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   259篇
  免费   7篇
  国内免费   10篇
林业   58篇
农学   22篇
基础科学   5篇
  11篇
综合类   114篇
农作物   33篇
水产渔业   1篇
畜牧兽医   16篇
园艺   11篇
植物保护   5篇
  2024年   1篇
  2023年   3篇
  2022年   9篇
  2021年   11篇
  2020年   5篇
  2019年   4篇
  2018年   7篇
  2017年   3篇
  2016年   9篇
  2015年   7篇
  2014年   5篇
  2013年   9篇
  2012年   34篇
  2011年   21篇
  2010年   16篇
  2009年   21篇
  2008年   26篇
  2007年   14篇
  2006年   20篇
  2005年   12篇
  2004年   7篇
  2003年   2篇
  2002年   4篇
  2001年   9篇
  2000年   8篇
  1999年   5篇
  1998年   3篇
  1997年   1篇
排序方式: 共有276条查询结果,搜索用时 15 毫秒
11.
栗瘿蜂危害下锥栗叶片中黄酮含量的变化   总被引:5,自引:2,他引:5  
通过定点定期连续采样结合实验室化学测试, 研究了栗瘿蜂危害不同时期锥栗叶片中黄酮含量的变化情况 结果表明: 随栗瘿蜂危害期的变化, 不同锥栗品种叶片中黄酮含量均存在着明显的动态变化 从6月中旬起, 各品种叶片中黄酮含量呈上升趋势, 至7月中旬栗瘿蜂幼虫孵化前达到峰值, 初孵幼虫取食危害后含量又迅速下降 幼虫孵化前, 黄酮含量的高低与品种抗性级别表现出一致性, 即抗栗瘿蜂品种叶片中黄酮含量高, 感虫品种叶片中黄酮含量低 初孵幼虫取食危害后, 抗虫品种叶片中黄酮含量下降值远高于感虫品种, 抗虫级别越高, 下降值越大 表明不同时期锥栗品种叶片中黄酮含量的多少与品种的抗性有密切关系  相似文献   
12.
苦荞叶提取物抗氧化性及其协同效应的研究   总被引:11,自引:0,他引:11  
从苦荞叶中提取抗氧化性物质,用光度法测定提取物中总黄酮的含量及对羟自由基(·OH)和超氧阴离子(O-2·)的清除作用,并采用碘量法研究了苦荞叶提取物对脂质过氧化的抑制作用及与其他物质的协同作用。结果表明,苦荞叶中总黄酮含量为57g/kg;苦荞叶提取物具有很强的抗氧化活性,可有效延缓油脂脂质过氧化反应;随着苦荞叶提取物添加量的增加,抗氧化作用增强,最有效的添加量为2g/kg;VC、VE和柠檬酸对苦荞叶提取物有一定的协同作用,增效次序为VC>VE>柠檬酸;苦荞叶提取物对羟自由基和超氧阴离子均有较强的清除能力。  相似文献   
13.
蜂胶黄酮增强免疫作用的研究   总被引:6,自引:1,他引:6  
以蜂胶黄酮(PF)为免疫增强剂,探讨其对免疫雏鸡血清抗体效价和外周血T淋巴细胞增殖以及对培养的鸡脾脏淋巴细胞增殖的影响。结果表明:PF能显著提高雏鸡的血清抗体效价,促进外周血淋巴细胞增殖,且有一定的量效和时效关系;在体外,也能促进鸡脾脏T淋巴细胞增殖,以低浓度的效果较好。证明PF具有较强的增强免疫活性,是蜂胶中增强免疫作用的有效成分。  相似文献   
14.
Sea stars or starfish (class Asteroidea) and holothurians or sea cucumbers (class Holothuroidea), belonging to the phylum Echinodermata (echinoderms), are characterized by different sets of glycosidic metabolites: the steroid type in starfish and the triterpene type in holothurians. However, herein we report the isolation of eight new triterpene glycosides, pacificusosides D–K (1–3, 5–9) along with the known cucumarioside D (4), from the alcoholic extract of the Far Eastern starfish Solaster pacificus. The isolated new compounds are closely related to the metabolites of sea cucumbers, and their structures of 1–3 and 5–9 were determined by extensive NMR and ESIMS techniques. Compounds 2, 5, and 8 have a new type of tetrasaccharide chain with a terminal non-methylated monosaccharide unit. Compounds 3, 6, and 9 contain another new type of tetrasaccharide chain, having 6-O-SO3-Glc as one of the sugar units. The cytotoxic activity of 1–9 against non-cancerous mouse epidermal cells JB6 Cl41 and human melanoma cell lines SK-MEL-2, SK-MEL-28, and RPMI-7951 was determined by MTS assay. Compounds 1, 3, 4, 6, and 9 showed potent cytotoxicity against these cell lines, but the cancer selectivity (SI > 9) was observed only against the SK-MEL-2 cell line. Compounds 1, 3, 4, 6, and 9 at the non-toxic concentration of 0.1 μM significantly inhibited neoplastic cell transformation of JB6 Cl41 cells induced by chemical carcinogens (EGF, TPA) or ionizing radiation (X-rays and UVB). Moreover, compounds 1 and 4 at the non-toxic concentration of 0.1 µM possessed the highest inhibiting activity on colony formation among the investigated compounds and decreased the colonies number of SK-MEL-2 cells by 64% and 70%, respectively. Thus, triterpene glycosides 1 and 4 can be considered as prospective cancer-preventive and anticancer-compound leaders.  相似文献   
15.
