全文获取类型
收费全文 | 1230篇 |
免费 | 23篇 |
国内免费 | 3篇 |
专业分类
化学 | 715篇 |
晶体学 | 7篇 |
力学 | 13篇 |
数学 | 109篇 |
物理学 | 412篇 |
出版年
2021年 | 5篇 |
2020年 | 10篇 |
2019年 | 19篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 25篇 |
2014年 | 25篇 |
2013年 | 71篇 |
2012年 | 54篇 |
2011年 | 77篇 |
2010年 | 39篇 |
2009年 | 40篇 |
2008年 | 78篇 |
2007年 | 75篇 |
2006年 | 70篇 |
2005年 | 86篇 |
2004年 | 78篇 |
2003年 | 51篇 |
2002年 | 46篇 |
2001年 | 26篇 |
2000年 | 15篇 |
1999年 | 15篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 16篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 14篇 |
1992年 | 13篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 19篇 |
1984年 | 26篇 |
1983年 | 8篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 12篇 |
1973年 | 7篇 |
1972年 | 5篇 |
1968年 | 4篇 |
排序方式: 共有1256条查询结果,搜索用时 15 毫秒
1.
Prof. Isao Fujii Dr. Makoto Hashimoto Kaori Konishi Akiko Unezawa Haruka Sakuraba Kenta Suzuki Harue Tsushima Miho Iwasaki Satsuki Yoshida Akane Kudo Rina Fujita Aika Hichiwa Koharu Saito Dr. Takashi Asano Dr. Jun Ishikawa Dr. Daigo Wakana Dr. Yukihiro Goda Ayumi Watanabe Mamoru Watanabe Yui Masumoto Dr. Junichiro Kanazawa Dr. Hajime Sato Prof. Masanobu Uchiyama 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(22):8542-8548
Shimalactones A and B are neuritogenic polyketides possessing characteristic oxabicyclo[2.2.1]heptane and bicyclo[4.2.0]octadiene ring systems that are produced by the marine fungus Emericella variecolor GF10. We identified a candidate biosynthetic gene cluster and conducted heterologous expression analysis. Expression of ShmA polyketide synthase in Aspergillus oryzae resulted in the production of preshimalactone. Aspergillus oryzae and Saccharomyces cerevisiae transformants expressing ShmA and ShmB produced shimalactones A and B, thus suggesting that the double bicyclo-ring formation reactions proceed non-enzymatically from preshimalactone epoxide. DFT calculations strongly support the idea that oxabicyclo-ring formation and 8π-6π electrocyclization proceed spontaneously after opening of the preshimalactone epoxide ring through protonation. We confirmed the formation of preshimalactone epoxide in vitro, followed by its non-enzymatic conversion to shimalactones in the dark. 相似文献
2.
Prof. Dr. Takanori Iwasaki Prof. Dr. Nobuaki Kambe 《Chemical record (New York, N.Y.)》2023,23(9):e202300033
Carbon-fluorine bonds are stable and have demonstrated sluggishness against various chemical manipulations. However, selective transformations of C−F bonds can be achieved by developing appropriate conditions as useful synthetic methods in organic chemistry. This review focuses on C−C bond formation at monofluorinated sp3-hybridized carbons via C−F bond cleavage, including cross-coupling and multi-component coupling reactions. The C−F bond cleavage mechanisms on the sp3-hybridized carbon centers can be primarily categorized into three types: Lewis acids promoted F atom elimination to generate carbocation intermediates; nucleophilic substitution with metal or carbon nucleophiles supported by the activation of C−F bonds by coordination of Lewis acids; and the cleavage of C−F bonds via a single electron transfer. The characteristic features of alkyl fluorides, in comparison with other (pseudo)halides as promising electrophilic coupling counterparts, are also discussed. 相似文献
3.
4.
5.
6.
Takuya Miura Saki FujiokaHiroki Iwasaki Minoru OzekiNaoto Kojima Masayuki Yamashita 《Tetrahedron letters》2014
A skeleton transformation of 5-aryl-α-pyrones into dihydrofurans was developed. In the course of our study of the skeleton transformation reaction of α-pyrones by using dimethylsulfoxonium methylide, α-pyrones having an aryl group at the 5-position were converted into corresponding dihydrofurans as major products and bicyclo[3.1.0]hexanes as minor products. Selectivity for dihydrofurans was improved by optimizing the reaction conditions and investigating the substituent effect. 相似文献
7.
8.
9.
Kentaro Iwasaki Kazunori Umishita Shojun Hino Koichi Kikuchi Yohji Achiba 《Molecular Crystals and Liquid Crystals》2013,570(1):623-628
Abstract Ultraviolet photoelectron spectra of potassium dosed higher fullerenes are measured with a synchrotron radiation light source. Potassium dosing to higher fullerenes brings a new structure between the spectral onset of pristine fullerenes and the Fermi level. As the spectral edge of the new structure does not cross the Fermi level, potassium dosed higher fullerenes are not metallic but semiconductive. When the potassium is excessively dosed to the fullerenes, the lower binding energy structures above 5 eV become faint. In contrast to this phenomenon, four distinct structures appear between 5 and 14 eV. 相似文献
10.
Morphological studies of a hydrogen-bonded LC polymer obtained by photopolymerization in LC solvents
Hideyuki Kihara Corresponding author Toshiaki Miura Ryoichi Kishi Takashi Yoshida Mitsuhiro Shibata Ryutoku Yosomiya 《Liquid crystals》2013,40(7):799-809
Anisotropic morphologies and the phase behaviour of a hydrogen-bonded LC polymer obtained by photopolymerization in two kinds of LC solvent are discussed. The hydrogen-bonded LC monomer, 4-(6-acryloyloxyhexyloxy) benzoic acid (A6OBA), was photopolymerized in 4-cyano-4′-hexyloxybiphenyl (6OCB) and in 4-cyano-4′-undecyloxybiphenyl (11OCB), which show a nematic phase and a smectic A phase, respectively. After photo-polymerization, the LC media were removed by extraction and the pure polymer was observed by scanning electron microscopy. SEM images showed that the polymer possessed fibrous morphology with a fibre diameter of a few micrometers, based on polymerization-induced phase separation. The overall geometries reflected typical LC characteristics such as schlieren and focal-conic fan textures. It was found that the hydrogen bond between benzoic acid groups in the monomer was rigid enough to fix the anisotropic phase-separated structure forming during the early stage of phase separation; however, it could not permanently maintain the fibre structure due to dissociation at elevated temperature. X-ray measurements revealed that a well developed layer structure of the hydrogen-bonded mesogen existed in the polymer obtained from the smectic phase of 11OCB, whereas a polymer layer structure could develop only partially from the nematic phase of 6OCB. 相似文献