全文获取类型
收费全文 | 173篇 |
免费 | 30篇 |
国内免费 | 3篇 |
专业分类
化学 | 73篇 |
晶体学 | 2篇 |
力学 | 5篇 |
综合类 | 1篇 |
数学 | 63篇 |
物理学 | 62篇 |
出版年
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 10篇 |
2013年 | 8篇 |
2012年 | 11篇 |
2011年 | 18篇 |
2010年 | 9篇 |
2009年 | 13篇 |
2008年 | 11篇 |
2007年 | 12篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 6篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1974年 | 2篇 |
排序方式: 共有206条查询结果,搜索用时 0 毫秒
121.
Alessandra Furtado da Silva Bernhard Welz Adilson J. Curtius 《Spectrochimica Acta Part B: Atomic Spectroscopy》2002,57(12):2031-2045
Iridium, palladium, rhodium and ruthenium, thermally deposited on the platform, were investigated as permanent modifiers for the determination of mercury in ash, sludge, marine and river sediment reference materials, ground to a particle size of 50 μm, using solid sampling graphite furnace atomic absorption spectrometry. A total mass of 250 μg of each modifier was applied using 25 injections of 20 μl of modifier solution (500 mg l−1), and executing a temperature program for modifier conditioning after each injection. The performance of palladium was found to be most consistent, taking the characteristic mass as the major criterion, resulting in an excellent correlation between the measured integrated absorbance values and the certified mercury contents. Mercury was found to be lost in part from aqueous solutions during the drying stage in the presence of all the investigated permanent modifiers, as well as in the presence of the palladium and magnesium nitrates modifier added in solution. A loss-free determination of mercury in aqueous solutions could be reached only after the addition of potassium permanganate, which finally made possible the use of aqueous standards for the direct analysis of solid samples. A characteristic mass of 55–60 pg Hg was obtained for the solid samples, using Pd as a permanent modifier, and also in aqueous solutions after the addition of permanganate. The results obtained for mercury in ash, sludge and sediment reference materials, using direct solid sapling and calibration against aqueous standards, as well as the detection limit of 0.2 mg kg−1 were satisfactory for a routine procedure. 相似文献
122.
Hoogesteger FJ van Walree CA Jenneskens LW Roest MR Verhoeven JW Schuddeboom W Piet JJ Warman JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(16):2948-2959
The photophysical properties of a bicyclohexylidene (1DA) and a bicyclohexyl (2DA) substituted with an anilino electron donor and a dicyanoethylene electron acceptor have been studied. Quenching of local donor emission is observed for these compounds as well as quenching of the "pseudo-local" acceptor emission. Transient absorption spectra show dialkylanilino-type radical-cation and dicyanoethylene-type radical-anion absorptions. These results show that intramolecular charge separation takes place in 1DA and 2DA. This was corroborated by time-resolved microwave conductivity measurements from which large excited-state dipole moments were found for both 1DA and 2DA. Time-resolved fluorescence spectroscopy revealed that in the charge-separated state in cyclohexane for 2DA, molecular folding takes place on a nanosecond timescale. For 1DA in cyclohexane, either charge separation takes place in a (fully) folded conformation or very rapid (subnanosecond timescale) folding takes place subsequent to charge separation. In addition to this difference in conformational behavior, the presence of the exocyclic double bond between the cyclohexyl-type rings results in efficient quenching of the anilino donor triplet state and acceleration of the charge recombination rate by a factor of 20. 相似文献
123.
Pessatti Marcos L. Fontana José D. Furtado Maria F. D. Guimãraes Manoel F. Zanette Lorenzo R. S. Costa Walliana T. Baron Madalena 《Applied biochemistry and biotechnology》1995,51(1):197-210
Applied Biochemistry and Biotechnology - Toxins, enzymes, and biologically active peptides are the main components of snake venoms from the genusBothrops. Following the venom inoculation, the local... 相似文献
124.
