全文获取类型
收费全文 | 128篇 |
免费 | 5篇 |
专业分类
化学 | 94篇 |
力学 | 4篇 |
数学 | 2篇 |
物理学 | 33篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 1篇 |
2020年 | 7篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 6篇 |
2012年 | 9篇 |
2011年 | 8篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 9篇 |
2007年 | 10篇 |
2006年 | 2篇 |
2005年 | 6篇 |
2004年 | 3篇 |
2003年 | 12篇 |
2002年 | 2篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1991年 | 1篇 |
排序方式: 共有133条查询结果,搜索用时 15 毫秒
41.
Daichi KakutaYukio Hitotsuyanagi Naofumi MatsuuraHaruhiko Fukaya Koichi Takeya 《Tetrahedron》2003,59(39):7779-7786
Four new Stemona alkaloids, sessilifoliamides A-D (1-4), were isolated from the roots of Stemona sessilifolia, along with five known alkaloids, stenine (5), 2-oxostenine (6), stemoninoamide (7), tuberostemonone (8), and neotuberostemonol (9). The structures and absolute configurations of the new alkaloids were determined by the spectral studies (HRMS, IR, 1H, 13C, and 2D NMR), single-crystal X-ray analyses, and chemical correlations. The absolute configuration of 7 was also determined by the modified Mosher's method. 相似文献
42.
43.
Naofumi Nakamura Kimihiro Suzuki 《Journal of polymer science. Part A, Polymer chemistry》1996,34(16):3319-3328
The kninetics of acid-catalyzed acetalization and ketalization of poly(vinyl alcohol) (PVA) were systematically studied in completely homogeneous media with carefully selected solvents. Thus the acetalization reaction was run in water with six aldehydes [R1CHO (R1 = H, CH3, C2H5, n-C3H7, i-C3H7, ClCH2)], whereas the ketalization in dimethylslfoxide with 11 ketones [R2CH3CO (R2 = CH3, C2H5, n-C3H7, i-C3H7, n-C4H9, i-C4H9, tert-C4H9, C6H5CH2, C6H5CH2CH2), cyclopentanone, and cyclohexanone]. The latter was difficult to proceed in aqueous media. Both reactions were reversible and bimolecular and, despite the use of different solvents, gave similar heats of reaction (7.5 kcal/mol) and activation energies (ca. 15 kcal/mol) except for the case of formaldehyde and chloroacetaldehyde; however the equilibrium constants at 25°C showed that the acetalization is thermodynamically much more favored than the ketalization (ca. 5000 vs. 0.01–0.9), probably because of steric hindrance of the ketone substrate. The rate constants of hydrolysis (reverse reactions) for the poly(vinyl acetal) and poly(vinyl ketal) followed the Hammett-Taft equation to give a single p* (=3.60) that is very close to that for the hydrolysis of diethyl acetal and ketal. From these and other data, it was concluded that the polymer hydrolysis, as well as PVA acetalization and ketalization, are all electrophilic reaction where the formation of hemiacetal or hemiketal is the rate-determining step. © 1996 John Wiley & Sons, Inc. 相似文献
44.
Naofumi Nishida Yuuki Hori Akane Yamauchi Makoto Sakurai Hiroyuki A. Sakaue Daiji Kato 《X射线光谱测定》2020,49(1):74-77
The electron beam ion source (Kobe EBIS) has been developed to perform modification of surfaces using highly charged ions (HCIs) at the Kobe University, Japan. Recent study revealed that periodic intermission of electron beam improves charge state distribution of extracted ions. The period of intermission is in the order of 100 ms, and the width of beam-off time is 1 ms or less. This operational mode (pulse mode) makes it possible to produce Ar15+ to Ar17+ effectively, whereas the charge is limited less than 14+ under the ordinary operational mode with direct current (DC) electron beam. A spike of HCIs with a peak current in the order of nA is also observed at each moment of electron beam off. The measurement of the time evolution of Ar16+ intensity around the timing of mode change revealed that the intensity of extracted Ar16+ changes slowly after mode change with a time constant of few seconds. 相似文献
45.
Rib waveguide analysis by theimaginary-distance vectorialbeam-propagation method based on Yee's mesh
Yamauchi Junji Morohashi Naofumi Nakano Hisamatsu 《Optical and Quantum Electronics》1998,30(5-6):397-401
The effective index and the mode profile of rib waveguides are calculated using the vectorial beam-propagation method using the imaginary-distance procedure. Yee's mesh originally developed in the finite-difference time-domain method is employed to discretize a waveguide geometry. The refractive index at the interface between two different media is determined by Ampere's circuital law. The field discontinuities at the interface and singularities at the corners of the waveguide are clearly displayed. 相似文献
46.
Naofumi Tsukada 《Journal of organometallic chemistry》2003,687(2):436-443
Dinuclear palladium complexes bridged by a novel PNNP ligand, N,N′-bis[(2-diphenylphosphino)phenylformamidinate (dpfam), were found to be very efficient and selective catalysts for the double carbonylation of iodobenzene with diethylamine using K3PO4 as base and 1,4-dioxane as solvent with a TON up to 105 and selectivity of 96%. 相似文献
47.
Naofumi Kozai Shinya Yamasaki Toshihiko Ohnuki 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(3):1581-1587
To elucidate the sorption behaviors of radionuclides in multi-mineral systems and the mutual effects of minerals on this sorption, we carried out the sorption and desorption experiments of neptunium(V) on Na-montmorillonite-based two-mineral phasic systems (montmorillonite–calcite, montmorillonite–apatite). In the montmorillonite–calcite system, the sorption on the montmorillonite moiety decreased with increasing calcite content due to interference by the calcium ions dissolved from the calcite moiety, while no accumulation of Np to the calcite was observed. Total sorption of Np on the montmorillonite–apatite system was larger than that on apatite-free Na-montmorillonite, but the sorption on the montmorillonite moiety in this system was less than that on apatite-free Na-montmorillonite. Under weakly acid and neutral pH conditions, Np accumulated on the apatite moiety in a short period. At final pH 4 or less, though the pH condition was sufficient to dissolve the apatite moiety completely, the sorption very slowly increased with time and the increased Np was unexchangeable with 1 M KCl solution. This increase of the unexchangeable sorption cannot be explained by the knowledge accumulated so far. 相似文献
48.
49.
Based on the complex Ginzburg-Landau equation (CGLE), a new mapping model of oscillatory media is proposed. The present dynamics is fully determined by an effective phase field renormalized by amplitude. The model exhibits phase turbulence, amplitude turbulence, and a frozen state reported in the CGLE. In addition, we find a state in which the phase and amplitude have spiral structures with opposite rotational directions. This state is found to be observed also in the CGLE. Thus, one concludes that the behaviors observed in the CGLE can be described by only the phase dynamics appropriately constructed. 相似文献
50.
A single step on-line concentration and separation method for peptides in non-aqueous capillary electrophoresis was developed. ACN containing 50 mM tetraethylammonium perchlorate was used as the electrophoretic medium; angiotensins I-IV were separated as a result of the differences in the magnitudes of their interactions with perchlorate anions. When the sample solution (ACN containing 0.5% trifluoroacetic acid and angiotensins) was injected as a large-volume plug, the analytes were concentrated at the inlet end of the capillary by both sweeping and stacking mechanisms; the separation procedure then started automatically without any operations such as polarity change. It was found that the concentration of analytes, injection period, and concentration of tetraethylammonium perchlorate in the electrophoretic medium were important factors for both separation and concentration efficiencies. The angiotensins were concentrated and separated with the large-volume injection of up to 80% of the effective capillary length. 相似文献