全文获取类型
收费全文 | 303篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
化学 | 173篇 |
晶体学 | 4篇 |
力学 | 2篇 |
数学 | 64篇 |
物理学 | 69篇 |
出版年
2023年 | 4篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 9篇 |
2014年 | 10篇 |
2013年 | 12篇 |
2012年 | 17篇 |
2011年 | 28篇 |
2010年 | 10篇 |
2009年 | 7篇 |
2008年 | 18篇 |
2007年 | 18篇 |
2006年 | 13篇 |
2005年 | 8篇 |
2004年 | 7篇 |
2003年 | 4篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1967年 | 2篇 |
1959年 | 3篇 |
1958年 | 3篇 |
1956年 | 5篇 |
1948年 | 3篇 |
1947年 | 5篇 |
1946年 | 4篇 |
1944年 | 2篇 |
排序方式: 共有312条查询结果,搜索用时 171 毫秒
101.
Gradient echo single scan inversion recovery: application to proton and fluorine relaxation studies
下载免费PDF全文
![点击此处可从《Magnetic resonance in chemistry : MRC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Single scan longitudinal relaxation measurement experiments enable rapid estimation of the spin‐lattice relaxation time (T1) as the time series of spin relaxation is encoded spatially in the sample at different slices resulting in an order of magnitude saving in time. We consider here a single scan inversion recovery pulse sequence that incorporates a gradient echo sequence. The proposed pulse sequence provides spectra with significantly enhanced signal to noise ratio leading to an accurate estimation of T1 values. The method is applicable for measuring a range of T1 values, thus indicating the possibility of routine use of the method for several systems. A comparative study of different single scan methods currently available is presented, and the advantage of the proposed sequence is highlighted. The possibility of the use of the method for the study of cross‐correlation effects for the case of fluorine in a single shot is also demonstrated. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
102.
103.
A dipalladium complex [Pd2( L )Cl2](PF6)2 ( 2 ), via the substitution of (PhCN)2PdCl2 with 5‐phenyl‐2,8‐bis(6′‐bipyridinyl)‐1,9,10‐anthyridine ( L ) followed by the anion exchange, was found to be a good pre‐catalyst for the reduction of nitroarenes to yield the corresponding anilines under atmospheric pressure of hydrogen in methanol. This method provides a straightforward access to a diverse array of functionalized anilines, exhibiting a possible application in synthetic chemistry. The catalytic activity of this complex is enhanced by the di‐metallic system via the synergistic effect. 相似文献
104.
105.
Mandula Tirumala Rao Srinivasan Ramanathan 《Journal of Solid State Electrochemistry》2017,21(11):3155-3167
Journal of Solid State Electrochemistry - The dissolution of niobium electrode in anodic regime in hydrofluoric acid was studied using electrochemical techniques. In the active region, complex... 相似文献
106.
V. Thanikachalam J. Jayabharathi A. Arunpandiyan P. Ramanathan 《Journal of fluorescence》2014,24(2):377-387
This article presents a facile synthesis of novel class of bluish-green fluorescent 2-((E)-2-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenol [PPIVP] and their optical, electrochemical and thermal properties. Detailed photophysical and quantum chemical studies have been performed to elucidate the origin of the dual emission shifts. PPIVP undergo excited state intramolecular proton transfer (ESIPT) reaction leading a large Stoke’s shifted fluorescence emission from the phototautomer. The results of quantum chemical investigations not only confirmed the intramolecular charge transfer characteristics of the ESIPT tautomers but also provided a rational for the observed high fluorescence quantum efficiency in the solid state. The high photoluminescence quantum yield in the solid state is ascribed to twisted chromophores due to phenyl substituents at 1,2-position of the phenanthroimidazole ring which restricted intramolecular motion, leading to an optically allowed lowest optical transition without self quenching. 相似文献
107.
Satish S. More Akula Raghunadh Ramanathan Shankar Navin B. Patel Dinesh S. Bhalerao Unniaran K. Syam Kumar 《Helvetica chimica acta》2014,97(3):404-413
The first total synthesis of the α‐oxo amide‐based natural product, N‐(3‐guanidinopropyl)‐2‐(4‐hydroxyphenyl)‐2‐oxoacetamide ( 3 ), isolated from aqueous extracts of hydroid Campanularia sp., has been achieved. The α‐oxo amide 12 , prepared via the oxidative amidation of 1‐[4‐(benzyloxy)phenyl]‐2,2‐dibromoethanone ( 9a ) with 4‐{[(tert‐butyl)(dimethyl)silyl]oxy}butan‐1‐amine ( 10a ), has been used as the key intermediate in the total synthesis of 3 as HBr salt. On the way, an expeditious total synthesis of polyandrocarpamide C ( 2c ), isolated from marine ascidian Polyandrocarpa sp., was carried out in four steps. 相似文献
108.
The effect of isoelectric transition metals (TM) Nb and Ta on the magnetism of the V(001) surface is investigated from first principles using Density functional theory (DFT), with the generalized gradient approximation (GGA). Ferromagnetic (FM) moments of 2.5 μB and 2.2 μB are obtained for the relaxed surface V monolayer (ML) in the V/Nb(001) and the V/Ta(001) systems respectively, at T = 0 K. The values are almost twice of those obtained with Mo and W of group VIB and can be attributed to the comparatively smaller bandwidths of the substrates Nb and Ta. Small induced magnetic moments are present on the Nb and Ta interfacial layers, which are coupled anti-ferromagnetically with the V ML. 相似文献
109.
Chetan Kumar Arya Swati Yadav Jonathan Fine Ana Casanal Gaurav Chopra Gurunath Ramanathan Kutti R. Vinothkumar Ramaswamy Subramanian 《Angewandte Chemie (International ed. in English)》2020,59(39):16961-16966
N,N‐dimethyl formamide (DMF) is an extensively used organic solvent but is also a potent pollutant. Certain bacterial species from genera such as Paracoccus, Pseudomonas, and Alcaligenes have evolved to use DMF as a sole carbon and nitrogen source for growth via degradation by a dimethylformamidase (DMFase). We show that DMFase from Paracoccus sp. strain DMF is a halophilic and thermostable enzyme comprising a multimeric complex of the α2β2 or (α2β2)2 type. One of the three domains of the large subunit and the small subunit are hitherto undescribed protein folds of unknown evolutionary origin. The active site consists of a mononuclear iron coordinated by two Tyr side‐chain phenolates and one carboxylate from Glu. The Fe3+ ion in the active site catalyzes the hydrolytic cleavage of the amide bond in DMF. Kinetic characterization reveals that the enzyme shows cooperativity between subunits, and mutagenesis and structural data provide clues to the catalytic mechanism. 相似文献
110.
Use of dipolar and quadrupolar couplings for quantum information processing (QIP) by nuclear magnetic resonance (NMR) is described.
In these cases, instead of the individual spins being qubits, the 2
n
energy levels of the spin-system can be treated as an n-qubit system. It is demonstrated that QIP in such systems can be carried out using transition-selective pulses, in CH3CN, 13CH3CN, 7Li (I=3/2) and 133Cs (I=7/2), oriented in liquid crystals yielding 2 and 3 qubit systems. Creation of pseudopure states, implementation of logic
gates and arithmetic operations (half-adder and subtractor) have been carried out in these systems using transition-selective
pulses. 相似文献