全文获取类型
收费全文 | 79篇 |
免费 | 0篇 |
专业分类
化学 | 65篇 |
晶体学 | 1篇 |
数学 | 2篇 |
物理学 | 11篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2017年 | 1篇 |
2014年 | 2篇 |
2013年 | 3篇 |
2012年 | 3篇 |
2011年 | 6篇 |
2010年 | 2篇 |
2009年 | 3篇 |
2008年 | 10篇 |
2007年 | 13篇 |
2006年 | 4篇 |
2005年 | 4篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1980年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有79条查询结果,搜索用时 15 毫秒
1.
Positive and negative chemical ionization (CI) mass spectrometry is studied for hydrofluorocarbons (HFCs), hydrofluorocarbon ethers (HFEs), and perfluoroalkenes (PFCs) using various kinds of reagent gas. While no quasi-molecular ion was observed under electron impact ionization for saturated MFCs, [M-F]+ is detected under CI conditions using methane as a reagent gas. Mechanisms for the generation of [M-F]+ are discussed. Furthermore, nitrogen monoxide can be used as a reagent gas to observe [M + NO]+ for many HFCs and HFEs. In negative mode chloroform is also available to generate [M + Cl]− for HFCs and HFEs containing -CHF- groups. 相似文献
2.
Hironobu Tahara Yudai Tanaka Shoko Yamamoto Shigeki Yonemori Bun Chan Hiroto Murakami Takamasa Sagara 《Chemical science》2021,12(13):4872
Redox-active ionic liquids (RAILs) are gaining attention as a material that can create a wide range of functions. We herein propose a charge-transfer (CT) RAIL by mixing two RAILs, specifically a carbazole-based ionic liquid ([CzC4ImC1][TFSI]) as a donor and a viologen-based ionic liquid ([C4VC7][TFSI]2) as an acceptor. We investigated the effect of CT interaction on the physicochemical properties of the CT ionic liquid (CT-IL) using the results of temperature-dependent measurements of UV-vis absorption, viscosity, and ionic conductivity as well as cyclic voltammograms. We employed the Walden analysis and the Grunberg–Nissan model to elucidate the effect of the CT interaction on the viscosity and ionic conductivity. The CT interaction reduces the viscosity by reducing the electrostatic attraction between the dicationic viologen and TFSI anion. It also reduces the ionic conductivity by the CT association of the dicationic viologen and carbazole. The electrochemically reversible responses of the viologens in [C4VC7][TFSI]2 and CT-IL are consistent with the Nernstian and the interacting two-redox site models. Notably, the transport and electrochemical properties are modulated by CT interaction, leading to unique features that are not present in individual component ILs. The inclusion of CT interaction in RAILs thus provides a powerful means to expand the scope of functionalized ionic liquids.A redox-active ionic liquid (RAIL) consisting of a carbazole and viologen shows charge transfer (CT) interaction. The physicochemical properties are modulated by the CT interaction by comparison with the individual RAILs. 相似文献
3.
New conformationally restricted analogues of tumor promoter (−)-indolactam-V (1), indolinelactam-Vs (8, 11) and their hexyl derivatives at position 1 or 7 (9, 10, 12, 13), were synthesized from 1. (3R)-Indolinelactam-V (8) adopted a conformation similar to the twist form of 1 with a cis amide, while the conformation of (3S)-indolinelactam-V (11) was close to that of the sofa form of 1 with a trans amide. 7-Hexyl derivatives of 8 and 11 (10, 13) showed binding affinities for C1 domains of protein kinase C (PKC) isozymes compared to 1, but exhibited little selectivity among these PKC isozymes. However, introduction of the hexyl group at position 1 of 8 and 11 significantly enhanced their binding selectivity for novel PKC isozymes. The best selectivity for novel PKC isozymes was observed in (3S)-1-hexylindolinelactam-V (12) with a sofa-like conformation. These results suggest that a sofa-restricted analogue of 1 with a hydrophobic chain at an appropriate position would be a promising lead for designing agents with a high selectivity for novel PKC isozymes. 相似文献
4.
