全文获取类型
收费全文 | 318篇 |
免费 | 10篇 |
国内免费 | 16篇 |
专业分类
林业 | 42篇 |
农学 | 24篇 |
11篇 | |
综合类 | 130篇 |
农作物 | 67篇 |
水产渔业 | 4篇 |
畜牧兽医 | 35篇 |
园艺 | 5篇 |
植物保护 | 26篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 18篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 16篇 |
2014年 | 19篇 |
2013年 | 25篇 |
2012年 | 32篇 |
2011年 | 22篇 |
2010年 | 35篇 |
2009年 | 20篇 |
2008年 | 9篇 |
2007年 | 14篇 |
2006年 | 32篇 |
2005年 | 7篇 |
2004年 | 6篇 |
2003年 | 3篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1997年 | 3篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有344条查询结果,搜索用时 15 毫秒
121.
122.
Two new amide alkaloids, named 3-isopropyl-tetrahydropyrrolo [1,2-a] pyrimidine-2,4(1H,3H)-dione (1) and 1-acetyl-2,3,6-triisopropyl-tetrahydropyrimidin-4(1H)-one (2), were isolated from the roots of Aconitum taipeicum. Their chemical structures were characterized on the basis of MS, 1D- and 2D NMR. The anti-leukaemia activities of the compounds were also tested. The results indicated that the compounds exhibited more significant cell growth inhibitory activities against HL-60 cells than adriamycin, with the IC50 of 1.1 ± 0.03 μg/mL and 1.6 ± 0.07 μg/mL respectively. In addition, two compounds showed anti-tumor activities against K562 cells as well. 相似文献
123.
Eight steroidal alkaloids, puqienine A, puqienine B, puqienine C, puqienine D, puqienine E, puqietinone, puqiedine and peimisine were isolated from Fritillaria puqiensis G. D. Yu et. G. Y. Chen, and their anti-hypertensive effect were assessed in vitro based on the inhibition of the purified angiotensin converting enzyme (ACE) using high-performance liquid chromatography assay. The results showed that puqienine E, puqienine B and puqienine A exhibited better inhibitory activity against ACE than others, with inhibition ratios of 70.2 ± 0.5%, 24.7 ± 0.5% and 20.4 ± 2.8%, respectively at the concentration of 200 μM. The 50% inhibiting concentration of puqienine E was determined to be 68 µM. 相似文献
124.
Marie Pascaline Rahelivao Margit Gruner Hanta Andriamanantoanina Bakolinirina Andriamihaja Ingmar Bauer Hans-Joachim Kn?lker 《Marine drugs》2015,13(7):4197-4216
Several species of red algae (Rhodophyta) from the coastal regions of Madagascar have been investigated for their natural products. The most abundant compound was cholesterol (5) in combination with a series of oxidized congeners. The brominated indoles 1–3 along with the sesquiterpene debilone (4) have been isolated from Laurencia
complanata. For the first time, debilone (4) has been obtained from a marine plant. From the methanol extract of Calloseris sp., we have achieved the second isolation of the unusual A-ring contracted steroids (−)-2-ethoxycarbonyl-2β-hydroxy-A-nor-cholest-5-en-4-one (9) and phorbasterone B (10). The crude extracts of Laurencia
complanata exhibited antimicrobial activity against Bacillus cereus, Staphylococcus aureus, Streptococcus pneumoniae, and Candida albicans. 相似文献
125.
Lamiaa A. Shaala Diaa T. A. Youssef Jihan M. Badr Mansour Sulaiman Alaa Khedr 《Marine drugs》2015,13(4):1621-1631
In a continuation of our efforts to identify bioactive compounds from Red Sea Verongid sponges, the organic extract of the sponge Suberea species afforded seven compounds including two new dibrominated alkaloids, subereamollines C and D (1 and 2), together with the known compounds aerothionin (3), homoaerothionin (4), aeroplysinin-1 (5), aeroplysinin-2 (6) and a revised subereaphenol C (7) as ethyl 2-(2,4-dibromo-3,6-dihydroxyphenyl)acetate. The structures of the isolated compounds were assigned by different spectral data including optical rotations, 1D (1H and 13C) and 2D (COSY, multiplicity-edited HSQC, and HMBC) NMR and high-resolution mass spectroscopy. Aerothionin (3) and subereaphenol C (7) displayed potent cytotoxic activity against HeLa cell line with IC50 values of 29 and 13.3 µM, respectively. In addition, aeroplysinin-2 (6) showed potent antimigratory activity against the human breast cancer cell line MDA-MB-231 with IC50 of 18 µM. Subereamollines C and D are new congeners of the previously reported compounds subereamollines A and B with methyl ester functionalities on the side chain. These findings provide further insight into the biosynthetic capabilities of members of the genus Suberea and the chemical diversity as well as the biological activity of these compounds. 相似文献
126.
