全文获取类型
收费全文 | 692篇 |
免费 | 30篇 |
国内免费 | 1篇 |
专业分类
化学 | 535篇 |
晶体学 | 14篇 |
力学 | 4篇 |
数学 | 33篇 |
物理学 | 137篇 |
出版年
2023年 | 6篇 |
2021年 | 8篇 |
2020年 | 21篇 |
2019年 | 13篇 |
2018年 | 14篇 |
2017年 | 5篇 |
2016年 | 15篇 |
2015年 | 17篇 |
2014年 | 21篇 |
2013年 | 33篇 |
2012年 | 42篇 |
2011年 | 46篇 |
2010年 | 35篇 |
2009年 | 32篇 |
2008年 | 46篇 |
2007年 | 49篇 |
2006年 | 59篇 |
2005年 | 50篇 |
2004年 | 38篇 |
2003年 | 39篇 |
2002年 | 35篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有723条查询结果,搜索用时 31 毫秒
231.
232.
Kohei Morioka Yoshikatsu Suito Yutaka Isobe Shigeki Habaue Yoshio Okamoto 《Journal of polymer science. Part A, Polymer chemistry》2003,41(21):3354-3360
The radical polymerization of an optically active methacrylamide, N‐[(R)‐α‐methoxycarbonylbenzyl]methacrylamide, was carried out in the absence and presence of Lewis acids such as yittribium trifluoromethanesulfonate [Yb(OTf)3] and scandium trifluoromethanesulfonate [Sc(OTf)3]. Catalytic amounts of the Lewis acids significantly affected the stereoregularity of the obtained polymers. The polymerization with Yb(OTf)3 in tetrahydrofuran afforded isotactic polymers (up to mm = 87%), whereas the conventional radical method without the Lewis acid produced polymers rich in syndiotacticity (up to rr = 88%). The radical polymerization in the presence of MgBr2 proceeded in a heterotactic‐selective manner (mr = 63%). Thus, the isotactic, syndiotactic, and heterotactic poly(methacrylamide)s were synthesized by the radical processes. The chiral recognition abilities of the obtained optically active poly(methacrylamide)s were affected by the stereoregularity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3354–3360, 2003 相似文献
233.
234.
235.
Sankar J Mori S Saito S Rath H Suzuki M Inokuma Y Shinokubo H Kim KS Yoon ZS Shin JY Lim JM Matsuzaki Y Matsushita O Muranaka A Kobayashi N Kim D Osuka A 《Journal of the American Chemical Society》2008,130(41):13568-13579
meso-Aryl-substituted [28]hexaphyrins(1.1.1.1.1.1) have been examined by (1)H, (13)C, and (19)F NMR spectroscopies, UV-vis absorption spectroscopy, magnetic circular dichroism spectroscopy, and single-crystal X-ray diffraction analysis. All of these data consistently indicate that [28]hexaphyrins(1.1.1.1.1.1) in solution at 25 degrees C exist largely as an equilibrium among several rapidly interconverting twisted M?bius conformations with distinct aromaticities, with a small contribution from a planar rectangular conformation with antiaromatic character at slightly higher energy. In the solid state, [28]hexaphyrins(1.1.1.1.1.1) take either planar or M?bius-twisted conformations, depending upon the meso-aryl substituents and crystallization conditions, indicating a small energy difference between the two conformers. Importantly, when the temperature is decreased to -100 degrees C in THF, these rapid interconversions among M?bius conformations are frozen, allowing the detection of a single [28]hexaphyrin(1.1.1.1.1.1) species having a M?bius conformation. Detailed analyses of the solid-state M?bius structures of compounds 2b, 2c, and 2f showed that singly twisted structures are achieved without serious strain and that cyclic pi-conjugation is well-preserved, as needed for exhibiting strong diatropic ring currents. Actually, the harmonic-oscillator model for aromaticity (HOMA) values of these structures are significantly large (0.85, 0.69, and 0.71, respectively), confirming the first demonstration of stable M?bius aromatic systems consisting of free-base expanded porphyrins without the assistance of metal coordination. 相似文献
236.
237.
238.
Eiki Tomita Dr. Masahiro Kojima Dr. Yuki Nagashima Prof. Dr. Ken Tanaka Dr. Haruki Sugiyama Prof. Dr. Yasutomo Segawa Dr. Atsushi Furukawa Prof. Dr. Katsumi Maenaka Prof. Dr. Satoshi Maeda Dr. Tatsuhiko Yoshino Prof. Dr. Shigeki Matsunaga 《Angewandte Chemie (International ed. in English)》2023,62(21):e202301259
The synthesis, characterization, and catalytic performance of an iridium(III) catalyst with an electron-deficient cyclopentadienyl ligand ([CpEIrI2]2) are reported. The [CpEIrI2]2 catalyst was synthesized by complexation of a precursor of the CpE ligand with [Ir(cod)OAc]2, followed by oxidation, desilylation, and removal of the COD ligand. The electron-deficient [CpEIrI2]2 catalyst enabled C−H amidation reactions assisted by a weakly coordinating ether directing group. Experimental mechanistic studies and DFT calculations suggested that the high catalytic performance of [CpEIrI2]2 is due to its electron-deficient nature, which accelerates both C−H activation and IrV-nitrenoid formation. 相似文献
239.
Aromaticity Reversal in the Lowest Excited Triplet State of Archetypical Möbius Heteroannulenic Systems 下载免费PDF全文
Juwon Oh Dr. Young Mo Sung Woojae Kim Dr. Shigeki Mori Prof. Dr. Atsuhiro Osuka Prof. Dr. Dongho Kim 《Angewandte Chemie (International ed. in English)》2016,55(22):6487-6491
The aromaticity reversal in the lowest triplet state (T1) of a comparable set of Hückel/Möbius aromatic metalated expanded porphyrins was explored by optical spectroscopy and quantum calculations. In the absorption spectra, the T1 states of the Möbius aromatic species showed broad, weak, and ill‐defined spectral features with small extinction coefficients, which is in line with typical antiaromatic expanded porphyrins. In combination with quantum calculations, these results indicate that the Möbius aromatic nature of the S0 state is reversed to Möbius antiaromaticity in the T1 state. This is the first experimental observation of aromaticity reversal in the T1 state of Möbius aromatic molecules. 相似文献
240.
Koichi Nishimura Kei-ichi Sakakura Shigeki Tachihara Yutaka Aoyagi Takeshi Kinoshita 《Tetrahedron》2007,63(21):4558-4562
Three new diterpenoids, tricalysiolide H (1) and tricalysiones A (2) and B (3), with novel structural features were isolated from the wood of Tricalysia dubia, together with a known compound, cafestol (4). The structures of 1-3 were elucidated on the basis of 2D NMR spectroscopy and X-ray crystallographic analysis. 相似文献