I posted a similar question in .Net Standard project
All credit goto @benaadams
You can find the missing apis in: ApiCompatBaseline.net461.txt
I checked the file and find 52 entry (more than 43 !).
The 52 missing APIs are:
Member 'System.AppContext.GetData(System.String)'
Member 'System.AppContext.TargetFrameworkName.get()'
Type 'System.StringNormalizationExtensions'
Type 'System.Data.Common.DbColumn'
Type 'System.Data.Common.DbDataReaderExtensions'
Type 'System.Data.Common.IDbColumnSchemaGenerator'
Type 'System.Diagnostics.StackFrameExtensions'
Type 'System.Diagnostics.Tracing.EventCounter'
Member 'System.Diagnostics.Tracing.EventSource.add_EventCommandExecuted(System.EventHandler<System.Diagnostics.Tracing.EventCommandEventArgs>)'
Member 'System.Diagnostics.Tracing.EventSource.remove_EventCommandExecuted(System.EventHandler<System.Diagnostics.Tracing.EventCommandEventArgs>)'
Type 'System.Globalization.GlobalizationExtensions'
Member 'System.Linq.Enumerable.Append<TSource>(System.Collections.Generic.IEnumerable<TSource>, TSource)'
Member 'System.Linq.Enumerable.Prepend<TSource>(System.Collections.Generic.IEnumerable<TSource>, TSource)'
Member 'System.Linq.Expressions.Expression<TDelegate>.Compile(System.Boolean)'
Member 'System.Linq.Expressions.LambdaExpression.Compile(System.Boolean)'
Member 'System.Net.Http.HttpClientHandler.CheckCertificateRevocationList.get()'
Member 'System.Net.Http.HttpClientHandler.CheckCertificateRevocationList.set(System.Boolean)'
Member 'System.Net.Http.HttpClientHandler.ClientCertificates.get()'
Member 'System.Net.Http.HttpClientHandler.DefaultProxyCredentials.get()'
Member 'System.Net.Http.HttpClientHandler.DefaultProxyCredentials.set(System.Net.ICredentials)'
Member 'System.Net.Http.HttpClientHandler.MaxConnectionsPerServer.get()'
Member 'System.Net.Http.HttpClientHandler.MaxConnectionsPerServer.set(System.Int32)'
Member 'System.Net.Http.HttpClientHandler.MaxResponseHeadersLength.get()'
Member 'System.Net.Http.HttpClientHandler.MaxResponseHeadersLength.set(System.Int32)'
Member 'System.Net.Http.HttpClientHandler.Properties.get()'
Member 'System.Net.Http.HttpClientHandler.ServerCertificateCustomValidationCallback.get()'
Member 'System.Net.Http.HttpClientHandler.ServerCertificateCustomValidationCallback.set(System.Func<System.Net.Http.HttpRequestMessage, System.Security.Cryptography.X509Certificates.X509Certificate2, System.Security.Cryptography.X509Certificates.X509Chain, System.Net.Security.SslPolicyErrors, System.Boolean>)'
Member 'System.Net.Http.HttpClientHandler.SslProtocols.get()'
Member 'System.Net.Http.HttpClientHandler.SslProtocols.set(System.Security.Authentication.SslProtocols)'
Type 'System.Net.Sockets.SocketReceiveFromResult'
Type 'System.Net.Sockets.SocketReceiveMessageFromResult'
Type 'System.Net.Sockets.SocketTaskExtensions'
Type 'System.Runtime.Serialization.DataContractSerializerExtensions'
Type 'System.Runtime.Serialization.ISerializationSurrogateProvider'
Type 'System.Security.SecureStringMarshal'
Type 'System.Security.Cryptography.ECCurve'
Member 'System.Security.Cryptography.ECDsa.Create(System.Security.Cryptography.ECCurve)'
Member 'System.Security.Cryptography.ECDsa.Create(System.Security.Cryptography.ECParameters)'
Member 'System.Security.Cryptography.ECDsa.ExportExplicitParameters(System.Boolean)'
Member 'System.Security.Cryptography.ECDsa.ExportParameters(System.Boolean)'
Member 'System.Security.Cryptography.ECDsa.GenerateKey(System.Security.Cryptography.ECCurve)'
Member 'System.Security.Cryptography.ECDsa.ImportParameters(System.Security.Cryptography.ECParameters)'
Type 'System.Security.Cryptography.ECParameters'
Type 'System.Security.Cryptography.ECPoint'
Type 'System.Security.Cryptography.IncrementalHash'
Member 'System.Text.RegularExpressions.Regex.CapNames.get()'
Member 'System.Text.RegularExpressions.Regex.CapNames.set(System.Collections.IDictionary)'
Member 'System.Text.RegularExpressions.Regex.Caps.get()'
Member 'System.Text.RegularExpressions.Regex.Caps.set(System.Collections.IDictionary)'
Type 'System.Threading.PreAllocatedOverlapped'
Type 'System.Threading.ThreadPoolBoundHandle'
Type 'System.Xml.XPath.XDocumentExtensions'
I checked most of these API and found that they are not available in net461, but available in netstandard2
Update Nov, 2017:
With the final release of .NET Framework 4.7.1, all missing APIs in 4.6.1 are implemented.
List of implemented API
Now .Net Standard 2.0 are built right into the .NET Framework 4.7.1 itself without the need to install .Net Standard 2.0 supported binaries.