全文获取类型
收费全文 | 115篇 |
免费 | 15篇 |
国内免费 | 7篇 |
专业分类
化学 | 119篇 |
综合类 | 1篇 |
数学 | 1篇 |
物理学 | 1篇 |
综合类 | 15篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 13篇 |
2014年 | 3篇 |
2013年 | 2篇 |
2012年 | 6篇 |
2011年 | 9篇 |
2010年 | 2篇 |
2009年 | 2篇 |
2008年 | 3篇 |
2007年 | 5篇 |
2006年 | 4篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 6篇 |
2002年 | 11篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有137条查询结果,搜索用时 625 毫秒
61.
Joseph B. Lambert Lidia Kania William J. Schulz 《Journal of polymer science. Part A, Polymer chemistry》1993,31(7):1697-1700
Efforts to optimize the formation of the cyclic D5 oligomer (D = Me2SiO) of polydimethylsiloxane have led to the development of a new class of redistribution catalyst, the silyl perchlorates. Where as previous Lewis and Bronsted acid catalysts have transformed D3 almost exclusively into D3n oligomers, use of phenyldimethylsilyl perchlorate as the catalyst gives predominantly D4, D5, and other non-D3n oligomers. This redistribution reaction is particularly useful for obtaining large amounts of the difficulty available D5. Similar studies of D4 with variation of solvent and catalyst led to little redistribution. © 1993 John Wiley & Sons, Inc. 相似文献
62.
Kita M Hirayama Y Sugiyama M Kigoshi H 《Angewandte Chemie (International ed. in English)》2011,50(42):9871-9874
Tied up: A PEG-linked biotin derivative of marine macrolide aplyronine?A (ApA; see scheme) is shown to exhibit potent cytotoxicity and cause actin disassembly in tumor cells. This method of introducing a PEG linker at the end of the aliphatic tail should offer perspectives for developing and using versatile actin-targeting molecular probes. PEG=poly(ethylene glycol). 相似文献
63.
A novel method of cotton cellulose depolymerization is investigated in this paper. In this work, a three-electrode system, which contains a Pb/PbO2 anode, two copper cathodes and a reference saturated calomel electrode (SCE), is applied to electrocatalytic depolymerization of cotton cellulose. After electrocatalytic depolymerization of cotton cellulose in 0.5M sulfuric acid solution using Pb/PbO2 anode at room temperature (25 °C), the average degree of polymerization (DP) can be reduced to the minimum 367 from 1100. The effects of operating parameters, such as supporting electrolyte, current density and reaction time are investigated as well. The composition of the products in filtrate is characterized by phenol-sulfuric acid method, extraction, NMR, GC-MS and High Performance Liquid Chromatography (HPLC). In addition, the solid sample is analyzed via SEM images, XRD diffractogram, Ubbelohde capillary viscometer and FT-IR spectra. The results suggest that it is effective to convert cotton cellulose to soluble sugar, 5-hydroxymethylfurfural (5-HMF) and other products by electrocatalytic methods. However, the yield of products is low and needs further study. A novel method to significantly convert cotton cellulose to biofuels and biomaterials can be hopefully developed if the selectivity of cotton cellulose electrocatalytic depolymerization is improved in the future. 相似文献
64.
Hidayah Ariffin Haruo Nishida Yoshihito Shirai Mohd Ali Hassan 《Polymer Degradation and Stability》2010,95(8):1375-5497
Highly selective transformation of poly[(R)-3-hydroxybutyric acid] (PHB) into trans-crotonic acid was achieved by thermal degradation using Mg compounds: MgO and Mg(OH)2 as catalysts. Through catalytic action, not only the temperature and Ea value of degradation were lowered by 40-50 °C and 11-14 kJ mol−1, respectively, but also significant changes in the selectivity of pyrolyzates were observed. Notably, Mg(OH)2 showed nearly complete selectivity (∼100%) to trans-crotonic acid. Kinetic analysis of TG profiles revealed that the catalytic thermal degradation of PHB was initiated by some random degradation reactions, followed by the unzipping β-elimination from crotonate chain-ends as a main process. It was suggested that the Mg catalysts promote the totality of the β-elimination reactions by acting throughout the beginning and main processes, resulting in a lowering in the degradation temperature and the completely selective transformation of PHB. 相似文献
65.
M. Zain H. Kazmi Abhoy Karmakar Vladimir K. Michaelis Florence J. Williams 《Tetrahedron》2019,75(11):1465-1470
A mild method for the separation of cellulose/hemicellulose from extractives free sawdust is described. Sequential treatments with an equimolar mixture of BCl3 and BBr3 remove polysaccharide components from a white pine sawdust sample. Spectroscopic analyses, including solution and solid-state NMR spectroscopy, confirm a reduction in the amount of aliphatic sugars in solid samples and show that extracted components consist only of polymeric sugars and are free of aromatics. Staining with fluorescent and colorimetric dyes confirm that the sawdust sample after boron trihalide treatment is primarily lignin, with no detectable polysaccharides. 相似文献
66.
