全文获取类型
收费全文 | 5170篇 |
免费 | 68篇 |
国内免费 | 34篇 |
专业分类
化学 | 3293篇 |
晶体学 | 72篇 |
力学 | 158篇 |
数学 | 1012篇 |
物理学 | 737篇 |
出版年
2020年 | 39篇 |
2016年 | 67篇 |
2015年 | 53篇 |
2014年 | 59篇 |
2013年 | 234篇 |
2012年 | 184篇 |
2011年 | 210篇 |
2010年 | 117篇 |
2009年 | 107篇 |
2008年 | 199篇 |
2007年 | 212篇 |
2006年 | 239篇 |
2005年 | 219篇 |
2004年 | 193篇 |
2003年 | 174篇 |
2002年 | 141篇 |
2001年 | 81篇 |
2000年 | 75篇 |
1999年 | 61篇 |
1998年 | 50篇 |
1997年 | 75篇 |
1996年 | 87篇 |
1995年 | 79篇 |
1994年 | 96篇 |
1993年 | 97篇 |
1992年 | 63篇 |
1991年 | 90篇 |
1990年 | 84篇 |
1989年 | 66篇 |
1988年 | 72篇 |
1987年 | 55篇 |
1986年 | 59篇 |
1985年 | 104篇 |
1984年 | 103篇 |
1983年 | 64篇 |
1982年 | 99篇 |
1981年 | 98篇 |
1980年 | 78篇 |
1979年 | 96篇 |
1978年 | 86篇 |
1977年 | 83篇 |
1976年 | 79篇 |
1975年 | 65篇 |
1974年 | 84篇 |
1973年 | 94篇 |
1972年 | 48篇 |
1971年 | 45篇 |
1970年 | 41篇 |
1969年 | 36篇 |
1968年 | 34篇 |
排序方式: 共有5272条查询结果,搜索用时 10 毫秒
41.
Herman Ziffer Kuninbu Kabuto D.T. Gibson V.M. Kobal Donald M. Jerina 《Tetrahedron》1977,33(19):2491-2496
The absolute stereochemistry of a series of 3-substituted cis-dihydrodiols obtained by microbial oxidation of toluene, ethylbenzene, chlorobenzene, and biphenyl has been assigned from chemical and spectrophotometric studies. ?-Halogenated toluenes also have been investigated as substrates in these oxidations, and the corresponding cis-dihydrodiols isolated. Implications from the observation that some of the cis-dihydrodiols are racemic are discussed. Oxidation of an olefin, (±)-3-methylcyclohexene, by these microorganisms leads only to cis-diols whose absolute stereochemistry about the hydroxyl-bearing carbons is the same as that found for the cis-dihydrodiols formed from the aromatic substrates. 相似文献
42.
A scaleable synthesis of 2-bromo-3-fluorobenzonitrile via the NaOMe-catalyzed bromodeboronation of 2-cyano-6-fluorophenylboronic acid was developed. The generality of this transformation was demonstrated through the halodeboronation of a series of aryl boronic acids. Both aryl bromides and aryl chlorides were formed in good to excellent yields when the corresponding aryl boronic acid was treated with 1,3-dihalo-5,5-dimethylhydantoin and 5 mol % NaOMe. 相似文献
43.
A diversity-oriented solution and solid-phase synthesis of tetrahydroquinoline-based tricyclic derivatives has been achieved from enantiomerically pure, natural product-like bicyclic scaffold. The solution synthesis of enantiopure bicyclic scaffold was developed by asymmetric hetero Michael reaction. Our approach for the synthesis of polycyclic derivatives utilized regio- and stereoselective hetero Michael reaction and ring-closing metathesis as key steps in solution and on solid phase. 相似文献
44.
4-(4-Hydroxyphenyl)-2-phenylamino-1,8-naphthyridine was prepared via cyclisation of N-phenyl-N′-3-(4-hydroxyphenethen-1-yl)pyridin-2-ylthiourea in the presence of mercuric oxide. Derivatives of 4-methyl-2-aminoquinolines were prepared in a similar manner from 2-vinylphenylthioureas. 相似文献
45.
