全文获取类型
收费全文 | 1226篇 |
免费 | 42篇 |
国内免费 | 4篇 |
专业分类
化学 | 895篇 |
晶体学 | 9篇 |
力学 | 40篇 |
数学 | 160篇 |
物理学 | 168篇 |
出版年
2023年 | 12篇 |
2022年 | 37篇 |
2021年 | 54篇 |
2020年 | 21篇 |
2019年 | 26篇 |
2018年 | 17篇 |
2017年 | 14篇 |
2016年 | 45篇 |
2015年 | 25篇 |
2014年 | 48篇 |
2013年 | 85篇 |
2012年 | 69篇 |
2011年 | 105篇 |
2010年 | 50篇 |
2009年 | 40篇 |
2008年 | 79篇 |
2007年 | 80篇 |
2006年 | 67篇 |
2005年 | 74篇 |
2004年 | 73篇 |
2003年 | 40篇 |
2002年 | 35篇 |
2001年 | 10篇 |
2000年 | 15篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1944年 | 1篇 |
1940年 | 1篇 |
排序方式: 共有1272条查询结果,搜索用时 453 毫秒
91.
An eco-friendly tandem tosylation/Ferrier N-glycosylation of amines catalyzed by Er(OTf)3 in 2-MeTHF
Monica Nardi Natividad Herrera Cano Antonio De Nino Maria Luisa Di Gioia Loredana Maiuolo Manuela Oliverio Ana Santiago Diletta Sorrentino Antonio Procopio 《Tetrahedron letters》2017,58(18):1721-1726
Er(OTf)3 in 2-MeTHF provides a new and eco-friendly process for Ferrier glycosylation of sulfonamides and amino acids with various N-nucleophiles.The stereoselective synthesis of 2,3-unsaturated-N-pseudoglycals was carried out with 3,4,6-tri-O-acetyl-d-glucal and different nucleophiles affording good results in a short time. 相似文献
92.
Composition assessment of ferric oxide by accurate peak fitting of the Fe 2p photoemission spectrum
下载免费PDF全文
![点击此处可从《Surface and interface analysis : SIA》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M. Bravo Sanchez J. A. Huerta‐Ruelas D. Cabrera‐German A. Herrera‐Gomez 《Surface and interface analysis : SIA》2017,49(4):253-260
A quantitative study of the surface composition of ferric oxide employing photoemission spectra is presented. It was possible to accurately reproduce the expected composition (Fe2.00±0.05O3) by modeling the background as a combination of Shirley‐type (Shirley–Vegh–Salvi–Castle) and slope backgrounds through the active approach. The line‐shape employed to fit apparent peak asymmetries was the double‐Lorentzian. It was possible to resolve a previously unreported satellite located at ~729 eV. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
93.
Alex Alberto Silva Huerta Flvio Augusto Sanzovo Fiorelli Otvio de Mattos Silvares 《Experimental Thermal and Fluid Science》2007,31(8):957-966
This work presents the results of an experimental study with pure refrigerants R-134a and R-600a and refrigerant–oil mixtures flowing through capillary tubes in order to analyse the metastable flow. A large number of experiments were carried out to verify the influence of several variables on the underpressure of vaporization, mainly the inlet subcooling, internal diameter and inlet pressure. Capillary tubes with internal diameter of 0.69 mm and 0.82 mm were tested for condensation temperatures between 40 °C and 50 °C and subcooling degrees between 3 °C and 12 °C. Measurements for oil concentrations of 1% and 3% were conducted and compared with those for pure refrigerant R-134a. The oil influence on the metastable flow was tested and the effect on the underpressure of vaporization is addressed for lower oil concentrations. 相似文献
94.
The possibility provided by Chemometrics to extract and combine (fusion) information contained in NIR and MIR spectra in order to discriminate monovarietal extra virgin olive oils according to olive cultivar (Casaliva, Leccino, Frantoio) has been investigated.Linear discriminant analysis (LDA) was applied as a classification technique on these multivariate and non-specific spectral data both separately and jointly (NIR and MIR data together).In order to ensure a more appropriate ratio between the number of objects (samples) and number of variables (absorbance at different wavenumbers), LDA was preceded either by feature selection or variable compression. For feature selection, the SELECT algorithm was used while a wavelet transform was applied for data compression.Correct classification rates obtained by cross-validation varied between 60% and 90% depending on the followed procedure. Most accurate results were obtained using the fused NIR and MIR data, with either feature selection or data compression.Chemometrical strategies applied to fused NIR and MIR spectra represent an effective method for classification of extra virgin olive oils on the basis of the olive cultivar. 相似文献
95.
