全文获取类型
收费全文 | 1498篇 |
免费 | 18篇 |
国内免费 | 11篇 |
专业分类
化学 | 1105篇 |
晶体学 | 15篇 |
力学 | 18篇 |
数学 | 83篇 |
物理学 | 306篇 |
出版年
2020年 | 6篇 |
2019年 | 19篇 |
2018年 | 20篇 |
2017年 | 9篇 |
2016年 | 23篇 |
2015年 | 16篇 |
2014年 | 21篇 |
2013年 | 73篇 |
2012年 | 57篇 |
2011年 | 82篇 |
2010年 | 42篇 |
2009年 | 34篇 |
2008年 | 92篇 |
2007年 | 75篇 |
2006年 | 88篇 |
2005年 | 93篇 |
2004年 | 78篇 |
2003年 | 77篇 |
2002年 | 87篇 |
2001年 | 44篇 |
2000年 | 31篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 30篇 |
1993年 | 28篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 21篇 |
1985年 | 25篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 20篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1973年 | 13篇 |
1972年 | 11篇 |
1967年 | 5篇 |
排序方式: 共有1527条查询结果,搜索用时 31 毫秒
81.
Pd‐initiated polymerization of diazo compounds bearing dialkoxyphosphinyl group and hydrolysis of the resulting polymers and oligomers to afford phosphonic acid‐containing products 下载免费PDF全文
Hiroaki Shimomoto Akira Oda Motoki Kanayama Tomoya Sako Tomomichi Itoh Eiji Ihara Naohiro Hoshikawa Akihiko Koiwai Naoki Hasegawa 《Journal of polymer science. Part A, Polymer chemistry》2016,54(12):1742-1751
Pd‐initiated polymerization and oligomerization of diazo compounds containing a dialkoxyphosphinyl group are described. Polymerization of 2‐dialkoxyphosphinylethyl diazoacetates with π‐allylPdCl‐based initiating systems afforded C? C main chain polymers bearing phosphonate on each main chain carbon atom. The quantitative transformation of the side chain phosphonate to phosphonic acid resulted in the formation of water soluble polymers having the acid groups accumulated around their main chains, although the carbonyl ester linkage in the side chain was cleaved via intramolecular acid‐assisted hydrolysis in water at 80 °C. Pd‐initiated oligomerization of diethyl diazomethylphosphonate yielded an oligomeric product bearing diethoxyphosphiny groups directly attached to its main chain carbons, with unexpected incorporation of azo group in the main chain framework. Hydrolysis of the phosphonate of the oligomer afforded a water‐soluble product, which was revealed to show higher proton conductivity than poly(vinylphosphonic acid) under certain conditions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1742–1751 相似文献
82.
83.
Tae Seok Kwon Sadanori Kumazawa Shuji Kondo† Koji Takagi Hideo Kunisada Yasuo Yuki 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(12):1895-1913
Abstract 1,4-Bis(p-tert-butylphenylselenomethyl) benzene was synthesized, and used as a bifunctional photoiniferter for the polymerization of styrene. Both the polymer yields and the number average of molecular weights (n) of polymers increased with the polymerization. The polymerization of styrene by this iniferter permitted telechelic polystyrene containing arylseleno groups at both chain ends, and the degree of functionality was 1.9. The seleno groups of both chain ends of polystyrene were reduced quantitatively by tri-n-butyltin hydride. These seleno groups in polystyrene were also eliminated by treatment with hydrogen peroxide to give telechelic polystyrene with carbon-carbon double bond at both chain ends. Further, polystyrene with double bonds was converted to telechelic polystyrene carrying terminal functional groups as epoxy, hydroxy, and iodide group, respectively. 相似文献
84.
Venkataprasad Jalli Suvratha Krishnamurthy Hiroyoshi Kawasaki Tetsuji Moriguchi Akihiko Tsuge 《合成通讯》2013,43(19):2216-2226
An efficient and facile method for the synthesis of novel spiro[indole-2,2′-pyrroles] from N-methyl-3-isatin imines, t-butyl isocyanide, and dialkyl acetylenedicarboxylate has been achieved by [3 + 2] cyclo addition reaction. All the products were purified by column chromatography as yellow solids and confirmed with 1H NMR, 13C NMR, fast atom bombardment, mass, and infrared. Compound 11 was further confirmed with x-ray analysis. 相似文献
85.
Ryohei Yamakado Shin-ichi Matsuoka Masato Suzuki Koji Takagi Kosuke Katagiri Isao Azumaya 《Tetrahedron》2013,69(5):1516-1520
m-Calix[3]amide bearing three pyrenes (1a) was prepared by the condensation reaction of 3-nonylaminobenzoic acid derivative using Ph3PCl2. Pyrenyl groups were found to be aligned in the screw-like fashion by m-calix[3]amide as confirmed by the X-ray crystallography. Aromatic proton signals observed at the up-field region in the 1H NMR spectrum at low temperature indicated that pyrenyl groups in 1a are aligned in close proximity in THF solution. UV–vis absorption and fluorescence emission spectra did not show marked peak shift nor concentration fluorescence quenching compared with reference compounds implying no significant electronic interaction between pyrenyl groups. These results can be explained by the steric effect of the m-calix[3]amide platform. On the other hand, an excimer emission was observed for m-calix[3]amide having a flexible spacer between pyrene and m-calix[3]amide (1b). 相似文献
86.
