全文获取类型
收费全文 | 918篇 |
免费 | 89篇 |
国内免费 | 179篇 |
专业分类
化学 | 1137篇 |
晶体学 | 8篇 |
力学 | 4篇 |
综合类 | 3篇 |
物理学 | 34篇 |
出版年
2023年 | 9篇 |
2022年 | 20篇 |
2021年 | 24篇 |
2020年 | 23篇 |
2019年 | 26篇 |
2018年 | 35篇 |
2017年 | 27篇 |
2016年 | 41篇 |
2015年 | 43篇 |
2014年 | 38篇 |
2013年 | 107篇 |
2012年 | 39篇 |
2011年 | 48篇 |
2010年 | 28篇 |
2009年 | 46篇 |
2008年 | 46篇 |
2007年 | 55篇 |
2006年 | 52篇 |
2005年 | 40篇 |
2004年 | 48篇 |
2003年 | 56篇 |
2002年 | 37篇 |
2001年 | 24篇 |
2000年 | 35篇 |
1999年 | 34篇 |
1998年 | 31篇 |
1997年 | 27篇 |
1996年 | 23篇 |
1995年 | 22篇 |
1994年 | 22篇 |
1993年 | 18篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 4篇 |
排序方式: 共有1186条查询结果,搜索用时 31 毫秒
991.
Xing Zhu Nianchen Zhou Jian Zhu Zhengbiao Zhang Wei Zhang Zhenping Cheng Yingfeng Tu Xiulin Zhu 《Macromolecular rapid communications》2013,34(12):1014-1019
An unprecedented strategy for the high‐efficiency preparation of the cyclic polymers is developed. In this strategy, the atom transfer radical polymerization, the substitution of chain‐end halide by azide group and Cu‐catalyzed alkyne–azide cyclization, i.e., the frequently used three separated steps for the preparation of cyclic polymers, are integrated into a one‐pot reaction by the introduction of a “regulator”. The kernel of this novel strategy is the utilization of the different rates between the competitive ATRP propagation and SN2 substitution of a tertiary‐carbon halogen and secondary‐carbon halogen. 0.55 g (yield = 59%) cyclic poly(methyl methacrylate) is obtained from 3.0 mL reaction solution. This work proposed a high‐efficiency and bright promising strategy for the preparation of cyclic polymer, which would evoke more research interests on cyclic polymer.
992.
Thereisconsiderablecurrentinterestinorgamcreactionsunderndcrowaveirradiationl.SomereactionsthatneededalongtAnetocomplete(i.e.severalhoursorseveraldays)couldbecatriedoutinseveralminutesunderndcrowavepromotion'-',andasthecasemaybe,somellewreactionswerefound'.Generally,ketalsareusuallyobtainedwhenethylortho-formatereactswithvariousketonesunderacidiccondihons"',butinthesamesituaioftanabnormalreachonalsotookplaceundermicrowaveirmdiahon(75owx7o$5oHz),andaseriesofnewcompounds(5,6,7,8)wereobtainedfr… 相似文献
993.
James V. Crivello 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):3036-3052
An investigation of the photoactivated cationic ring‐opening frontal polymerizations of a series of alkyl glycidyl ethers was carried out with the aid of a novel technique, optical pyrometry. With this technique, the effects of various experimental parameters, such as the photoinitiator type and concentration, as well as the effects of the monomer structure on the frontal behavior of these monomers were examined. Upon irradiation with UV light, the photopolymerizations of many alkyl glycidyl ethers displayed a prominent induction period at room temperature as the result of the formation of long‐lived, relatively stable secondary oxonium ions. The input of only a small amount of thermal activation energy was required to induce the further reaction of these species with the consequent autoaccelerated exothermic ring‐opening polymerization. Photoactivated frontal polymerizations were observed for both mono‐ and polyfunctional alkyl glycidyl ether monomers. The ability of monomers to exhibit frontal behavior was found to be related to their ability to stabilize the secondary oxonium ion intermediates through hydrogen‐bonding effects. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3036–3052, 2006 相似文献
994.
A. V. Shastin L. B. Romanova L. T. Eremenko V. V. Zakharov G. V. Lagodzinskaya G. G. Aleksandrov I. L. Eremenko 《Russian Chemical Bulletin》2006,55(8):1452-1454
1,4-Bis(chloromethyl)-and 1,4-bis(bromomethyl)cubanes were synthesized by the reactions of triphenylphosphine with CCl4 and
NBS, respectively. The structures of the compounds were studied by X-ray diffraction analysis.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1399–1401, August, 2006. 相似文献
995.
996.
