全文获取类型
收费全文 | 249篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
化学 | 217篇 |
力学 | 5篇 |
数学 | 8篇 |
物理学 | 31篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 9篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 10篇 |
2014年 | 14篇 |
2013年 | 27篇 |
2012年 | 16篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 3篇 |
2008年 | 10篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1918年 | 1篇 |
排序方式: 共有261条查询结果,搜索用时 15 毫秒
61.
Prof. Carlos O. Areán Dr. Sachin Chavan Carlos P. Cabello Prof. Edoardo Garrone Dr. Gemma T. Palomino 《Chemphyschem》2010,11(15):3237-3242
Interaction between adsorbed hydrogen and the coordinatively unsaturated Mg2+ and Co2+ cationic centres in Mg‐MOF‐74 and Co‐MOF‐74, respectively, was studied by means of variable‐temperature infrared (VTIR) spectroscopy. Perturbation of the H2 molecule by the cationic adsorbing centre renders the H? H stretching mode IR‐active at 4088 and 4043 cm?1 for Mg‐MOF‐74 and Co‐MOF‐74, respectively. Simultaneous measurement of integrated IR absorbance and hydrogen equilibrium pressure for spectra taken over the temperature range of 79–95 K allowed standard adsorption enthalpy and entropy to be determined. Mg‐MOF‐74 showed ΔH0=?9.4 kJ mol?1 and ΔS0=?120 J mol?1 K?1, whereas for Co‐MOF‐74 the corresponding values of ΔH0=?11.2 kJ mol?1 and ΔS0=?130 J mol?1 K?1 were obtained. The observed positive correlation between standard adsorption enthalpy and entropy is discussed in the broader context of corresponding data for hydrogen adsorption on cation‐exchanged zeolites, with a focus on the resulting implications for hydrogen storage and delivering. 相似文献
62.
Sudrik SG Chaki NK Chavan VB Chavan SP Chavan SP Sonawane HR Vijayamohanan K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(3):859-864
In this work we report the unique electrocatalytic role of benzoic acid protected silver nanoclusters (Ag(n), mean core diameter 2.5 nm) in the Wolff rearrangement (Scheme 1) of alpha-diazoketones. More specifically, the presence of a Ag(n) (0)/Ag(n) (+) redox couple facilitates a nonclassical electron-transfer process, involving chemical reaction(s) interposed between two electron-transfer steps occurring in opposite directions. Consequently, the net electron transfer between the electron mediator (Ag(n)) and alpha-diazoketone is zero. In-situ UV-visible studies using pyridine as a nucleophilic probe indicate the participation of alpha-ketocarbene/ketene as important reaction intermediates. Controlled potential coulometry of alpha-diazoketones using Ag(n) as the anode results in the formation of Wolff rearranged carboxylic acids in excellent yield, without sacrificing the electrocatalyst. 相似文献
63.
Sudrik SG Sharma J Chavan VB Chaki NK Sonawane HR Vijayamohanan KP 《Organic letters》2006,8(6):1089-1092
[reaction: see text] We report Wolff rearrangement of alpha-diazoketones by in situ generated silver nanoclusters (Ag(n)(), 2-4 nm) from silver(I) oxide (Ag(2)O) involving a nonclassical electron-transfer process. Our results show that Ag(n)()(+)/Ag(n)()(0) redox couple allows the initial removal of an electron from alpha-diazoketone and its back-donation after chemical reaction(s). Controlled potential coulometry (CPC) of various alpha-diazoketones results in the realization of Wolff-rearranged carboxylic acids in excellent yields. 相似文献
64.
Satyajit Saha 《Tetrahedron letters》2010,51(6):912-1467
We have designed and synthesized N-arylprolinamides 7-10 with a potential to involve in the binding of electrophilic aldehydes via two N-H?O hydrogen bonds for application in organocatalytic aldol reactions. The catalyst 10 is shown to afford aldol products in excellent isolated yields with very high diastereo- and enantioselectivites. In addition to enhanced acidity and double hydrogen bonding, the stacking interactions of the p-toluenesulfonyl ring in 10 with the electrophilic aldehyde are proposed to stabilize the transition state. 相似文献
65.
A rapid and efficient method for stereoselective synthesis of new substituted tetrahydro-α-carbolines using Diels-Alder reaction under microwave irradiation has been developed. Further, dehydrogenation of these adducts resulted in synthesis of new substituted α-carbolines. 相似文献
66.
Identification and characterization of vilazodone metabolites in rats and microsomes by ultrahigh‐performance liquid chromatography/quadrupole time‐of‐flight tandem mass spectrometry
下载免费PDF全文
![点击此处可从《Rapid communications in mass spectrometry : RCM》网站下载免费的PDF全文](/ch/ext_images/free.gif)
67.
N-n-octylaniline in xylene is used for the extractive separation of gold(III) from halide media. Gold(III) was extracted quantitatively with 10 ml of 2% reagent in xylene from 0.5-10 M and 0.5-8 M hydrochloric acid and hydrobromic acid, respectively. It was stripped from the organic phase with ammonia buffer solution (pH 10.1) and estimated spectrophotometrically with stannous chloride. The effect of metal ion, acids, reagent concentration and of various foreign ions has been investigated. Method is applicable to the analysis of synthetic mixtures containing platinum metals and alloy samples. The method is fast, accurate and precise. 相似文献
68.
69.
The thermoelectric power of ferroelectric sodium vanadate doped with different concentrations of lanthanum oxide has been
measured in the temperature range covering their transition temperatures. It has been observed that the thermoelectric power
increases with temperature, attains maximum value and with further increase in the temperature decreases to zero, indicating
Curie temperature of the respective samples; however, it changes the sign for higher temperature. The thermoelectric power
of sodium vanadate increases to maximum with increase in doping concentration of lanthanum oxide from 0.025 to 0.1 mol%; however,
it decreases for higher concentrations. Pure as well as lanthanum oxide doped sodium vanadate samples showp-type behaviour in the ferroelectric region andn-type behaviour in the paraelectric region. 相似文献
70.
Satyajit Dey 《Tetrahedron letters》2005,46(33):5483-5486
The first synthesis of BE-23254, an unusual angucycline antibiotic, is reported. It involves regioselective condensation of naphthalenone 4 and chlorine-containing isobenzofuranone 16 as the key step. 相似文献