全文获取类型
收费全文 | 670篇 |
免费 | 25篇 |
国内免费 | 2篇 |
专业分类
化学 | 554篇 |
晶体学 | 5篇 |
力学 | 10篇 |
数学 | 76篇 |
物理学 | 52篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 32篇 |
2021年 | 45篇 |
2020年 | 23篇 |
2019年 | 24篇 |
2018年 | 19篇 |
2017年 | 22篇 |
2016年 | 29篇 |
2015年 | 33篇 |
2014年 | 25篇 |
2013年 | 48篇 |
2012年 | 45篇 |
2011年 | 61篇 |
2010年 | 25篇 |
2009年 | 31篇 |
2008年 | 30篇 |
2007年 | 37篇 |
2006年 | 26篇 |
2005年 | 28篇 |
2004年 | 25篇 |
2003年 | 19篇 |
2002年 | 17篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1969年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有697条查询结果,搜索用时 0 毫秒
11.
Determination of valproic acid in the drug was carried out on the aluminum silica gel 60F254 plates and using acetone–water–chloroform–ethanol–ammonia at a volume ratio of 30:1:8:5:11 as the mobile phase, respectively. Two methods of detection of valproic acid were used. The first was a 2% aqueous CuSO4×5H2O solution, and the second was a 2′,7′-dichlorofluorescein-aluminum chloride-iron (III) chloride system. The applied TLC-densitometric method is selective, linear, accurate, precise, and robust, regardless of the visualizing reagent used for the determination of valproic acid in Convulex capsules. It has low limits of detection (LOD) and limits of quantification (LOQ), which are equal to 5.8 μg/spot and 17.4 μg/spot using a 2% aqueous CuSO4×5H2O solution as visualizing agent and also 0.32 μg/spot and 0.97 μg/spot using a 2′,7′-dichlorofluorescein-aluminum chloride-iron (III) chloride system as visualizing reagent, respectively. The described analytical method can additionally be used to study the identity of valproic acid in a pharmaceutical preparation. The linearity range was found to be 20.00–80.00 μg/spot and 1.00–2.00 μg/spot for valproic acid detected on chromatographic plates using a 2% aqueous CuSO4×5H2O solution and the 2′,7′-dichlorofluorescein-aluminum chloride-iron (III) chloride system, respectively. A coefficient of variation that was less than 3% confirms the satisfactory accuracy and precision of the proposed method. The results of the assay of valproic acid equal 96.2% and 97.0% in relation to the label claim that valproic acid fulfill pharmacopoeial requirements. The developed TLC-densitometric method can be suitable for the routine analysis of valproic acid in pharmaceutical formulations. The proposed TLC-densitometry may be an alternative method to the modern high-performance liquid chromatography and square wave voltammetry in the control of above-mentioned substances, and it can be applied when other analytical techniques is not affordable in the laboratory. 相似文献
12.
13.
Aleksandra Stegliska Anastasiia Bekhter Pawe Wawrzyniak Alina Kunicka-Styczyska Konrad Jastrzbek Micha Fidler Krzysztof
migielski Beata Gutarowska 《Molecules (Basel, Switzerland)》2022,27(5)
The purpose of the study was to select an environmentally friendly plant biopesticide to protect seed potatoes against phytopathogens. The scope included the evaluation of the antimicrobial activities of 22 plant water extracts, 22 water-glycol extracts, and 3 subcritical carbon dioxide extracts using the agar diffusion method against 10 potato phytopathogens. For the most effective extracts, minimal inhibitory concentration (MIC), chemical composition analysis by gas chromatography–mass spectrometry and in situ assays on seed potatoes were performed. Garlic water extract was finally selected as the most effective in phytopathogen growth inhibition, both in vitro and in situ, with MIC values ranging between 6.3–25 mg/mL. 5-Hydroxymethylfurfural was determined to be the main component of this extract (33.24%). Garlic water extract was proposed as a potential biopesticide against potato phytopathogens. 相似文献
14.
Two-component laminates made of conductors distributed non-periodically as laminas along one direction are considered in this note. The macroscopic properties of these laminates are described by continuous slowly-varying functions across laminas. In order to analyse heat conduction, the approach, called the tolerance modelling, is used. The aim of this note is to use averaged equations of the tolerance model for transversally graded laminates to analyse stationary heat conduction across laminas. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
15.
