全文获取类型
收费全文 | 289篇 |
免费 | 26篇 |
国内免费 | 19篇 |
专业分类
化学 | 282篇 |
数学 | 2篇 |
物理学 | 50篇 |
出版年
2023年 | 12篇 |
2022年 | 18篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 14篇 |
2016年 | 10篇 |
2015年 | 21篇 |
2014年 | 11篇 |
2013年 | 11篇 |
2012年 | 29篇 |
2011年 | 24篇 |
2010年 | 31篇 |
2009年 | 31篇 |
2008年 | 19篇 |
2007年 | 23篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
排序方式: 共有334条查询结果,搜索用时 78 毫秒
91.
测定天然和栽培缬草根金属元素的微波和干灰化消解-FAAS法 总被引:6,自引:0,他引:6
采用微波消化法和马弗炉干灰法处理天然和栽培缬草根样品,火焰原子吸收光谱法连续测定样品中金属元素,分别检出12种和11种元素,其中Zn、Cu、Fe、Co、Mn、Ni、Cr为生命必需微量元素;两种样品各用两种消化法处理,测得金属元素及含量有差异,干灰法操作简单,但消化温度高、时间长、易挥发、元素容易损失,使检测值偏低;而微波消化法简便、省时、损失减少;两种消化法的加标回收率分别为95%-100%和96%-105%。 相似文献
92.
A simple, rapid, and sensitive non-aqueous capillary electrophoresis procedure with head-column field-amplified sample stacking concentration for the analysis of fangchinoline and tetrandrine is established. Optimum separation and stacking conditions were obtained when the sample was injected at 8 kV for 50 s after preliminary pressure injection of ethanol (16.9 kPa) for 0.6 s and separated with the buffer containing 50 mM ammonium acetate, 0.5% (v/v) acetic acid, and 50% (v/v) acetonitrile in methanol medium at 24 kV applied voltage. The analytes were detected by UV at 214 nm. The two bisbenzylisoquinoline alkaloids can be separated within 6 min and quantified with high sensitivity. The detection limits were 0.30 ng mL(-1) for fangchinoline and 0.34 ng mL(-1) for tetrandrine, which indicated that the sensitivities were at least 1000-fold enhanced over those reported in the literature as obtained by UV detection. The method was applied to the analysis of fangchinoline and tetrandrine in Radix Stephaniae tetrandrae and its medicinal preparations with good results. 相似文献
93.
A capillary electrophoretic method for simultaneous determination of six bioactive ingredients (berberine, palmatine, baicalin, sennoside B, emodin, and sennoside A) in the Chinse herbal formula San-huang-hsieh-hsin-tang was established. A carrier composed of aqueous buffer solution (50 mM sodium cholate, 15 mM sodium dihydrogen phosphate, and 4.25 mM sodium borate)-acetonitrile (3:2) was found to be the most suitable electrolyte for this separation. Contents of these constituents in a non-pretreated methanol-water extract of San-huang-hsieh-hsin-tang sample could be easily determined within 20 min. The effects of borate, cholate, and organic modifier (acetonitrile) concentration of the carrier on the migration behavior of the solutes were also studied. 相似文献
94.
桔梗等中药微量元素初探 总被引:5,自引:0,他引:5
对中药桔梗、怀牛膝,华山参、鹿角胶,龟甲胶及阿胶进行了微量元素研究。结果发现:同一种中药因产地不同,其微量元素的含量不同。同一种植物药,其部位不同,所含微量元素多少不等。同一类型的中药,其品种、来源不同,微量元素的含量高低也不相同。本研究为今后对这些中药进行真伪鉴别,合理开发或综合利用都提供了科学的依据。 相似文献
95.
反相高效液相色谱法测定大黄药材中游离及结合型蒽醌类衍生物的含量 总被引:25,自引:0,他引:25
建立了同时测定大黄药材中蒽醌类衍生物含量的RP HPLC法。色谱柱为HypersilC1 8柱 (2 5 0mm×4 6mmi.d .,1 0 μm) ,流动相为甲醇 乙腈 水 (3∶5∶2 ,磷酸调pH 2 .8) ,流速为 1 .0mL min ,柱温为 2 5℃ ,检测波长为 2 2 5nm。在此色谱条件下 ,各组分在 2 0min内均得到良好分离。平均回收率为 98.83 %~ 1 0 0 .9% ;相对标准偏差 0 .68%~ 1 .5 8%。 相似文献
96.
97.