Yiliang Wu Jun-Ichi Mamiya Osamu Tsutsumi Akihiko Kanazawa Takeshi Shiono Tomiki Ikeda 《Liquid crystals》2013,40(6):749-753
Photoinduced alignment in a polymer liquid crystal prepared from 6-{1-[4-(2-cyano-4-nitrophenylazo)phenyl]piperazino}hexyl acrylate and 4'-[6-(methacryloyloxy)hexyloxy]-4-cyanobiphenyl was investigated for the first time on irradiation with a polarized He-Ne laser beam at 633 nm. The azobenzene moieties as well as the inert cyanobiphenyl mesogenic units were aligned with the molecular long axis perpendicular to the polarization direction of the irradiation light. Alignment induced on short irradiation was reversible, while that induced under prolonged irradiation was irreversible due to the occurrence of crosslinking which might be caused by photoinduced decomposition of the azobenzene moieties during the photoirradiation process. 相似文献
87.
Akira Hasegawa Takashi Ando Akihiko Kameyama Makoto Kiso 《Journal of carbohydrate chemistry》2013,32(5):645-658
Abstract Stereocontrolled synthesis of sialyl Lex epitope and its ceramide derivative with regard to the introduction of galactose or β-D-galactosyl ceramide into the terminal N-acetylglucosamine residue of sialyl Lex determinant is described. Königs-Knorr condensation of 2-(trimethylsilyl)ethyl 2, 4, 6-tri-O-benzyl-β-D-galactopyranoside (4) with 3, 4, 6-tri-O-acetyl-2-deoxy-2-phthalimido-D-glucopyranosyl bromide (5) gave the desired β-glycoside 6, which was converted into 2-(trimethylsilyl)ethyl O-(2-acetamido-4, 6-O-benzylidene-2-deoxy-β-D-glucopyranosyl)-(l→3)-2, 4, 6-tri-O-benzyl-β-D-galactopyranoside (8) via removal of the phthaloyl and O-acetyl groups, followed by N-acetylation and 4, 6-O-benzylidenation. Glycosylation of 8 with methyl 2, 3, 4-tri-O-benzyl-1-thio-β-L-fucopyranoside (9) gave the α-glycoside (10), which was transformed by reductive ring-opening of the benzyliderie acetal into the acceptor (11). Dimethyl(methylthio)sulfonium triflate (DMTST)-promoted coupling of 11 with methyl O-(methyl 5-acetamido-4, 7, 8, 9-tetra-O-acetyl-3, 5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-2, 4, 6-tri-O-benzoyl-l-thio-β-D-galactopyra-noside (12) afforded the desired pentasaccharide (13), which was converted into the α-trichloroacetimidate 16 via reductive removal of the benzyl groups, then O-acetylation, removal of the 2-(trimethyIsilyl)ethyl group and treatment with trichloroacetonitrile. Condensation of 16 with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-l, 3-diol (18) gave the β-glycoside 19, which was transformed into the title compound 21, via reduction of the azido group, coupling with octadecanoic acid, O-deacylation and hydrolysis of the methyl ester group. On the other hand, O-deacylation of 13 and subsequent hydrolysis of the methyl ester group gave the pentasaccharide epitope 17. 相似文献
88.
Akihiko Kameyama Hideharu Ishida Makoto Kiso Akira Hasegawa 《Journal of carbohydrate chemistry》2013,32(5):799-804
Abstract Sialoglycoconjugates such as glycoproteins and glycolipids are present as components of cell memberanes and play important roles1,2 in biological systems. Sialyl neolactotetrasyl ceramide (IV3NeuAcnLc4Cer), a complex type of ganglioside, was isolated as the major ganglioside of human erythrocytes3 and was shown to be a receptor of that this glycolipid induces granulocytic differentiation of human premyelocytic leukemia cell. 相似文献
89.
Atsutoshi Yamada Yuki Watanabe Kyoko Noda Sumitaka Itoh Koji Ishihara Masahiko Inamo Refat Moustafa Hassan Hideo D. Takagi 《Journal of solution chemistry》2014,43(9-10):1479-1486
The reduction reaction of the Cu(II)–pitn complex (pitn = 1,3-di(pyridine-2-carboxaldimino)propane) by decamethylferrocene [Fe(Cp*)2] was examined in acetonitrile. The observed pseudo-first-order rate constants exhibited saturation kinetics with increasing excess amount of [Fe(Cp*)2]. Detailed analyses revealed that the reaction is controlled by a structural change prior to the electron transfer step, rather than a conventional bimolecular electron transfer process preceded by ion pair (encounter complex) formation. The rate constant for the structural change was estimated to be 275 ± 13 s?1 at 298 K (?H* = 33.3 ± 1.0 kJ·mol?1, ?S* = 86 ± 5 J·mol?1·K?1), which is the fastest among gated reactions involving CuN4 complexes. It was confirmed by EPR measurement and Conflex calculations that the dihedral angle between the two N–N planes is significantly large (40°) in solution whereas it is merely 17.14° in the crystal. 相似文献
90.
Ariaki Murata Ryota Akaike Tatsuya Kawahashi Ryo Tsuchiya Hiroyuki Takemoto Toshiyuki Ohnishi Yasushi Todoroki Nobuyuki Mase Mineyuki Yokoyama Kazuteru Takagi Peter Winterhalter Naoharu Watanabe 《Tetrahedron》2014
A flower-inducing compound, LDS1, was isolated from a free-floating aquatic plant, Lemna paucicostata. The chemical structure and the absolute stereochemistry of LDS1 were determined as (9R,13R,11E,15Z)-9,13-dihydroxy-10-oxooctadeca-11,15-dienoic acid for its most abundant diastereomer. LDS1 was enzymatically produced when the plant was exposed to drought stress, and induced flowering at a concentration of 10 nM. 相似文献