Jan Eric Neuburger Alina Gazizova Sven Tiedemann Prof. Dr. Jan von Langermann 《European journal of organic chemistry》2023,26(34):e202201471
This study highlights the straight-forward synthesis of substituted 1,2-amino alcohols from simple and readily available aromatic methyl ketones. Starting from acetophenone derivatives, the straight-forward synthesis strategy involved an initial bromination of the alpha-positioned methyl group in the first step, followed by a simple hydrolysis to the hydroxyketone (2-hydroxyacetophenone). The hydroxylated intermediate was subsequently converted from Silicibacter pomeroyi to the final 1,2-amino alcohol by using the transaminase. The transaminase-catalyzed reaction proceeded with yields up to 62 % and always excellent enantiomeric excess of >99 %. Interestingly, the keto-enol-tautomerism of the hydroxyl ketone yields an unexpected amino alcohol isomer. 相似文献
16.
Gisle Atsang Kiki Raluca Maria Pop Octavia Sabin Ioana Corina Bocsan Veronica Sanda Chedea Sonia Ancua Socaci Alina Elena Prvu Egre Finsia Takvou Francis Zramah Mathieu Anca Dana Buzoianu 《Molecules (Basel, Switzerland)》2022,27(17)
Dichrostachys cinerea (L.) Wigth & Arn. (DC) is widely used in traditional medicine against several inflammatory diseases, especially rheumatoid arthritis, because of its antioxidant and anti-inflammatory effects. This study aimed to characterize the polyphenol-rich DC fruit extracts and investigate the analgesic, anti-inflammatory, and antioxidant effects in a rat inflammation model induced by complete Freund’s adjuvant (CFA). Water and ethanolic extracts were characterized using liquid chromatography coupled with mass spectrometry (LC-MS), Fourier-transform infrared (FTIR) spectroscopy, and gas chromatography coupled with mass spectrometry (GC-MS). The polyphenol-rich extracts were administered in three different concentrations for 30 days. Pain threshold, thermal hyperalgesia, edema, and serum biomarkers specific to inflammatory processes or oxidative stress were evaluated. Both extracts were rich in polyphenolic compounds, mainly flavan-3-ols, proanthocyanidins, and flavone glycosides, which had important in vitro antioxidant capacity. DC fruit extracts administration had the maximum antinociceptive and anti-inflammatory effects after one day since the CFA injection and showed promising results for long-term use as well. The measurement of pro-inflammatory cytokines, cortisol, and oxidative stress parameters showed that DC extracts significantly reduced these parameters, being dose and extract-type dependent. These results showed potential anti-inflammatory, analgesic, and antioxidative properties and revealed the necessity of using a standardized polyphenolic DC extract to avoid result variability. 相似文献
17.
Dumitru Condrat Cristina Mosoarca Alina D. Zamfir Florin Cri?an Maria R. Szabo Alfa X. Lupea 《Central European Journal of Chemistry》2010,8(3):530-535
This study presents the results obtained from qualitative and quantitative analysis of gallic acid from hydro-alcoholic extracts
(methanol, ethanol) of plants from Plantae regnum. Plant qualitative analysis was performed using a novel mass spectrometric (MS) method based on fully automated chip-nanoelectrospray
ionization (nanoESI) high capacity ion trap (HCT) while quantitative analysis was carried out by high performance liquid chromatography
(HPLC). These methods were applied to Alchemilla vulgaris — common lady’s-mantle (aerial part), Allium ursinum — bear’s garlic (leaves), Acorus calamus — common sweet flag (roots), Solidago virga-aurea — goldenrod (aerial part). Obtained results indicated that methanol extracts (96%, 80%) have a gallic acid content ranging
between 0.0011–0.0576 mg mL−1 extract while the ethanol extracts (96%, 60%) exhibit a gallic acid concentration that varies between 0.0010–0.0182 mg mL−1 extract.
相似文献
18.
Cover Picture: Densely Packed Hydrophobic Clustering: Encapsulated Valerates Form a High‐Temperature‐Stable {Mo132} Capsule System (Angew. Chem. Int. Ed. 23/2016) 下载免费PDF全文
19.
JPC – Journal of Planar Chromatography – Modern TLC - Fatty acids from pentanoic to tricosanoic have been separated on RP-18 HPTLC plates, with and without concentrating zone, with... 相似文献
20.
Optimized conditions for copper-catalyzed N-arylation of methyl pyroglutamate are described. These studies permitted the synthesis of methyl N-naphthylpyroglutamate, which was then cyclized to a ketone. The known dehydration of amidoketones by PPA was extended to this new scaffold to lead to a novel condensed benzo[de]quinoline with potential antioxidative activity. 相似文献