全文获取类型
收费全文 | 624篇 |
免费 | 8篇 |
国内免费 | 8篇 |
专业分类
化学 | 339篇 |
晶体学 | 2篇 |
力学 | 30篇 |
数学 | 66篇 |
物理学 | 203篇 |
出版年
2018年 | 6篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 32篇 |
2012年 | 24篇 |
2011年 | 33篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 38篇 |
2007年 | 26篇 |
2006年 | 27篇 |
2005年 | 22篇 |
2004年 | 27篇 |
2003年 | 21篇 |
2002年 | 18篇 |
2001年 | 11篇 |
2000年 | 18篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 12篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1968年 | 3篇 |
1967年 | 3篇 |
1935年 | 3篇 |
1933年 | 4篇 |
排序方式: 共有640条查询结果,搜索用时 15 毫秒
511.
Middelthon-Bruer TM Gjelstad A Rasmussen KE Pedersen-Bjergaard S 《Journal of separation science》2008,31(4):753-759
Thirty-five different basic drugs were extracted by electro membrane extraction (EME), from acidified samples containing HCl as the BGE, through an organic solvent immobilized in the pores in the wall of a porous hollow fiber (supported liquid membrane, SLM), and into an acidified acceptor solution (HCl) in the lumen of the hollow fiber by the application of an electrical potential difference of 50 V. With 2-nitrophenyl pentyl ether (NPPE) as the SLM, and with 10 mM HCl as BGE in the sample and acceptor solution, singly charged basic drugs with log P >2 were extracted with recoveries in the range 30-81% within 5 min. For doubly charged basic drugs, extraction was effectively enhanced by decreasing the concentration of HCl in the sample from 10 to 0.1 mM, reducing the ionization of the analytes. For medium polar analytes (1 < log P < 2), an ion balance of 0.01 was combined with addition of tris-(2-ethylhexyl) phosphate (TEHP) to the SLM, and this provided recoveries in the range 36-70%. The ion balance was defined as the concentration ratio of BGE between the sample and the acceptor solution. For the most polar drugs (log P <1), EME was accomplished with an ion balance of 0.01 and with di-(2-ethylhexyl) phosphate (DEHP) added to the SLM, but in spite of this, recoveries were in the range of only 4-17%. 相似文献
512.
Günter Grampp Prof. Birgit Großmann Dr. Jürgen Heinze Prof. Stephan Landgraf Dr. Kenneth Rasmussen Dr. 《Chemphyschem》2008,9(6):854-860
Rate constants khom and khet are reported for the homogeneous electron‐self‐exchange and the heterogeneous electrochemical electron‐transfer reactions, respectively, of the cyclooctatetraene/cyclooctatetraene? (COT/COT.?) redox couple. In acetonitrile, the values khom (298 K)=(5±3)×105 M ?1 s?1 and khet (295 K)=8×10?3 cm s?1 are found, whereas slightly faster rates are obtained in dimethylformamide, namely, khom (298 K)=(1.6±0.6)×106 M ?1 s?1 and khet (295 K)=2×10?2 cm s?1. The khom rates are obtained from electron spin resonance (ESR) line broadening whereas the khet rates are measured at a mercurized Pt electrode by using Nicolson’s method. The slowness of both electron‐transfer reactions is caused by the high inner‐sphere reorganization energy that results from the inevitable conformational change that takes place upon going from the tub‐like COT molecule to the planar COT.? anion. The rates are well‐understood in terms of Marcus theory, including an additional medium inner‐sphere mode which is responsible for the flattening of COT. 相似文献
513.
We present an efficient method to construct coarse-grained (CG) models from models of finer resolution. The method estimates the free energies in a generated sample of the CG conformational space and then fits the entire effective potential surface in the high-dimensional CG conformational space. A jump-in-sample algorithm that uses a random jumping walk in the CG sample is used to iteratively estimate the free energies. We test the method in a tetrahedral molecular fluid where we construct the intermolecular effective potential and evaluate the CG molecular model. Our algorithm for calculating the free energy involves an improved Wang-Landau (WL) algorithm, which not only works more efficiently than the standard WL algorithm, but also can work in high-dimensional spaces. 相似文献
514.
Ole Hassager Jose Manuel Roman Marin Kaijia Yu Henrik Koblitz Rasmussen 《Rheologica Acta》2010,49(6):543-554
We use a transient 3D free surface finite element method to simulate flow of entangled polymer fluids in the dual cylinder
wind-up extensional rheometer. The constitutive equations are K-BKZ integral representations of the Doi–Edwards models with
and without the independent alignment approximation (IA). It is demonstrated that the actual kinematics in this rheometer
is a mixture of planar and uniaxial extension. Moreover, the ratio of planar to uniaxial deformation is highly dependent upon
whether IA is invoked. Without IA, the flow has a tendency toward planar extension, while it tends to be more uniaxial with
IA invoked. As a second illustration of the techniques, we simulate the phenomenon of delayed rupture after rapid extension
of entangled polymer systems. It is demonstrated that this phenomenon can be explained on the basis of the Doi–Edwards model
in terms of a Considere-type instability after chain stretch relaxation. 相似文献
515.
