出现下面错误时

PackagesNotFoundError: The following packages are not available from current channels:
  - sklearn

Current channels:

  - https://conda.anaconda.org/conda-forge/win-64
  - https://conda.anaconda.org/conda-forge/noarch
  -  To search for alternate channels that may provide the conda package you're looking for, navigate to
 
    https://anaconda.org 
    
    and use the search bar at the top of the page.

解决方法：
conda install -c https://conda.anaconda.org/需要的模块名 python=版本号
例子如下：

(python3) C:\system32>conda install -c https://conda.anaconda.org/sklearn python=3
#**想要安装sklearn时，python版本3**