不同版本.net引用同一个项目

项目文件.csproj文件内容如下：

重点是：不能有其他的

netstandard2;net40;net45;net46;net6

<Project Sdk="Microsoft.NET.Sdk"><PropertyGroup><TargetFrameworks>netstandard2;net40;net45;net46;net6</TargetFrameworks></PropertyGroup><ItemGroup Condition="'$(TargetFramework)'=='net40' OR '$(TargetFramework)'=='net45' OR '$(TargetFramework)'=='net46'"><Reference Include="System" /><Reference Include="System.Core" /><Reference Include="Microsoft.CSharp" /><Reference Include="System.Data" /></ItemGroup><ItemGroup Condition="'$(TargetFramework)'=='net45' OR '$(TargetFramework)'=='net46'"><Reference Include="System.ComponentModel.DataAnnotations" /></ItemGroup><ItemGroup><Folder Include="Http\" /><Folder Include="Log\" /><Folder Include="Ftp\" /><Folder Include="File\" /><Folder Include="EncryDecry\" /><Folder Include="FileZip\" /></ItemGroup></Project>