全文获取类型
收费全文 | 696篇 |
免费 | 37篇 |
国内免费 | 160篇 |
出版年
2024年 | 5篇 |
2023年 | 16篇 |
2022年 | 25篇 |
2021年 | 23篇 |
2020年 | 37篇 |
2019年 | 46篇 |
2018年 | 25篇 |
2017年 | 25篇 |
2016年 | 32篇 |
2015年 | 27篇 |
2014年 | 33篇 |
2013年 | 118篇 |
2012年 | 28篇 |
2011年 | 46篇 |
2010年 | 28篇 |
2009年 | 24篇 |
2008年 | 37篇 |
2007年 | 50篇 |
2006年 | 39篇 |
2005年 | 35篇 |
2004年 | 25篇 |
2003年 | 26篇 |
2002年 | 20篇 |
2001年 | 14篇 |
2000年 | 16篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 5篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有893条查询结果,搜索用时 31 毫秒
11.
《Bioscience, biotechnology, and biochemistry》2013,77(12):2023-2033
A series of 1,2-dithiolanes, 1,2-dithianes and related compounds bearing a nitrogen-containing substituent were synthesized and their pesticidal activity was tested. A new general synthetic route to 1,2-dithiolanes was established from 1,3-diols. A variation in the position and character of the nitrogen atom is shown to be allowable to some extent for promoting insecticidal activity, unlike the case of sulfur atoms. Most compounds showed acaricidal activity, the strongest being displayed by cis-3,5-bis(dimethylaminomethyl)-1,2-dithiolane. 相似文献
12.
Green tea contains active ingredients which are beneficial for health. While numerous studies have been conducted on the components extracted from green tea, few studies have investigated the active ingredients in tea residue. In this study, proteins were extracted from green tea residue via an optimised alkaline extraction combined with enzymatic hydrolysis, of which, an acidic protease was selected to prepare an enzymatic hydrolysate because of its high angiotensin converting enzyme (ACE) inhibitory activity. The composition characteristics of extracted green tea proteolysis products were elucidated, including amino acid composition, molecular weight distribution and possible amino acid sequences. In addition, the protein hydrolysate had anti-digestive properties, maintained its activity of inhibiting ACE enzyme at different temperatures, pH and metal ions, and exhibited antihypertensive activity in animals. In conclusion, the optimised alkaline extraction and enzymatic hydrolysis conditions of a ACE inhibitory peptide from green tea residue is an optimal extraction method to maintain its antihypertensive activity, providing the basis for the clinical application of green tea for blood pressure reduction. 相似文献
13.
14.
以紫斑牡丹(Paeonia suffruticosa var. papaveracea)花瓣为原料,采用隔离窨制,对牡丹花茶窨制过程中花坯、配花量等主要影响因子进行研究。结果表明,密闭箱桶温度21 ℃、相对湿度90%、窨制时间48 h条件下经一窨一提获得的花茶,感官评审花与茶叶的协调度高、香气高锐持久、茶汤滋味醇正鲜爽。采用气相色谱-质谱联用仪分析花茶香气成分,新鲜花瓣与茶叶配比5:1窨制48 h的花茶苯乙醇、香叶醇、橙花醇含量较高,其香气高扬、茶汤醇正鲜爽,配比2.5:1的花茶上述成分含量和感官其次,而拌和型茶品透素欠鲜爽。发酵或发酵揉捻花瓣窨制的花茶乙醇、环氧芳樟醇及高级烷烃含量较高,其主要赋香物质低于新鲜花瓣含量,渥味明显,茶汤有浊气欠鲜爽。 相似文献
15.
16.
17.
18.
基于代谢组学技术,比较室内自然萎凋和空气能萎凋两种萎凋工艺对白茶萎凋过程代谢物与品质的影响。结果表明,不同代谢物对2种萎凋工艺的响应存在差异,体现三种变化规律:第一类代谢物受萎凋工艺影响小,如咖啡碱、表没食子儿茶素和2'-羟基二氢大豆素等;第二类代谢物含量变化速率在空气能萎凋时加快,但其最终含量受影响小,如表没食子儿茶素没食子酸酯、聚酯型儿茶素A和木麻黄素等;第三类代谢物则受萎凋时间影响大,如茶没食子素与奎宁酸等。两种萎凋工艺对白茶品质影响存在差异,自然萎凋下黄酮(醇)糖苷类、儿茶素聚合体等含量更高,这些物质多在萎凋中后期含量提升;空气能萎凋下酚酸、茶氨酸含量更高,这些物质在自然萎凋后期含量大幅下降。萎凋时长是两种萎凋工艺导致代谢物含量差异的重要因素。 相似文献
19.
Diets rich in fruits and vegetables delay the onset of many age-related diseases, and contain a complex mixture of antioxidants (including ascorbate, carotenoids, vitamin E and other phenolics such as the flavonoids). However, diet also contains pro-oxidants, including iron, copper, H2O2, haem, lipid peroxides and aldehydes. Nitrite is frequently present in diet, leading to generation of reactive nitrogen species in the stomach. In considering the biological importance of dietary antioxidants, attention has usually focussed on those that are absorbed through the gastrointestinal tract into the rest of the body. In the present paper we develop the argument that the high levels of antioxidants present in certain foods (fruits, vegetables, grains) and beverages (e.g. green tea) play an important role in protecting the gastrointestinal tract itself from oxidative damage, and in delaying the development of stomach, colon and rectal cancer. Indeed, carotenoids and flavonoids do not seem to be as well absorbed as vitamins C and E. Hence their concentrations can be much higher in the lumen of the GI tract than are ever achieved in plasma or other body tissues, making an antioxidant action in the GI tract more likely. Additional protective mechanisms of these dietary constituents (e.g. effects on intercellular communication, apoptosis, cyclooxygenases and telomerase) may also be important. 相似文献
20.
《Redox report : communications in free radical research》2013,18(4):150-154
AbstractObjectivesRegular intake of green tea associates with lower DNA damage and increased resistance of DNA to oxidant challenge. However, in vitro pro-oxidant effects of green tea have been reported. Both effects could be mediated by hydrogen peroxide (H2O2) which is generated by autoxidation of tea catechins. In large amounts, H2O2 is genotoxic, but low concentrations could activate the redox-sensitive antioxidant response element (ARE) via the Keap-1/Nrf2 redox switch, inducing genoprotective adaptations. Our objective was to test this hypothesis.MethodsPeripheral lymphocytes from healthy volunteers were incubated for 30 minutes at 37°C in freshly prepared tea solutions (0.005, 0.01, 0.05%w/v (7, 14, 71 µmol/l total catechins) in phosphate buffered saline (PBS), with PBS as control) in the presence and absence of catalase (CAT). H2O2 in tea was measured colorimetrically. Oxidation-induced DNA lesions were measured by the Fpg-assisted comet assay.ResultsH2O2 concentrations in 0.005, 0.01, and 0.05% green tea after 30 minutes at 37°C were, respectively, ~3, ~7, and ~52 µmol/l. Cells incubated in 0.005 and 0.01% tea showed less (P < 0.001) DNA damage compared to control cells. Cells treated with 0.05% green tea showed ~50% (P < 0.001) more DNA damage. The presence of CAT prevented this damage, but did not remove the genoprotective effects of low-dose tea. No significant changes in expression of ARE-associated genes (HMOX1, NRF2, KEAP1, BACH1, and hOGG1) were seen in cells treated with tea or tea + CAT.ConclusionGenoprotection by low-dose green tea could be due to direct antioxidant protection by green tea polyphenols, or to H2O2-independent signalling pathways. 相似文献