全文获取类型
收费全文 | 909篇 |
免费 | 25篇 |
国内免费 | 7篇 |
专业分类
941篇 |
出版年
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 6篇 |
2020年 | 17篇 |
2019年 | 15篇 |
2018年 | 16篇 |
2017年 | 24篇 |
2016年 | 18篇 |
2015年 | 19篇 |
2014年 | 30篇 |
2013年 | 40篇 |
2012年 | 11篇 |
2011年 | 35篇 |
2010年 | 28篇 |
2009年 | 39篇 |
2008年 | 44篇 |
2007年 | 39篇 |
2006年 | 52篇 |
2005年 | 38篇 |
2004年 | 28篇 |
2003年 | 42篇 |
2002年 | 32篇 |
2001年 | 19篇 |
2000年 | 18篇 |
1999年 | 15篇 |
1998年 | 5篇 |
1997年 | 13篇 |
1996年 | 7篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 14篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1987年 | 5篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 18篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 19篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 18篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1972年 | 3篇 |
排序方式: 共有941条查询结果,搜索用时 15 毫秒
101.
Pregnane glycosides from Caralluma adscendens var. fimbriata 总被引:1,自引:0,他引:1
Kunert O Rao VG Babu GS Sujatha P Sivagamy M Anuradha S Rao BV Kumar BR Alex RM Schühly W Kühnelt D Rao GV Rao AV 《化学与生物多样性》2008,5(2):239-250
Eleven novel pregnane glycosides, 2-7 and 9-13, of which four, i.e., 10-13, comprised a new pregnane-type genin exhibiting a hydroxymethylene instead of a Me group at C(19), and the known pregnane glycoside stalagmoside V (8) were isolated from whole plants of Caralluma adscendens var. fimbriata, a native Indian succulent plant. Their structures were elucidated by extensive 2D-NMR spectroscopic studies. 相似文献
102.
Linda Saxe Einbond Ye Wen-Cai Kan He Hsan-au Wu Erica Cruz Marc Roller Fredi Kronenberg 《Phytomedicine》2008,15(6-7):504-511
The purpose of this report is to explore the growth inhibitory effect of extracts and compounds from black cohosh and related Cimicifuga species on human breast cancer cells and to determine the nature of the active components. Black cohosh fractions enriched for triterpene glycosides and purified components from black cohosh and related Asian species were tested for growth inhibition of the ER− Her2 overexpressing human breast cancer cell line MDA-MB-453. Growth inhibitory activity was assayed using the Coulter Counter, MTT and colony formation assays.Results suggested that the growth inhibitory activity of black cohosh extracts appears to be related to their triterpene glycoside composition. The most potent Cimicifuga component tested was 25-acetyl-7,8-didehydrocimigenol 3-O-β-d-xylopyranoside, which has an acetyl group at position C-25. It had an IC50 of 3.2 μg/ml (5 μM) compared to 7.2 μg/ml (12.1 μM) for the parent compound 7,8-didehydrocimigenol 3-O-β-d-xylopyranoside. Thus, the acetyl group at position C-25 enhances growth inhibitory activity.The purified triterpene glycoside actein (β-d-xylopyranoside), with an IC50 equal to 5.7 μg/ml (8.4 μM), exhibited activity comparable to cimigenol 3-O-β-d-xyloside. MCF7 (ER+Her2 low) cells transfected for Her2 are more sensitive than the parental MCF7 cells to the growth inhibitory effects of actein from black cohosh, indicating that Her2 plays a role in the action of actein. The effect of actein on Her2 overexpressing MDA-MB-453 and MCF7 (ER+Her2 low) human breast cancer cells was examined by fluorescent microscopy. Treatment with actein altered the distribution of actin filaments and induced apoptosis in these cells.These findings, coupled with our previous evidence that treatment with the triterpene glycoside actein induced a stress response and apoptosis in human breast cancer cells, suggest that compounds from Cimicifuga species may be useful in the prevention and treatment of human breast cancer. 相似文献
103.
A. N. Mazeika A. M. Popov V. I. Kalinin S. A. Avilov A. S. Sil’chenko E. Ya. Kostetsky 《Biophysics》2008,53(5):409-416
The ability of holothurian triterpene glycosides (cucumarioside A2-2 from Cucumaria japonica, cucumarioside G1 from C. fraudatrix, frondoside A from C. frondosa, and holotoxin A1 from Apostichopus japonicus) to form supramolecular lipid-saponin complexes was studied. TEM demonstrated that all the studied compounds form supramolecular cholesterol-saponin complexes (nanoparticles) in aqueous medium. The complexes formed by cucumarioside A2-2, holotoxin A1, and frondoside A had a tubular structure and fundamentally differed in the structure from the particles produced by cucumarioside G1. The morphology of the nanoparticles formed by cucumarioside A2-2, holotoxin A1, and cucumarioside G1 changed depending on the fraction of cholesterol in the lipid-saponin system; however, this pattern was not observed for frondoside A. At the same molar fraction of cholesterol in the lipid-saponin system, cucumarioside A2-2 formed the particles with the most pronounced tubular structure; the cholesterol-saponin complexes of holotoxin A1 had a less pronounced tubular structure, whereas the structure of frondoside A particles was extremely heterogeneous. Comparative analysis of the morphology of the described supramolecular complexes and specific structural features of the glycosides demonstrated that the structure of the corresponding nanoparticles depended on the degree of branching of the carbohydrate moiety in the glycoside molecule and the complexation with cholesterol was determined by the specific features of aglycone structure. Thus, the feasibility of producing new generation antigen carriers using the complexes in question was proved. 相似文献
104.
