首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   227篇
  免费   12篇
  国内免费   8篇
化学   188篇
综合类   8篇
数学   2篇
物理学   49篇
  2023年   5篇
  2022年   41篇
  2021年   16篇
  2020年   7篇
  2019年   9篇
  2018年   10篇
  2017年   11篇
  2016年   5篇
  2015年   11篇
  2014年   4篇
  2013年   15篇
  2012年   7篇
  2011年   3篇
  2010年   6篇
  2009年   11篇
  2008年   11篇
  2007年   9篇
  2006年   7篇
  2005年   3篇
  2004年   14篇
  2003年   10篇
  2002年   7篇
  2000年   6篇
  1999年   3篇
  1998年   2篇
  1997年   4篇
  1995年   4篇
  1994年   3篇
  1993年   1篇
  1988年   2篇
排序方式: 共有247条查询结果,搜索用时 11 毫秒
131.
132.
Sumamry Soybean, rape and sunflower lipids have been extracted with a focused microwave-assisted Saxhlet extractor. The main factors affecting extraction efficiency, namely microwave irradiation power, number of cycles and microwave irradiation time were optimised by means of a power, number of cycles and microwave irradiation time were optimised by means of a central composite design based on a two-level-three-factor factorial design. A study of the influence of particle size on the extraction procedure was also performed. The results obtained were compared with those obtained by use of an ISO method using a conventional Soxhlet extractor. Quantitative results for lipid content based on gravimetric determinations and qualitative results based on analysis of fatty acid methyl esters and polymeric compounds were similar to those obtained by Soxhlet extraction with hexane. Substantial reduction of sample manipulation. analysis time and solvent wastage is achieved by use of the proposed method.  相似文献   
133.
三岛柴胡种子中的柴胡皂甙(英文)   总被引:3,自引:0,他引:3  
利用溶剂萃取、正相硅胶柱层析及RP -8硅胶柱层析 ,从伞形科柴胡属植物三岛柴胡的种子中分离出三种柴胡皂甙 ,即 :柴胡皂甙c ,柴胡皂甙d ,6″-乙酰基柴胡皂甙d。它们的结构通过IR、UV、MS、1HNMR、13CNMR等现代波谱技术以及与标准样品对照确定。  相似文献   
134.
Four new benzoylamide derivatives, lepidiumamide B–E (1–4), were isolated from the seeds of Lepidium apetalum Willd. The structures were determined by a combination of MS and NMR analyses. All compounds were evaluated for their protective effects against NRK-52e cell injury induced by lipopolysaccharide (LPS) in vitro. These compounds showed significantly protective activity and ameliorated LPS-induced NRK52e cells via the Nrf2/Keap1 pathway. The discovery of these active compounds is important for the prevention and treatment of renalinjury.  相似文献   
135.
The acid composition of seed oil ofAmaranthus cruentus and the synthesis of their glycidyl and pyridinecontaining esters are studied. It is demonstrated that 67% of the total acids are C18-polyunsaturated linoleic and linolenic. A new method for preparing glycidyl esters of C18-unsaturated carboxylic acids is developed by reacting their salts with ECG in an aprotic medium to produce the corresponding glycidyl esters. The reaction of the glycidyl esters and pyridine salts with carboxylic and phosphonic acids produces the propanolpyridine esters of the acids that combine the properties of the acids and pyridinium salts and are promising in the search for biologically active compounds.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Scientific Center, Russian Academy of Sciences. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 217–219, May–June, 2000.  相似文献   
136.
Reddy KH  Prasad NB  Reddy TS 《Talanta》2003,59(3):425-433
The analytical properties of 1-phenyl-1,2-propanedione-2-oxime thiosemi-carbazone (PPDOT) are described for the first time. The reagent gives colour reactions with copper(II) and nickel(II) in sodium acetate-acetic acid buffer medium. The copper complex shows maximum absorbance at 465 nm while the nickel complex at 395 nm. Therefore, these colour reactions have been advantageously used for the simultaneous spectrophotometric determination of copper(II) and nickel(II) in synthetic mixture and also in edible oils and seeds.  相似文献   
137.
The extraction and identification of bioactive compounds from herbs is of great interest. In this study, accelerated solvent extraction (ASE) technique was used to analyze the secondary volatile profiles in Nigella sativa seeds obtained from two different origins, Egypt and Bangladesh. The main extraction parameters, including extraction temperature, pressure and static extraction time, were investigated and optimized. Identification and quantification of the major constituents in nonpolar extracts (hexane) were achieved by means of GC‐FID/GC‐MS analysis with external standards. The two seeds showed a similar variety of chemical composition; however, the secondary volatiles profile of Bangladesh seed was higher than that of the Egyptian seed. A total of 25 compounds were identified from the ASE extract under the following optimum extraction conditions: 100°C, 1500 psi and 5 min, for extraction temperature, pressure and static time, respectively. The proposed technique can be used for the characterization of N. sativa varieties or cultivars. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
138.
The seeds of grapevine (Vitis vinifera) are a byproduct of wine production. To examine the potential value of grape seeds, grape seeds from seven sources were subjected to fingerprinting using direct analysis in real time coupled with time‐of‐flight mass spectrometry combined with chemometrics. Firstly, we listed all reported components (56 components) from grape seeds and calculated the precise m/z values of the deprotonated ions [M–H]. Secondly, the experimental conditions were systematically optimized based on the peak areas of total ion chromatograms of the samples. Thirdly, the seven grape seed samples were examined using the optimized method. Information about 20 grape seed components was utilized to represent characteristic fingerprints. Finally, hierarchical clustering analysis and principal component analysis were performed to analyze the data. Grape seeds from seven different sources were classified into two clusters; hierarchical clustering analysis and principal component analysis yielded similar results. The results of this study lay the foundation for appropriate utilization and exploitation of grape seed samples. Due to the absence of complicated sample preparation methods and chromatographic separation, the method developed in this study represents one of the simplest and least time‐consuming methods for grape seed fingerprinting.  相似文献   
139.
Thiram fungicide contamination in canola seeds, water and soil samples was monitored using headspace solid-phase microextraction (HS-SPME) combined with ion mobility spectrometer (IMS) to assess its environmental relevance. The influence of the various analytical parameters on microextraction procedure including pH, ionic strength, equilibrium time and temperature has been evaluated and optimised. HS-SPME-IMS allowed the determination of thiram in the concentration range of 10–300 ng mL?1 (R2 > 0.99). The detection limit and relative standard deviation were 6 ng mL?1 and 8% for five replicate analyses, respectively. The HS-SPME-IMS method with polypyrrole film doped with dodecylsulfate (PPy-DS) as solid phase provided an effective sample clean-up for the monitoring of thiram in canola and soil samples. The main advantages of this method are sensitive, good repeatability, organic solvent-free, less time-consuming and relatively inexpensive.  相似文献   
140.
Two new glycosides,nor-rubrofusarin-6-O-β-D-(6′-O-acetyl)glucopyranoside(1) and 1-desmethylaurantio-obtusin-2-O-β-D-glucopyranoside (2) were isolated from the seeds of Cassia obtusifolia and their structures were established by chemical and spectral evidences.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号