Youngchan Jang Dai Seung Choi Shin Han 《Journal of polymer science. Part A, Polymer chemistry》2004,42(5):1164-1173
The activation of a metal alkyl‐free Ni‐based catalyst with B(C6F5)3 was investigated in the polymerization of 1,3‐butadiene. A catalyst of bis(1,5‐cyclooctadiene)nickel (Ni(COD)2)/B(C6F5)3 was found to have high catalytic activity and 1,4‐cis stereoregularity. The catalyst was also found to provide polybutadiene having a molecular weight (Mw) of up to 117,000, even in the absence of AlR3 and MAO. Variations in the mol ratio of B(C6F5)3 to Ni affected catalytic activity, 1,4‐cis stereoregularity, and the Mw of polybutadiene, while the molecular weight distribution (MWD) of polybutadiene showed little correlation with the mol ratio of B(C6F5)3 to Ni. The use of other borane compounds such as B(C6H5)3, BEt3, and BF3 etherate in place of B(C6F5)3 clearly showed the two main functions of B(C6F5)3 in the present catalyst. The high Lewis acidity of B(C6F5)3 enabled it to activate catalytic complexes, thus inducing the polymerization. The steric bulkiness of B(C6F5)3 suppressed chain transfer reactions, contributing to the production of polybutadiene with a high Mw. Kinetic studies showed that the catalyst had an induction period, possibly due to the time needed for the formation of catalytic complexes starting from Ni(COD)2. A plot of ?ln (1?X), where X is the fractional conversion, as a function of time resulted in a linear relationship, showing that the present catalyst system followed first‐order kinetics with respect to monomer concentration. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1164–1173, 2004 相似文献
997.
Ionic liquids based on 1,3-dialkylimidazolinium methanesulfonate have been used as effective reusable reaction media in the esterification of several carboxylate sodium salts with different alkyl halides. Products are easily isolated by extraction with ether, and the protocol is mild and green, compared to the existing methods based on toxic solvents. Proper ‘design’ of the ionic liquid allows us to obtain esters always in quantitative yields. 相似文献
998.
Tsutomu Oishi Yong‐Kyung Lee Akira Nakagawa Kenjiro Onimura Hiromori Tsutsumi 《Journal of polymer science. Part A, Polymer chemistry》2002,40(11):1726-1741
Chiral poly(acrylamide) macromonomers (PMB‐1, PMB‐2, PPAE‐1, and PPAE‐2) were synthesized from 2‐methacryloyloxyethyl isocyanate and prepolymers, that is, poly[(S)‐methylbenzyl acrylamide] or poly(L ‐phenylalanine ethylester acrylamide with a terminal carboxylic acid or hydroxy group. Radical homopolymerizations of poly(acrylamide) macromonomers were carried out under several conditions to obtain the corresponding optically active polymers. A strong temperature dependence on the specific optical rotation was observed for poly(PPAE‐2) in comparison with that for the corresponding prepolymer. This might have resulted from a change in the conformation caused by hydrogen bonds between polymer‐graft branches in the polymacromonomer. Radical copolymerizations of poly(acrylamide) macromonomers with styrene and methyl methacrylate were performed with azobisisobutyronitrile in tetrahydrofuran at 60 °C. Chiroptical properties of the copolymers were slightly influenced by comonomer units. Chiral stationary phases were prepared by the radical polymerization of poly(acrylamide) macromonomers in the presence of silica gel containing vinyl groups on the surface. Some racemic compounds such as menthol and mandelic acid were resolved on the chiral stationary phases for high‐performance liquid chromatography. The conformation based on hydrogen bonds between polymer‐graft branches in the polymacromonomers may play an important role in chiral discrimination. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1726–1741, 2002 相似文献
999.
R. Gertzmann 《Tetrahedron letters》2005,46(39):6659-6662
A catalyst for the reaction of blocked isocyanates (blocking agent diisopropylamine and dimethyl pyrazole) and carboxylic acids was identified. Magnesium and in some instances calcium salts proved to be highly active as catalyst. This reaction gives amides in quantitative yield and excellent selectivity and is suitable for coating and general chemical purposes. 相似文献
1000.
Tadahiro Kiguchi Hiroyuki Aota Akira Matsumoto 《Journal of polymer science. Part A, Polymer chemistry》2003,41(21):3243-3248
As part of our continuing studies concerned with the elucidation of the crosslinking polymerization mechanism leading to interpenetrating polymer network (IPN) formation, in which IPNs consist of both polymethacrylates and polyurethane (PU) networks, this article explores the polyaddition crosslinking reactions of multifunctional poly(methyl methacrylate‐co‐2‐methacryloyloxyethyl isocyanate) [poly(MMA‐co‐MOI)] [MMA/MOI = 90/10] with various diols leading to PU network formation. Thus, the equimolar polyaddition crosslinking reactions of poly(MMA‐co‐MOI) with ethylene glycol (EG), 1,6‐hexane diol, and 1,10‐decane diol (DD) were carried out in N‐methyl pyrrolidone at a 0.25 mol/L isocyanate group concentration at 80 °C. The second‐order rate constants decreased from EG to DD. The deviation of the actual gel point from the theoretical one was smaller from EG to DD. The intrinsic viscosity of resulting prepolymer demonstrated almost no variation with progressing polymerization for the EG system, whereas it gradually increased with conversion for the DD system. Close to the gel point conversion it increased rather drastically for both systems. The swelling ratio of resulting gel was higher from EG to DD. These are discussed mechanistically in terms of the significant occurrence of intramolecular cyclization and intramolecular crosslinking reactions leading to shrinkage of the molecular size. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3243–3248, 2003 相似文献