全文获取类型
收费全文 | 194篇 |
免费 | 13篇 |
国内免费 | 41篇 |
专业分类
化学 | 210篇 |
晶体学 | 4篇 |
力学 | 18篇 |
数学 | 9篇 |
物理学 | 7篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 10篇 |
2020年 | 14篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 16篇 |
2013年 | 18篇 |
2012年 | 18篇 |
2011年 | 10篇 |
2010年 | 8篇 |
2009年 | 8篇 |
2008年 | 5篇 |
2007年 | 12篇 |
2006年 | 16篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 2篇 |
排序方式: 共有248条查询结果,搜索用时 750 毫秒
231.
光催化反应比传统催化反应条件温和,不但能利用太阳能作为光源,同时,也避免了一些强氧化剂、危险还原剂和有毒物质的使用,极大地满足了人们对能源和环境的要求。通过优化光催化体系可以实现对目标产物的选择性合成,从而为有机合成提供一种绿色、节能的途径。本文综述了近年来光催化选择性合成有机物的催化剂类型,影响选择性因素和提高选择性的途径,重点就光催化材料的晶型、催化剂的合成与表面修饰、溶剂种类、催化条件等因素在聚合反应、芳香族的羟基化反应、胺的氧化反应、烯烃环氧化反应、羰基反应选择性合成有机物方面作一评述,并对光催化在选择性合成有机物的研究和进展进行了展望。 相似文献
232.
Inside Back Cover: Near‐Infrared‐Light‐Mediated Imaging of Latent Fingerprints based on Molecular Recognition (Angew. Chem. Int. Ed. 6/2014) 下载免费PDF全文
233.
2,4-Diaryl-2,3-dihydro-1H-1,5-benzodiazepines readily undergo a ring contraction to generate 2-aryl-1-styrylbenzimidazoles in the presence of some Lewis acids. Copper acetate shows high efficiency compared with other Lewis acids. The ring contraction includes Lewis acid-catalyzed intramolecular addition, ammonium-induced ring-opening of the generated four-membered azetidine ring, deprotonation, and amine-promoted nucleophilic styryl 1,2-shift and elimination. Copper acetate serves as Lewis acid, base, and oxidant. The current reaction provides an efficient method for the convenient synthesis of 2-aryl-1-styrylbenzimidazole derivatives from readily available 2,4-diaryl-2,3-dihydro-1H-1,5-benzodiazepines. 相似文献
234.
Jiaxi Xu Jiayi Wang Osman M. Bakr Nikos Hadjichristidis 《Angewandte Chemie (International ed. in English)》2023,62(12):e202217418
Aggregation-induced emission (AIE) polymers with expected emission wavelength/color and fluorescence efficiency are valuable in applications. However, most AIE polymers exhibit irregular emission wavelength/color changes compared to the original AIE monomers. Here, we report the synthesis of AIE polymers with unchanged emission wavelength by ring-opening (co)polymerizations of 4-(triphenylethenyl)phenoxymethyloxirane (TPEO) and other epoxides or phthalic anhydride. The chemical structures/physical properties of all (co)polymers were characterized by NMR, SEC, MALDI-TOF, and DSC. The co-polyether microstructures were revealed by calculating the reactivity ratios and visualized by Monte Carlo simulation. The photoluminescence quantum yields of all the (co)polymers were determined in the solid state. We systematically correlated the fluorescence performance with molecular weights, crystallinity, monomer compositions, glass transition temperatures, side lengths, and flexibility/rigidity. 相似文献
235.
236.
Jiaxi Cui Omar Azzaroni Arnzazu del Campo 《Macromolecular rapid communications》2011,32(21):1699-1703
Photolabile polymer brushes with tailored length containing a photoremovable protecting group (NVOC) are prepared via the SI‐ATRP method. Upon light irradiation, the NVOC group is removed to generate controlled densities of free amine groups (PAMA) randomly distributed along the brush. The presence of the ionizable groups induces a photo‐triggered swelling response. The swelling degree can be tuned by the irradiation dose. A dual (light and pH), tunable response is demonstrated.
237.
Cui J Gropeanu RA Stevens DR Rettig J del Campo A 《Journal of the American Chemical Society》2012,134(18):7733-7740
The efficient synthesis, physicochemical and photolytical properties of a photoactivable BAPTA-based Ca(2+) cage containing two photosensitive o-nitrobenzhydryl groups attached to the aromatic core are described. Ca(2+) release in living cells was evaluated. The double substitution with the chromophores caused a significant improvement of the Ca(2+) release properties of nitr-T versus singly substituted reported nitr-x derivatives without compromising Ca(2+)/Mg(2+) selectivity or pH insensitivity. Our results demonstrate a general strategy to improve light-triggered Ca(2+) release which may result in more efficient, selective, and pH-insensitive photolabile Ca(2+) chelators. 相似文献
238.
The ring expansion of small-ring compounds provides a powerful method for the construction of various cyclic compounds. Herein, nitrene equivalent mediated metal-free ring expansions of alkylidenecyclopropanes (ACPs) and an alkylidenecyclobutane (ACB) were described. In this synthesis, a series of aryl-substituted cyclobutylidene and cyclopentylidene hydrazine derivatives were obtained under mild conditions in moderate to good yields. [reaction: see text] 相似文献
239.
[reaction: see text] A more practical and efficient catalytic asymmetric Friedel-Crafts alkylation of indoles with nitroalkenes using bifunctional tridentate bis(oxazoline)-Zn(OTf)(2) as catalyst has been developed. Various types of the nitroalkylated indoles were obtained in excellent yields (85-99%) and high enantioselectivities (up to 98% ee). 相似文献
240.
Xin Wang Jiaxi Xu Zhenjiang Li Jingjing Liu Jie Sun Nikos Hadjichristidis Kai Guo 《Chemical science》2021,12(32):10732
The “coordination-insertion” ring-opening polymerization (ROP) mechanism has so far been the monopoly of metal catalysts. In this work, we present a metal-free “coordination-insertion” ROP of trimethylene carbonate (TMC) and ε-caprolactone (ε-CL), as well as their sequential block copolymerization, with N-trimethylsilyl-bis (trifluoromethanesulfonyl)imide (TMSNTf2) as the non-metallic initiator/catalyst. TMSNTf2 was proposed to work through an unprecedented metal-free “coordination-insertion” mechanism, which involves the coordination of monomer to the Si atom of TMSNTf2, the nucleophilic attack of the –NTf2 group on the coordinated monomer, and the cleavage of the acyl–oxygen bond of the monomer. The proposed metal-free “coordination-insertion” ROP was studied by NMR, SEC, and MALDI-TOF analyses. In addition, the TMSNTf2-mediated ROP of TMC and ε-CL led to linear and cyclic polymers following two-stage first-order polymerization processes, as evidenced by structural analyses and kinetics study, which further demonstrated the metal-free “coordination-insertion” mechanism.The first metal-free “coordination-insertion” ROP of cyclic carbonate and lactones mediated by N-trimethylsilyl-bis(trifluoromethanesulfonyl)imide (TMSNTf2) was proposed, which in the past was exclusively the monopoly of metal complex catalysts. 相似文献