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   217篇
  免费   12篇
  国内免费   26篇
妇产科学   1篇
基础医学   9篇
口腔科学   4篇
临床医学   20篇
内科学   6篇
皮肤病学   9篇
神经病学   1篇
外科学   2篇
综合类   29篇
预防医学   37篇
药学   70篇
中国医学   64篇
肿瘤学   3篇
  2024年   4篇
  2023年   8篇
  2022年   9篇
  2021年   9篇
  2020年   14篇
  2019年   4篇
  2018年   3篇
  2017年   7篇
  2016年   9篇
  2015年   10篇
  2014年   13篇
  2013年   25篇
  2012年   18篇
  2011年   14篇
  2010年   8篇
  2009年   8篇
  2008年   17篇
  2007年   6篇
  2006年   6篇
  2005年   9篇
  2004年   2篇
  2003年   2篇
  2002年   6篇
  2001年   1篇
  2000年   5篇
  1999年   2篇
  1998年   2篇
  1997年   3篇
  1996年   3篇
  1995年   3篇
  1994年   2篇
  1993年   1篇
  1992年   3篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1986年   2篇
  1985年   3篇
  1984年   1篇
  1981年   1篇
  1979年   1篇
  1977年   1篇
  1976年   2篇
  1971年   1篇
  1969年   1篇
排序方式: 共有255条查询结果,搜索用时 15 毫秒
1.
Our purpose was to determine the effects of six cigarette toxicants (pyridine, nicotine, 2-ethylpyridine, 3-ethylpyridine, p-cresol, and pyrazine) on three types of cultured mammalian cells (human umbilical vein endothelial cells [HUVECs], human microvascular endothelial cells [HMVECs], and NIH 3T3 cells) using a cell proliferation/survival assay. Synchronized cells were cultured in proliferation or survival medium containing various doses (10(-18)M-10(-2)M) of the tested chemicals. After 48 h, cells were counted using a hemacytometer. The no observable adverse effect level (NOAEL), lowest observable adverse effect level (LOAEL), and the efficacy were determined for each compound in the cell proliferation and survival assays. Pyridine and p-cresol did not show significant effects with any cell types, except at high doses. Derivitization of the pyridine ring altered its potency, especially when an ethyl group or nitrogen was added. In survival medium, nicotine stimulated proliferation of all three cell types at doses found in smoker's serum (10(-8)M-10(-7)M). For HUVEC and HMVEC, 2-ethylpyridine, 3-ethylpyridine, and pyrazine inhibited proliferation in proliferation medium and induced cell death in survival medium at attomolar and femtomolar doses. All chemicals, except pyridine and pyrazine, stimulated NIH 3T3 cell proliferation at low doses and induced cell death at high doses. LOAELs and efficacies revealed that endothelial cells from a developing organ (umbilical cord) were more sensitive to these chemicals than endothelial cells from an adult organ (lung). 3-Ethylpyridine and pyrazine, which induced cell death at low doses, are added to consumer products and should be subjected to further toxicological testing.  相似文献   
2.
王冰倩  周瑾欣  魏星  于生  张丽  吴啟南  单鸣秋 《中草药》2023,54(17):5541-5549
目的 通过超声辅助大孔树脂对荆芥穗Schizonepetae Spica水提物中总黄酮和总酚类化合物进行富集并对比处理前后化合物含量及活性变化。方法 从7种不同类型树脂中筛选超声辅助最佳树脂型号,在吸附动力学和吸附热力学研究下,对超声温度、功率、上样质量浓度及解吸溶剂百分比等影响因素进行工艺优化。测定了优化处理前后各成分含量及活性变化。结果 动力学和热力学的研究表明,荆芥穗总黄酮适用于Langmuir模型,且吸附过程为自发吸热熵增,总酚则为自发放热熵减并适用于Freundlich模型,据此不同的吸附机制优化了2类成分同时富集的最佳工艺,在超声辅助AB-8大孔树脂,温度25 ℃、时间2.5 h,功率150 W,上样质量浓度0.1 g/mL,70%乙醇解吸附的过程下,荆芥穗水提物中总黄酮和总酚类化合物含量增加2~3倍,其单体成分的含量及抗氧化和神经氨酸酶抑制活性均显著增加。结论 超声辅助大孔树脂技术为荆芥穗总黄酮和总酚类成分的有效可行富集技术。  相似文献   
3.
