首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   49篇
  免费   3篇
  国内免费   1篇
化学   52篇
物理学   1篇
  2022年   1篇
  2020年   1篇
  2019年   1篇
  2017年   2篇
  2016年   1篇
  2015年   2篇
  2014年   7篇
  2013年   3篇
  2012年   5篇
  2011年   3篇
  2010年   5篇
  2009年   1篇
  2008年   3篇
  2007年   2篇
  2006年   3篇
  2005年   2篇
  2004年   1篇
  2003年   1篇
  1995年   2篇
  1994年   1篇
  1993年   3篇
  1992年   2篇
  1991年   1篇
排序方式: 共有53条查询结果,搜索用时 15 毫秒
1.
2.
A simple and convenient method for the chemoselective reduction of nitriles into aldehydes using a 1,1,3,3-tetramethyldisiloxane (TMDS)/triisopropoxyvanadium(V) oxide reducing system is described. Aromatic as well as aliphatic nitriles are reduced into the corresponding aldehydes in moderate to good yields.  相似文献   
3.
In the title compound, catena‐poly[bis[(2,2′‐bipyridine‐κ2N,N′)(1,1,3,3‐tetracyano‐2‐ethoxypropenido‐κN)copper(II)]‐μ4‐hexanedioato‐κ6O1,O1′:O1:O6,O6′:O6], [Cu2(C9H5N4O)2(C6H8O4)(C10H8N2)2]n, the adipate (hexanedioate) dianion lies across a centre of inversion in the space group P. The CuII centre adopts a distorted form of axially elongated (4+2) coordination, and the CuII and adipate components form a one‐dimensional coordination polymer from which the 2,2′‐bipyridine and 1,1,3,3‐tetracyano‐2‐ethoxypropenide components are pendent, and where each adipate dianion is bonded to four different CuII centres. The coordination polymer chains are linked into a three‐dimensional framework structure by a combination of C—H...N and C—H...O hydrogen bonds, augmented by a π–π stacking interaction.  相似文献   
4.
反式-1-氯-3, 3, 3-三氟丙烯 (HCFO-1233zd (E))是近年来正在研发的第四代发泡剂,其大气臭氧消耗潜能值为0.00024,温室效应潜能值为7.0,毒性低,常态下不燃,使用安全;它也是合成含氟精细化工品的中间体,以及合成氟树脂和氟弹性体的单体。本论文制备了Al,Zn,Co改性的Cr2O3催化剂,将其成功应用于1, 1, 3, 3-四氯丙烯(HCC-1230za)与氟化氢反应中,高选择性地合成HCFO-1233zd (E),复合催化剂Zn / Cr2O3显示高稳定性,其中HCC-1230za转化率高达99.4%,HCFO-1233zd(E)的选择性高达98.2%。反应条件诸如反应物HF / HCC-1230za 的摩尔比和反应温度等对产物分布有显着影响。在相对较低的温度(200?C)和较大的HF / HCC-1230za 摩尔比(10:1)下,对HCFO-1233zd(E)的选择性有利。通过XRD,XPS,BET和V70吡啶吸附红外光谱技术对复合催化剂Zn / Cr2O3进行了表征。 XRD结果表明,催化剂中大多数无定形Cr2O3和高度分散微晶相Cr2O3共同导致催化剂的高活性和高稳定性。HCC-1230za的转化率与预氟化处理催化剂Zn / Cr2O3的比表面积有关,催化剂的比表面积越高,催化活性越高。XPS光谱表明,在预氟化过程中,表面铬氧化物可能与F原子强烈相互作用,从而导致Cr原子的化学环境发生广泛变化。V70吡啶吸附红外光谱和氨-程序升温脱附技术结果证明尚未失活的催化剂Lewis 酸和Br?nsted酸中心的数目和强度与新制备的催化剂相比明显提高。  相似文献   
5.
Highly toxic polyallylamine (PA) was reacted with a varying amount of a novel linker, 6‐(N,N,N′,N′‐tetramethylguanidinium chloride) hexanoic acid (Tmg‐HA), to prepare a series of tetramethylguanidinium‐PA (Tmg‐PA) polymers, which were used as vectors for gene transfection. The extent of attachment of the linker, Tmg‐HA, to the PA backbone was determined by 2,4,6‐trinitrobenzene sulfonic acid assay. The modified polymers (Tmg‐PAs), when complexed with pDNA, exhibited good condensation ability. The nanoparticles, so formed, were characterized by their size and zeta potential and were subsequently evaluated for their toxicity and transfection ability on various mammalian cells, viz., HeLa, CHO, and HEK 293 cells. Mobility shift assay revealed that on increasing the percent substitution of Tmg‐HA onto PA (from Tmg‐PA1 to Tmg‐PA6), relatively higher amounts of modified polymers were required to retard the mobility of a fixed amount of DNA. Besides, Tmg‐PA polymers provided sufficient protection (ca. 84–88%) to bound DNA against nucleases and one of the formulations, Tmg‐PA2 (ca. 15% substitution) displayed the highest transfection efficiency outcompeting the commercial transfection reagent, Lipofectamine? with minimal cytotoxicity. More impressively, the transfection efficiency increased despite recording a decrease in the buffering capacity of the grafted polymers suggesting that buffering capacity is not the sole parameter in determining the gene delivery efficiency of a vector system. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012  相似文献   
6.
The three-component direct Mannich reaction between aldehydes, p-toluenesulfonamide, and enolizable ketones was achieved for the first time with organic bases as the catalysts. The corresponding N-tosylated β-aminoketones were obtained in high yields and good to excellent diastereoselectivities using TMG as the catalyst. Through reduction of the ketone group, the reaction product may be converted into β-aminol with excellent diastereoselectivity.  相似文献   
7.
8.
A simple and practical procedure for the reduction of acetals to ethers is described. It is based on the use of a 1,1,3,3-tetramethyldisiloxane (TMDS)-Pd/C system in the presence of a Brønsted acid as the co-catalyst. The reaction occurs under mild conditions and ethers are obtained in high yields.  相似文献   
9.
10.
An efficient reduction of the nitro group with a catalytic amount of Fe(acac)3 and TMDS in THF at 60 °C affording the corresponding amine is described.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号