全文获取类型
收费全文 | 31622篇 |
免费 | 3634篇 |
国内免费 | 6834篇 |
专业分类
化学 | 24270篇 |
晶体学 | 705篇 |
力学 | 1502篇 |
综合类 | 733篇 |
数学 | 4254篇 |
物理学 | 10626篇 |
出版年
2024年 | 47篇 |
2023年 | 254篇 |
2022年 | 852篇 |
2021年 | 902篇 |
2020年 | 759篇 |
2019年 | 769篇 |
2018年 | 674篇 |
2017年 | 919篇 |
2016年 | 1051篇 |
2015年 | 1155篇 |
2014年 | 1384篇 |
2013年 | 2324篇 |
2012年 | 2464篇 |
2011年 | 2747篇 |
2010年 | 1931篇 |
2009年 | 2245篇 |
2008年 | 2451篇 |
2007年 | 2263篇 |
2006年 | 2051篇 |
2005年 | 2035篇 |
2004年 | 2360篇 |
2003年 | 1569篇 |
2002年 | 1558篇 |
2001年 | 1070篇 |
2000年 | 1003篇 |
1999年 | 744篇 |
1998年 | 500篇 |
1997年 | 421篇 |
1996年 | 375篇 |
1995年 | 327篇 |
1994年 | 285篇 |
1993年 | 311篇 |
1992年 | 259篇 |
1991年 | 185篇 |
1990年 | 181篇 |
1989年 | 191篇 |
1988年 | 165篇 |
1987年 | 134篇 |
1986年 | 123篇 |
1985年 | 131篇 |
1984年 | 141篇 |
1983年 | 103篇 |
1982年 | 93篇 |
1981年 | 92篇 |
1980年 | 79篇 |
1979年 | 50篇 |
1978年 | 34篇 |
1977年 | 37篇 |
1976年 | 29篇 |
1974年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
11.
12.
Guizellini Filipe Corrêa Franzin Bruno Trevizan da Silva Matheus Antonio Abra Luciana Mazotti Hojo Ossamu Pastre Iêda Aparecida Ribeiro Clóvis Augusto Paiva-Santos Carlos de Oliveira Fertonani Fernando Luis 《Journal of Thermal Analysis and Calorimetry》2021,143(1):47-60
Journal of Thermal Analysis and Calorimetry - The aim of this work is to synthesize and characterize a new structured silver–clay dried, calcined or sintered at different temperatures... 相似文献
13.
14.
15.
16.
Studies on metabolites and metabolic pathways of bulleyaconitine A in rat liver microsomes using LC‐MSn combined with specific inhibitors
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hongbin Zhu Fengrui Song Zhiqiang Liu Shuying Liu 《Biomedical chromatography : BMC》2015,29(7):1027-1034
Bulleyaconitine A (BLA) from Aconitum bulleyanum plants is usually used as anti‐inflammatory drug in some Asian countries. It has a variety of bioactivities, and at the same time some toxicities. Since the bioactivities and toxicities of BLA are closely related to its metabolism, the metabolites and the metabolic pathways of BLA in rat liver microsomes were investigated by HPLC–MSn. In this research, the 12 metabolites of BLA were identified according to the results of HPLC‐MSn data and the relevant literature. The results showed that there are multiple metabolites of BLA in rat liver microsomes, including demethylation, deacetylation, dehydrogenation deacetylation and hydroxylation. The major metabolic pathways of BLA in rat liver microsomes were clarified by HPLC‐MS combined with specific inhibitors of CYP450 isoforms. As a result, CYP3A and 2C were found to be the principal CYP isoforms contributing to the metabolism of BLA. Moreover, CYP2D6 and 2E1 are also more important CYP isoforms for the metabolism of BLA. While CYP1A2 only affected the formation rate of M11, its effect on the metabolism of BLA is very small. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
17.
18.
19.
20.
When dealing with simple phenols such as caffeic acid (CA) and ferulic acid (FA), found in a variety of plants, it is very important to have control over the most important factors that accelerate their degradation reactions. This is the first report in which the stabilities of these two compounds have been systematically tested by exposure to various different factors. Forced degradation studies were performed on pure standards (trans-CA and trans-FA), dissolved in different solvents and exposed to different oxidative, photolytic and thermal stress conditions. Additionally, a rapid, sensitive, and selective stability-indicating gas chromatographic-mass spectrometric method was developed and validated for determination of trans-CA and trans-FA in the presence of their degradation products. Cis-CA and cis-FA were confirmed as the only degradation products in all the experiments performed. All the compounds were perfectly separated by gas chromatography (GC) and identified using mass spectrometry (MS), a method that additionally elucidated their structures. In general, more protic solvents, higher temperatures, UV radiation and longer storage times led to more significant degradation (isomerization) of both trans-isomers. The most progressive isomerization of both compounds (up to 43%) was observed when the polar solutions were exposed to daylight at room temperature for 1 month. The method was validated for linearity, precision as repeatability, limit of detection (LOD) and limit of quantitation (LOQ). The method was confirmed as linear over tested concentration ranges from 1−100 mg L−1 (r2s were above 0.999). The LOD and LOQ for trans-FA were 0.15 mg L−1 and 0.50 mg L−1, respectively. The LOD and LOQ for trans-CA were 0.23 mg L−1 and 0.77 mg L−1, respectively. 相似文献