“however”主要有两个意思，分别等同于“but”和“in whatever way”。虽然在前者的情况下“however”必须作为副词存在，但正像下文句中那样，错将其作为连词来使用的例子也时有发生。
- [误] I would like to go to a movie, however I have no money.
- [正] I would like to go to a movie, but I have no money.
- [正] I would like to go to a movie. However, I have no money.
- [误] The argument given in Ref.  may be correct, however it is not convincing.
- [正] The argument given in Ref.  may be correct, but it is not convincing.
- [正] The argument given in Ref.  may be correct. However, it is not convincing.
- [正] Although/While/ the argument given in Ref.  may be correct, it is not convincing.
Compared to other hydrofunctionalization methods, however, transition metal-catalyzed hydrothiolation is relatively underexplored, likely due to sulfur’s strong coordinating ability and ensuing catalyst deactivation.
Over 160 chiral vicinal bromochlorinated natural products have been identified; however, a lack of synthetic methods for the selective incorporation of halogens into organic molecules has hindered their synthesis. 引用：10.1021/jacs.5b08398
There was good agreement between our observations and computational predictions. No reaction or low yields were seen for substrates 7a–7e (entries 1–5). However, when the calculated DG and the oxidative addition barrier were favourable, substantial formation of product 8a was observed (entries 6 and 7) 引用：10.1038/nature14615
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