In this paper we have derived an exact expression for the molecular size distribution in living polymers for batch polymerization
when depropagation is simultaneously operative. This expression is valid at a point of time when inhomogeneity is slightly
greater than half that of the final equilibrium distribution.
The authors felicitate Prof. D S Kothari on his eightieth birthday and dedicate this paper to him on this occasion. 相似文献
67.
Kena Li Jens Prothmann Margareta Sandahl Sara Blomberg Charlotta Turner Christian Hulteberg 《Molecules (Basel, Switzerland)》2021,26(10)
Base-catalyzed depolymerization of black liquor retentate (BLR) from the kraft pulping process, followed by ultrafiltration, has been suggested as a means of obtaining low-molecular-weight (LMW) compounds. The chemical complexity of BLR, which consists of a mixture of softwood and hardwood lignin that has undergone several kinds of treatment, leads to a complex mixture of LMW compounds, making the separation of components for the formation of value-added chemicals more difficult. Identifying the phenolic compounds in the LMW fractions obtained under different depolymerization conditions is essential for the upgrading process. In this study, a state-of-the-art nontargeted analysis method using ultra-high-performance supercritical fluid chromatography coupled to high-resolution multiple-stage tandem mass spectrometry (UHPSFC/HRMSn) combined with a Kendrick mass defect-based classification model was applied to analyze the monomers and oligomers in the LMW fractions separated from BLR samples depolymerized at 170–210 °C. The most common phenolic compound types were dimers, followed by monomers. A second round of depolymerization yielded low amounts of monomers and dimers, while a high number of trimers were formed, thought to be the result of repolymerization. 相似文献
68.
Rapid,On‐Command Debonding of Stimuli‐Responsive Cross‐Linked Adhesives by Continuous,Sequential Quinone Methide Elimination Reactions
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hyungwoo Kim Hemakesh Mohapatra Scott T. Phillips 《Angewandte Chemie (International ed. in English)》2015,54(44):13063-13067
Adhesives that selectively debond from a surface by stimuli‐induced head‐to‐tail continuous depolymerization of poly(benzyl ether) macro‐cross‐linkers within a poly(norbornene) matrix are described. Continuous head‐to‐tail depolymerization provides faster rates of response than can be achieved using a small‐molecule cross‐linker, as well as responses to lower stimulus concentrations. Shear‐stress values for glass held together by the adhesive reach 0.51±0.10 MPa, whereas signal‐induced depolymerization via quinone methide intermediates reduces the shear stress values to 0.05±0.02 MPa. Changing the length of the macro‐cross‐linkers alters the time required for debonding, and thus enables the programmed sequential release of specific layers in a glass composite material. 相似文献
69.
Snapshots of lignin oxidation and depolymerization in archaeological wood: an EGA‐MS study
下载免费PDF全文
![点击此处可从《Journal of mass spectrometry : JMS》网站下载免费的PDF全文](/ch/ext_images/free.gif)
D. Tamburini J‐J. Łucejko E. Ribechini M‐P. Colombini 《Journal of mass spectrometry : JMS》2015,50(10):ii-ii
Evolved gas analysis‐mass spectrometry (EGA‐MS) was used for the first time to study archaeological wood, in order to investigate its chemical degradation. The archaeological wood was from an oak pile from a stilt house found in the Neolithic ‘La Marmotta’ village (Lake Bracciano, Rome, Italy). The sampling was performed from the external to the internal part of the pile, following the annual growth rings in groups of five. In addition, sound oak wood and isolated wood components (holocellulose and cellulose) were also analyzed, and the results were used to highlight differences because of degradation. Our study demonstrated that EGA‐MS provides information on the thermo‐chemistry of archaeological wood along with in‐depth compositional data thanks to the use of MS. Our investigations not only highlighted wood degradation in terms of differences between carbohydrates and lignin content, but also showed that lignin oxidation and depolymerization took place in the archaeological wood. Mass spectral data revealed differences among the archaeological samples from the internal to the external part of the pile. An increase in the formation of wood pyrolysis products bearing a carbonyl group at the benzylic position and a decrease in the amount of lignin dimers were observed. These were related to oxidation and depolymerization reactions, respectively. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
70.
We reported previously a method for the separation and quantification of sulfated polysaccharides, dextran sulfate sodium (DSS), using fluorometric labeling and size-exclusion chromatography (SEC). In the present study, we evaluated chemical depolymerization of DSS. In fluorometric analyses using SEC, pyridylamino-DSS (PA-DSS) was depolymerized under acidic conditions, but not under alkaline conditions. In addition, we used ion-pair liquid chromatography (IPLC) and UV analyses for the separation and quantification of sulfate. Sulfate was considerably depleted from DSS under alkaline conditions, but little depleted under acidic conditions. Spectrophotometric studies using toluidine blue revealed that molecular mass is an important factor and a minimum molecular mass of 2500 is needed to induce metachromasia. Fluorometric analyses using SEC and UV analyses using IPLC allow for the detection of DSS, reactants and sulfate. 相似文献