全文获取类型
收费全文 | 505篇 |
免费 | 55篇 |
国内免费 | 1篇 |
专业分类
化学 | 483篇 |
晶体学 | 2篇 |
力学 | 3篇 |
数学 | 14篇 |
物理学 | 59篇 |
出版年
2023年 | 5篇 |
2022年 | 13篇 |
2021年 | 14篇 |
2020年 | 17篇 |
2019年 | 24篇 |
2018年 | 9篇 |
2017年 | 4篇 |
2016年 | 24篇 |
2015年 | 26篇 |
2014年 | 35篇 |
2013年 | 37篇 |
2012年 | 31篇 |
2011年 | 56篇 |
2010年 | 19篇 |
2009年 | 16篇 |
2008年 | 20篇 |
2007年 | 35篇 |
2006年 | 22篇 |
2005年 | 33篇 |
2004年 | 34篇 |
2003年 | 20篇 |
2002年 | 16篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有561条查询结果,搜索用时 15 毫秒
471.
The synthesis of well-defined regular and miktoarm star-branched polymers by a convergent iterative methodology using core-functionalized 3-arm star-branched polymer with 1,1-diphenylethylene (DPE) moiety and a specially designed DPE derivative is described. The methodology involves the following two reaction steps in the entire iterative synthetic sequence: 1) a coupling reaction of a star-branched polymer having an anion at the core with a DPE derivative with two benzyl bromide moieties, 1-{4-[5,5-bis(3-bromomethylphenyl)-7-methylnonyl]phenyl}-1-phenylethylene, and 2) an addition reaction of the resulting core-DPE-functionalized star-branched polymer with sec-BuLi to convert the DPE moiety to a DPE-derived anion. The iterative synthetic sequence including these two reaction steps, 1) and 2), was repeated to successively synthesize star-branched polymers with more arms. Iteration of this synthetic sequence doubled the number of the arms in the star-branched polymer. With this methodology, 6-arm, 12-arm, and 14-arm regular star-branched polystyrenes as well as 6-arm A2B2C2, A4B2, and 12-arm A4B4C4 and A8B4 miktoarm star-branched polymers with well-defined structures have been successfully synthesized. 相似文献
472.
473.
Tomoya Higashihara Mao‐Chun Fu Takaaki Uno Mitsuru Ueda 《Journal of polymer science. Part A, Polymer chemistry》2016,54(8):1153-1158
Random copolycyanurates with a low number of amide units in the main chain have been developed as a candidate of dismantlable adhesives based on the rapid decrease of the molecular weights during the rearrangement to polyisocyanurates by a thermal treatment. The random copolycyanurates were prepared by the phase‐transfer‐catalyzed polycondensation of 2,4‐dichloro‐6‐methoxy‐1,3,5‐triazine with bisphenol A and a new bisphenol containing an amide unit in the presence of tetrabutylammonium bromide. They exhibited an excellent adhesive property for the silicon and copper deposited on the silicon substrate after the high thermal treatment of 240 °C under 0.6 MPa compression, and the die shear strengths of these polymers dramatically decreased at 260 °C for 1 h. Random copolycyanurates containing the amide unit are shown to be promising materials for dismantlable adhesion. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1153–1158 相似文献
474.
Kousuke Tsuchiya Eisuke Goto Yoshihito Ishida Tomoya Higashihara Atsushi Kameyama Mitsuru Ueda 《Journal of polymer science. Part A, Polymer chemistry》2015,53(5):692-698
Polyisocyanurates have been successfully prepared by the thermal rearrangement of polycyanurates, which were obtained from 2,4‐dichloro‐6‐methoxy‐1,3,5‐triazine and bisphenol monomers. The thermal rearrangement was carried out in the presence of a small amount of tetrabutylammonium bromide (TBAB) as a catalyst at 200 °C for 30 or 60 min in an argon atmosphere, and the degree of arrangement was greater than 95%. Transparent and amorphous polyisocyanurate films were obtained and showed a good thermal stability with a 5% weight loss temperature above 340 °C in nitrogen and the glass transition temperature above 210 °C. Films with a 10‐µm thickness exhibited an excellent transparency above 90% at 400 nm. Furthermore, the thermal rearrangement of 2,6‐bis(4‐methoxyphenyl)‐6‐methoxy‐1,3,5‐triazine to 1,3‐bis(4‐methoxyphenyl)‐5‐methyl‐1,3,5‐triazinane‐2,4,6‐trione was investigated in detail. It was found that the complete thermal rearrangement was successfully accomplished in the presence of 2 wt % TBAB at 150 °C for 20 min in an argon atmosphere. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 692–698 相似文献
475.
476.