建立了固相萃取(SPE)-定量核磁共振波谱(qNMR)技术测定板蓝根饮片中有效成分表告依春含量的方法.样品用水超声提取两次,采用SPE对提取液进行富集浓缩,用qNMR测定表告依春的含量.考察了样品预处理和qNMR实验条件对测定结果的影响,选择氘代二甲基亚砜为溶剂,用基准试剂邻苯二甲酸氢钾标定的2,3,5-三碘苯甲酸为内标,选择脉冲宽度P1=14.1 μs,延迟时间d1=5 s,扫描次数NS=256为qNMR定量测定表告依春的最佳实验条件.表告依春的定量峰为δ 5.365~5.399 (H-7b, d,1H).结果表明,日内测量精密度(RSD)为0.5%,日间精密度为0.8%,表告依春与三碘苯甲酸峰面积比与质量比的零截距标准曲线线性相关系数为0.9991,且斜率与理论值相符.根据响应值标准偏差和标准曲线斜率法确定此法测定表告依春的检测限(LOD)为0.05 mg/g;定量限(LOQ, S/N ≥ 150)为0.19 mg/g.包括样品提取过程的表告依春的回收率为97.4%~101.7%.采用本方法测定板蓝根饮片中的表告依春的含量为<0.19~1.26 mg/g.研究结果表明,采用SPE进行富集,扩大了qNMR的应用范围,可用于低含量复杂样品的定量分析. 相似文献
98.
Hong Shen Jie Wu Liu‐Qing Di Ling‐Ying Zhu Jun Xu Ru Yan Song‐Lin Li 《Biomedical chromatography : BMC》2013,27(5):556-562
Glycyrrhizae Radix (GR) is often prescribed together with Aconiti Laterlis Radix (ALR) (a so‐called compatible drug pair) in traditional Chinese medicinal practice to reduce toxicity of ALR. However, the mechanisms involved remain to be addressed. In this study, the metabolic interactions between GR–ALR drug pair were investigated for the first time. First, an HPLC‐TQ‐MS/MS method was developed to analyze hypaconitine, a major bioactive and toxic component of ALR, in rat liver S9. Then the in vitro metabolic rates of hypaconitine by different rat liver S9 were compared using the established method. The experiments were designed in four groups: pure hypaconitine (group I) and ALR extract (group II) incubated with liver S9 of normal rats, and pure hypaconitine (group III) and ALR extract (group IV) incubated with liver S9 of GR‐pretreated rats. When incubated for more than 4 h, the metabolic rates of hypaconitine in group III were significantly higher than those in group I, and when incubated for more than 2 h, the metabolic rates of hypaconitine in group IV were significantly higher than those in group II, suggesting that GR can enhance metabolic rate of hypaconitine, the mechanism of which might be related to hepatic metabolizing enzyme induction by GR. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
99.
Long Song Hong Zhang Xin Liu Zhi‐Li Zhao Shi‐Lin Chen Zheng‐Tao Wang Hong‐Xi Xu 《Biomedical chromatography : BMC》2012,26(12):1567-1574
Yunaconitine (YAC) is a toxic aconite alkaloid that is considered to be a hidden aconite poison since it is frequently found in body fluids from aconite poisoning patients, but has not been well studied in commonly used herbal drugs. In this paper, a rapid and sensitive ultra high‐performance liquid chromatography–tandem mass spectrometry (UHPLC‐MS/MS) detection combined with microwave‐assisted extraction (MAE) was developed for high throughput simultaneous determination of YAC and six other toxic aconite alkaloids in 31 samples of crude, processed aconites and aconite‐containing drugs. The optimized method showed excellent linearity, precision, accuracy and recovery for all target compounds with short run time. YAC was detected in some samples with contents from 0.015 to 10.41 mg/g. This is the first report on the determination of YAC in Radix Aconiti, Radix Aconiti Kusnezoffii and aconite‐containing drugs. This newly developed method facilitates the rapid screening of YAC and related toxic aconite alkaloids and allows YAC to be used as a chemical marker for the quality control of aconites and aconite‐containing drugs. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
100.
Establish a quantitative analysis of multi-components by the single marker (QAMS) method for quality evaluation and validate its feasibilities by the simultaneous quantitative assay of four main components in Linderae Reflexae Radix. Four main components of pinostrobin, pinosylvin, pinocembrin, and 3,5-dihydroxy-2-(1-p-mentheneyl)-trans-stilbene were selected as analytes to evaluate the quality by RP-HPLC coupled with a UV-detector. The method was evaluated by a comparison of the quantitative results between the external standard method and QAMS with a different HPLC system. The results showed that no significant differences were found in the quantitative results of the four contents of Linderae Reflexae Radix determined by the external standard method and QAMS (RSD <3%). The contents of four analytes (pinosylvin, pinocembrin, pinostrobin, and Reflexanbene I) in Linderae Reflexae Radix were determined by the single marker of pinosylvin. This fingerprint was the spectra determined by Shimadzu LC-20AT and Waters e2695 HPLC that were equipped with three different columns. 相似文献