516.
Taeseok Jang Paul G. Rasmussen 《Journal of polymer science. Part A, Polymer chemistry》1998,36(14):2619-2629
The 2-(1-methyl-4,5-dicyanoimidazolyl) group was attached to poly(diallylamine) and polyethylenimine, affording polymers containing an electron-withdrawing pendant group. The key to their preparation is high reactivity of 1-methyl-2-fluoro-4,5-dicyanoimidazole (1) toward nucleophilic aromatic substitution (NAS) reactions with aliphatic amines. Cyclic voltammograms of these polymers show reduction waves at −2.6 to −2.7 V vs. Ag/Ag+ but no reoxidation waves, unlike those of monomeric and oligomeric model compounds, which are quasi-reversible. The cyclic voltammetry studies of oligomeric model compounds with different alkyl spacers show that the degree of quasi-reversibility decreases as dicyanoimidazoles are crowded together in a molecule, suggesting that a certain degree of chemical reaction occurs between reduced dicyanoimidazole groups. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2619–2629, 1998 相似文献
517.
B. K. Annis G. D. Wignall Alan R. Hopkins Paul G. Rasmussen Rafil A. Basheer 《Journal of Polymer Science.Polymer Physics》1997,35(17):2765-2774
The structure of blends of Nylon 6 with deuterated polyaniline emeraldine base (D-PANI-EB) and fully doped D-PANI salts (D-PANI-ES) formed from camphorsulfonic acid (CSA), methanesulfonic acid (MSA), or dodecyl benzenesulfonic acid (DBSA) were investigated by small-angle neutron (SANS) and X-ray scattering. The blends were formed from hexafluoro-2-propanol solutions and had volume fractions of 0.038, 0.20, and 0.40 for D-PANI/CSA, 0.20 and 0.40 for D-PANI/MSA, 0.24 and 0.44 for D-PANI/DBSA, and 0.07, 0.14, and 0.31 for D-PANI-EB. The SANS results are compared with a number of standard models for two-phase systems. No evidence was found for significant molecular mixing. In some cases the inverse power law model is in reasonable agreement with observations, and in the case of the lowest concentration of D-PANI/CSA there is an indication of mass fractal structure. This was not found at the higher concentrations. The results establish that the blends with the smaller more polar dopants CSA and MSA behave similarly and are unlike either the D-PANI/DBSA blends or those with D-PANI-EB. There is evidence that the simple picture of two pure phases is inadequate for these materials. With the exception of the D-PANI/DBSA blend which has a relatively low scattering contrast, the results indicate that the lower limit of volume fraction for application of SANS is a few percent D-PANI-ES in Nylon 6. X-ray scattering was used to demonstrate the presence of Nylon 6 lamellae and residual peaks attributable to the pure components. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2765–2774, 1997 相似文献
518.
519.
Henrik T. Rasmussen Robert McDonough Robert J. Gargiullo Bruce P. McPherson 《Journal of separation science》1996,19(6):359-361
A validated gas chromatographic method for the determination of triclosan in human dental plaque is described. Based on plaque sample weights of 10 mg, the limit of detection (2 × S/N) is 0.5 μg/g. The method is linear (r = 0.9986) from the limit of detection to 50 μg/g. Recoveries from placebos spiked with 2.0, 25, and 50 μg/g of triclosan were 105.6%±7.5%, 107.2%±3.1%, and 99.1%±1.1%, respectively (n = 3 at each level). Twenty replicate preparations and analyses of a homogenized sample, conducted by two operators over the course of 4 days, showed agreement to within 9% RSD. Analyses of dental plaque collected from patients after brushing with dental cream containing triclosan, shows triclosan to be retained in dental plaque at concentrations above the minimum inhibitory concentration (1 μg/g) after 12 h. 相似文献
520.
M.萨哈伊 朱胜江 甘翠云 朱凌燕 杨利明 许瑞清 全明吉 姜卓 张征 J.H.Hamilton A.V.Ramayya B.R.S.Babu J.K.Hwang W.C.Ma J.Komicki J.D.Cole R.Aryaeinejad M.W.Dirgert J.O.Rasmussen M.A 《中国物理 C》2000,24(11):1018-1023
通过对252Cf自发裂变产生的瞬发γ谱的测量,对丰中子奇A核145,147Ce的高自旋态进行了研究,首次识别了145Ce的集体带结构,扩展了147Ce的集体带结构,扩展了147Ce的能级,并新识别了3个边带,粒子–转子模型的计算指出,145,147Ce的晕带可能来自于νi13/2轨道的耦合,145Ce基态起源于(νh9/2νf7/2)组态混合,而147Ce基态则起源于νh9/2轨道.在这两个核中未观测到明显的八极形变带,然而,在147Ce中观测到的一个边带,可能显露出八极关联的迹象. 相似文献