Transition metal-catalyzed monoreduction of dichlorooligosilanes with Grignard reagents is reported. Among the examined catalysts, group 4 metal chlorides such as TiCl4 and Cp2TiCl2 gave the highest reactivity and good selectivity. The reducing power is effectively controlled by changing the catalysts and Grignard reagents to achieve sufficient selectivity depending on the oligosilane substrates. 相似文献
5.
Yoshitake T Ichinose F Yoshida H Todoroki K Kehr J Inoue O Nohta H Yamaguchi M 《Biomedical chromatography : BMC》2003,17(8):509-516
A highly sensitive, selective and simple method is described for the determination of histamine by high-performance liquid chromatography (HPLC) with fluorescence detection. The method is based on an intramolecular excimer-forming fluorescence derivatization of histamine with 4-(1-pyrene)butyric acid N-hydroxysuccinimide ester (PSE), followed by reversed-phase HPLC. Histamine, having two amino moieties in a molecule, was converted to the dipyrene-labeled derivative by reaction with PSE. The derivative afforded intramolecular excimer fluorescence (450-540 nm), which can clearly be discriminated from the monomer fluorescence (370-420 nm) emitted from PSE. Typically, a 10 micro L sample solution was mixed with 100 micro L of derivatization reagent solution, which was a mixture of 0.5 mm PSE in acetonitrile and 0.5 mm potassium carbonate in water (8:2, v/v). The derivatization was carried out at 100 degrees C for 90 min. The PSE derivative of histamine could be separated by reversed-phase ODS column with isocratic elution using acetonitrile:water (82:18, v/v) containing 0.03% triethylamine. The detection limit (singnal-to-noise ratio = 3) of histamine was 0.5 fmol for a 30 micro L injection. The method was successfully applied to the determination of histamine in human urine, and had enough selectivity and sensitivity for urinary histamine quantification. 相似文献
6.
Takahiro Miyata Kozo Matsumoto Takeshi Endo Shigeaki Yonemori Shoji Watanabe 《Journal of polymer science. Part A, Polymer chemistry》2012,50(15):3046-3051
A styrene‐based monomer having a five‐membered cyclic carbonate structure, 4‐vinylbenzyl 2,5‐dioxoran‐3‐ylmethyl ether (VBCE), was prepared by lithium bromide‐catalyzed addition of carbon dioxide to 4‐vinylbenxyl glycidyl ether (VBGE). Radical polymerization of the obtained VBCE was carried out using 2,2′‐azobisisobutyronitrile as an initiator. PolyVBCE with number‐averaged molecular weight higher than 13,800 was obtained by a solution polymerization in N,N‐dimethylformamide, N,N‐dimethylacetamide, dimethyl sulfoxide, and methyl ethyl ketone. The glass transition temperature and 5 wt % decomposition temperature of the polyVBCE were determined to be 52 and 305 °C by differential scanning calorimetry and thermal gravimetry analysis, respectively. It was confirmed that a polymer consisting of the same VBCE repeating unit can be also obtained via chemical modification of polyVBGE, that is, a lithium‐bromide‐catalyzed addition of carbon dioxide to a polyVBGE prepared from a radical polymerization of VBGE. Further copolymerization of VBCE with styrene gave the corresponding copolymer in a high yield. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
7.
Let S be a normal surface over an algebraically closed field k and let be a standard boundary. We consider index 1 covers of the purely log terminal pair (S,). We prove that when S is smooth and char k=p3, then is canonical under some conditions. To prove this, we classify the boundary =(1–1/bi)Di which makes (S,) a purely log terminal pair, and then reduce equations defining singularity of to the normal forms of RDP. Unfortunately there are some counterexamples in p=2, and we classify them. These results give partial solutions to the index 1 cover conjecture in positive characteristic.Mathematical Subject Classification (2000): 14E20 相似文献
8.