This Article reveals a rare synthesis of pure Pr(2)O(2)CO(3) (POC) nanopowder by thermolysis (700 °C) of a single chemical precursor in an autogenic reaction. The autogenic thermolysis of praseodymium acetate is a solvent-free, efficient, and straightforward approach yielding luminescent POC nanoparticles. The as-prepared POC nanopowder converted to PrO(1.833) (PO) powder via combustion. Methodical morphological, structural, and compositional characterizations of POC and PO powders are carried out, supported by mechanistic elucidation and the photoluminescent properties. 相似文献
96.
Iuliu O. Marian Nicolae Bonciocat Cecilia Cristea Robert Săndulescu Monica Bucşa Mircea Vlassa 《Electroanalysis》2010,22(5):542-548
The electrochemical and spectroelectrochemical behavior of 9‐substituted with ? CN and ? COOH acridine N‐oxides with potential antitumor activity was investigated. In SER spectra of the investigated compounds, the ring stretching vibration at 1568 cm?1 for 9‐CN‐substituted compound respectively 1639 cm?1 for 9‐COOH‐substituted compound was analyzed. Cyclic voltammograms indicates that the reduction potential ?0.766 V for ? CN substituted compound increase towards ?0.745 V for ? COOH substituted compound. The proposed theoretical method in the electrochemical impedance spectroscopy uses a reference redox dielectrode and a multielectrode containing the compound. To account for the change of electrochemical impedance we have considered two theoretical quantities: a pseudocapacitance and a pseudo inductance. Two possible arrangements of them: in series, respective in parallel can be used like criteria of drug classification. 相似文献
97.
The synthesis of two oligomers, of a bifunctional diketopiperazine scaffold DKP-1, formally derived from the cyclization of l-aspartic acid and (S)-2,3-diaminopropionic acid, is reported. A trimeric and a tetrameric structure were prepared by solution-phase peptide synthesis (Boc strategy). Conformational analysis of these derivatives was carried out by a combination of 1H NMR spectroscopy, CD spectroscopy, and molecular modeling, and revealed the formation of β-bend ribbon involving 10-membered H-bonded rings and a reverse turn of the growing peptide chain. 相似文献
98.
Chlorella minutissima—A Promising Fuel Alga for Cultivation in Municipal Wastewaters 总被引:1,自引:0,他引:1
Ashish Bhatnagar Monica Bhatnagar Senthil Chinnasamy K. C. Das 《Applied biochemistry and biotechnology》2010,161(1-8):523-536
It is imperative to slash the cost of algal oil to less than $50 bbl?1 for successful algal biofuel production. Use of municipal wastewater for algal cultivation could obviate the need for freshwater and the nutrients—N and P. It would also add CO2 through bacterial activity. Chlorella minutissima Fott et Nova dominated the entire phycoflora year around and through each stage of the wastewater treatment at the oxidation pond system of Wazirabad (Delhi) in India. The ability to grow so profusely in such varied and contrasting situations made this alga unique. Besides pollution tolerance, it grew heterotrophically in dark under acidic conditions and as a mixotroph in presence of light over a range of organic C substrates. It could utilize both ammoniacal and nitrate nitrogen, survived anaerobicity, 5% NaCl and ?10 bar of osmotic stress. C. minutissima grew at pH 4–11 and raised the pH set initially by 1 to 3 units in 7.5 h. It showed gigantism and largely kept afloat in presence of utilizable organic carbon, while flocculated in mineral medium and on aging. The alga also possessed potential for biofuel production. The studied parameters indicate why C. minutissima was a potential biomass builder in municipal sewage and could be used to determine which other alga(e) may serve the purpose. 相似文献
99.
Jutta Lintelmann Monica Heil França Evelyn Hübner Georg Matuschek 《Journal of chromatography. A》2010,1217(10):1636-1646
The development, optimization and validation of a liquid chromatography–atmospheric pressure photoionization tandem mass spectrometric (LC–APPI/MS/MS) method for the determination of 15 azaarenes (4-azafluorene, benzo[h] and -[f]quinoline, phenanthridine, acridine, 1-azafluoranthene, 4-azapyrene, benz[a]- and -[c]acridine, -10-azabenzo[a]pyrene, 7,9- and 7,10-dimethylbenz[c]acridine, dibenz[a,j]-, -[c,h] and [a,i]acridine) in airborne particulate matter is described. Each compound was detected and quantified operating in multiple reaction monitoring mode. Extraction of azaarenes was achieved using accelerated solvent extraction (ASE) with dichlormethane/methanol (50/50, v/v). After extraction, no additional clean-up procedure like solid phase or liquid/liquid extraction was necessary. Limits of quantification (S/N × 10) ranged from 0.2 pg/μl to 1.4 pg/μl, matrix dependent recoveries were between 57% and 94%, with relative standard deviations from 8% to 17%. Applicability of the method was demonstrated analyzing 10 samples of particulate matter (PM2.5) collected in winter 2008. In all samples dimethylbenz[c]acridines as well as dibenzacridines were below the limit of quantification, concentration of the remaining analytes were in the range from 0.002 ng/m3 to 0.356 ng/m3. 相似文献
100.