全文获取类型
收费全文 | 63篇 |
免费 | 20篇 |
国内免费 | 13篇 |
专业分类
化学 | 59篇 |
晶体学 | 4篇 |
力学 | 1篇 |
综合类 | 3篇 |
数学 | 5篇 |
物理学 | 24篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 1篇 |
2015年 | 4篇 |
2014年 | 2篇 |
2013年 | 8篇 |
2012年 | 9篇 |
2011年 | 2篇 |
2010年 | 5篇 |
2009年 | 5篇 |
2008年 | 9篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2002年 | 1篇 |
2000年 | 3篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有96条查询结果,搜索用时 281 毫秒
1.
2.
Villamena FA Merle JK Hadad CM Zweier JL 《The journal of physical chemistry. A》2005,109(27):6089-6098
The formation of the superoxide radical anion (O2*-) adduct of the nitrone 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as detected by electron paramagnetic resonance (EPR) spectroscopy is one of the most common techniques for O2*- detection in chemical and biological systems. However, the nature of DMPO-O2H has confounded spin-trapping investigators over the years, since there has been no independently synthesized DMPO-O2H to date. A density functional theory (DFT) approach was used to predict the isotropic hyperfine coupling constants arising from the N, beta-H, and gamma-H nuclei of DMPO-O2H using explicit interactions with water molecules as well as via a bulk dielectric effect employing the polarizable continuum model (PCM). Theoretical calculation on the thermodynamics of DMPO-O2H decay shows favorable intramolecular rearrangement to form a nitrosoaldehyde and a hydroxyl radical as products, consistent with experimental observations. Some pathways for the bimolecular decomposition of DMPO-O2H and DMPO-OH have also been computed. 相似文献
3.
The hydroxyl radical (*OH) is an important mediator of biological oxidative stress, and this has stimulated interest in its detection. 5,5-Dimethyl-1-pyrroline N-oxide (DMPO) and its alkoxycarbonyl and alkoxyphosphoryl analogues have been employed as spin traps for electron paramagnetic resonance (EPR) spectroscopic radical detection. Energies of optimized geometries of nitrones and their corresponding *OH adducts were calculated using density functional theory (DFT) at the B3LYP/6-31+G//B3LYP/6-31G level. Calculations predict that the trans adduct formation is favored in alkoxycarbonyl nitrones, while cis adducts with intramolecular H-bonding is favored for alkoxyphosphoryl nitrones. Addition of *OH to a phosphoryl-substituted nitrone is more exoergic than the carbonylated nitrones. Charge and spin densities on the nitrone spin traps were correlated with their rates of addition with *OH, and results show that the charge density on the nitronyl C, the site of *OH addition, is more positive in phosphorylated nitrones compared to DMPO and the alkoxycarbonyl nitrones. The dihedral angle between the beta-H and nitroxyl O bonds is smaller in phosphorylated nitrones, and that aspect appears to account for the longer half-lives of the spin adducts compared to those in DMPO and alkoxycarbonyl nitrones. Structures of nitrones with trifluoromethyl-, trifluoromethylcarbonyl-, methylsulfonyl-, trifluoromethylsulfonyl-, amido-, spiropentyl-, and spiroester substituents were optimized and their energies compared. Amido and spiroester nitrones were predicted to be the most suitable nitrones for spin trapping of *OH due to the similarity of their thermodynamic and electronic properties to those of alkoxyphosphoryl nitrones. Moreover, dimethoxyphosphoryl substitution at C-5 was found to be the most efficient substitution site for spin trapping of *OH, and their spin adducts are predicted to be the most stable of all of the isomeric forms. 相似文献
4.
5.
学习体验是学生对学习内容、过程、方法、意义的自我感受和评估,对学生学习志趣、学习素养提升有积极正向作用。以钠及其化合物复习为例,将各类别物质间转化关系的构建、物质制备原理和条件的优选作为学习体验对象,依据学习体验的内在发展历程设计学习任务及活动,引导学生亲身体验学科认知方式、学科思维方法、学科应用价值,评价体验结果,激励学生自主学习发生。 相似文献
6.
建立了超高效液相色谱-电喷雾离子源-串联三重四极杆质谱(UPLC-ESI MS/MS)分析饮用水中高氯酸盐的方法.以300Extend-C18为分析柱,10%甲醇水溶液为流动相,ESI MS/MS串联质谱为检测器,以多重反应监测(MRM)模式监测高氯酸盐m/z 99.5→82.9离子对.方法的线性范围为0.2 ~10 μg/L,相关系数为r2=0.999 9,方法检出限为0.15 μg/L,平均加标回收率为82%,相对标准偏差为4.4%.应用UPLC-ESI MS/MS法测定北京市部分城区饮用水中的高氯酸盐,其中5个水样中检出ClO-4,质量浓度为0.040 ~0.262 μg/L,但在安全阈值范围内,不会对居民健康构成威胁. 相似文献
7.
计算表明,与场的相干态类似的原子相干态,具有不同于场的相干态的压缩行为;进一步证明:直接类比于(?)(ξ)不能得到“原子压缩算符”. 相似文献
8.
9.
Durand G Choteau F Pucci B Villamena FA 《The journal of physical chemistry. A》2008,112(48):12498-12509
Nitrones have exhibited pharmacological activity against radical-mediated pathophysiological conditions and as analytical reagents for the identification of transient radical species by electron paramagnetic resonance (EPR) spectroscopy. In this work, competitive spin trapping, stopped-flow kinetics, and density functional theory (DFT) were employed to assess and predict the reactivity of O(2)(*-) and HO(2)(*) with various para-substituted alpha-phenyl-N-tert-butylnitrone (PBN) spin traps. Rate constants of O(2)(*-) trapping by nitrones were determined using competitive UV-vis stopped-flow method with phenol red (PR) as probe, while HO(2)(*) trapping rate constants were calculated using competition kinetics with 5,5-dimethylpyrroline N-oxide (DMPO) by employing EPR spectroscopy. The effects of the para substitution on the charge density of the nitronyl-carbon and on the free energies of nitrone reactivity with O(2)(*-) and HO(2)(*) were computationally rationalized at the PCM/B3LYP/6-31+G(d,p)//B3LYP/6-31G(d) level of theory. Theoretical and experimental data show that the rate of O(2)(*-) addition to PBN derivatives is not affected by the polar effect of the substituents. However, the reactivity of HO(2)(*) follows the Hammett equation and is increased as the substituent becomes more electron withdrawing. This supports the conclusion that the nature of HO(2)(*) addition to PBN derivatives is electrophilic, while the addition of O(2)(*-) to PBN-type compounds is only weakly electrophilic. 相似文献
10.
本文采用取样直流极谱, 常规脉冲极谱, 微分脉冲极谱和交流极谱考察了,2,2,6,6-四甲基-4-羟基哌啶 -1-氧和2,2,6,6-四甲基-4-氧哌啶 -1-氧由基及2,2,6,6-四甲基哌啶 -1-氧自由基在水溶液中的还原反应, 并研究了它们的还原经历电化学过程 。 相似文献