全文获取类型
收费全文 | 216篇 |
免费 | 9篇 |
专业分类
化学 | 162篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 24篇 |
物理学 | 35篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 6篇 |
2012年 | 23篇 |
2011年 | 18篇 |
2010年 | 11篇 |
2009年 | 10篇 |
2008年 | 15篇 |
2007年 | 9篇 |
2006年 | 11篇 |
2005年 | 11篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1970年 | 1篇 |
排序方式: 共有225条查询结果,搜索用时 0 毫秒
81.
A computational method for the evaluation of dispersion and repulsion contributions to the solvation energy is here presented in a formulation which makes use of a continuous distribution of the solvent, without introducing additional assumptions (e.g., local isotropy in the solvent distribution). The analysis is addressed to compare the relative importance of the various components of the dispersion energy (n = 6, 8, 10) and of the repulsion term, to compare several molecular indicators (molecular surface and volume, number of electrons) which may be put in relation to the dispersion-repulsion energy, and to define simplified computational strategies. The numerical examples refer to saturated hydrocarbons in water, treated with the homogeneous approximation of the distribution function which for this type of solution appears to be acceptable. 相似文献
82.
Katarzyna Borsuk Ivo F Eggen Paul B.W ten Kortenaar Floris P.J.T Rutjes 《Tetrahedron letters》2004,45(18):3585-3588
The use of differently substituted 2-(trimethylsilyl)ethyl esters for C-terminal protection in peptide synthesis has been investigated. While the use of the unsubstituted 2-(trimethylsilyl)ethyl ester resulted in a substantial amount of diketopiperazine at the dipeptide stage, use of the corresponding methyl-substituted silyl ester gave a significant reduction of this undesired pathway. Both esters could be deprotected by fluoride-induced cleavage under mild conditions. 相似文献
83.
Dr. Peter Spannring Dr. Indrek Reile M. Sc. Meike Emondts Dr. Philipp P. M. Schleker M. Sc. Niels K. J. Hermkens M. Sc. Nick G. J. van der Zwaluw M. Sc. Bram J. A. van Weerdenburg Dr. Paul Tinnemans Dr. Marco Tessari Prof. Dr. Bernhard Blümich Prof. Dr. Floris P. J. T. Rutjes Prof. Dr. Martin C. Feiters 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(27):9277-9282
NMR signal amplification by reversible exchange (SABRE) has been observed for pyridine, methyl nicotinate, N‐methylnicotinamide, and nicotinamide in D2O with the new catalyst [Ir(Cl)(IDEG)(COD)] (IDEG=1,3‐bis(3,4,5‐tris(diethyleneglycol)benzyl)imidazole‐2‐ylidene). During the activation and hyperpolarization steps, exclusively D2O was used, resulting in the first fully biocompatible SABRE system. Hyperpolarized 1H substrate signals were observed at 42.5 MHz upon pressurizing the solution with parahydrogen at close to the Earth's magnetic field, at concentrations yielding barely detectable thermal signals. Moreover, 42‐, 26‐, 22‐, and 9‐fold enhancements were observed for nicotinamide, pyridine, methyl nicotinate, and N‐methylnicotinamide, respectively, in conventional 300 MHz studies. This research opens up new opportunities in a field in which SABRE has hitherto primarily been conducted in CD3OD. This system uses simple hardware, leaves the substrate unaltered, and shows that SABRE is potentially suitable for clinical purposes. 相似文献
84.
Starting from the addition formula for q-disk polynomials, which is an identity in noncommuting variables, we establish a basic analogue in commuting variables of
the addition and product formula for disk polynomials. These contain, as limiting cases, the addition and product formula
for little q-Legendre polynomials. As q tends to 1 the addition and product formula for disk polynomials are recovered.
Date received: September 29, 1995. Date revised: May 20, 1996. 相似文献
85.
86.