Fernando Antonio Simas Vaz Arthur Damásio Moutinho Jose Paulo Rodrigues Furtado de Mendonça Ricardo Tavares de Araújo Sidney José Lima Ribeiro Ferminio César Polachini Younes Messaddeq Marcone Augusto Leal de Oliveira 《Microchemical Journal》2012
The preparation of photo-polymerized sol–gel monolithic stationary phases (MSP) within 100 μm internal diameter polyacrylate-coated fused-silica capillaries for use in capillary electrochromatography (CEC) was optimized. Eight mixtures containing different amounts of methacryloxypropyltrimethoxysilane (MPTMS) as the polymeric precursor, hydrochloric acid solution as the catalyst, toluene as the porogen and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819) as the photo-initiator were irradiated at 370 nm inside the capillaries in order to complete the MSP polymerization, according to a fractional factorial experimental design 2IV4-1. All the preparation procedure, from capillary pretreatment until the MSP is ready to use in CEC, were made in less than four hours in mild conditions. A high pressurization injection device (HPID) useful for micro-volume syringes was built in order to achieve practical, controlled and precise injections of sols, solvents and electrolytes in the capillaries. The eight MSP were equally washed, conditioned and submitted to CEC procedures via short-end injection, which showed higher efficiency and peak height taking shorter analysis time. Electrochromatographic behaviors of the MSP were corroborated with morphological characterizations by scanning electron microscopy. The optimum condition, which allowed the separation of standard mixture containing thiourea (marker compound), naphthalene, acenaphthene, fluorene, phenanthrene and anthracene in twelve minutes without external pressure assistance, showed efficiencies up to 51,460 N/m, relative standard deviation from 0.05 to 3.3% for migration/retention time and from 0.14 to 1.6% for relative area (considering thiourea as an internal standard) and also showed no statistical evidence that three MSP prepared at the same condition are different within 95% confidence interval. 相似文献
125.
本文报道了多光束共振光压作用下钠原子束偏转的实验研究结果。文中提出了用多光束与原子束相互作用以增大原子束的偏转量,并可大大降低对激光功率的要求。用一台染料激光器照射钠原子束得到1×10-2rad的偏转角,偏转距离约7.2mm,并用激光诱导原子束荧光的方法检测原子束的偏转。 相似文献
126.
In this contribution, we propose a new model for studying the confinement of a spin-half particle to a two-dimensional quantum ring for systems described by the Dirac equation by introducing a new coupling into the Dirac equation. We show that the introduction of this new coupling into the Dirac equation yields a generalization of the two-dimensional quantum ring model proposed by Tan and Inkson [W.-C. Tan, J.C. Inkson, Semicond. Sci. Technol. 11 (1996) 1635] for relativistic spin-half quantum particles. 相似文献
127.
Pedro E. G. Loureiro Antnio J. S. Fernandes Fernanda P. Furtado M. Graa V. S. Carvalho Dmitry V. Evtuguin 《Journal of Raman spectroscopy : JRS》2011,42(5):1039-1045
Ultraviolet‐resonance Raman (UV‐RR) micro‐spectroscopy is an appropriate and sensitive tool to assess the chromophore structures in bleached cellulosic pulps used for papermaking. The particular selectivity in detection and identification of chromophores in pulps is achieved by acquiring the UV‐RR spectra in the solid state with laser excitation at 325 nm. This wavelength corresponds to absorption of poly‐unsaturated chromophore structures in partially bleached/fully bleached pulps, and linearly correlated with the signal at ca 1600 cm−1 in the UV‐RR spectra. The characteristic vibrations from particular pulp chromophore structures have been assigned from experiments with model compounds, thus allowing the establishment of a UV‐RR database. Among the components of bleached pulp, the xylan–lignin complex was suggested to be an important source of chromophores. The monitoring of pulp bleaching by UV‐RR allowed us to suggest that it is the formation of new polysaccharide‐derived chromophores upon bleaching that hinders development of further brightness and is co‐responsible for the brightness reversion of fully bleached pulps. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
128.
In order to establish which are the contribution of linear (total), hyperbolic (partial) or parabolic inhibitions by cellobiose,
and also a special case of substrate inhibition, the kinetics of cellobiohydrolase Cel7A obtained from Trichoderma reesei was investigated. Values of kinetic parameters were estimated employing integrated forms of Michaelis–Menten equations through
the use of non-linear regression, and criteria for selecting inhibition models are discussed. With cellobiose added at the
beginning of the reaction, it was found that cellulose hydrolysis follows a kinetic model, which takes into account a mixed
hyperbolic inhibition, by cellobiose with the following parameter values: K
m 5.0 mM, K
ic 0.029 mM, K
iu 1.1 mM, k
cat 3.6 h−1 and k
cat′ 0.2 h−1. Cellulose hydrolysis without initial cellobiose added also follows the same inhibition model with similar values (4.7, 0.029
and 1.5 mM and 3.2 and 0.2 h−1, respectively). According to Akaike information criterion, more complex models that take into account substrate and parabolic
inhibitions do not increase the modulation performance of cellulose hydrolysis. 相似文献
129.
130.