全文获取类型
收费全文 | 503篇 |
免费 | 16篇 |
国内免费 | 3篇 |
专业分类
化学 | 347篇 |
晶体学 | 1篇 |
力学 | 6篇 |
数学 | 65篇 |
物理学 | 103篇 |
出版年
2023年 | 3篇 |
2022年 | 9篇 |
2021年 | 21篇 |
2020年 | 10篇 |
2019年 | 12篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 18篇 |
2015年 | 17篇 |
2014年 | 20篇 |
2013年 | 21篇 |
2012年 | 19篇 |
2011年 | 36篇 |
2010年 | 41篇 |
2009年 | 20篇 |
2008年 | 29篇 |
2007年 | 28篇 |
2006年 | 32篇 |
2005年 | 23篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 14篇 |
2001年 | 7篇 |
2000年 | 11篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1968年 | 1篇 |
1910年 | 1篇 |
排序方式: 共有522条查询结果,搜索用时 449 毫秒
131.
Gomes Antonio Taylon Aguiar Pereira Rayanne Rocha Duarte Junior Anivaldo Pereira da Cruz Rodrigues Antonio Manoel Remédios Claudio Marcio Rocha Brasil Davi do Socorro Barros Morais Luiz Roberto Barbosa Silva-Júnior José Otávio Carréra Ribeiro-Costa Roseane Maria 《Journal of Thermal Analysis and Calorimetry》2022,147(1):355-365
Journal of Thermal Analysis and Calorimetry - Native Amazon palm trees have been target of research and product development especially because of their oil and fat. Tucumã-do-Pará... 相似文献
132.
The results of the Young experiment can be analyzed either by classical or Quantum Physics. The later one though leads to a more complete interpretation, based on two different patterns that appear when one works either with single or double slits. Here we show that the two patterns can be derived from a single principle, in the context of General Relativity, if one assumes an additional spatial dimension to the four known today. The found equations yield the same results as those in Quantum Mechanics. 相似文献
133.
Lívia Barros Salum Napoleão Fonseca Valadares 《Journal of computer-aided molecular design》2010,24(10):803-817
Alzheimer’s disease is an ultimately fatal neurodegenerative disease, and BACE-1 has become an attractive validated target
for its therapy, with more than a hundred crystal structures deposited in the PDB. In the present study, we present a new
methodology that integrates ligand-based methods with structural information derived from the receptor. 128 BACE-1 inhibitors
recently disclosed by GlaxoSmithKline R&D were selected specifically because the crystal structures of 9 of these compounds
complexed to BACE-1, as well as five closely related analogs, have been made available. A new fragment-guided approach was
designed to incorporate this wealth of structural information into a CoMFA study, and the methodology was systematically compared
to other popular approaches, such as docking, for generating a molecular alignment. The influence of the partial charges calculation
method was also analyzed. Several consistent and predictive models are reported, including one with r
2 = 0.88, q
2 = 0.69 and r
pred2 = 0.72. The models obtained with the new methodology performed consistently better than those obtained by other methodologies,
particularly in terms of external predictive power. The visual analyses of the contour maps in the context of the enzyme drew
attention to a number of possible opportunities for the development of analogs with improved potency. These results suggest
that 3D-QSAR studies may benefit from the additional structural information added by the presented methodology. 相似文献
134.
J. Salgado J. Proupín M. Villanueva J. A. Rodríguez-Añón N. Barros 《Journal of Thermal Analysis and Calorimetry》2010,99(3):911-916
Differential scanning calorimetry was applied to assess on seasonally soil organic matter changes. Soils were collected in
two sites located in Viveiro (Galicia, Spain). One of them has been used as arable land and the other one was under pinewood.
Soil samples were seasonally collected during a year. The heat of combustion and the ignition temperature of the soil organic
matter were calculated by analyzing the thermograms obtained by differential scanning calorimetry. The shape and the maximum
and end temperatures of the two exothermic peaks observed in the thermograms, yielded information about the relations between
the labile and recalcitrant pools, and hence information about carbon stabilization degree in both soils. 相似文献
135.
Synthesis and structure elucidation of five series of aminoflavones using 1D and 2D NMR spectroscopy
Twenty-six new aminoflavones have been synthesised by two different methods and the structure elucidation was accomplished using extensive 1D (1H, 13C) and 2D NMR spectroscopic studies (COSY, HSQC and HMBC experiments). 相似文献
136.
