全文获取类型
收费全文 | 94篇 |
免费 | 3篇 |
专业分类
化学 | 86篇 |
数学 | 2篇 |
物理学 | 9篇 |
出版年
2024年 | 1篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2016年 | 1篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 9篇 |
2012年 | 3篇 |
2011年 | 6篇 |
2010年 | 4篇 |
2009年 | 3篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 2篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1997年 | 2篇 |
1994年 | 3篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有97条查询结果,搜索用时 95 毫秒
1.
The self-organizing map (a neural network) was applied to the spectral pattern recognition of voice quality in 34 subjects: 15 patients operated on because of insufficient glottal closure and 19 subjects not treated for voice disorders. The voice samples, segments of sustained /a/, were perceptually rated by six experts. A self-organized acoustic feature map was first computed from tokens of /a/ and then used for the analysis of the samples. The locations of the samples on the map were determined and the distances from a normal reference were compared with the perceptual ratings. The map locations corresponded to the degree of audible disorder: the samples judged as normal were overlapping or close to the normal reference, whereas the samples judged as dysphonie were located further away from it. The comparison of pre- and postoperative samples of the patients showed that the perceived improvement of voice quality was also detected by the map. 相似文献
2.
Roser Cervellera Xavier Ramis Josep Maria Salla Ana Mantecn Angels Serra 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):2873-2882
N,N‐Dimethylaminopyridine (DMAP) was used as initiator to cure mixtures of diglycidylether of bisphenol A (DGEBA) and 1,3‐dioxan‐2‐one (TMC) or 5,5‐dimethyl‐1,3‐dioxan‐2‐one (DMTMC). The curing was studied by differential scanning calorimetry (DSC) and Fourier transform infrared in the attenuated‐total‐reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and to quantify the evolution of the groups involved in the curing. We observed the formation of five‐membered cyclic carbonates and anionic carbonate groups that remain unreacted at the chain ends. The formation of these groups was explained by the attack of the anionic propagation species on the methylene carbon of the carbonate group, which leads to an alkyl‐oxygen rupture. By performing the cure in the thermobalance we could evaluate the loss of CO2 produced in the samples containing carbonates. The kinetics were studied by DSC and analyzed with isoconversional procedures. The addition of carbonates slows down the curing rate. Thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA) experiments were used to evaluate the properties of the materials obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2873–2882, 2006 相似文献
3.
The importance of natural antioxidants principally relates to their health-promoting properties. The discovery of new sources of established compounds or more potent compounds is a costly exercise and any technique capable of aiding this procedure would be highly significant. An approach combining chromatographic separation, component analysis and post-column identification of free radical scavenging has been reported. However, its effectiveness is dependent upon various factors and the number of samples analyzed without operator intervention is restricted. A more applicable technique using a 10% to 100% methanol with 2% acetic acid mobile phase and a citric acid-sodium citrate buffered methanolic 1,1-diphenyl-2-picrylhydrazyl free radical reagent is presented, whereby free radical scavengers can be detected within crude extracts of variable polarity without special considerations. As an illustration, acetone, 70% (aq.) methanol and acetonitrile-soluble extracts were prepared from sage (Salvia officinalis L.) for extraction of polar and non-polar radical scavengers and analyzed. Radical scavenging components were identified as carnosic, caffeic and rosmarinic acids and luteolin-7-O-glycoside. Others radical scavengers were tentatively identified as benzoic and hydroxycinnamic acid derivatives, flavonoids and diterpenoids. Through the application of this technique, carnosic acid and rosmarinic acid were identified as the principal free radical scavengers. 相似文献
4.