Arya P Couve-Bonnaire S Durieux P Laforce D Kumar R Leek DM 《Journal of combinatorial chemistry》2004,6(5):735-745
A solid-phase synthesis of tetrahydroquinoline-derived polycyclic 4, having a medium size ring with an enamide functionality, was achieved from tetrahydroquinoline derivative 3 in five steps with overall 40-45% yield. An enantiopure, tetrahydroquinoline-derived beta-amino ester, 1, was converted into compound 2 that has a free phenolic hydroxyl group as an anchoring site for solid-phase synthesis. The solid-phase worked well for this sequence, in which the synthesis of the unsaturated eight-membered enamide lactam was obtained by a ring-closing metathesis approach. Compound 4 is a novel, natural product-like polycyclic derivative that could further be utilized in library generation for developing small molecule chemical probes. 相似文献
46.
Donald R. Dimmel Charles A. Wilkie Paul J. Lamothe 《Journal of mass spectrometry : JMS》1975,10(1):18-25
The mass spectra of (Me3Sn)nCH4?n, where n varies from 1 to 4, (Me3Sn)2CClX, where X equals H, Cl, Br or I, together with some tetraalkyltin compounds and Me3SnCCl3, are presented. Comparisons with mass spectra of the silicon analogs1 show a large number of similarities, including the appearance of allylic ions which require Group IV metal to carbon π-bonding. Multiple rearrangements are observed with the halogenated tin compounds which bring the α-halogen into direct bonding with the tin atom. 相似文献
47.
The volumes of activation in cm3 mol?1 for the aquation of Co(CN)5X3? were determined at 40°C and μ = 1 M (NaClO4) to be + 7.8 ± 0.5 for X = Cl?, + 7.6 ± 0.6 for X = Br?, + 14.0 ± 0.7 for X = I?, and + 16.8 ± 0.5 for X = N3? (0.1 M HClO4), respectively. The volumes of activation for the aquation of Co(CN)5Cl3? at μ = 0.1 M are + 10.0 ± 0.6 cm3 mol?1 and ± 9.1 ± 0.3 cm3 mol?1 at 40°C and 25°C, respectively. The corresponding values for the anation of Co(CN)5OH22? (at 40°C) and μ = 1 M by Br?, I?, and NCS? are +8.4 ± 1.0, +9.4 ± 1.6, and +8.2 ± 0.9 cm3 mol?1, respectively. These data are discussed in terms of a dissociative (D) mechanism. 相似文献
48.
49.
Ronald I. Trust J. Donald Albright F. M. Lovell N. A. Perkinson 《Journal of heterocyclic chemistry》1979,16(7):1393-1403
Synthetic methods for the preparation of 6-aryl-1,2,4-triazolo[4,3-b]-1,2,4-triazines ( 1 ) and the 7-aryl isomers ( 2 ) are described. Compounds 1 were prepared from aryl glyoxaldoximes 76 via 6-aryl-1,2,4-triazin-3(2H)ones ( 75 ). A simple procedure for the preparation of the 7-aryl isomers was effected using arylglyoxals 11 and the triazoles ( 4, 12a and 12b ). However, complete regioselectivity was not realized in all cases, especially when the triazoles were substituted at the C-5 position. A regiospecific synthesis of the 7-aryl isomers 2 was developed via the 3-methylthio-5-aryl-1,2,4-triazines ( 61 ). The structure of the parent 6-phenyl derivative 5 was confirmed by x-ray crystallography. 相似文献
50.
1-Phenyl-2-(benzenesulphonyl)-ethylene and 1-phenyl-2-(benzenesulphonyl)-prop-1-ene have been shown to undergo ,-photoisomerisation, whereas 2-benzenesulphonylindene readily forms [π2 + π2] photoadducts with 2,3-dimethylbut-2-ene, cyclopentene, and cyclohexene. 相似文献