全文获取类型
收费全文 | 139篇 |
免费 | 6篇 |
专业分类
化学 | 118篇 |
数学 | 13篇 |
物理学 | 14篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 7篇 |
2014年 | 5篇 |
2013年 | 6篇 |
2012年 | 13篇 |
2011年 | 10篇 |
2010年 | 5篇 |
2009年 | 11篇 |
2008年 | 12篇 |
2007年 | 11篇 |
2006年 | 7篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 1篇 |
2000年 | 3篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1978年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有145条查询结果,搜索用时 15 毫秒
81.
María Victoria de Gálvez José Aguilera Jean‐Luc Bernabó Cristina Sánchez‐Roldán Enrique Herrera‐Ceballos 《Photochemistry and photobiology》2015,91(4):966-970
The rising incidence of skin cancers attributable to excessive sun exposure has become a major health concern worldwide. While numerous studies have analyzed the sun protective effect of sunscreens, clothing and antioxidants, none to date have measured the photoprotective effect of hair, despite clinical evidence that individuals with balding or thinning hair are at greater risk of skin lesions that can progress to cancer, hence the recommendation to use hats or umbrellas. We analyzed the level of protection offered by hair according to hair density, thickness and color using the spectral transmittance and corrected for relative erythema effectiveness. Our results show that hair provides a barrier against both UVB and UVA radiation which is significantly increased with respect to the hair density, thickness and the presence of melanins. This is the first study to quantify sun protection factor offered by hair, namely hair ultraviolet protection factor (HUPF). We believe that hair should be recognized as an important natural sun barrier in the prevention of UV‐induced skin cancers. 相似文献
82.
Hollow‐fiber solvent bar microextraction with gas chromatography and electron capture detection determination of disinfection byproducts in water samples
下载免费PDF全文
![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Liliana Correa Jhon Alex Fiscal Sandra Ceballos Alberto de la Ossa Gonzalo Taborda Cristina Nerin Milton Rosero‐Moreano 《Journal of separation science》2015,38(22):3945-3953
A liquid‐phase microextraction method that uses a hollow‐fiber solvent bar microextraction technique was developed by combining gas chromatography with electron capture detection for the analysis of four trihalomethanes (chloroform, dichlorobromomethane, chlorodibromomethane, and bromoform) in drinking water. In the microextraction process, 1‐octanol was used as the solvent. The technique operates in a two‐phase mode with a 5 min extraction time, a 700 rpm stirring speed, a 30°C extraction temperature, and NaCl concentration of 20%. After microextraction, one edge of the membrane was cut, and 1 μL of solvent was collected from the membrane using a 10 μL syringe. The solvent sample was directly injected into the gas chromatograph. The analytical characteristics of the developed method were as follows: detection limits, 0.017–0.037 ng mL−1; linear working range, 10–900 ng mL−1; recovery, 74 ± 9–91 ± 2; relative standard deviation, 5.7–10.3; and enrichment factor, 330–455. A simple, fast, economic, selective, and efficient method with big possibilities for automation was developed with a potential use to apply with other matrices and analytes. 相似文献
83.
Di Chenna PH Veleiro AS Sonego JM Ceballos NR Garland MT Baggio RF Burton G 《Organic & biomolecular chemistry》2007,5(15):2453-2457
A procedure for the synthesis of 6,19-cyclopregnanes is described involving an intramolecular alkylation reaction of Delta(4)-3-keto steroids with a 19-mesylate in the presence of KOH in isopropanol. Three 6,19-cyclopregnanes were prepared (4, 5 ,9); in the rat, 6,19-cycloprogesterone (4) and its 21-hydroxy derivative 5 displaced [3H]-dexamethasone from glucocorticoid receptors, the former compound being more active. Both compounds did not compete with [3H]-aldosterone for kidney mineralocorticoid receptors nor with [3H]-R5020 for uterus progesterone receptors. 相似文献
84.
García Ruano JL Alemán J Alonso I Parra A Marcos V Aguirre J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(21):6179-6195
N-Arylarylideneamines react with sulfinylbenzyl carbanions derived from 2-(p-tolylsulfinyl)toluenes (S)-1 and (S)-2, affording epimeric mixtures at C1 of 1,2-diarylethyl- and 1,2-diarylpropylamine derivatives. The sulfinyl group completely controls the configuration at C2 in the reactions of (S)-2. The configuration at C1 depends on the electron density of the ring adjacent to the iminic carbon atom which is modulated by pi-pi stacking interactions with the ring joined to the carbanionic centre. The stereoselectivity was controlled by modifying the acceptor character of the arylideneamine ring with appropriate substituents, the formation of the highly selective (R) configuration at C1 being made possible by electron-donating groups. N-(2,4,6-Trimethoxyphenyl)arylideneamines have been shown to be suitable starting materials for the preparation of (R)-1,2-diarylethyl- and (1R,2S)-1,2-diarylpropylamines (syn epimers) in a highly stereoselective manner. 相似文献
85.