Kobayashi S Waki T Nakanishi I Matsumoto K Anzai K 《Chemical & pharmaceutical bulletin》2010,58(11):1442-1446
New potent antioxidants conjugating the catechol (=pyrocatechol; pyrCat) group to two N-termini of modified double-stranded tyrosine residues were synthesized and showed radical scavenging activity with 2,2-diphenyl-1-picrylhydrazyl radical (DPPH radical, DPPH˙) as a free radical model, second-order rate constants for the DPPH˙ scavenging reaction, and the results from electron spin resonance (ESR) studies. It was found that the tyrosine (Tyr) residue and pyrCat containing new antioxidants developed in the study have about 3-20 times more potent antioxidative activity than Trolox, pyrCat, and L-ascorbic acid (VC). In order to elucidate the relationship between antioxidant activity and the molecular orbital states, and to design potent antioxidants we present an interesting approach using an absolute hardness (η)-absolute electronegativity (χ) diagram based on chemical hardness. It was shown that quantum chemicals were required to develop potent antioxidants. 相似文献
9.
Matsuyama Kiyoshi Mishima Kenji Hayashi Ken-ichiro Matsuyama Hideto 《Journal of nanoparticle research》2003,5(1-2):87-95
A novel preparation method is reported for the microencapsulation of TiO2 nanoparticles by rapid expansion of supercritical solution with a nonsolvent. A suspension of TiO2 nanoparticles in carbon dioxide containing a cosolvent and dissolved polymer is sprayed through a nozzle to atmospheric pressure. After rapid expansion, polymer microspheres were obtained. The microspheres do not tend to agglomerate, since the pure cosolvent is a nonsolvent for the polymer. The structure and morphology of microspheres were investigated by SEM, TEM and XRD. The obtained polymer microspheres are microcapsules of TiO2 nanoparticles. The mean particle diameter and particle size distribution of microcapsules, could be controlled by changing the polymer concentration, pre-expansion pressure, temperature and injection distance. The polymer feed compositions are more effective than other factors on the control of particle size. 相似文献
10.
Kazuhiko Mase Mitsuru Nagasono Shin-ichiro Tanaka Tsuneo Urisu Eiji Ikenaga Tetsuji Sekitani Ken-ichiro Tanaka 《Surface science》1997,390(1-3):97-101
Ion desorption induced by a resonant excitation of O 1s of condensed amorphous H2O has been studied by total ion and total electron yield spectroscopy, nonderivative Auger electron spectroscopy (AES) and Auger electron photo-ion coincidence (AEPICO) spectroscopy. The spectrum of total ion yield divided by total electron yield exhibits a characteristic threshold peak at hν = 533.4 eV, which is assigned to the 4a1 ← O 1s resonant transition. The AES at the 4a1 ← O 1s resonance is interpreted as being composed of the spectator-AES of the surface H2O, and the normal-AES of the bulk H2O, where the 4a1 electron is delocalized before Auger transitions. H+ is found to be the only ion species in AEPICO spectra measured at the 4a1 ← O 1s resonance and at the O 1s ionization (hν = 560 eV). The electron kinetic energy dependence of the AEPICO yield (AEPICO yield spectrum) at the 4a1 ← O 1s resonance is found to be greatly different from that at the O 1s ionization. The peak positions of the AEPICO yield spectrum at the 4a1 ← O 1s resonance are found to correspond to those of the spectator-AES of the surface H2O, which is extracted from the AES at the 4a1 ← O 1s resonance. Furthermore, the AEPICO yield is greatly enhanced at the 4a1 ← O 1s resonance as compared with that at the O 1s ionization. On the basis of these results, a spectator-Auger-stimulated ion desorption mechanism and/or ultra-fast ion desorption mechanism are concluded to be responsible for the H+ desorption at the 4a1 ← O 1s resonance. The enhancement of the H+ yield is ascribed to the O---H anti-bonding character of the 4a1 orbital. 相似文献