全文获取类型
收费全文 | 484篇 |
免费 | 9篇 |
国内免费 | 13篇 |
专业分类
化学 | 439篇 |
力学 | 1篇 |
综合类 | 9篇 |
数学 | 1篇 |
物理学 | 56篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 50篇 |
2020年 | 20篇 |
2019年 | 19篇 |
2018年 | 18篇 |
2017年 | 20篇 |
2016年 | 17篇 |
2015年 | 22篇 |
2014年 | 19篇 |
2013年 | 19篇 |
2012年 | 30篇 |
2011年 | 30篇 |
2010年 | 24篇 |
2009年 | 17篇 |
2008年 | 22篇 |
2007年 | 22篇 |
2006年 | 20篇 |
2005年 | 18篇 |
2004年 | 18篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有506条查询结果,搜索用时 609 毫秒
111.
《Arabian Journal of Chemistry》2022,15(10):104147
Refuse tea is industrially identified as broken mixed fannings (BMF). It is a primary raw material for instant tea production. The aroma escape during the process affects the quality of instant tea used for application in the food and beverage industries. Capturing and adding back aroma to the instant tea is commercially important to overcome this drawback. Hence, the study was focused on profiling the aroma of BMF and respective instant tea based on low country (0–300 m MASL) and upcountry (>600 m MASL) elevation categories of Sri Lanka to identify the impact of growing elevation on aroma profiles to explore blending proportions for better aroma profiles. Furthermore, volatiles that escaped with steam during the instant tea production process were condensed, and this aroma extract was added back to the tea concentrate prior to spray drying to produce the aroma blended instant tea sample (ABIT). Solid-phase microextraction followed by gas chromatography–mass spectrometry was used to identify the volatile compounds in the headspace of instant tea, BMF and ABIT samples. BMF samples significantly contained linalool (9.94 ± 2.94 %), cis-linalool oxide (Furanoid) (4.69 ± 1.80 %), geraniol (2.47 ± 1.44 %), and 3-hexen-1-ol (3.46 ± 2.06 %); however, the volatile profile of instant tea samples had high amounts of hydrocarbons (51.60 ± 9.34 %) that did not contribute to creating a pleasant aroma for the product. Hexanal, geraniol, citral, cis-jasmon, α-ionone, nerol and E-2-Z-4-hexadienal are characteristic in upcountry BMF and were absent in the low country tea, indicating a difference in the aroma profiles with elevation. ABIT sample showed that there is a clear improvement in the aroma profile by retaining compounds such as linalool (5.48 %), geraniol (0.95 %), hotrienol (0.92 %), and γ-muurolene (0.22 %), which give a pleasant flowery aroma to the product. This study concluded the possibility to improve the aroma profile of instant tea to give the unique aroma of Ceylon tea as per customer requirements in an economically viable manner and this technology can be applied globally. 相似文献
112.
113.
建立了快速滤过型净化(m-PFC)结合气相色谱-串联质谱(GC-MS/MS)测定茶叶中10种拟除虫菊酯类农药残留的方法。比较了采用不同提取溶剂(乙腈、丙酮和乙酸乙酯)和不同提取方式(不加水浸泡和加水浸泡)时10种农药的提取效率;比较了2种QuEChERS净化管和m-PFC柱对茶叶提取液的净化效果和农药残留的回收率。结果表明,茶叶样品不加水浸泡,用乙腈提取效果最好;m-PFC柱对茶叶提取液净化效果良好,而且能保证较高的农药回收率。10种拟除虫菊酯农药在相应的范围内有良好的线性关系,相关系数(R2)大于0.9980;10种农药在4个水平添加下的回收率为87.5%~111.3%,RSD为2.1%~8.9%。方法的检出限为0.001~0.015 mg/kg,定量限为0.003~0.05 mg/kg。利用该方法检测市售50例茶叶样品中10种拟除虫菊酯农药的残留,检出率为48%,但农药残留量均在国家标准限量值以下。与传统QuEChERS法和固相萃取法相比,该方法具有操作简单、准确度和精密度良好等优点,为多种拟除虫菊酯类农药在茶叶中的残留测定提供了快速检测的新方法。 相似文献
114.
Free amino acids, the key quality components of tea, are contained in higher amounts in higher grade teas. Among free amino
acids in tea, the content of theanine, which is the amino acid of the highest amount, shows high correlation to the price
of green tea. A capillary isotachophoresis (CITP) method was developed for the analysis of L-theanine in tea and food supplements.
The optimized electrolyte system was following: 0.01 mol/l HCl + 0.02 mol/l TRIS + 0.05% HEC (leading electrolyte), 0.01 mol/L-valine
+ barium hydroxide to pH 10 (terminating electrolyte). Good separation of L-theanine from other components of sample was achieved
within 20 min. Method characteristics, i.e., linearity (0–200 mg/l), accuracy (99 ± 2 %), intra-assay (1.5 %), quantification limit (2 mg/l), and detection limit (0.7
mg/l) were determined. Sufficient sensitivity, low labouriousness (extraction only) and low running cost are important attributes
of this method. It was proved that the developed method is suitable for the routine analysis of L-theanine in green tea and
food supplements containing green tea extract. 相似文献
115.
116.
Mohammad Abul Hossain Mikio Kumita Yoshimasa Michigami Shigeru Mori 《Adsorption》2005,11(5-6):561-568
Dynamic characteristics of Cr(VI) sorption on used black tea leaves (UBTLs) as a low-cost adsorbent are studied. Batch experiments
were conducted to evaluate the effects of Cr(VI) concentration, solution pH and temperature on the removal process. Both of
adsorption and reduction, involved in the process, are affected by the processing parameters. The adsorption kinetics is described
successfully using pseudo-second order rate equation and the rate constant decreases with increasing the initial concentration
of Cr(VI) up to 150 mg/L (for 0.1 g/L UBTLs) then becomes slow. Experimental and calculated kinetic data for equilibrium are
well expressed by Langmuir isotherm. The solution pH has a profound effect on the adsorption rate. The rate constant increases
linearly with an increase in temperature, and the low value of activation energy of adsorption, 16.3 kJ/mol, indicates that
Cr(VI) is easily adsorbed on UBTLs. The maximum Cr(VI) adsorptive conditions, with a minimum reduction, were achieved from
the dynamics of operational parameters: the initial Cr(VI) concentration < 150 mg/L (for 0.1 g/L UBTLs); the initial solution
pH = 1.54–2.00 and the processing temperature < 50 ∘C, for the possibility of its practical application. 相似文献
117.
偶氮胂酸型荧光试剂测定铝的研究 总被引:10,自引:1,他引:10
比较了5种新试剂及偶氮胂-I的铝铬合物的荧光性能,讨论了试剂结构与性能之间的关系。试验出7-〔(4-甲基-2-胂酸基苯)偶氮〕-8-羟基喹啉-5-磺酸为铝的优良荧光试剂,并用其测定茶叶、含茶叶饲料,以及大白鼠排泄物中的铝和水样中的铝,结果满意。 相似文献
118.
119.
120.
火焰原子吸收法连续测定茶叶中铅、铜、锌、镉含量 总被引:9,自引:2,他引:9
采用火焰原子吸收方法连续测定了茶叶中铜,铜,锌,镉的含量,方法灵敏,准确。测定时无需富集,萃取,操作简便,回收率93.0%-98.1%,相对标准偏差不超过5.3%。 相似文献