全文获取类型
收费全文 | 652篇 |
免费 | 85篇 |
专业分类
化学 | 597篇 |
晶体学 | 1篇 |
数学 | 41篇 |
物理学 | 98篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 17篇 |
2019年 | 26篇 |
2018年 | 12篇 |
2017年 | 4篇 |
2016年 | 40篇 |
2015年 | 36篇 |
2014年 | 18篇 |
2013年 | 38篇 |
2012年 | 48篇 |
2011年 | 39篇 |
2010年 | 23篇 |
2009年 | 31篇 |
2008年 | 55篇 |
2007年 | 47篇 |
2006年 | 37篇 |
2005年 | 51篇 |
2004年 | 27篇 |
2003年 | 35篇 |
2002年 | 14篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有737条查询结果,搜索用时 15 毫秒
31.
32.
Hwang IW Kamada T Ahn TK Ko DM Nakamura T Tsuda A Osuka A Kim D 《Journal of the American Chemical Society》2004,126(49):16187-16198
meso-Pyridine-appended zinc(II) porphyrins Mn and their meso-meso-linked dimers Dn assemble spontaneously, in noncoordinating solvents such as CHCl3, into tetrameric porphyrin squares Sn and porphyrin boxes Bn, respectively. Interestingly, formation of Bn from Dn proceeds via homochiral self-sorting assembly, which has been verified by optical separations of B1 and B2. Optically pure enantiomers of B1 and B2 display strong Cotton effects in the CD spectra, which reflect the length of the pyridyl arm, thus providing evidence for the exciton coupling between the noncovalent neighboring porphyrin rings. Excitation energy migration processes within Bn have been investigated by steady-state and time-resolved spectroscopic methods in conjunction with polarization anisotropy measurements. Both the pump-power dependence on the femtosecond transient absorption and the transient absorption anisotropy decay profiles are directly associated with the excitation energy migration process within the Bn boxes, where the exciton-exciton annihilation time and the polarization anisotropy rise time are well described in terms of the F?rster-type incoherent energy hopping model by assuming a number of hopping sites of N = 4 and an exciton coherence length of L = 2. Consequently, the excitation energy hopping rates between the zinc(II) diporphyrin units have been estimated for B1 (48 ps)(-1), B2 (98 +/- 3 ps)(-1), and B3 (361 +/- 6 ps)(-1). Overall, the self-assembled porphyrin boxes Bn serve as a well-defined three-dimensional model for the light-harvesting complex. 相似文献
33.
Hiroshi Hata Dr. Shigeru Yamaguchi Goro Mori Satomi Nakazono Taisuke Katoh Keishi Takatsu Satoru Hiroto Hiroshi Shinokubo Prof. Dr. Atsuhiro Osuka Prof. Dr. 《化学:亚洲杂志》2007,2(7):849-859
Highly regioselective and efficient borylation of a variety of porphyrins has been achieved by reaction with bis(pinacolato)diboron through C? H bond activation under iridium catalysis on the basis of the synthetic protocol developed by Miyaura, Hartwig, and Smith. A boryl group can be selectively introduced at sterically uncongested positions in the peripheral aryl groups of porphyrin substrates whose peripheral β‐positions are sterically hindered. Curiously, β substituents adjacent to the aryl group to be borylated have unexpectedly large effects on the regioselectivity, because the iridium catalyst can discriminate between subtle steric differences. Chemoselective borylation was also achieved for several functionalized porphyrins. This borylation protocol can be applied to various monomeric and oligomeric functional porphyrins, hence offering an efficient route to elaborate multiporphyrin‐based molecular constructs. 相似文献
34.
35.
36.
Dr. Tsubasa Nakashima Haruka Fujimori Dr. Kohsuke Ohmatsu Prof. Takashi Ooi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(36):9253-9256
Intermediary radical cations, generated through single-electron oxidation of enol silyl ethers by excited Ir-based photocatalysts, can be exploited as Brønsted acids for the activation of heteroarylcyanides. This strategy enables the direct allylic C−H heteroarylation of enol silyl ethers under visible-light irradiation. 相似文献
37.
38.
39.
40.
Abstract The copolymerization system of styrene (ST) and citraconic (α-methymaleic) anhydride (CA) was found to form semi-alternating copolymers when polymerized with a total monomer concentration of 4 mol/L in CCl4 at 50°C, with alternating copolymers being formed only when the CA mole fraction in feed was greater than 0.9. More than 50% of the linkage configurations at the cyclic CA units in the copolymers were found to be in cis configuration. This, together with the following observations, is consistent with a participation of the electron donor-acceptor (EDA) complex formed between ST and CA: (a) the complex participation model fits best, although only marginally, to the experimental triad mole fraction of alternating sequences; (b) the alternating monomer unit sequences and the cis linkage configuration at the cyclic CA units are more efficiently formed in non polar CCl4 solutions than in polar methy ethyl ketone. The equilibrium constant for the EDA complexation of ST and CA in CCl4 at 23°C is determined to be 0.142 ± 0.015 L/mol. 相似文献