中文摘要：

研究了一类有未知参数的非线性系统观测器的设计问题．在先前的研究中，与未知参数有无的项只同输入输出有关，或者系统的相对阶为一．现对相对阶为二的二维系统提出了一种观测器的设计方法，允许和未知参数相关的项与所有状态有关；同时对高维情况也作了初步考虑，并举例说明了本方法的有用性．

英文摘要：

The paper dealed with the problem of adaptive observer design for a class of nonlinear systems. It was required in the previous study that the uncertain term only depends on the input and output or that the system had the relative degree one. A method of adaptive observer design for two-dimensional systems with relative degree two was presented. The uncertain term depended on all state variables and input. An extension to high-dimensional systems was also considered. An example is presented to illustrate the utility of the result.