红芪愈伤组织中黄酮代谢途径的探讨   总被引:3,自引:1,他引:2  
在红氏供试材料中苯丙氨酸转氨酶活性在分化愈伤组织中最高,但游离苯氨丙酸含量在分化愈伤组织中并无明显降低,说明游离氨基酸的积累主要来自蛋白质的分解。黄酮含量的变化以褐化愈伤组织中含量最高,因此我们推测:黄酮合成的最后几步,可能发生在褐化愈伤组织中,从可溶性蛋白质的SDS-PAGE平板电泳结果表明,分化愈伤组织与褐化愈伤组织相比蛋白质谱带发生了明显的变化,这可能与控制黄酮合成的有关酶的活性变化有关。  相似文献   
16.
目的 研究红花中的黄酮类物质。方法 乙醇浸泡提取,固相萃取分离,液相色谱法进行纯度检测,结果 采用的红花中有两种黄酮类物质。结论 洗脱液V(H2O):V(C4H5OH)=3:7,能很好的分离红花中的两种黄酮类物质。  相似文献   
17.
通过对受拉缘蝽不同程度为害的卵叶小蜡叶片的单宁、黄酮、总酚含量的测定,结果表明:受害的卵叶小蜡叶片的单宁含量随着拉缘蝽若、成虫为害程度的加重而发生变化,在受害初期显著增加,但随着为害程度的加重,而呈逐渐下降的趋势;受害卵叶小蜡叶片中黄酮含量随着受害程度的加剧,呈先上升、而后再下降的特点;叶部总酚的含量随着受害程度的不断加重,总酚的含量呈现上升的趋势。说明卵叶小蜡应激反应的过程是一种随着受害程度的不同而不断变化的动态过程。  相似文献   
18.
紫苏子皮提取物中抗氧化性成分及作用研究   总被引:7,自引:2,他引:7  
对紫苏子皮的成分及性质进行研究,用实验方法证明该皮含有丰富的黄酮及多酚类化合物,具有防止油脂氧化的功能。可用于代替化学合成抗氧化剂。不仅无毒,而且不具有保健作用。  相似文献   
19.
The cytotoxic effects of thirteen triterpene glycosides from Holothuria scabra Jaeger and Cucumaria frondosa Gunnerus (Holothuroidea) against four human cell lines were detected and their cytotoxicity-structure relationships were established. The apoptosis-inducing activity of a more potent glycoside echinoside A (1) in HepG2 cells was further investigated by determining its effect on the morphology, mitochondrial transmembrane potential (Δψm) and mRNA expression levels of the apoptosis-related genes. The results showed that the number of glycosyl residues in sugar chains and the side chain of aglycone could affect their cytotoxicity towards tumor cells and selective cytotoxicity. 1 significantly inhibited cell viability and induced apoptosis in HepG2 cells. 1 also markedly decreased the Δψm and Bcl-2/Bax mRNA express ratio, and up-regulated the mRNA expression levels of Caspase-3, Caspase-8 and Caspase-9 in HepG2 cells. Therefore, 1 induced apoptosis in HepG2 cells through both intrinsic and extrinsic pathway. These findings could potentially promote the usage of these glycosides as leading compounds for developing new antitumor drugs.  相似文献   
20.
A. Tyrach  W. Horn 《Plant Breeding》1997,116(4):377-381
The flower colour of Gerbera, an important ornamental cut flower, is derived from carotenoids and flavonoids. The knowledge of enzymological and genetic control of flavonoid biosynthesis is still incomplete. The present paper summarizes the results obtained at our institute between 1981 and 1993. The material for the investigation of phenotypic segregation and segregation of flavonoids after chromatographic analysis came from 408 progenies of controlled crosses. Phenotypic segregation analysis showed acyanic genotypes to be homozygous recessive and recessive epistatic over cyanic genotypes, respectively. This was confirmed by the existence of two loci controlling steps in biosynthesis (fht, dfr or ans) showing recessive mutants and complementary gene action after crosses. Flavone formation is effected by one dominant allele (fns+); dominant and recessive genotypes are now available. Regarding anthocyanidin inheritance, an unusual epistasis of 4′-hydroxylation (pelargonidin formation) over 3′,4′-hydroxylation (cyanidin formation) was observed. Final proof of the postulated gene actions will come from enzymological and molecular biological investigations of the chemogenetically defined Gerbera genotypes now available.  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