全文获取类型
收费全文 | 551篇 |
免费 | 44篇 |
专业分类
化学 | 472篇 |
晶体学 | 5篇 |
力学 | 8篇 |
数学 | 21篇 |
物理学 | 89篇 |
出版年
2023年 | 7篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 12篇 |
2019年 | 19篇 |
2018年 | 9篇 |
2017年 | 3篇 |
2016年 | 29篇 |
2015年 | 19篇 |
2014年 | 24篇 |
2013年 | 39篇 |
2012年 | 49篇 |
2011年 | 33篇 |
2010年 | 26篇 |
2009年 | 31篇 |
2008年 | 32篇 |
2007年 | 25篇 |
2006年 | 39篇 |
2005年 | 27篇 |
2004年 | 31篇 |
2003年 | 19篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1998年 | 4篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1966年 | 3篇 |
排序方式: 共有595条查询结果,搜索用时 15 毫秒
1.
Bo Huang Hirokazu Kobayashi Tomokazu Yamamoto Takaaki Toriyama Syo Matsumura Yoshihide Nishida Katsutoshi Sato Katsutoshi Nagaoka Masaaki Haneda Wei Xie Yusuke Nanba Michihisa Koyama Fenglong Wang Shogo Kawaguchi Yoshiki Kubota Hiroshi Kitagawa 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2252-2257
Ru is an important catalyst in many types of reactions. Specifically, Ru is well known as the best monometallic catalyst for oxidation of carbon monoxide (CO) and has been practically used in residential fuel cell systems. However, Ru is a minor metal, and the supply risk often causes violent fluctuations in the price of Ru. Performance‐improved and cost‐reduced solid‐solution alloy nanoparticles of the Cu‐Ru system for CO oxidation are now presented. Over the whole composition range, all of the CuxRu1?x nanoparticles exhibit significantly enhanced CO oxidation activities, even at 70 at % of inexpensive Cu, compared to Ru nanoparticles. Only 5 at % replacement of Ru with Cu provided much better CO oxidation activity, and the maximum activity was achieved by 20 at % replacement of Ru by Cu. The origin of the high catalytic performance was found as CO site change by Cu substitution, which was investigated using in situ Fourier transform infrared spectra and theoretical calculations. 相似文献
2.
Haruka Takeuchi Prof. Dr. Shinsuke Inuki Kohei Nakagawa Takaaki Kawabe Dr. Atsuhiko Ichimura Prof. Dr. Shinya Oishi Prof. Dr. Hiroaki Ohno 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(47):21396-21401
We report herein a nonbiomimetic strategy for the total synthesis of the plicamine-type alkaloids zephycarinatines C and D. The key feature of the synthesis is a stereoselective reductive radical ipso-cyclization using visible-light-mediated photoredox catalysis. This cyclization enabled the construction of a 6,6-spirocyclic core structure through the addition of a carbon-centered radical onto the aromatic ring. Biological evaluation of zephycarinatines and their derivatives revealed that the synthetic derivative with a keto group displays moderate inhibitory activity against LPS-induced NO production. This approach could offer future opportunities to expand the chemical diversity of plicamine-type alkaloids as well as providing useful intermediates for their syntheses. 相似文献
3.
Frontispiece: An Optically and Thermally Switchable Electronic Structure Based on an Anthracene–BODIPY Conjugate 下载免费PDF全文
4.
Dr. Hironobu Hayashi Nao Hieda Dr. Mitsuaki Yamauchi Yee Seng Chan Prof. Dr. Naoki Aratani Prof. Dr. Sadahiro Masuo Prof. Dr. Hiroko Yamada 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(66):15079-15083
The photo-induced generation of unstable molecules generally requires stringent conditions to prevent oxidation and the concomitant decomposition of the products. The visible-light-induced conversion of two heptacene precursors to heptacene was studied. Single crystals of bis- and mono-α-diketone-type heptacene precursors ( 7-DK2 and 7-DK1 , respectively), were prepared to investigate the effect of precursor structure on reactivity. The photoirradiation of a 7-DK2 single crystal cleaved only one α-diketone group, forming an intermediate bearing a pentacene subunit, while that of a 7-DK1 single crystal gave rise to characteristic absorption peaks of heptacene and their increase in intensity with photoirradiation time, indicating the generation of heptacene without decomposition. Heptacene production was not observed when the precursors were photoirradiated in solution, implying that the single crystal interior provided isolation from the external environment, thus preventing heptacene oxidation. 相似文献
5.
Aromaticity Relocation in Perylene Derivatives upon Two‐Electron Oxidation To Form Anthracene and Phenanthrene 下载免费PDF全文
Akinobu Matsumoto Dr. Mitsuharu Suzuki Dr. Hironobu Hayashi Dr. Daiki Kuzuhara Dr. Junpei Yuasa Prof. Dr. Tsuyoshi Kawai Prof. Dr. Naoki Aratani Prof. Dr. Hiroko Yamada 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(41):14462-14466
We prepared perylene dications 1 2+ and 2 2+ by using “capped” perylene derivatives, and for the first time, successfully obtained single crystals of a perylene dication 1 2+ that enabled us to perform its structural analysis. We realized that the substituted aryl groups on perylene control the positions of positive charges, thus the remaining electronic system satisfies Clar's sextet rule toward the highest number of localized sextets. Experimental and theoretical evidence proved that Clar's aromatic π‐sextet rule could be applied even for the dicationic perylenes in a very simple way. 相似文献
6.