Interlaboratory studies are decisive tools to help the validation of a specific analytical methodology or to assess the reproducibility of the use of different methods to analyze a given compound or compounds in certain sample matrices. In this work, homogeneous samples of two white wines (“White Wine” and “White Liqueur Wine”) and one red wine (“Red Fortified Wine”) from Portugal with different production techniques and characteristics, namely in alcohol strength (10.5%, 16.0% and 19.0% ethanolic content, respectively), were analyzed for their contents in ochratoxin A (OTA), a mycotoxin generated from fungal contamination. White Liqueur Wine was naturally contaminated, whereas the other two wine type were spiked with ethanolic OTA solutions. The participation of 24 laboratories from 17 countries of five continents was ensured for this study. Although with no restrictions in terms of analytical methodology to employ, 75% of the laboratories resorted to immunoaffinity columns clean-up followed by high performance liquid chromatography with fluorescence detection (HPLC-FD), most of them in accordance with the European Standard EN 14133. For White Wine samples, the general mean OTA concentration was 1.96 μg/l (two outliers) with interlaboratorial standard deviation (sL) of 0.53 μg/l; for White Liqueur Wine, mean of 1.59 μg/l (one outlier), with sL = 0.59 μg/l; and for Red Fortified Wine, mean of 2.73 μg/l (no outliers), with sL = 0.96 μg/l. Outliers were determined by Cochran and Grubbs tests. The Horrat index, recommended by the Association of Official Analytical Chemists (AOAC) for the quality assurance of the collaborative study was, on average, 1.7. This study proved that OTA determination in wines is reproducible, regardless of the methodology employed. 相似文献
137.
Soares do Rêgo Barros O Nogueira CW Stangherlin EC Menezes PH Zeni G 《The Journal of organic chemistry》2006,71(4):1552-1557
We present here carbon-nitrogen bond formation via a coupling reaction of 2-iodo-selenophene catalyzed by Cu(I) in the presence of a base and an inexpensive ligand, and establish the first route to obtaining 2-nitrogen-selenophene derivatives in good yields. We can anticipate that this reaction works well with oxazolidinones, lactams, and aliphatic and aromatic amides, as nitrogen sources, in the absence of any supplementary additives. In addition, the reaction proceeded cleanly under mild reaction conditions and was sensitive to the ratio of amide/2-iodo-selenophene, as well as the nature of the ligand, base, and solvent. 相似文献
138.
The organic acids present in beer provide important information on the product's quality and history, determining organoleptic properties and being useful indicators of fermentation performance. NMR spectroscopy may be used for rapid quantification of organic acids in beer and different NMR-based methodologies are hereby compared for the six main acids found in beer (acetic, citric, lactic, malic, pyruvic and succinic). The use of partial least squares (PLS) regression enables faster quantification, compared to traditional integration methods, and the performance of PLS models built using different reference methods (capillary electrophoresis (CE), both with direct and indirect UV detection, and enzymatic essays) was investigated. The best multivariate models were obtained using CE/indirect detection and enzymatic essays as reference and their response was compared with NMR integration, either using an internal reference or an electrical reference signal (Electronic REference To access In vivo Concentrations, ERETIC). NMR integration results generally agree with those obtained by PLS, with some overestimation for malic and pyruvic acids, probably due to peak overlap and subsequent integral errors, and an apparent relative underestimation for citric acid. Overall, these results make the PLS-NMR method an interesting choice for organic acid quantification in beer. 相似文献
139.
Alexandre Monteiro Pacheco Diego Romão Gondim Luciana Rocha Barros Gonçalves 《Applied biochemistry and biotechnology》2010,161(1-8):209-217
In this work, cashew apple bagasse (CAB) was used for Saccharomyces cerevisiae immobilization. The support was prepared through a treatment with a solution of 3% HCl, and delignification with 2% NaOH was also conducted. Optical micrographs showed that high populations of yeast cells adhered to pre-treated CAB surface. Ten consecutive fermentations of cashew apple juice for ethanol production were carried out using immobilized yeasts. High ethanol productivity was observed from the third fermentation assay until the tenth fermentation. Ethanol concentrations (about 19.82–37.83 g L?1 in average value) and ethanol productivities (about 3.30–6.31 g L?1 h?1) were high and stable, and residual sugar concentrations were low in almost all fermentations (around 3.00 g L?1) with conversions ranging from 44.80% to 96.50%, showing efficiency (85.30–98.52%) and operational stability of the biocatalyst for ethanol fermentation. Results showed that cashew apple bagasse is an efficient support for cell immobilization aiming at ethanol production. 相似文献
140.
Batchelor-McAuley C Gonçalves LM Xiong L Barros AA Compton RG 《Chemical communications (Cambridge, England)》2010,46(47):9037-9039
Graphite is a highly versatile electrode substrate material but the recorded voltammetric response is regularly complicated by varying degrees of adsorption of the analyte to the surface leading to voltammetry which is complex to analyse. We report how through the pre-adsorption of acetone the electro-activity of the substrate is unhindered but adsorption of an electro-active species is effectively blocked, hence the experimentalist is able to readily tailor the electrode so as to effectively switch the adsorption of the analyte 'on' or 'off'. 相似文献