全文获取类型
收费全文 | 1468篇 |
免费 | 90篇 |
国内免费 | 76篇 |
专业分类
化学 | 1364篇 |
晶体学 | 1篇 |
力学 | 7篇 |
综合类 | 11篇 |
数学 | 21篇 |
物理学 | 230篇 |
出版年
2024年 | 2篇 |
2023年 | 32篇 |
2022年 | 118篇 |
2021年 | 82篇 |
2020年 | 96篇 |
2019年 | 87篇 |
2018年 | 67篇 |
2017年 | 105篇 |
2016年 | 80篇 |
2015年 | 39篇 |
2014年 | 46篇 |
2013年 | 100篇 |
2012年 | 54篇 |
2011年 | 58篇 |
2010年 | 45篇 |
2009年 | 73篇 |
2008年 | 40篇 |
2007年 | 69篇 |
2006年 | 60篇 |
2005年 | 51篇 |
2004年 | 47篇 |
2003年 | 55篇 |
2002年 | 43篇 |
2001年 | 28篇 |
2000年 | 35篇 |
1999年 | 23篇 |
1998年 | 18篇 |
1997年 | 20篇 |
1996年 | 12篇 |
1995年 | 21篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 5篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1978年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1634条查询结果,搜索用时 15 毫秒
991.
992.
采用粒径为25 nm的锐钛矿和金红石型混合相二氧化钛(TiO2)材料(P25)替代常规锐钛矿型TiO2, 制备了基于石墨氮化碳(g-C3N4)/混合相TiO2(g-C3N4/P25)的可见光激发光电敏感体系. 研究结果表明, 石墨氮化碳(g-C3N4)大的平面结构不仅能够成为TiO2纳米材料合适的高分散载体, 其高效载流子传输能力还赋予了复合体系优异的光电性能. 当g-C3N4掺杂质量分数仅为0.5%时, 复合体系的光电流响应信号可提高至原来的4.5倍, 增敏效果最好. 该光敏体系的研制显著简化了制备工艺并降低了成本, 同时有效提高了体系的可见光利用效率. 基于该g-C3N4/P25光电敏感复合体系, 首次采用光电化学方法实现了中草药抗氧化容量的测定, 为量化中药体系抗氧化性能评估提供了新的思路. 相似文献
993.
994.
毛细管电泳技术在药物分离分析中的研究与应用 总被引:2,自引:0,他引:2
综述了近5年毛细管电泳在手性药物拆分、药物制剂及中草药分析中的应用.在手性药物拆分的应用中主要探讨了手性选择剂的种类及毛细管分离方法;在药物制剂、中草药的应用中主要介绍该法对药效成分进行的分离及定量分析,总结方法的检出限、线性范围和检测方法;最后,探讨了毛细管电泳在求取药物水解常数上的应用.提出毛细管电泳在药物分析中将有广阔的应用前景. 相似文献
995.
Marcin Gackowski Anna Przybylska Stefan Kruszewski Marcin Koba Katarzyna Mdra-Gackowska Artur Bogacz 《Molecules (Basel, Switzerland)》2021,26(14)
The present review summarizes scientific reports from between 2010 and 2019 on the use of capillary electrophoresis to quantify active constituents (i.e., phenolic compounds, coumarins, protoberberines, curcuminoids, iridoid glycosides, alkaloids, triterpene acids) in medicinal plants and herbal formulations. The present literature review is founded on PRISMA guidelines and selection criteria were formulated on the basis of PICOS (Population, Intervention, Comparison, Outcome, Study type). The scrutiny reveals capillary electrophoresis with ultraviolet detection as the most frequently used capillary electromigration technique for the selective separation and quantification of bioactive compounds. For the purpose of improvement of resolution and sensitivity, other detection methods are used (including mass spectrometry), modifiers to the background electrolyte are introduced and different extraction as well as pre-concentration techniques are employed. In conclusion, capillary electrophoresis is a powerful tool and for given applications it is comparable to high performance liquid chromatography. Short time of execution, high efficiency, versatility in separation modes and low consumption of solvents and sample make capillary electrophoresis an attractive and eco-friendly alternative to more expensive methods for the quality control of drugs or raw plant material without any relevant decrease in sensitivity. 相似文献
996.
