全文获取类型
收费全文 | 147篇 |
免费 | 4篇 |
专业分类
化学 | 121篇 |
力学 | 3篇 |
数学 | 1篇 |
物理学 | 26篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 1篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 6篇 |
2012年 | 5篇 |
2011年 | 12篇 |
2010年 | 5篇 |
2009年 | 9篇 |
2008年 | 10篇 |
2007年 | 11篇 |
2006年 | 3篇 |
2005年 | 4篇 |
2004年 | 7篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1968年 | 1篇 |
1965年 | 2篇 |
1891年 | 2篇 |
排序方式: 共有151条查询结果,搜索用时 465 毫秒
1.
Arata Yajima Ayumi Yamaguchi Fumihiro Saitou Tomoo Nukada Goro Yabuta 《Tetrahedron》2007,63(5):1080-1084
A convergent synthetic strategy for abietane diterpenoids via B-alkyl Suzuki-Miyaura coupling and Lewis acid-mediated cyclization reactions is established. Asymmetric total synthesis of 12-deoxyroyleanone, an antileishmanial diterpene, is described. 相似文献
2.
Arata YajimaFumihiro Saitou Mayu SekimotoShoichiro Maetoko Goro Yabuta 《Tetrahedron letters》2003,44(36):6915-6918
Total synthesis of cordiaquinone K, a new antifungal and larvicidal meroterpenoid, is reported. The absolute configuration of cordiaquinone K was confirmed by the synthesis. 相似文献
3.
The polymerization of isobutyl vinyl ether was studied in a heterogeneous system using iron (II) sulfate calcined in air at various temperatures as a catalyst. The maximum activity was shown by the catalyst calcined at 700°C, which effected the polymerization at room temperature in a few seconds, while the sulfate treated at 750°C was totally inactive. Poly(vinyl ethyl ether) was also obtained by the FeSO4 (700°C) catalyst at room temperature. This catalyst formed the crystalline polymer (melting temperature 135–138°C) when the reaction was performed in toluene as solvent at room temperature. Poisoning experiments with Hammett indicators were carried out with the FeSO4 (700°C) catalyst. The treatment with n-butylamine rendered it inactive in the reaction of isobutyl vinyl ether, while its catalytic activity was little affected by dicinnamalacetone. On the basis of the observed results, the nature of active sites of catalyst is discussed. 相似文献
4.
H Itokawa K Saitou H Morita K Takeya K Yamada 《Chemical & pharmaceutical bulletin》1992,40(11):2984-2989
Metabolites of antitumor cyclic hexapeptides, RA-VII and -X which were isolated from Rubia cordifolia were studied by hepatic microsomal biotransformation in rats and in bile juice of rabbits to which these drugs were administered intravascularly. Their structures and conformations were elucidated by two-dimensional nuclear magnetic resonance techniques, temperature effect on NH protons and nuclear Overhauser effect experiments. Specific N-demethylation of Tyr-3, O-demethylation and hydroxylation at aromatic rings of Tyr-3 and -5 were observed. Compared with metabolites of RA-VII, most of RA-X was excreted unchanged in the bile juice. Relationship among their structures, conformations and antitumor activities is also discussed. 相似文献
5.
The hydronaphthalene moieties of mevinic acids are synthesized enantioselectively by using the asymmetric intramolecular Diels-Alder reaction catalyzed by a chiral titanium reagent. 相似文献
6.
Yoshiaki Sugihara Naoto Inai Masayasu Taki Thomas Baumgartner Ryosuke Kawakami Takashi Saitou Takeshi Imamura Takeshi Yanai Shigehiro Yamaguchi 《Chemical science》2021,12(18):6333
The use of donor–π–acceptor (D–π–A) skeletons is an effective strategy for the design of fluorophores with red-shifted emission. In particular, the use of amino and boryl moieties as the electron-donating and -accepting groups, respectively, can produce dyes that exhibit high fluorescence and solvatochromism. Herein, we introduce a dithienophosphole P-oxide scaffold as an acceptor–spacer to produce a boryl- and amino-substituted donor–acceptor–acceptor (D–A–A) π-system. The thus obtained fluorophores exhibit emission in the near-infrared (NIR) region, while maintaining high fluorescence quantum yields even in polar solvents (e.g. λem = 704 nm and ΦF = 0.69 in CH3CN). A comparison of these compounds with their formyl- or cyano-substituted counterparts demonstrated the importance of the boryl group for generating intense emission. The differences among these electron-accepting substituents were examined in detail using theoretical calculations, which revealed the crucial role of the boryl group in lowering the nonradiative decay rate constant by decreasing the non-adiabatic coupling in the internal conversion process. The D–A–A framework was further fine-tuned to improve the photostability. One of these D–A–A dyes was successfully used in bioimaging to visualize the blood vessels of Japanese medaka larvae and mouse brain.Combination of electron-accepting diarylboryl terminal groups and dithienophosphole oxide spacers with electron-donating triarylamine moieties produces donor–acceptor–acceptor type π-systems, which exhibit emissions in the near-infrared region. 相似文献
7.
Arata Yajima 《Tetrahedron》2005,61(38):9164-9172
A versatile methodology for the synthesis of various terpenoids via B-alkyl Suzuki-Miyaura coupling as a key step is established. Synthesis of cordiaquinone J and K, new antifungal and larvicidal meroterpenoids, was achieved by using this methodology. The absolute configurations of cordiaquinone J and K were confirmed by the synthesis. 相似文献
8.
The title reactions were studied with a solid superacid, which was prepared by exposing Zr(OH)4 to 1 N H2SO4, followed by calcination at 650°C in air. Pentane and isopentane were converted into isopentane and isobutane, respectively, the selectivities being 84% under short contact conditions at 80°C.
, - Zr(OH)4 1 N- H2SO4 650°C . , , 84% 80°C.相似文献
9.
10.
Recent progress in the chemistry and chemical biology of microbial signaling molecules: quorum-sensing pheromones and microbial hormones 总被引:1,自引:0,他引:1
Communication among microorganisms is mediated by secretion and detection of microbial signaling molecules such as quorum-sensing pheromones and microbial hormones. The molecules elicit the regulation of important genes necessary for microbial survival and often play important roles in interspecies or even inter-kingdom communication. Recent progress in the study of the signaling molecules has enabled us to eavesdrop on microbial conversations to gain insight on their intercellular communication system. This review summarizes the recent advances in the chemistry and chemical biology of these important microbial signaling molecules: acyl-homoserine lactones (AHLs), AI-2, CAI-1 related α-hydroxy ketones (AHKs), ComX pheromones, diffusible signal factors (DSFs), diffusible extracellular factor (DF), and Phytophthora mating hormones. 相似文献