干姜超临界CO2提取物质量控制的研究   总被引:3,自引:0,他引:3  
目的:建立干姜超临界CO2提取物的有效部位质量控制的方法。方法∶采用薄层色谱法,以石油醚(60~90℃)醋酸乙酯冰醋酸(8∶3∶0.2)为展开剂,5%香草醛硫酸溶液为显色剂,对本品进行鉴别;并采用紫外双波长分光光度法和高效液相色谱法对本品进行总酚及有效成分6姜酚的含量测定。结果∶总酚在9.668~38.67μg·mL-1呈良好线性关系(r=0.9999),平均回收率为97.7%,RSD1.96%;6姜酚在0.20~2.00μg呈良好线性关系(r=0.9999),平均回收率为97.9%,RSD0.33%。结论∶方法准确,灵敏、专属性强,可作为该原料的全面质量控制标准。  相似文献   
4.
南川木波罗根皮的化学成分   总被引:1,自引:0,他引:1  
目的:研究南川木波罗根皮的化学成分。方法:采用硅胶、Diaion HP20大孔吸附树脂、MCI gel CHP 20P树脂凝胶、Sephadex LH-20凝胶、ODS等柱色谱分离手段,对南川木波罗根皮醇提物的乙酸乙酯部位进行化学成分的分离纯化,根据化合物的理化性质及光谱数据鉴定其结构。结果:分离了9个化合物,分别鉴定为4-羟基苯甲醛(p-hydroxybenzaldehyde)(1),2,4-二羟基苯甲酸(2,4-dihydroxybenzoic acid)(2),香豆酸(p-coumaric acid)(3),儿茶素[(+)catechin](4),(E)-阿魏酸甲酯[(E)-ferulic acid methyl ester](5),E-对-羟基肉桂酸甲酯(p-E-hedroxycinnamic acid methyl ester)(6),norartocarpetin(7),反式氧化白黎芦醇(trans-oxyresveratrol)(8),moracin M(9)。结论:化合物1,2,5,6为首次从桑科植物中获得,化合物3为首次在波罗蜜属植物中发现,而化合物7~9为首次从南川木波罗中分离得到。  相似文献   
5.
目的:优选合适的显色体系,建立傣药肾茶中主要酚类物质的含量测定方法,对不同产地样品进行含量测定。方法以迷迭香酸为对照品、亚硝酸钠-硝酸铝-氢氧化钠为显色剂、检测波长为500 nm、采用比色法测定19个不同产地样品的主要酚类物质含量。结果迷迭香酸在8.792~17.584μg/ml范围内线性关系良好(r2=0.9993),平均加样回收率为100.73%,相对标准偏差(RSD)为0.85%。不同产地样品中主要酚类物质的质量分数为1.16%~3.49%。结论该方法简单、准确、重复性好,适合傣药肾茶中主要酚类物质的含量测定。结果显示不同产地样品中以云南产肾茶中主要酚类物质含量相对较高。  相似文献   
6.
目的 筛选大孔树脂分离纯化地菍中总酚类物质的最佳工艺.方法 采用静态与动态吸附-解吸方法,以紫外分光光度法测定地菍总酚的量对工艺进行评价.结果 HPD 100大孔吸附树脂分离效果较好,总酚可达50%以上.其最佳工艺为药液浓度0.2 g(生药)/mL、pH值为2.7~4.5,以3 BV/h进行吸附,5 BV的60%乙醇以3BV/h进行洗脱效果最佳.结论 该方法简便可行,分离效果好,能满足大生产的要求.  相似文献   
7.