Barbara Parrino Anna Carbone Gloria Di Vita Cristina Ciancimino Alessandro Attanzio Virginia Spanò Alessandra Montalbano Paola Barraja Luisa Tesoriere Maria Antonia Livrea Patrizia Diana Girolamo Cirrincione 《Marine drugs》2015,13(4):1901-1924
A new series of nortopsentin analogues, in which the imidazole ring of the natural product was replaced by thiazole and the indole unit bound to position 2 of the thiazole ring was substituted by a 7-azaindole moiety, was efficiently synthesized. Two of the new nortopsentin analogues showed good antiproliferative effect against the totality of the NCI full panel of human tumor cell lines (~60) having GI50 values ranging from low micromolar to nanomolar level. The mechanism of the antiproliferative effect of these derivatives, investigated on human hepatoma HepG2 cells, was pro-apoptotic, being associated with externalization of plasma membrane phosphatidylserine and mitochondrial dysfunction. Moreover, the compounds induced a concentration-dependent accumulation of cells in the subG0/G1phase, while confined viable cells in G2/M phase. 相似文献
127.
以兴安杜鹃叶为原料,采用超声波提取、旋转蒸发、离心等方法结合提取总生物碱,以盐酸小檗碱为标准品,采用紫外-可见分光光度法测定兴安杜鹃叶提取物的总生物碱含量,采用抑菌圈法和二倍稀释法对总生物碱提取物抑菌活性以及最低抑菌浓度进行测试,并对总生物碱提取物进行抗氧化性能力测试。结果表明:兴安杜鹃叶中总生物碱的提取率为1.5mg·g~(-1),对大肠杆菌和金黄色葡萄球菌均有抑制作用,最低抑菌质量浓度均为0.63g·L~(-1);对羟基自由基、亚硝酸根离子和超氧阴离子均有清除能力,随着总生物碱提取物质量浓度的增大,清除能力逐渐增强,清除羟基自由基的IC50值为3.71mg·L~(-1),清除亚硝酸根离子的IC50值为4.58mg·L~(-1),清除超氧阴离子的IC50值为3.19mg·L~(-1),对超氧阴离子的清除效果优于对羟自由基和亚硝酸盐。 相似文献
128.
为探讨秦艽中总生物碱的提取工艺,采用含氨乙醇浸渍提取,以总碱浓缩物收率和总生物碱含量为指标,应用L9(34)正交设计,考察提取溶媒中10%氨水与乙醇的比例、溶媒用量、提取次数、提取时间四个因素的影响。结果显示:最佳提取工艺为:药材8倍量含氨乙醇(10%氨水∶乙醇=7∶50),浸提3次,每次2 h。所确定的提取工艺中总生物碱得率稳定、操作简便,易于工业化生产控制,为实际生产提供了科学依据。 相似文献
129.
130.
小果博落回生物碱对几种农业害虫的生物活性 总被引:5,自引:0,他引:5
为确定小果博落回生物碱的杀虫作用方式和杀虫谱,室内测定小果博落回生物碱对粘虫3龄幼虫、菜青虫5龄幼虫、小菜蛾3龄幼虫、棉铃虫3龄幼虫、桃蚜和麦二叉蚜无翅成虫的杀虫活性.结果表明:小果博落回生物碱对试虫具有拒食、胃毒和杀卵等多种作用方式,其中,对粘虫、菜青虫和小菜蛾48 h AFC50值和96 h LC50值分别为0265、0557、0543 g·L-1和0106、0123、0166 g·L-1;对桃蚜和麦二叉蚜有较高的触杀作用,48 h LC50值分别为0362、0710 g·L-1;对棉铃虫3龄幼虫具有一定的生长发育抑制作用,7 d的生长抑制率为695%(5 g·L-1);此外,对粘虫还具有一定的杀卵作用,5 d的卵孵化率和幼虫存活率仅为588%和226%(25 g·L-1). 相似文献