Rossella Gottardo Anna Chiarini Ilaria Dal Prà Catia Seri Claudia Rimondo Giovanni Serpelloni Ubaldo Armato Franco Tagliaro 《Journal of mass spectrometry : JMS》2012,47(1):141-146
Since 2004, a number of herbal blends containing different synthetic compounds mimicking the pharmacological activity of cannabinoids and displaying a high toxicological potential have appeared in the market. Their availability is mainly based on the so‐called “e‐commerce”, being sold as legal alternatives to cannabis and cannabis derivatives. Although highly selective, sensitive, accurate, and quantitative methods based on GC–MS and LC–MS are available, they lack simplicity, rapidity, versatility and throughput, which are required for product monitoring. In this context, matrix‐assisted laser desorption ionization‐time of flight mass spectrometry (MALDI‐TOF MS) offers a simple and rapid operation with high throughput. Thus, the aim of the present work was to develop a MALDI‐TOF MS method for the rapid qualitative direct analysis of herbal blend preparations for synthetic cannabinoids to be used as front screening of confiscated clandestine preparations. The sample preparation was limited to herbal blend leaves finely grinding in a mortar and loading onto the MALDI plate followed by addition of 2 µl of the matrix/surfactant mixture [α‐cyano‐4‐hydroxy‐cinnamic acid/cetyltrimethylammonium bromide (CTAB)]. After drying, the sample plate was introduced into the ion source for analysis. MALDI‐TOF conditions were as follows: mass spectra were analyzed in the range m/z 150–550 by averaging the data from 50 laser shots and using an accelerating voltage of 20 kV. The described method was successfully applied to the screening of 31 commercial herbal blends, previously analyzed by GC–MS. Among the samples analyzed, 21 contained synthetic cannabinoids (namely JWH‐018, JWH‐073, JWH‐081, JWH‐250, JWH‐210, JWH‐019, and AM‐694). All the results were in agreement with GC–MS, which was used as the reference technique. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
997.
《Journal of separation science》2018,41(11):2488-2497
Adverse drug reactions of Danshen injection mainly manifested as pseudoallergic reactions. In the present study, salvianolic acid A and a pair of geometric isomers (isosalvianolic acid C and salvianolic acid C) were identified as pseudoallergic components in Danshen injection by a high‐expression Mas‐related G protein coupled receptor X2 cell membrane chromatography coupled online with high‐performance liquid chromatography with electrospray ionization tandem mass spectrometry. Their pseudoallergic activities were evaluated by in vitro assay, which were consistent with the retention times on the cell membrane chromatography column. Salvianolic acid C, the most outstanding compound, was further found to induce pseudoallergic reaction through Mas‐related G protein coupled receptor X2. All the results above indicated that the system developed in this study is an effective method for simultaneously analyzing pseudoallergic components, even those with similar structures and the microcomponents in complex samples (salvianolic acid C in Danshen injection). 相似文献
998.
Paeonol is the active component in the traditional Chinese medicines (TCMs), such as Cynanchum paniculatum, which has been used to treat many diseases, such as eczema. In this work, a simple, rapid and sensitive method was developed for the determination of paeonol in rabbit plasma, which was based on headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS). The extraction parameters of fiber coating, sample temperature, extraction time, stirring rate and ion strength were systemically optimized; the method linearity, detection limit and precision were also investigated. It was shown that the proposed method provided a good linearity (0.02-20 μg mL−1, R2 > 0.990), low detection limit (2.0 ng mL−1) and good precision (R.S.D. value less than 8%). Finally, GC/MS following HS-SPME was applied to fast determination of paeonol in rabbit plasma at different time point after oral demonstration of Cynanchum paniculatum essential oil. The experimental results suggest that the proposed method provided an alternative and novel approach to the pharmacokinetics study of paeonol in the TCMs. 相似文献
999.
中草药微量元素数据的数据库管理 总被引:2,自引:0,他引:2
中草药微量元素数据库收集有四百多种常用中草药六十多种元素的测定数据,具有检索、打印、统计等多种功能,对逐步建立中草药微量元素背景值,促进中草药微量元素的研究具有重要的作用。 相似文献
1000.
红外光谱在中药定性定量分析中的应用 总被引:7,自引:13,他引:7
红外光谱灵敏度高、操作简便、谱带的专属性强,特别适合于中药材的无损快速鉴别和定量分析,它正在成为中药质量控制方面的一种有效手段。文章综述了红外光谱在中药定性和定量研究中的应用现状,对红外光谱在中药材(同一药材不同部位,不同产地、品种的同种中药材,易混淆、真伪中药材等)和中成药(中药配方颗粒和注射剂等)的鉴别分析与有效成分含量测定等方面的应用进行了详细评述。随着傅里叶变换红外光谱和计算机技术的不断发展,它必将在中国中药的现代化和国际化道路上起到关键作用。 相似文献