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   173篇
  免费   5篇
  国内免费   39篇
化学   207篇
晶体学   1篇
物理学   9篇
  2023年   2篇
  2022年   3篇
  2021年   2篇
  2020年   5篇
  2019年   3篇
  2017年   5篇
  2016年   6篇
  2015年   3篇
  2014年   8篇
  2013年   33篇
  2012年   6篇
  2011年   9篇
  2010年   7篇
  2009年   10篇
  2008年   8篇
  2007年   10篇
  2006年   8篇
  2005年   16篇
  2004年   11篇
  2003年   10篇
  2002年   1篇
  2001年   11篇
  2000年   9篇
  1999年   4篇
  1998年   4篇
  1997年   4篇
  1996年   4篇
  1995年   5篇
  1994年   1篇
  1993年   2篇
  1992年   1篇
  1991年   3篇
  1990年   1篇
  1989年   2篇
排序方式: 共有217条查询结果,搜索用时 0 毫秒
71.
依据离子液体1-甲基-3-正己基咪唑氯盐([HeMIM]Cl)和1-甲基-3-正辛基咪唑氯盐([OcMIM]Cl)在常温下呈液态,且能与氯气反应生成三氯离子的特性,将其作为吸收氯气的反应媒介,并将所形成的含三氯离子的离子液体作为氯代试剂用于一些有机化合物,如烯烃、酮、芳香化合物的氯代反应之中,取得了令人满意的结果.这两种离子液体的最大吸收氯气含量分别达到25.9%和23.1%(质量分数),而且这些含有氯离子或三氯离子的离子液体作为吸收媒介或氯代试剂可以重复利用.  相似文献   
72.
An efficient method for the synthesis of substituted quinolines is described. By FeCl3-promoted C–C bond formation, 2,3-disubstituted and 2,3,4-trisubstituted quinolines were successfully synthesized from the reaction between imines and electron-deficient alkynes in good yields. The reaction can also be performed in a sequential three-component manner by using aromatic amines and aromatic aldehydes instead of the corresponding imines.  相似文献   
73.
Abstract

A simple and very fast process of transfer of a phosphorus atom, performed by a simple molecule acting as catalyst in an almost infinite catalytic cycle is described. The catalyst donates a P atom to a mixture of two different Grignard reagents giving, in a very fast and in a highly selective manner, only one phosphorus-containing compound with an enormous rate enhancement with respect to the corresponding no-catalyzed reaction which gives a final cluttered mixture of many organophosphorus products. The focal factor to explain this highly selective process of P transport lies in the folded structure of the reagent with particular angles around the phosphorus atom which can facilitate the formation of cyclic trigonal bipyramidal pentacoordinated species and then its catalytic activity. In a similar manner, RNA can adopt, in a precise position, a particular three-dimensional structure that might facilitate the formation of pentacoordinated species leading to the catalytic function.  相似文献   
74.
A mild and efficient method has been developed for the preparation of acylals from aldehydes catalyzed by antimony trichloride under solvent‐free conditions in very good to excellent yields. The easy availability, low cost, and ease of handling of the catalyst make this procedure especially attractive for large‐scale synthesis.  相似文献   
75.
IrCl3·3H2O or FeCl3-catalyzed convenient synthesis of 3-hydroxyphthalates has been achieved by a Diels-Alder reaction of furans with dimethyl acetylenedicarboxylate, followed by ring-opening aromatization reaction of the Diels-Alder adducts, 7-oxabicyclo[2.2.1]hepta-2,5-diene derivatives. In addition, 7-azabicyclo[2.2.1]hepta-2,5-diene derivative, derived from N-Boc-pyrrole and dimethyl acetylenedicarboxylate, also converted into 3-aminophthalate derivative.  相似文献   
76.
The kinetic parameters of photoinduced electron transfer reaction of two phenothiazine dyes, methylene blue and methylene green with titanium trichloride, were determined in water and different aqueous-alcoholic solvents at different acidities by using a specially designed optical system. The rate of photoinduced electron transfer reaction was measured by determining the quantum yield of the reaction. The methylene green had a higher reactivity as compared to methylene blue with titanium trichloride. The graphical analysis showed that the reaction of dye with titanium trichloride follows pseudo–first-order kinetics. A reaction mechanism was proposed by considering the different excited states of dye and their possible interaction with the solvent and titanium trichloride. The different steps in the reaction mechanism were taken into consideration for deriving rate equations, which were used to determine the different rate constants in the reaction mechanism in different solvents.  相似文献   
77.
合成有机锗倍半硫化物的新方法   总被引:5,自引:0,他引:5  
有机锗倍半硫化物的合成是有机锗抗癌药物研究中的热点之一。在路易斯碱(如吡啶或三乙胺)存在下,经有机锗三氯化物溶液中通干燥的硫化氢气体制得有机锗倍半硫化物的方法有许多缺点,如无法计算吸收的硫化氢的量、设备复杂、操作困难并产生硫化氢臭味和毒性。我们用无水硫化钠直接与有机锗三氯化物作用即可得到有机锗倍半硫化物。利用此法合成了8种有机锗倍半硫化物:  相似文献   
78.
Green crystals of Me2NTiCl3 associate to a chain polymer via four Ti‐Cl‐Ti bonds and generation of hexacoordinated Ti atoms. Like Et2NTiCl3 its amino group is not involved into forming Ti‐N‐Ti bridges. This is due to a short Ti‐N bond to the planar coordinated N atom of the Me2N group.  相似文献   
79.
《中国化学会会志》2017,64(10):1147-1155
The kinetics of photoinduced electron transfer reaction of methylene blue (MB) and titanium trichloride was investigated in water and different aqueous–alcoholic solvents. The reaction is pseudo‐first order, dependent only on the concentration of titanium trichloride at a fixed concentration of MB. The effect of water and aqueous–alcoholic solvents was studied in the acidic pH range (4–7). It was observed that the quantum yield (ϕ ) of the reaction increased with increase in polarity of the reaction medium. The quantum yield was high under acidic conditions and decreased with further increase in acidity. The addition of ions and increase in temperature increased the rate and quantum yield of the reaction. The absence of any reaction intermediate was confirmed by spectroscopic investigations. A mechanism for the reaction has been proposed in accordance with the kinetics of the reaction. The activation energy (E a) was calculated by the Arrhenius relation. Thermodynamic parameters such as E a, enthalpy change (ΔH ), free energy change (ΔG ), and entropy change (ΔS ) were also evaluated.  相似文献   
80.
Addition of the Allenic amine H2C═C═CHNMe2 and the corresponding N-morpholinoallene to a solution of an aromatic or heteroaromatic aldehyde, RCH═O, and lithium bromide in tetrahydrofuran followed by treatment of the reaction mixture with a small amount of acetic acid at elevated temperatures affords the aldehydes RCH═C(CH2NR'2)CH═O (NR'2=NMe2 or morpholino) in reasonable yields.  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