首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1498篇
  免费   48篇
  国内免费   31篇
  2023年   19篇
  2022年   18篇
  2021年   27篇
  2020年   30篇
  2019年   35篇
  2018年   31篇
  2017年   30篇
  2016年   21篇
  2015年   29篇
  2014年   35篇
  2013年   68篇
  2012年   23篇
  2011年   39篇
  2010年   37篇
  2009年   32篇
  2008年   54篇
  2007年   62篇
  2006年   41篇
  2005年   55篇
  2004年   39篇
  2003年   45篇
  2002年   28篇
  2001年   16篇
  2000年   19篇
  1999年   26篇
  1998年   11篇
  1997年   17篇
  1996年   21篇
  1995年   9篇
  1994年   21篇
  1993年   18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   25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1577条查询结果,搜索用时 15 毫秒
31.
Fourteen alkaloids were isolated from the stem bark and aerial parts of Melodinus guillauminii. They were 11-hydroxytabersonine, venalstonine, venalstonidine, 14,15-seco-3-oxokopsinal, 3-oxovenalstonine, 11-methoxy-Δ14– vincamenine, 3-oxo-hydroxykopsinine, 11-methoxy-Δ14-vincanol, kopsinine, 15-α-hydroxykopsinine, 11-methoxy- tabersonine, pleiocarpamine, 19-β-hydroxyvenalstonine and guillauminiine.  相似文献   
32.
From the mycelium of Penicillium cyclopium a biologically active fraction (P-factor) was isolated, which increases conidiation and the formation of the benzodiazepine alkaloids cyclopenin and cyclopenol. Its activity was determined by measuring the increase of alkaloid formation in strain SM 72. On a preparative scale P-factor preparations were obtained from fermenter-grown hyphae of mutant dev 63 by extraction with water at 120°. P-factor is strongly hydrophilic but it is not a protein. It was active if added during conidiospore germination and early growth phase, causing an acceleration of protein biosynthesis. The action on alkaloid biosynthesis and sporulation is indirect and resembles that of a developmental hormone.  相似文献   
33.
The 13C NMR spectra of nine pyrrolizidine alkaloids of the macrocyclic diester type, seven of the corresponding N-oxides and of the parent base retronecine have been recorded and the signals assigned. The 13C NMR signals were found to be sensitive to structural variation in both the diester moiety and the heterocyclic ring system, providing useful information for structural elucidation, particularly when the 1H NMR spectra may be difficult to interpret.  相似文献   
34.
The qualitative and quantitative compositions of necines in plants of 20 Heliotropium species collected in Mexico and the U.S.A. and one species from Spain are reported. Trachelanthamidine, supinidine and retronecine were found in all species after hydrolysis of their alkaloids; lindelofidine was detected in most species, whereas heliotridine only in four. Trachelanthamidine, lindelofidine, and supinidine were dominant in four, two and one species, respectively; retronecine was dominant in 15 species, whereas heliotridine only in one. The dominant necine in H. ternatum was either retronecine or lindelofidine depending on the collection locality. Qualitative as well as quantitative differences depending on the collection locality were found in H. curassavicum. Plants from Oaxaca, Mexico, contained lindelofidine and a pyrrolizidine-diol as major necines, trachelanthamidine as minor, and traces of retronecine. Plants originating from two other localities contained trachelanthamidine (dominant), retronecine, and supinidine. The necine patterns found in the examined species differ significantly from those previously reported for 21 species mainly collected in Asia, the Middle East and Australia.  相似文献   
35.
36.
Stems and leaves of Myrtopsis macrocarpa, M. myrtoidea, M. novae-caledoniae and M. sellingii yielded terpenes, sterols, coumarins, alkaloids (furoquinolines and quinolones) and amides. A new quinolone (8-methoxy flindersine) occurs in Myrtopsis macrocarpa, a new amide (N-benzoyltryptamine) in M. myrtoidea, two new coumarins (myrsellin and myrsellinol) and a new dihydrofuroquinoline (myrtopsine) in M. sellingii. Structures of the new compounds are proposed from chemical and spectroscopic evidence.  相似文献   
37.
A new alkaloid, majvinine, was isolated from aerial parts of Vinca major. Its structure was determined by chemical and spectroscopic investigations  相似文献   
38.
Three new alkaloids have been identified from Papaver bracteatum, 14-β-hydroxycodeinone, 14-β-hydroxycodeine and N-methylcorydaldine. The presence of alpinigenine was also confirmed.  相似文献   
39.
40.
作者对新疆维吾尔自治区的9个市、县进行了药用延胡索的资源调查,采集植物标本70余份,弄清药用种类主要是3种,即Corydalis glaucescens Regel,C.ledebouriana Kir.et Kar.和C.schanginii(Pall.)Fedtsch.;初步了解了3种药用延胡索植物的分布状况,并对块茎中总生物碱的含量作了分析。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号