Near infrared reflectance spectroscopy for the fast identification of PVC-based films 总被引:2,自引:0,他引:2
Laasonen M Rantanen J Harmia-Pulkkinen T Michiels E Hiltunen R Räsänen M Vuorela H 《The Analyst》2001,126(7):1122-1128
Near infrared (NIR) reflectance spectroscopy was used to develop a non-destructive and rapid qualitative method for the analysis of plastic films used by the pharmaceutical industry for blistering. Three types of films were investigated: 250 microm PVC [poly(vinyl chloride)] films, 250 microm PVC films coated with 40 g m(-2) of PVDC [poly(vinylidene dichloride)] and 250 microm PVC films coated with 5 g m(-2) of TE (Thermoelast) and 90 g m(-2) of PVDC. Three analyses were carried out using different pre-treatment options and a PLS (partial least squares) algorithm. Each analysis was aimed at identifying one type of film and rejecting all types of false sample (different thickness, colour or layer). True and false samples from four plastics manufacturers were included in the calibration sets in order to obtain robust methods that were suitable regardless of the supplier. Specificity was demonstrated by testing validation sets against the methods. The tests showed 0% of type I (false negative identification) and 1% of type II errors (false positive identification) for the PVC method, 13 and 3%, respectively, for the PVC-PVDC method and no error for the PVC-TE-PVDC method. Type II errors, mostly due to the slight sensitivity of the methods to film thickness, are easily corrected by simple thickness measurements. This study demonstrates that NIR spectroscopy is an excellent tool for the identification of PVC-based films. The three methods can be used by the pharmaceutical industry or plastics manufacturers for the quality control of films used in blister packaging. 相似文献
5.
A One‐Pot Synthesis of N‐Aryl‐2‐Oxazolidinones and Cyclic Urethanes by the Lewis Base Catalyzed Fixation of Carbon Dioxide into Anilines and Bromoalkanes
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Teemu Niemi Dr. Jesus E. Perea‐Buceta Dr. Israel Fernández Otto‐Matti Hiltunen Vili Salo Sari Rautiainen Dr. Minna T. Räisänen Prof. Timo Repo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10355-10359
The multicomponent assembly of pharmaceutically relevant N‐aryl‐oxazolidinones through the direct insertion of carbon dioxide into readily available anilines and dibromoalkanes is described. The addition of catalytic amounts of an organosuperbase such as Barton's base enables this transformation to proceed with high yields and exquisite substrate functional‐group tolerance under ambient CO2 pressure and mild temperature. This report also provides the first proof‐of‐principle for the single‐operation synthesis of elusive seven‐membered ring cyclic urethanes. 相似文献
6.
Mingyue Zhou Yan Chen Manohar Salla Hang Zhang Xun Wang Srinivasa Reddy Mothe Qing Wang 《Angewandte Chemie (International ed. in English)》2020,59(34):14286-14291
Aqueous organic redox flow batteries (AORFBs) have received considerable attention for large‐scale energy storage. Quinone derivatives, such as 9,10‐anthraquinone‐2,7‐disulphonic acid (2,7‐AQDS), have been explored intensively owing to potentially low cost and swift reaction kinetics. However, the low solubility in pH‐neutral electrolytes restricts their application to corrosive acidic or caustic systems. Herein, the single molecule redox‐targeting reactions of 2,7‐AQDS anolyte are presented to circumvent its solubility limit in pH‐neutral electrolytes. Polyimide was employed as a low‐cost high‐capacity solid material to boost the capacity of 2,7‐AQDS electrolyte to 97 Ah L?1. Through in situ FTIR spectroscopy, a hydrogen‐bonding mediated reaction mechanism was disclosed. In conjunction with NaI as catholyte and nickel hexacyanoferrate as the catholyte capacity booster, a single‐molecule redox‐targeting reaction‐based full cell with energy density up to 39 Wh L?1 was demonstrated. 相似文献
7.
