全文获取类型
收费全文 | 170篇 |
免费 | 33篇 |
国内免费 | 1篇 |
专业分类
化学 | 202篇 |
物理学 | 2篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 12篇 |
2014年 | 11篇 |
2013年 | 21篇 |
2012年 | 5篇 |
2011年 | 15篇 |
2010年 | 17篇 |
2009年 | 9篇 |
2008年 | 9篇 |
2007年 | 10篇 |
2006年 | 12篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 9篇 |
2002年 | 1篇 |
2001年 | 2篇 |
1999年 | 2篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1989年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有204条查询结果,搜索用时 0 毫秒
111.
112.
Harunobu Komatsu Dr. Shinya Tsukiji Dr. Masato Ikeda Prof. Itaru Hamachi 《化学:亚洲杂志》2011,6(9):2368-2375
Supramolecular hydrogels constructed through molecular self‐assembly of small molecules have unique stimuli‐responsive properties; however, they are mechanically weak in general, relative to conventional polymer gels. Very recently, we developed a zwitterionic amino acid tethered amphiphilic molecule 1 , which gave rise to a remarkably stiff hydrogel comparable with polymer‐based agarose gel, retaining reversible thermal‐responsive properties. In this study, we describe that rational accumulation of multiple and orthogonal noncovalent interactions in the supramolecular nanofibers of 1 played crucial roles not only in the mechanical reinforcement but also in the multistimuli responsiveness. That is, the zwitterionic amino acid moiety and the C C double bond unit of the hydrogelator 1 can function as a pH‐responsive unit and a light‐responsive unit, respectively. We also demonstrated that this stiff and multistimuli‐responsive supramolecular hydrogel 1 is applied as a unique mold for 2D and 3D‐patterning of various substances. More significantly, we succeeded in the fabrication of a collagen gel for spatial patterning, culturing, and differentiation of live cells by using hydrogel 1 molds equipped with 2D/3D microspace channels (100–200 μm in diameter). 相似文献
113.
The zwitterionic 1 : 1 intermediates generated by addition of N‐heterocycles to activated acetylenes are trapped by trichloroacetonitrile to afford 1,2‐ or 1,4‐disubstituted N‐heterocycles in moderate to good yields under mild reaction conditions. 相似文献
114.
115.
116.
On the Reactivity of Tetrakis(trifluoromethyl)cyclopentadienone towards Carbon‐Based Lewis Bases 下载免费PDF全文
Sigrid Holle Dr. Daniel Escudero Dr. Blanca Inés Jörg Rust Prof. Walter Thiel Dr. Manuel Alcarazo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(7):2744-2749
The reactivitiy of tetrakis(trifluoromethyl)cyclopentadienone towards different C‐based Lewis bases, such as N‐heterocyclic carbenes (NHC), ylides and isonitriles, are reported. While sterically not hindered carbenes were found to yield kinetic adducts by regiospecific nucleophilic attack at the position adjacent to the carbonyl group of the ketone, bulkier nucleophiles afforded the thermodynamically more stable O‐bridged zwitterions. Interestingly, isonitriles were found to dimerize and trimerize under the same reaction conditions, forming bicyclic products that evolve differently depending on the nature of the substituents. 相似文献
117.
118.
Three novel alkaloids, macropodumines A-C (1-3), were isolated from the stem of Daphniphyllum macropodum Miq. Interestingly, the structure of macropodumine A (1) was characterized as having a fused pentacyclic system including an unusual eleven-membered macrolactone ring, whereas macropodumine B (2) contains a rare cyclopentadienyl carbanion, which is stabilized as a zwitterion by an internal iminium cation. The structures of these new metabolites were established on the basis of their detailed spectroscopic analysis. In particular, the unique structure of zwitterion 2 was further confirmed by using single-crystal X-ray diffraction analysis. 相似文献
119.
Kjeldsen F Silivra OA Zubarev RA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(30):7920-7928
A new method of detecting the presence of deprotonation and determining its position in gas-phase polypeptide cations is described. The method involves 157-nm ultra-violet photodissociation (UVPD) and is based on monitoring the losses of CO2 (44 Da) from electronically excited deprotonated carboxylic groups relative to competing COOH losses (45 Da) from neutral carboxylic groups. Loss of CO2 is a strong indication of the presence of a zwitterionic [(+)...(-)...(+)] salt bridge in the gas-phase polypeptide cation. This method provides a tool for studying, for example, the nature of binding within polypeptide clusters. Collision-activated dissociation (CAD) of decarboxylated cations localizes the position of deprotonation. Fragment abundances can be used for the semiquantitative assessment of the branching ratio of deprotonation among different acidic sites, however, the mechanism of the fragment formation should be taken into account. Cations of Trp-cage proteins exist preferentially as zwitterions, with the deprotonation position divided between the Asp9 residue and the C terminus in the ratio 3:2. The majority of dications of the same molecule are not zwitterions. Furthermore, 157-nm UVPD produces abundant radical cations M*+ from protonated molecules through the loss of a hydrogen atom. This method of producing M*+ ions is general and can be applied to any gas-phase peptide cation. The abundance of the molecular radical cations M*+ produced is sufficient for further tandem mass spectrometry (MS/MS), which, in the cases studied, yielded side-chain loss of a basic amino acid as the most abundant fragmentation channel together with some backbone cleavages. 相似文献
120.
Dino Wu Nicole A. Fohn Jeffrey W. Bode 《Angewandte Chemie (International ed. in English)》2019,58(32):11058-11062
Potassium acyltrifluoroborates (KATs) are increasingly important functional groups, and general methods for their preparation are of great current interest. We report a bifunctional iminium reagent bearing both a tin nucleophile and a trifluoroborate, which was applied in chemoselective Pd0‐catalyzed Migita–Kosugi–Stille cross‐coupling reactions owith aryl and vinyl halides. This method gives access to previously inaccessible aromatic and α,β‐unsaturated acyltrifluoroborates, including precursors to amino‐acid derived KATs. 相似文献