全文获取类型
收费全文 | 1484篇 |
免费 | 48篇 |
国内免费 | 30篇 |
出版年
2023年 | 19篇 |
2022年 | 18篇 |
2021年 | 26篇 |
2020年 | 30篇 |
2019年 | 35篇 |
2018年 | 29篇 |
2017年 | 30篇 |
2016年 | 21篇 |
2015年 | 29篇 |
2014年 | 35篇 |
2013年 | 67篇 |
2012年 | 23篇 |
2011年 | 38篇 |
2010年 | 37篇 |
2009年 | 29篇 |
2008年 | 53篇 |
2007年 | 61篇 |
2006年 | 41篇 |
2005年 | 55篇 |
2004年 | 39篇 |
2003年 | 44篇 |
2002年 | 28篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 27篇 |
1998年 | 11篇 |
1997年 | 17篇 |
1996年 | 21篇 |
1995年 | 9篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 11篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 19篇 |
1987年 | 15篇 |
1985年 | 48篇 |
1984年 | 43篇 |
1983年 | 22篇 |
1982年 | 36篇 |
1981年 | 34篇 |
1980年 | 54篇 |
1979年 | 39篇 |
1978年 | 34篇 |
1977年 | 32篇 |
1976年 | 34篇 |
1975年 | 45篇 |
1974年 | 47篇 |
1973年 | 47篇 |
1972年 | 17篇 |
排序方式: 共有1562条查询结果,搜索用时 26 毫秒
41.
Nigel J. Kilby David L. Griggs Stephanie F. Berry 《Plant Cell, Tissue and Organ Culture》1992,28(3):275-280
Intra-population quinoline alkaloid profiles surveying quinine, quinidine, cinchonine and cinchonidine were determined for each of five populations of Cinchona ledgeriana grown as shoot-culture for 125 days. No significant difference in respect of mean alkaloid content between populations was detected. In contrast, there was considerable between-seedling variation in alkaloid content within each population. When nutrients were delivered to shoot-cultures in droplet form by means of an aerosol spray (as compared to the supply of nutrients direct from agar-or liquid-based reservoirs) alkaloid profile was greatly perturbed; most notable in this respect was a four-fold increase in the production of cinchonidine concomitant with a four-fold decrease in the production of cinchonine. These data are discussed with reference to the optimisation of quinoline alkaloid production by juvenile shoot-cultures of Cinchona ledgeriana. 相似文献
42.
By means of thin layer chromatography in conjunction with mass spectrometry the pyrrolizidine alkaloid patterns derived fromSymphytum asperum, several cytotypes ofS. officinale agg. and the artificial hybrids of the former taxa, were compared. The obtained patterns were not essentially affected by
variation in cytotype, harvesting times and -location of plants. Lycopsamine, acetyl-lycopsamine and symphytine or their isomers
were generally found in theS. officinale cytotypes, echimidine and symphytine inS. asperum. The interspecific hybrids contained all alkaloids mentioned. The definite lack of echimidine in the 2 n=40 cytotype proves
that it is conspecific withS. officinale and does not belong to a hybrid-swarmS. asperum × S. officinale with 2 n=48.
Part I of this series of contributions. 相似文献
43.
Serially propagated Cinchona ledgeriana and C. succirubra (Rubiaceae) leaf, root and unorganized suspension cultures established from germinated seeds were studied for quinine and quinidine production. Leaf organ cultures were grown and subcultured in Murashige and Skoog's Revised Tobacco Medium supplemented with benzyladenine; root organ cultures were grown on the same medium supplemented with indolebutyric acid; and unorganized suspension cultures were grown on the same medium supplemented with 2,4-dichlorophenoxyacetic acid and benzyladenine. On a dry weight basis, leaf organ cultures of C. ledgeriana contained 0.06 % quinine and 0.05 % quinidine and of C. succirubra contained 0.04 % quinine and 0.04 % quinidine. No quinine and quinidine were detected in either root organ or unorganized suspension cultures. 相似文献
44.
45.
Catharanthine and akuammicine, together with ajmalicine and strictosidine, were isolated from a culture strain of Catharanthus roseus suspension cells. The biosynthetic capability of the cultured cells to produce akuammicine, catharanthine and vindoline was confirmed by feeding experiments with dl-tryptophan-[3-14C] to yield the radioactive alkaloids. 相似文献
46.
During the separation of an extract from Tabernaemontana glandulosa, small amounts of a new alkaloid were obtained for which the structure 19-hydroxycoronaridine was deduced. This new alkaloid and 19-hydroxyibogamine, which can be obtained from it, show marked antibiotic activity in the agar plate diffusion test. 相似文献
47.
Dhavadee Ponglux Tanomjit Supavita Robert Verpoorte David Phillipson 《Phytochemistry》1980,19(9):2013-2016
The major alkaloids of a sample of leaves of Uncaria attenuata obtained from Thailand have been identified as the pentacyclic heteroyohimbine alkaloids tetrahydroalstonine, rauniticine and the novel 14-β-hydroxy-3-iso-rauniticine. Evidence for the structure of the new alkaloid was obtained from a study of UV, IR, MS, 1H NMR and 1C NMR spectra. 相似文献
48.
David L. Dreyer 《Phytochemistry》1980,19(5):941-944
The chemical constituents of three Mexican Esenbeckia species have been determined. Rutaevin was the main limonoid present in the seeds of all three species, E. litoralis, E. flava and E. berlandieri. The husks, leaves, wood and bark contained a wide array of known furocoumarins and furoquinoline alkaloids. In addition, 1-hydroxy-3-methoxy-N-methylacridone was obtained from E. litoralis bark and a new natural 2-quinolone alkaloid, formulated as 3,3-diisopropyl-N-methyl-2,4-quinoldione, was obtained from E. flava wood. The structure was assigned from spectroscopic considerations and conversion to N-methylhaplofoline. 相似文献
49.
Chemical investigation of the roots of G. mauritiana resulted in the isolation of two new alkaloids; 1-hydroxy-3-methoxy-2-(3-methylbut-2-enyl)-N-methylacridan-9-one (1) and 4,8-dimethoxy-3-(3-methylbut-2-enyl)-N-methyl-2-quinolone (6). The structures of these new bases have been established by chemical and spectroscopic methods and confirmed in the case of 6 by its synthesis. Interestingly, the formic acid-catalysed cyclisation of 1 gave the dealkylated product 3 along with the pyrano-[2, 3-a]-acridine (4). 相似文献
50.