Han Ding Hongwei Li Pengchang Liu J. Kalervo Hiltunen Yuqing Wu Zhijun Chen Jiacong Shen 《Mikrochimica acta》2014,181(9-10):1029-1034
Fluorescent gold nanoclusters (AuNCs) were synthesized using a drug target bacterial enoyl-ACP reductase (FabI) as a template. The physical and chemical properties of the AuNCs were studied by UV-vis absorption, fluorescence, X-ray photoelectron spectroscopy and TEM. The AuNCs-FabI conjugate was prepared by in situ reduction of tetrachloroaurate in the presence of FabI. The conjugated particles were loaded onto nylon membranes by taking advantage of the electrostatic interaction between the negatively charged AuNCs@FabI and the nylon film which is positively charged at pH 7.4. This results in the formation of a test stripe with sensor spots that can be used to detect Hg(II) ion in the 1 nM to 10 μM concentration range. The test stripes are simple, convenient, selective, sensitive, and can be quickly read out with bare eyes after illumination with a UV lamp. Figure
Fluorescent gold nanoclusters (AuNCs) were synthesized using a drug target bacterial enoyl-ACP reductase (FabI) as a template. The synthesized AuNCs@FabI were loaded onto nylon membranes forming a paper-based sensor that can be used to detect Hg(II) ion in the 1 nM to 10 μM concentration range. The test stripes are simple, convenient, selective, sensitive, and can be quickly read out with bare eyes after illumination with a UV lamp. 相似文献
8.
Tremoy G Vimeux F Cattani O Mayaki S Souley I Favreau G 《Rapid communications in mass spectrometry : RCM》2011,25(23):3469-3480
The new infrared laser spectroscopic techniques enable us to measure the isotopic composition (δ(18)O and δ(2)H) of atmospheric water vapor. With the objective of monitoring the isotopic composition of tropical water vapor (West Africa, South America), and to discuss deuterium excess variability (d=δ(2)H - 8δ(18)O) with an accuracy similar to measurements arising from isotope-ratio mass spectrometry (IRMS), we have conducted a number of tests and calibrations using a wavelength-scanned cavity ring-down spectroscopy (WS-CRDS) technique. We focus in this paper on four main aspects regarding (1) the tubing material, (2) the humidity calibration of the instrument, (3) the water vapor concentration effects on δ, and (4) the isotopic calibration of the instrument. First, we show that Synflex tubing strongly affects δ(2)H measurements and thus leads to unusable d values. Second, we show that the mixing ratio as measured by WS-CRDS has to be calibrated versus atmospheric mixing ratio measurements and we also suggest possible non-linear effects over the whole mixing ratio range (~2 to 20 g/kg). Third, we show that significant non-linear effects are induced by water vapor concentration variations on δ measurements, especially for mixing ratios lower than ~5 g/kg. This effect induces a 5 to 10‰ error in deuterium excess and is instrument-dependent. Finally, we show that an isotopic calibration (comparison between measured and true values of isotopic water standards) is needed to avoid errors on deuterium excess that can attain ~10‰. 相似文献
9.
Khriachtchev L Tapio S Domanskaya AV Räsänen M Isokoski K Lundell J 《The Journal of chemical physics》2011,134(12):124307
We report on a new noble-gas molecule HXeOBr prepared in a low-temperature xenon matrix from the HBr and N(2)O precursors by UV photolysis and thermal annealing. This molecule is assigned with the help of deuteration experiments and ab initio calculations including anharmonic methods. The H-Xe stretching frequency of HXeOBr is observed at 1634 cm(-1), which is larger by 56 cm(-1) than the frequency of HXeOH identified previously. The experiments show a higher thermal stability of HXeOBr molecules in a xenon matrix compared to HXeOH. 相似文献
10.
Cristina Mas Ana Mantecn Angels Serra Xavier Ramis Josep Maria Salla 《Journal of polymer science. Part A, Polymer chemistry》2005,43(11):2337-2347
3,4‐Epoxycyclohexylmethyl 3,4‐epoxycyclohexane carboxylate was cured with different proportions of γ‐butyrolactone with lanthanum, samarium, and ytterbium triflates as catalysts. The curing was studied with differential scanning calorimetry (DSC) and Fourier transform infrared in the attenuated‐total‐reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and to quantify the evolution of the epoxide, lactone, and intermediate spiroorthoester groups. The glass‐transition temperature of the crosslinked materials was high and increased when the proportion of lactone decreased. The kinetics were studied with DSC experiments and were analyzed with isoconversional procedures. The differences in the reactivities of the systems were related to the Lewis acidity of the lanthanide salt used as the initiator. An increase in the proportion of lactone produced an increase in the reaction rate. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2337‐2347, 2005 相似文献