全文获取类型
收费全文 | 425篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
化学 | 368篇 |
晶体学 | 2篇 |
力学 | 4篇 |
数学 | 24篇 |
物理学 | 38篇 |
出版年
2021年 | 6篇 |
2020年 | 7篇 |
2018年 | 3篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 9篇 |
2013年 | 18篇 |
2012年 | 31篇 |
2011年 | 22篇 |
2010年 | 14篇 |
2009年 | 15篇 |
2008年 | 29篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 21篇 |
2004年 | 16篇 |
2003年 | 14篇 |
2002年 | 12篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1992年 | 2篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1975年 | 8篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1968年 | 14篇 |
1967年 | 9篇 |
1966年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有436条查询结果,搜索用时 15 毫秒
41.
42.
Vibrational circular dichroism (VCD) spectra were measured on the chloroform solutions of a series of mixed-ligand diamagnetic Co(III) complexes, [Co(tfac)(n)(acac)(3-n)] (n = 0-3, tfac = 1,1,1-trifluoro-2,4-pentanedionato; acac = acetylacetonato). Distinct differences were observed in the VCD spectra among the geometrical isomers of the same ligand composition. Such differentiation was hardly possible by their infra-red spectra alone. The structural identification of these isomers was performed in conjunction with DFT calculations. 相似文献
43.
Syun-ichi Kiyooka Yushi Takeshita Yoshinori Tanaka Takafumi Higaki Yosuke Wada 《Tetrahedron letters》2006,47(26):4453-4456
A dicationic ((−)-sparteine)palladium complex underwent a superior catalytic enantioselective aldol reaction of aldehydes with 1-phenyl-1-trimethylsilyloxyethene performing satisfactorily, starting with ((−)-sparteine)PdCl2 and AgSbF6 as catalyst precursors (1 mol % loading) in the presence of 3 Å molecular sieves over the reaction. 相似文献
44.
45.
Takahiro Nakae Ryuji Ohnishi Yoshiharu Kitahata Tatsuya Soukawa Hisako Sato Shigeki Mori Tetsuo Okujima Hidemitsu Uno Hiroshi Sakaguchi 《Tetrahedron letters》2012,53(13):1617-1619
6,13-Diiododibenzo[a,h]anthracene and 5,8-diiodopicene were synthesized by AuCl-catalyzed double cyclization. The highly selective reaction yielded a new class of peri-halogenated fused aromatics. 相似文献
46.
Michael Widhalm Michael Abraham Vladimir B. Arion Siret Saarsalu Uno Maeorg 《Tetrahedron: Asymmetry》2010,21(16):1971-1982
A group of five phosphino hydrazones with a pendant binaphthyl unit as a chiral modifier has been synthesized from non-racemic 2,2′-bis(bromomethyl)-1,1′-binaphthyl and 3,3′-diiodo-2,2′-bis(bromomethyl)-1,1′-binaphthyl as the key intermediates. Their efficiency as chiral ligands in palladium-catalyzed allylic alkylation reactions has been investigated showing up to 95% ee under optimized conditions. X-ray diffraction structures of mono- and dimeric Pd complexes are also reported. 相似文献
47.
48.
Kenji Tamura Hikaru Uno Hirohisa Yamada Kiyoshi Umeyama 《Journal of Polymer Science.Polymer Physics》2009,47(6):583-595
The effect of two different species of layered silicates on the morphology, mechanical properties, and methanol vapor barrier properties of polyamide‐6 (PA6) nanocomposites was examined using identical experimental conditions for both species. The layered silicate species used were natural montmorillonite (MMT) and synthetic expandable fluoro‐mica (FM), the chemical compositions of which were Na0.43(Al1.56Mg0.31Fe2+ 0.09)(Si3.95Al0.05)O10(OH)2 and Na0.66Mg2.68(Si3.98Al0.02)O10F2, respectively. The layered silicates were modified with a dodecylammonium salt (DDA) using an ion‐exchange method. The resulting organically modified layered silicates were melt‐kneaded with PA6 in a twin‐screw kneader at 260 °C. By quantitative analysis of the silicate layers dispersed in the PA6, the number‐average aspect ratio was estimated to be 76 for DDAMMT‐PA6 and 85 for DDAFM‐PA6. This confirmed that the primary particle size of the initial silicate did affect the aspect ratio. The rigidity and gas barrier properties of the nanocomposites appeared to depend upon the morphology of the nanocomposite. On the other hand, the elongation at break of the nanocomposites decreased as the amount of silicate increased. This reduction in ductility was ascribed to the difference in morphology of the nanocomposites, that is, distribution of silicate nanolayers in the polymer matrix. The homogeneity of the particle fraction of exfoliated nanolayers was clearly an important factor affecting the properties of the nanocomposites. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 583–595, 2009 相似文献
49.
The metabolites 3 and 4 of 2-(4-ethyl-1-piperazinyl)-4-phenylquinoline dimaleate (AS-2646, 1), a candidate as a gastric antisecretory and antiulcer drug, were synthesized to confirm the proposed structures. The effects of the metabolites 2-4 on ulcer induced by stress were determined. 相似文献
50.
An automatic aberration correction method has been implemented in scanning electron microscopes (SEM). Necessity of the automatic aberration correction is discussed. The procedure of the automatic aberration correction is explained in detail, where deconvolution techniques are used in order to extract probe information from SEM images. Due to the precise digitization and the usage of proper combinations of correction fields, linearity has been found between the amplitude of each aberration and the corresponding field strength. Experimental results are shown which demonstrate that the aberrations are corrected automatically by a linear feedback control method. After the automatic aberration correction, the image quality has been improved drastically. 相似文献