全文获取类型
收费全文 | 187篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 126篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 25篇 |
物理学 | 44篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 1篇 |
2017年 | 6篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 12篇 |
2012年 | 7篇 |
2011年 | 13篇 |
2010年 | 7篇 |
2009年 | 6篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 16篇 |
2005年 | 10篇 |
2004年 | 7篇 |
2003年 | 5篇 |
2002年 | 9篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1983年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有201条查询结果,搜索用时 15 毫秒
51.
R. Venegas F. Labenski de Kanter S. Acebal R. Grassi E. H. Rueda M. E. Aguirre C. Saragovi 《Hyperfine Interactions》1994,83(1):443-450
Bahia Blanca (Argentina) soils, in particular entisols, are studied by Mössbauer spectroscopy. X-ray diffraction and scanning electron microscopy are used to characterize the samples. Samples were treated with different chemical iron extraction methods, in order to determine relative Feo and Fed fractions. The Feo/Fed ratios are obtained and the relative effect of iron extraction treatment on spectra components are determined. In addition, the effect of extraction procedures, dithionite-citrate-bicarbonate and oxalate, in the residual soil fraction are analyzed. 相似文献
52.
This work studies and compares the effects on performance of local dominance and local recombination applied with different locality in multiobjective evolutionary algorithms on combinatorial 0/1 multiobjective knapsack problems. For this purpose, we introduce a method that creates a neighborhood around each individual and assigns a local dominance rank after alignment of the principle search direction of the neighborhood by using polar coordinates in objective space. For recombination a different neighborhood determined around a random principle search direction is created. The neighborhood sizes for dominance and recombination are separately controlled by two different parameters. Experimental results show that the optimum locality of dominance is different from the optimum locality of recombination. Additionally, it is shown that the performance of the algorithm that applies local dominance and local recombination with different locality is significantly better than the performance of algorithms applying local dominance alone, local recombination alone, or dominance and recombination globally as conventional approaches do. 相似文献
53.
Micromotor endoscope catheter for in vivo, ultrahigh-resolution optical coherence tomography 总被引:5,自引:0,他引:5
Herz PR Chen Y Aguirre AD Schneider K Hsiung P Fujimoto JG Madden K Schmitt J Goodnow J Petersen C 《Optics letters》2004,29(19):2261-2263
A distally actuated, rotational-scanning micromotor endoscope catheter probe is demonstrated for ultrahigh-resolution in vivo endoscopic optical coherence tomography (OCT) imaging. The probe permits focus adjustment for visualization of tissue morphology at varying depths with improved transverse resolution compared with standard OCT imaging probes. The distal actuation avoids nonuniform scanning motion artifacts that are present with other probe designs and can permit a wider range of imaging speeds. Ultrahigh-resolution endoscopic imaging is demonstrated in a rabbit with <4-microm axial resolution by use of a femtosecond Cr:forsterite laser light source. The micromotor endoscope catheter probe promises to improve OCT imaging performance in future endoscopic imaging applications. 相似文献
54.
Optical coherence microscopy (OCM) is demonstrated with a high-speed, broadband, reflective-grating phase modulator and a femtosecond Ti:Al2O3 laser. The novel system design permits high-resolution OCM imaging in a new operating regime in which a short coherence gate is used to relax the requirement for high-numerical-aperture confocal axial sectioning. In vivo cellular imaging is demonstrated in the Xenopus laevis tadpole and in human skin with a 3-microm coherence gate and a 30-microm confocal gate. The ability to achieve cellular imaging with a lower numerical aperture should facilitate the development of miniaturized probes for in vivo imaging applications. 相似文献
55.
Neves L Lima G Aguirre Gómez JG Monken CH Saavedra C Pádua S 《Physical review letters》2005,94(10):100501
We report an experiment to generate entangled states of D-dimensional quantum systems, qudits, by using transverse spatial correlations of two parametric down-converted photons. Apertures with D slits in the arms of the twin photons define the qudit space. By manipulating the pump beam correctly, the twin photons will pass only by symmetrically opposite slits, generating entangled states between these different paths. Experimental results for qudits with D = 4 and 8 are shown. We demonstrate that the generated states are entangled states. 相似文献
56.
Juliá n Aguirre Fernando Castañ eda Juan Carlos Peral. 《Mathematics of Computation》2004,73(245):323-331
We develop an algorithm for bounding the rank of elliptic curves in the family , all of them with torsion group and modular invariant . We use it to look for curves of high rank in this family and present four such curves of rank and of rank .
57.
[reaction: see text]. The chemistry of amino alcohols has been studied in superacidic media, and these compounds have been found to ionize cleanly to the dication intermediates. Several dicationic species have been directly observed by low-temperature 13C NMR, including those from epinephrine (adrenaline) and synephrine. Amino alcohols react (70-99% yields) with C6H6 in triflic acid (CF3SO3H) by electrophilic aromatic substitution. 相似文献
58.
Methoxycarbonylation of olefins catalyzed by palladium(II) complexes containing naphthyl(diphenyl)phosphine ligands 下载免费PDF全文
Santiago Zolezzi Sergio A. Moya Gonzalo Valdebenito Gabriel Abarca Jose Parada Pedro Aguirre 《应用有机金属化学》2014,28(5):364-371
Palladium(II) complexes containing phosphine donor ligands derived from naphthyl(diphenyl)phosphine were synthesized and characterized by NMR and elemental analysis. The complexes were studied as catalyst precursors in the methoxycarbonylation reaction of several aromatic and aliphatic olefins under mild conditions. The catalysts reported high chemoselectivities (over 96%) and regioselectivities between 44% and 93% for different olefins. The best results were obtained over a styrene substrate with 97% of conversion after 6 h of reaction, with high regioselectivity (93%). Kinetic studies permitted the determination of the rate law (v = k [substrate]1.21±0.02 [catalyst]0.94±0.11 [acid]0.52±0.03 [MeOH]0.53±0.05 [CO]0.65±0.03) for methoxycarbonylation of styrene. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
59.
García Camilo Navarro Freddy Ruíz-León Domingo Beltrán Olimpo García Aguirre María Jesús 《Journal of Solid State Electrochemistry》2017,21(1):243-253
Journal of Solid State Electrochemistry - In this work, a cationic porphyrin, ascribed as [Ttolyl(P-(C6H5)3)4]4+, where Ttolyl = 5,10,15,20 tetrakistolylporphyrin, was... 相似文献
60.
Alonso Aguirre‐Valderrama 《Journal of carbohydrate chemistry》2013,32(7):557-594
The conformational space of D and L, deoxy and nondeoxy, 5‐thio‐pyranoses with biological properties as enzymatic inhibitors was explored using MM and B3LYP/6–31+G* methods in gas phase and solution. The preferred ring conformation for α and β anomers of 5‐thio‐L‐fucopyranose was the 1C4 form (about 99%), and for 5‐thio‐D‐glucopyranose and 5‐thio‐D‐mannopyranose, the 4C1 one. The experimental conformational order (4C1>1C4>2SS) for L‐ido derivatives was reproduced only considering the solvent, though for 3‐O‐methyl‐5‐thio‐α‐L‐idopyranose, the inclusion of methyl in C3 changed the 2SS form to the B1,4 one. 相似文献