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   287篇
  免费   54篇
  国内免费   17篇
化学   352篇
力学   1篇
物理学   5篇
  2023年   3篇
  2022年   3篇
  2021年   2篇
  2020年   7篇
  2019年   10篇
  2018年   11篇
  2017年   16篇
  2016年   23篇
  2015年   27篇
  2014年   25篇
  2013年   32篇
  2012年   32篇
  2011年   23篇
  2010年   21篇
  2009年   9篇
  2008年   19篇
  2007年   13篇
  2006年   14篇
  2005年   7篇
  2004年   17篇
  2003年   12篇
  2002年   4篇
  2001年   6篇
  2000年   5篇
  1999年   5篇
  1998年   1篇
  1997年   4篇
  1996年   3篇
  1995年   2篇
  1993年   1篇
  1991年   1篇
排序方式: 共有358条查询结果,搜索用时 140 毫秒
111.
We report a novel approach to prepare microparticles via a dispersion polymerization using the amine‐catalyzed addition of a trithiol to a triacrylate. Microparticles loaded with various core materials were produced and applied in various systems to improve the desired characteristics of the given system. We determined that this type of microparticle could be used as either a stimulated release or controlled release system for certain desired core materials. These microparticles were able to prevent the interaction between a Lewis acid initiator and fumed silica, improving the rheological properties of an epoxy system containing the initiator. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011  相似文献   
112.
The polymerization of vinyl methacrylate (VMA) allows the synthesis of polymers with pendant double bonds. When this polymerization was undertaken in the presence of 2‐cyanopropyl dithiobenzoate as reversible addition–fragmentation chain transfer agent, it led almost exclusively to vinylester functional sidegroups, which were available for further reactions. The vinylester functionality could not be functionalized using common thiol‐ene catalysts, but could be activated using Candida antarctica lipase B (CAL‐B) (Novozyme 435). The reaction between PVMA and various thiols in N, N‐dimethyl formamide in the presence of CAL‐B led exclusively to the formation of the anti‐Markovnikov product. The rate of reaction between PVMA and 1‐butanethiol was monitored using 1H NMR. The reaction was complete within 72 h. Similar results were obtained with other small‐sized thiols such as 2‐mercaptoethanol, 3‐mercaptopropionic acid, and 2‐(trimethylsilyl)ethanethiol, while more bulky thiols, such as secondary thiols, thiols with long alkyl chains, and sterically demanding thiols, such as mono(6‐deoxy‐6‐mercapto)‐β‐cyclodextrin, only led to lower conversions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012  相似文献   
113.
N[β-(Hetero)arylvinyl] ketenimines and carbodiimides bearing adequately positioned 1,3-dioxolane functions experience a new class of tandem process consisting of a 6π electrocyclic ring closure followed by a rare retro-cheletropic ene reaction, the extrusion of 2-carbena-1,3-dioxolane. This mechanistic sequence is supported by a computational study using DFT methods, showing that the simultaneous recovery of aromaticity at two rings is the clue for the low energy barrier of the retro-cheletropic step. Moreover, the highly exergonic decomposition of 2-carbena-1,3-dioxolane into CO2 plus ethylene contribute to the success of the tandem sequences.  相似文献   
114.
Considering the large number of applications for hydrogels, a better understanding of the relation between molecular structure and mechanical properties for well‐defined hydrogel is essential. A new library has been compiled of poly(ethylene glycol) polymers (PEG) of different length end functionalized with diallyl, dithiol, and dimethacrylate, and crosslinked with complementary trifunctional crosslinkers. In this study, the hydrogels were initially analyzed by FT‐Raman and NMR to study the conversion ratio of the functional groups. The effects of solvent type, solid content concentration, curing time and length of the PEG chains on the final leaching, swelling and tensile properties of the hydrogels were studied. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011  相似文献   
115.
116.
We present a facile two‐stage UV/UV activation method for the polymerization of off‐stoichiometry thiol‐ene‐epoxy, OSTE+, networks. We show that the handling and processing of these epoxy‐based resins is made easier by introducing a material with a controlled curing technique based on two steps, where the first step offers excellent processing capabilities, and the second step yields a polymer with suitable end‐properties. We investigate the sequential thiol‐ene and thiol‐epoxy reactions during these steps by studying the mechanical properties, functional group conversion, water absorption, hydrolytic stability, and thermal stability in several different thiol‐ene‐epoxy formulations. Finally, we conclude that the curing stages can be separated for up to 24 h, which is promising for the usefulness of this technique in industrial applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2604‐2615  相似文献   
117.
118.
We report a facile method that combined sol–gel reaction, reversible addition–fragmentation chain transfer (RAFT)/macromolecular design via interchange of the xanthates process and thiol‐ene click reaction to prepare monodisperse silica core‐poly(N‐vinylimidazole) (PVim) shell microspheres of 200 nm in average diameters. First, silica with C = C double bonds was prepared by the sol–gel reaction of 3‐(trimethoxysilyl)propyl methacrylates (MPS) with tetraethoxysilane in ethanol; SiO2@PVim were subsequently prepared by grafting PVim chain (Mn = 9800 g/mol, polydispersity index = 1.22) to MPS‐SiO2 via the thiol‐ene click chemisty. The obtained SiO2@PVim microspheres show higher catalytic activity toward the hydrolysis of p‐nitrophenyl acetate compared with the PVim homopolymers. The as‐prepared composites have been characterized by scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis and Fourier transform infrared spectrometry analysis. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
119.
The isolation and characterization of a rhodacycle intermediate implicated in rhodium‐catalyzed reactions of alkylidenecyclopropanes (ACPs) is described. The structure of the metallacycle was unambiguously determined by X‐ray crystallography and is catalytically competent in the rhodium‐catalyzed carbocyclization and ene‐cycloisomerization reactions of ACPs. This work represents a rare example of the isolation of a metallacycle in a metal‐catalyzed higher‐order carbocyclization reaction and thereby provides important insight into the ligand requirements for the insertion of π‐components. Furthermore, it serves as a convenient synthon for the development of challenging higher‐order carbocyclization reactions, as exemplified by the reaction with an activated allene.  相似文献   
120.
Carbonyl–ene reactions of 2,3‐diketoesters catalyzed by [Cu{(S,S)‐tBu‐box}](SbF6)2 [box=bis(oxazoline)] generate chiral α‐functionalized α‐hydroxy‐β‐ketoesters in up to 94 % yield and 97 % ee. The 2,3‐diketoesters are conveniently accessed from the corresponding α‐diazo‐β‐ketoester, and a catalyst loading as low as 1.0 mol % can be achieved.  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