Electronic Properties of Mono‐Substituted Tetraferrocenyl Porphyrins in Solution and on a Gold Surface: Assessment of the Influencing Factors for Photoelectrochemical Applications 下载免费PDF全文
Dr. Andrea Vecchi Nathan R. Erickson Jared R. Sabin Prof. Barbara Floris Prof. Valeria Conte Prof. Mariano Venanzi Dr. Pierluca Galloni Prof. Victor N. Nemykin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):269-279
Two unsymmetric meso‐tetraferrocenyl‐containing porphyrins of general formula Fc3(FcCOR)Por (Fc=ferrocenyl, R=CH3 or (CH2)5Br, Por=porphyrin) were prepared and characterized by a variety of spectroscopic methods, whereas their redox properties were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) approaches. The mixed‐valence [Fc3(FcCOR)Por]n+ (n=1,3) were investigated using spectroelectrochemical as well as chemical oxidation methods and corroborated with density functional theory (DFT) calculations. Inter‐valence charge‐transfer (IVCT) transitions in [Fc3(FcCOR)Por]+ were analyzed, and the resulting data matched closely previously reported complexes and were assigned as Robin–Day class II mixed‐valence compounds. Self‐assembled monolayers (SAMs) of a thioacetyl derivative (Fc3(FcCO(CH2)5SCOCH3)Por) were also prepared and characterized. Photoelectrochemical properties of SAMs in different electrolyte systems were investigated by electrochemical techniques and photocurrent generation experiments, showing that the choice of electrolyte is critical for efficiency of redox‐active SAMs. 相似文献
87.
F. Abbattista D. Mazza M. Vallino A. Floris V. Maxia G. Spano 《Il Nuovo Cimento D》1988,10(7):875-879
Summary Experiments are performed to determine the effect of polyphasicity on YBa2Cu3O7−x critical temperature. Results are obtained which show thatT
c fluctuations up to 2 K exist, depending on phase mixing. 相似文献
88.
Mauro Bassetti Barbara Floris Gabriello Illuminati 《Journal of organometallic chemistry》1980,202(4):351-362
Product analyses have been carried out and reaction rates and activation parameters determined for the methoxymercuration of some styrene derivatives and related compounds in methanol. The behaviour of α- and β-alkyl substituted styrenes generally parallels that of the similarly substituted vinylferrocenes. The anomalous reactivity of β,β-dimethylstyrenes is suggested to arise from the structural features of this compound. The reaction of the stilbenes was found to be stereospecific. The results are consistent with an unsymmetrically bridged structure for the cationic intermediate possibly involving varying degrees of bridging depending on substrate. 相似文献
89.
Akoto L Vreuls RJ Irth H Floris V Hoogveld H Pel R 《Journal of chromatography. A》2008,1186(1-2):372-379
In this paper, we discuss the use of a direct thermal desorption (DTD) interface as an alternative to Curie-point flash pyrolysis system as an inlet technique in gas chromatography-combustion isotope-ratio mass spectrometry (GC/C-IRMS) analysis of whole/intact phytoplankton and zooplankton specimens. The DTD in combination with a combipal auto-injector is programmed to perform the injection, evaporation of solvents, transport of capped programmed-temperature vaporizer (PTV) liners to the PTV injector and chemical derivatisation (thermally assisted hydrolysis/methylation; THM) such that a profile of a cellular fatty acids is obtained. Flow-cytometric sorted microalgae and handpicked zooplankton are used as samples with trimethylsulfonium hydroxide (TMSH) as methylating reagent. A major advantage of this novel approach over the Curie-point technique is the automation of the total procedure, which allows unattended analysis of large sample series. The profiles and delta(13)C carbon isotopic signatures of the fatty acid methyl esters (FAMEs) produced are very similar to those obtained using the Curie-point flash pyrolysis method. It is shown that algal samples must be kept no longer than 48 h in the DTD sample tray prior to the THM-analysis in order to maintain the integrity of their FAME profile. 相似文献
90.