

英语、法语和汉语的被动语态虽然有一些相似，但是它们的差异还是主要的，本文认为在外语习得中，相似性较易被人接受，差异性却是外语学习者的难点，不容忽视。

It is the real difficulty to assess the aftereffect of supply chain risk caused by uncertain contingent events.

不确定偶发风险事件导致的供应链风险后果的估计是风险估计的难点所在。

Do not gum up the work by telling mother what we are going to do .

别告诉母亲我们要干的事，那会把事情搞糟的。

In recent years, application of the partial prestressed concrete beam s is developed.

近年来，随着部分预应力砼梁应用的推广，发现我国规范所采用的名义拉应力法的计算结果不稳定。