全文获取类型
收费全文 | 1196篇 |
免费 | 61篇 |
出版年
2021年 | 8篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2016年 | 10篇 |
2015年 | 19篇 |
2014年 | 34篇 |
2013年 | 41篇 |
2012年 | 45篇 |
2011年 | 35篇 |
2010年 | 36篇 |
2009年 | 15篇 |
2008年 | 23篇 |
2007年 | 25篇 |
2006年 | 38篇 |
2005年 | 28篇 |
2004年 | 34篇 |
2003年 | 21篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 19篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1989年 | 8篇 |
1985年 | 42篇 |
1984年 | 41篇 |
1983年 | 22篇 |
1982年 | 84篇 |
1981年 | 87篇 |
1980年 | 74篇 |
1979年 | 90篇 |
1978年 | 50篇 |
1977年 | 37篇 |
1976年 | 9篇 |
1973年 | 5篇 |
1969年 | 4篇 |
1966年 | 4篇 |
1960年 | 4篇 |
1933年 | 4篇 |
1870年 | 5篇 |
1869年 | 6篇 |
1868年 | 10篇 |
1864年 | 8篇 |
1853年 | 5篇 |
排序方式: 共有1257条查询结果,搜索用时 156 毫秒
41.
42.
Ferdinand Bohlmann Karl-Heinz Knoll Christa Zdero Pradip Kumar Mahanta Michael Grenz Albert Suwita Dorothea Ehlers Ngo Le Van Wolf-Rainer Abraham Arvind Anant Natu 《Phytochemistry》1977,16(7):965-985
Investigation of about 50 Senecio species has afforded many new substances, in addition to known compounds. Present in these plants are 23 fura 相似文献
43.
The investigation of further Othonna species affords 23 new furanoeremophilanes and a new benzofuran-derivative. All these compounds are closely related to those isolated before from other Othonna species. Highly oxidized furanoeremophilanes seem to be typical of this genus. 相似文献
44.
Ferdinand Bohlmann Pradip K. Mahanta Arvind A. Natu Robert M. King Harold Robinson 《Phytochemistry》1978,17(3):471-474
The investigation of two Isocarpha species has yielded eight new germacranolides most of them belonging to the heliangolides. In addition to known p-hydroxyacetophenone-derivatives, a new dihydroeuparine derivative was isolated. The chemotaxonomical aspects are discussed. 相似文献
45.
From three Mikania species, three new labdanic acid and two kaurenic acid derivatives have been isolated together with known compounds and four new germacranolides, differing only in the ester moiety. 相似文献
46.
The aerial parts of the South African composite Printzia laxa contain two manoyl oxides and three clerodane derivatives together with two further acids, which belong to a new type of diterpene, biogenetically closely related to the clerodanes. The structures have been elucidated by spectroscopic methods. The constituents may indicate some relationship of Printzia to the tribe Astereae. 相似文献
47.
Ferdinand Bohlmann 《Phytochemistry》1978,17(2):319-320
48.
The investigation of two species of Lasthenia afforded two new guaianolides and a new bisabolone derivative, in addition to already known compounds. The presence of an eremophilenic acid in these plants is remarkable. The results are discussed chemotaxonomically, since the tribal position of this genus is still debated. 相似文献
49.
Investigation of a further 27 Euryops species affords, besides known compounds, 55 new furanoeremophilanes together with several other compounds. The configuration of six furanoeremophilanes earlier given as 10β-H has to be changed to 10α-H. Furthermore 9 new eremophilenes were isolated; the configurations of four compounds of this type isolated before have had to be changed. One of the eremophilenes is esterified with 3-methylpent-3(E)-enoic acid, not found before in nature. Two hemiacetals, which are probable precursors of the furanoerephilanes, and a corresponding lactone are also present. Furthermore two benzylic esters, cis-caryophyllene, a bicyclo-germacrene derivative, and a new oplopanone derivative have been found. The structures are elucidated mainly by spectroscopic methods together with some chemical transformations. From the chemotaxonomic viewpoint, the high concentration of very variable furanoeremophilanes may be important. The proposed differentiation into sections however can not be clearly correlated with the chemical constituents, though some taxonomic conclusions seem to be supported by the chemical evidence. 相似文献
50.
An Australian member of the tribe Senecioneae, Bedfordia salicina, contains besides known compounds new dimeric eremophilenolides, new kolevane derivatives, a kaurenic acid and several further sesquiterpenes, most of them related to xanthatine. The structures are elucidated mainly by spectroscopic methods and by some chemical transformations. The chemotaxonomic aspects of these findings are discussed briefly. 相似文献