Synthesis and Metalation of Doubly o‐Phenylene‐Bridged Cyclic Bis(dipyrrin)s with Highly Bent Skeleton of Dibenzoporphyrin(2.1.2.1) 下载免费PDF全文
Dr. Daiki Kuzuhara Wataru Furukawa Aya Kitashiro Prof. Dr. Naoki Aratani Prof. Dr. Hiroko Yamada 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10671-10678
Facile synthesis of dibenzoporphyrins(2.1.2.1) has been successfully reported by the simple condensation reaction of o‐dipyrrolylbenzene with various aldehydes in the presence of a Lewis acid. This reaction enables the preparation of various dibenzoporphyrin(2.1.2.1) derivatives with p‐substituted phenyl groups, five‐membered heterocycles, and ethynyl groups at the meso‐positions. Dibenzoporphyrins(2.1.2.1) consist of two dipyrrin units that are connected by o‐phenylene bridges, which adopt highly bent saddle‐shaped structures; this was confirmed by X‐ray diffraction analysis. We found that dibenzoporphyrin(2.1.2.1) can be described as a 20π antiaromatic conjugated system, but practically, it is not an antiaromatic macrocycle, which we revealed by 1H NMR spectroscopy. The redox potentials had good correlations with Hammett substituent constant (σp) of the substituents at the meso‐positions. The free‐base dibenzoporphyrin(2.1.2.1) was able to form the metal complexes with nickel(II), copper(II), palladium(II), platinum(II), and tin(IV) ions. These results suggested that dibenzoporphyrin(2.1.2.1) derivatives can be utilized as novel macrocyclic dianionic tetradentate ligands for various metal ions to give complexes with varying optical and electrochemical properties. 相似文献
7.
8.
Crystal Structure of the Isopropylzinc Alkoxide of Pyrimidyl Alkanol: Mechanistic Insights for Asymmetric Autocatalysis with Amplification of Enantiomeric Excess 下载免费PDF全文
Dr. Arimasa Matsumoto Takaaki Abe Atsushi Hara Takayuki Tobita Taisuke Sasagawa Prof. Dr. Tsuneomi Kawasaki Prof. Dr. Kenso Soai 《Angewandte Chemie (International ed. in English)》2015,54(50):15218-15221
Asymmetric amplification during self‐replication is a key feature that is used to explain the origin of homochirality. Asymmetric autocatalysis of pyrimidyl alkanol in the asymmetric addition of diisopropylzinc to pyrimidine‐5‐carbaldehyde is a unique example of this phenomenon. Crystallization of zinc alkoxides of this 5‐pyrimidyl alkanol and single‐crystal X‐ray diffraction analysis of the alkoxide crystals reveal the existence of tetramer or higher oligomer structures in this asymmetric autocatalytic system. 相似文献
9.
Dr. Songlin Xue Dr. W. Ryan Osterloh Xiaojuan Lv Ningchao Liu Yimei Gao Dr. Haitao Lei Dr. Yuanyuan Fang Dr. Zhongti Sun Dr. Peifeng Mei Dr. Daiki Kuzuhara Dr. Naoki Aratani Dr. Hiroko Yamada Dr. Rui Cao Dr. Karl M. Kadish Dr. Fengxian Qiu 《Angewandte Chemie (International ed. in English)》2023,62(17):e202218567
The molecular structure, electrochemistry, spectroelectrochemistry and electrocatalytic oxygen reduction reaction (ORR) features of two CoII porphyrin(2.1.2.1) complexes bearing Ph or F5Ph groups at the two meso-positions of the macrocycle are examined. Single crystal X-ray analysis reveal a highly bent, nonplanar macrocyclic conformation of the complex resulting in clamp-shaped molecular structures. Cyclic voltammetry paired with UV/Vis spectroelectrochemistry in PhCN/0.1 M TBAP suggest that the first electron addition corresponds to a macrocyclic-centered reduction while spectral changes observed during the first oxidation are consistent with a metal-centered CoII/CoIII process. The activity of the clamp-shaped complexes towards heterogeneous ORR in 0.1 M KOH show selectivity towards the 4e− ORR pathway giving H2O. DFT first-principle calculations on the porphyrin catalyst indicates a lower overpotential for 4e− ORR as compared to the 2e− pathway, consistent with experimental data. 相似文献
10.
Prof. Dr. Tsutomu Ishi-i Honoka Tanaka Rihoko Kichise Christopher Davin Takaaki Matsuda Dr. Naoya Aizawa Dr. In Seob Park Prof. Dr. Takuma Yasuda Taisuke Matsumoto 《化学:亚洲杂志》2021,16(15):2136-2145
The regulation of multicolor fluorescence changes in mechanochromic fluorescence (MCF) remains a challenging task. Herein, we report the regulation of MCF using a donor-acceptor structure. Two crystal polymorphs, BTD-pCHO(O) and BTD-pCHO(R) produced by the introduction of formyl groups to an MCF dye, respond to a mechanical stimulus, allowing a three-color fluorescence change. Specifically, the orange-colored fluorescence of the metastable BTD-pCHO(O) polymorph changed to a deep-red color in the amorphous-like state to finally give a red color in the stable BTD-pCHO(R) polymorph. This change occurred by mechanical grinding followed by vapor fuming. The two different crystal packing patterns were selectively regulated by the electronic effect of the introduced functional groups. The two types of selectively formed crystals in BTD(F)-pCHO bearing fluorine atoms, and BTD(OMe)-pCHO bearing methoxy groups, respond to mechanical grinding, allowing for the regulation of multicolor MCL from a three-color change to two different types of two-color changes. 相似文献