Vanesa Bedoya-Betancur Elizabeth Correa Juan Pablo Rendn Andrs F. Yepes-Prez Wilson Cardona-Galeano Tonny W. Naranjo 《Molecules (Basel, Switzerland)》2022,27(20)
Seven styrylquinolines were synthesized in this study. Two of these styrylquinolines are new and were elucidated by spectroscopic analysis. The chemopreventive potential of these compounds was evaluated against SW480 human colon adenocarcinoma cells, its metastatic derivative SW620, and normal cells (HaCaT). According to the results, compounds 3a and 3d showed antiproliferative activity in SW480 and SW620 cells, but their effect seemed to be caused by different mechanisms of action. Compound 3a induced apoptosis independent of ROS production, as evidenced by increased levels of caspase 3, and had an immunomodulatory effect, positively regulating the production of different immunological markers in malignant cell lines. In contrast, compound 3d generated a pro-oxidant response and inhibited the growth of cancer cells, probably by another type of cell death other than apoptosis. Molecular docking studies indicated that the most active compound, 3a, could efficiently bind to the proapoptotic human caspases-3 protein, a result that could provide valuable information on the biochemical mechanism for the in vitro cytotoxic response of this compound in SW620 colon carcinoma cell lines. The obtained results suggest that these compounds have chemopreventive potential against CRC, but more studies should be carried out to elucidate the molecular mechanisms of action of each of them in depth. 相似文献
86.
Dr. Romain Tessier Prof. Dr. Raj Kumar Nandi Brendan G. Dwyer Dr. Daniel Abegg Charlotte Sornay Dr. Javier Ceballos Stéphane Erb Dr. Sarah Cianférani Dr. Alain Wagner Dr. Guilhem Chaubet Prof. Dr. Alexander Adibekian Prof. Dr. Jerome Waser 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(27)
87.
Vallejos Mara Evangelina Olmos Graciela Viviana Taleb Mara Claudia Felissia Fernando Esteban Ehman Nanci Vanesa Peresin Maria Soledad Area Mara Cristina Maximino Mirtha Graciela 《Cellulose (London, England)》2022,29(8):4645-4659
Cellulose - This study assesses the possibility of obtaining regenerated cellulose products (beads and films) from eucalyptus sawdust dissolving pulps produced by non-conventional processes,... 相似文献
88.
Javier Galbán Vanesa Sanz Susana de Marcos 《Analytical and bioanalytical chemistry》2010,398(5):2117-2124
Peracetic acid (PAA) is selectively determined in the presence of hydrogen peroxide (H2O2) by using the self-indicating UV–Vis molecular absorption properties of catalase. The PAA reacts with the protein giving
an intermediate (Cat-I) which is reduced back by the aminoacid core surrounding the hemegroup. Since the original form of
the enzyme and the Cat-I have different UV–Vis absorption properties, the absorbance changes can be used for PAA determination.
The H2O2/catalase reaction is extremely fast so that neither Cat-I compound nor kinetic interferences are observed. The method permits
PAA determination in the 5 × 10−7 to 1.5 × 10−5 M range, the reproducibility being between 1% and 10%. Using this method, PAA has been successfully determined in water samples
treated with commercial PAA/H2O2 biocides. A theoretical study has also been carried out for obtaining a mathematical model able to analytically describe
the process. 相似文献
89.
A number of studies published in the scientific literature have shown the relationship between sun exposure and nonmelanoma skin cancer (NMSC) and vitamin D synthesis. However, the paucity of medical data, particularly in developing countries, hampers a global assessment of the impact of sun exposure on NMSC and vitamin D. To improve knowledge on this subject, this paper presents UV index (UVI) measurements performed in São Paulo City (SPC) in the period 2005–2008. It was found that 65% of the UVI measured 2 h around local noon during the summer show very high (8 < UVI < 10) and extreme (UVI > 11) levels according to the World Health Organization (WHO) classification. During the winter, 40% of the measurements around noontime show high or very high levels. In spite of worrisome recent statistics from SPC, showing that NMSCs make up about 28% of over a million of new cases of cancer in 2008, sun protection is not considered a real problem in these urban areas. UV measurements also show that every month of the year UV levels are high enough to ensure vitamin D production in human skin from incidental sun exposure. 相似文献
90.