Sea Cucumbers Triterpene Glycosides, the Recent Progress in Structural Elucidation and Chemotaxonomy
Vladimir I. Kalinin Alexandra S. Silchenko Sergey A. Avilov Valentin A. Stonik Alexey V. Smirnov 《Phytochemistry Reviews》2005,4(2-3):221-236
Triterpene glycosides are characteristic metabolites of sea cucumbers (Holothurioidea, Echinodermata). Majority of the glycosides
belong to holostane type (lanostane derivatives with 18(20)-lactone). Carbohydrate chains of these glycosides contain xylose,
glucose, quinovose, 3-O-methylglucose and 3-O-methyl sylose. During the last 5 years, main investigations were focused on holothurians belonging to the order Dendrochirotida
collected in the North Pacific, North Atlantic, Antarctic and in subtropical waters. The glycosides of holothurians belonging
to the order Aspidochirotida have also been studied. The most uncommon structural features of carbohydrate chains of new glycosides
were: (1) the presence of quinovose as fifth terminal monosaccharide unit and the presence of two quinovose residues; (2)
the presence of glucose instead of common xylose as fifth terminal monosaccharide unit; (3) trisaccharide carbohydrate chain;
(4) the presence of two 3-O-methylxylose terminal monosaccharide units; (5) the presence of sulfate group at C-3 of quinovose residue. New glycosides
without lactone or with 18(16)-lactone and having shortened side chains have also been isolated. The presence of 17α and 12α-hydroxyls,
which are characteristic for glycosides from holothurians belonging to the family Holothuriidae (Aspidochirotida) in glycosides
of dendrochirotids confirms parallel and relatively independent character of evolution of glycosides. All three families belonging
to the order Aspidochirotida: Holothuriidae, Stichopodidae and Synallactidae have similar and parallel trends in evolution
of the glycosides carbohydrate chains, namely from non-sulfated hexaosides to sulfated tetraosides. Sets of aglycones in glycosides
from holothurians belonging to the genus Cucumaria (Cucumariidae, Dendrochirotida) are specific for each species. The carbohydrate chains are similar in all representatives
of the genus Cucumaria. 相似文献
105.
In our search for bioactive compounds from the whole plant of Picriafelterrae Lour., three new phenylethanoid glycosides, picfeosides A-C (1-3), along with five known phenylethanoid glycosides,namely wiedemannioside (4), acteoside (5), acteoside isomer (6), cis-acteoside isomer (7), and cis-acteoside (8), were isolated using several chromatographic purification steps, including semipreparation HPLC on RP-18. The structures of the new compounds were elucidated on the basis of extensive spectroscopic analysis. 相似文献
106.
T. A. Chupakhina V. O. Kur'yanov V. Ya. Chirva R. Ya. Grigorash S. A. Kotlyar G. L. Kamalov 《Russian Journal of Bioorganic Chemistry》2004,30(3):301-303
The crown ether-catalyzed glycosylation of phenol, 4-methoxyphenol, and 4-nitrophenol was studied under phase transfer conditions in solid–liquid system. The asymmetric dibenzocrown esters are superior to [3.3]dibenzo-18-crown-6 and 15-crown-5 in the catalysis of these reactions. 相似文献
107.
108.
一种新的肉苁蓉甙类化合物的分离方法 总被引:4,自引:2,他引:2
简单介绍了一种从肉苁蓉中提取得到肉苁蓉甙类化合物的方法,避免了乙酸乙酯和正丁醇的萃取,便于工业化应用,同时还可获得纯度较高有甜菜碱。 相似文献
109.
紫菀属化学成分及药理活性研究进展 总被引:5,自引:0,他引:5
紫菀属所含化学成分主要是三萜皂甙 ,此外还含其它萜类、肽类、香豆素、甾醇等 ;其中一些成分具有抗瘤 ,抗菌 ,消炎等活性。本文对其近 2 0多年来国内外学者分离到的化学成分及其药理活性的研究结果作一综述 ,为该属植物资源的进一步研究和开发提供参考。 相似文献
110.
仙茅中两个新的环阿尔廷醇型三萜皂苷 总被引:2,自引:0,他引:2
从仙茅(Curculigo orchioides)中分离得到2个新的环阿尔廷醉型三萜皂苷,通过波诺分析鉴定了它们的化学结构,即3β,11α,16β—三羟基环阿尔廷烷-24-酮-3-O-[β-D-吡喃葡糖(1→3)-β-D-吡喃葡糖(1→2)-β-吡喃葡糖]-16-O-α-L-阿拉伯糖苷(1)和(24S)-3β,11α,16β,24-四经基环阿尔廷烷-3-O-[β-D-吡喃葡糖(1→3)-β-D-吡喃葡糖(1→2)-β-D-吡喃葡糖]-24-O-β-D-吡喃葡糖苷(2)。 相似文献