In the natural environment, bacteria predominantly exist in matrix‐enclosed multicellular communities associated with various surfaces, referred to as biofilms. Bacteria in biofilms are extremely resistant to antibacterial agents thus causing serious problems for antimicrobial therapy. In this study, we showed that different plant phenolic compounds, at concentrations that did not or weakly suppressed bacterial growth, increased the capacity of Pseudomonas aeruginosa PAO1 to form biofilms. Biofilm formation of P. aeruginosa PAO1 was enhanced 3‐ to 7‐fold under the action of vanillin and epicatechin, and 2‐ to 2.5‐fold in the presence of 4‐hydroxybenzoic, gallic, cinnamic, sinapic, ferulic, and chlorogenic acids. At higher concentrations, these compounds displayed an inhibiting effect. Similar experiments carried out for comparison with Agrobacterium tumefaciens C58 showed the same pattern. Vanillin, 4‐hydroxybenzoic, and gallic acids at concentrations within the range of 40 to 400 μg/mL increased the production of N–3‐oxo‐dodecanoyl‐homoserine lactone in P. aeruginosa PAO1 which suggests a possible relationship between stimulation of biofilm formation and Las Quorum Sensing system of this bacterium. Using biosensors to detect N‐acyl‐homoserine lactones (AHL), we demonstrated that the plant phenolics studied did not mimic AHLs.  相似文献   
8.
The stem, leaf, and root of Tinospora cordifolia (willd.) have been highly exploited for medicinal preparations; however, the nutritional and nutraceutical potential of its attractive red berries (fruits) have not so far been studied. Pigments, berberine (107.0 mg/100 g) and lycopene (50.8 mg/100 g), were identified in the deseeded fruit. Total phenol content in the fruit was 3.2 mg gallic acid equivalent/g. The IC50 of DPPH (82, and 468 ppm) and OH (100, and 1,000 ppm) scavenging activity, and the EC50 of reducing power (2,616, and 1,472 ppm) of hexane and methanol extracts, respectively, were observed. Oxygen radical absorbance capacities of the fruit extracts (150 and 300 ppm) were 1,107 and 2,614 μM trolox equivalent/g, respectively. Nutrient composition including carbohydrate (18.4%), proteins (1.5%), lipids (6%) of which ~62% was unsaturated fatty acids, vitamins like ascorbic acid (0.24 μg), niacin (0.7 mg), and tocopherols (2.4 mg) in 100 g fruits were determined. Potassium content was 1.2 g/100 g dry tissue of berries. These findings show that components of T. cordifolia fruit could be bioactive and used in food, pharmaceutical, and cosmetics.  相似文献   
9.
10.
Cauliflower (Brassica oleraceae L. var. Botrytis) is a good source of bioactive compounds, such as glucosinolates, phenolic compounds and vitamins. In this study, the effects of some processes (i.e. boiling, steaming) on the sinigrin bioaccessibility as a major glucosinolate found in cruciferous vegetables after in vitro digestion, also in vitro antimutagenic activities, total phenols and total antioxidant capacities of cauliflower were determined. The sinigrin content was reduced by approximately 9.6% and 29.1% in steamed and boiled cauliflower (p > 0.05), respectively. After in vitro simulated digestion, sinigrin content was decreased by 26.4% in raw samples, increased by 29.5% and 114.7% in steamed and boiled samples, respectively. In all samples, mutagenic effect to Salmonella typhimurium TA 100 was not seen. When samples were steamed, phenol content was increased by 14.83%. After boiling total phenol content of cauliflower was decreased by 1.8%. Total antioxidant capacities (TAC) measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3 ethylbenzothiazoline-6-sulfonic acid) (ABTS) methods were increased by 47% and 39%, respectively (p < 0.05) in steamed samples and decreased by 8% and 7% with boiling, respectively (p > 0.05). TAC in raw sample of cauliflower, which was investigated in phosphomolybdenum assays, was determined as 18.7 mg ascorbic acid equivalents (AAE)/100 g. In all cases, the highest antioxidant activity was determined in the steamed samples, while the lowest antioxidant activity was in boiled samples.  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