A facile and convenient synthesis of the chiral phthalide framework catalyzed by cationic iridium was developed. The method utilized cationic iridium/bisphosphine‐catalyzed asymmetric intramolecular carbonyl hydroacylation of 2‐keto benzaldehydes to furnish the corresponding optically active phthalide products in good to excellent enantioselectivities (up to 98% ee). The mechanistic studies using a deuterium‐labelled substrate suggested that the reaction involved an intramolecular carbonyl insertion mechanism to iridium hydride intermediate. In addition, we investigated the kinetic isotope effect (KIE) of intramolecular hydroacylation with deuterated substrate and determined that the C?H activation step is not included in the turnover‐limiting step. 相似文献
477.
Hiroaki Itoh Kensuke Miura Koichi Kamiya Tomoya Yamashita Masayuki Inoue 《Angewandte Chemie (International ed. in English)》2020,59(11):4564-4571
We report a solid‐phase strategy for total synthesis of the peptidic natural product yaku'amide B ( 1 ), which exhibits antiproliferative activity against various cancer cells. Its linear tridecapeptide sequence bears four β,β‐dialkylated α,β‐dehydroamino acid residues and is capped with an N‐terminal acyl group (NTA) and a C‐terminal amine (CTA). To realize the Fmoc‐based solid‐phase synthesis of this complex structure, we developed new methods for enamide formation, enamide deprotection, and C‐terminal modification. First, traceless Staudinger ligation enabled enamide formation between sterically encumbered alkenyl azides and newly designed phosphinophenol esters. Second, application of Eu(OTf)3 led to chemoselective removal of the enamide Boc groups without detaching the resin linker. Finally, resin‐cleavage and C‐terminus modification were simultaneously achieved with an ester–amide exchange reaction using CTA and AlMe3 to deliver 1 in 9.1 % overall yield (24 steps from the resin). 相似文献
478.
In this study, we described the divergent synthesis of (+)-tanikolide and its analogues, such as (4S)- and (4R)-hydroxytanikolides, and nortanikolide, employing a stereoselective dirhodium(II)-catalyzed reaction to construct the quaternary chiral center of tanokolides. The key steps involve (a) a dirhodium(II)-catalyzed oxonium ylide formation–[2,3]-sigmatropic rearrangement, (b) an N-heterocyclic carbene-catalyzed ring-expansion lactonization of tetrahydrofurfural, or (c) an oxidative cleavage of tetrahydrofuran-5-methanol to γ-lactone using a 2-iodobenzamide catalyst. This route would provide high flexibility for analogue synthesis because the long side chain can be introduced at a later stage in the synthesis. 相似文献
479.
Dr. Bobo Dang Dr. Tomoya Kubota Dr. Kalyaneswar Mandal Prof. Dr. Ana M. Correa Prof. Dr. Francisco Bezanilla Prof. Dr. Stephen B. H. Kent 《Angewandte Chemie (International ed. in English)》2016,55(30):8639-8642
Ts3 is an alpha scorpion toxin from the venom of the Brazilian scorpion Tityus serrulatus. Ts3 binds to the domain IV voltage sensor of voltage‐gated sodium channels (Nav) and slows down their fast inactivation. The covalent structure of the Ts3 toxin is uncertain, and the structure of the folded protein molecule is unknown. Herein, we report the total chemical synthesis of four candidate Ts3 toxin protein molecules and the results of structure–activity studies that enabled us to establish the covalent structure of biologically active Ts3 toxin. We also report the synthesis of the mirror image form of the Ts3 protein molecule, and the use of racemic protein crystallography to determine the folded (tertiary) structure of biologically active Ts3 toxin by X‐ray diffraction. 相似文献
480.
Alternating Sequence Control for Carboxylic Acid and Hydroxy Pendant Groups by Controlled Radical Cyclopolymerization of a Divinyl Monomer Carrying a Cleavable Spacer
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof. Makoto Ouchi Marina Nakano Tomoya Nakanishi Prof. Mitsuo Sawamoto 《Angewandte Chemie (International ed. in English)》2016,55(47):14584-14589
By utilizing features of the hemiacetal ester (HAE) bond: easy formation from vinyl ether and carboxylic acid and easy cleavage into different functional groups (‐COOH and ‐OH), we achieved control of the alternating sequence of two functional pendant groups of a vinyl copolymer. Methacrylate‐ and acrylate‐based vinyl groups were connected through HAE bonds to prepare a cleavable divinyl monomer, which was cyclo‐polymerized under optimized conditions in a ruthenium‐catalyzed living radical polymerization. Subsequent cleavage of the HAE bonds in the resultant cyclo‐pendant led to a copolymer consisting of alternating methacrylic acid and 2‐hydroxyethyl acrylate units as analyzed by 13C NMR spectroscopy. The alternating sequence of ‐COOH and ‐OH pendants specifically provided a lower critical solution temperature (LCST) in an ether solvent, which was not observed with the random copolymer of same composition ratio. 相似文献