全文获取类型
收费全文 | 829篇 |
免费 | 31篇 |
国内免费 | 2篇 |
专业分类
化学 | 676篇 |
晶体学 | 8篇 |
力学 | 2篇 |
综合类 | 1篇 |
数学 | 58篇 |
物理学 | 117篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 7篇 |
2021年 | 17篇 |
2020年 | 11篇 |
2019年 | 21篇 |
2018年 | 11篇 |
2017年 | 7篇 |
2016年 | 20篇 |
2015年 | 24篇 |
2014年 | 24篇 |
2013年 | 45篇 |
2012年 | 51篇 |
2011年 | 55篇 |
2010年 | 31篇 |
2009年 | 31篇 |
2008年 | 57篇 |
2007年 | 58篇 |
2006年 | 79篇 |
2005年 | 58篇 |
2004年 | 45篇 |
2003年 | 43篇 |
2002年 | 35篇 |
2001年 | 11篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1974年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有862条查询结果,搜索用时 0 毫秒
11.
Michiko Iwamura Yuka Gotoh Tomoyuki Hashimoto Reiko Sakurai 《Tetrahedron letters》2005,46(37):6275-6277
Michael addition reactions of acetoacetates and malonates with acrylates in a 5 M KOH aqueous solution without using any other catalysts are described. When they are either tert-butyl or benzyl esters, the reaction proceeded very rapidly to afford moderate to high yields of the corresponding bis-Michael adducts that are unexpectedly stable under these conditions. 相似文献
12.
Koga T Taguchi K Kinoshita T Higuchi M 《Chemical communications (Cambridge, England)》2002,(3):242-243
A novel artificial protein with simple primary structure, poly(gamma-methyl-L-glutamate)-grafted polyallylamine, has been prepared and the resultant peptide has shown a unique property of pH-regulated conformation and morphology. 相似文献
13.
Tomoyuki Esumi 《Tetrahedron letters》2004,45(37):6941-6945
Isoplagiochin D, a highly strained macrocyclic bis(bibenzyls) with two biaryl units isolated from the liverwort Pladiochila fruticosa, was prepared in 10.6% overall yield for the 11 steps by an efficient synthetic approach involving the construction of two bibenzyl and one biaryl units using Horner-Wadsworth-Emmons and Suzuki-Miyaura protocols. 相似文献
14.
[reaction: see text] A concise and stereoselective synthesis of the chiral building block, dioxanylpiperidene 4 as a precursor for deoxyazasugars, starting from the Garner aldehyde 5 using catalytic ring-closing metathesis (RCM) for the construction of the piperidine ring is described. The asymmetric synthesis of 1-deoxygalactonojirimycin and its congeners 1-3 was carried out via the use of 4 in a highly stereocontrolled mode. 相似文献
15.
Keisuke Kato Chie Matsuba Hiroyuki Takayama Tomoyuki Mochida Tat'yana A. Peganova Oleg V. Gusev 《Tetrahedron》2006,62(42):9988-9999
The oxidative cyclization-carbonylation of meso-2-alkyl-2-propargylcyclohexane-1,3-diols mediated by Pd(II) with chiral bisoxazoline (box ligand) afforded bicyclic-β-alkoxyacrylates. Based on a ligand screening, 2,2′-isopropylidenebis[(4S,5R)-4,5-di(2-naphthyl)-2-oxazoline] ligand has been developed. The products with a chiral quaternary carbon were obtained in 71-100% yields with 85-95% ee. 相似文献
16.
[reaction: see text] Construction and characterization of the C-glycosidic moiety of telomerase inhibitor D8646-2-6 (1) are described. This is the first example of the C-glycosylation using electron-poor aromatics, 4-hydroxypyrone, as a glycosyl acceptor. The glycosylation reaction and base-promoted isomerization affords desired beta-C-glycoside in a 61% overall yield. 相似文献
17.
Funasaki N Ishikawa S Hirota S Neya S Nishimoto T 《Chemical & pharmaceutical bulletin》2004,52(6):708-713
The structure and ethanol complexation of a cyclic tetrasaccharide (CTS) in aqueous solution were investigated by proton NMR spectroscopy and molecular mechanics calculations. Two glucose units, A and B, of CTS are alternatively bonded by alpha-1,3 and alpha-1,6 linkages. The overlapped signals of protons A5, A6S, A6R, B3, B6S and B6R were resolved by spectral simulations to determine their chemical shifts and vicinal coupling constants. All vicinal coupling constants except for the A5-A6 spin system are consistent with the dihedral angles in the X-ray crystal structure. Each of protons A5, A6S, and A6R in the two units of A is equivalent with respect to the chemical shift. The vicinal coupling constants of (3)J(5-6S) and (3)J(5-6R) for unit A are close to the average of two rotamers that are present in crystals. The intensities of cross-peaks in the rotating frame nuclear Overhauser effect spectroscopy (ROESY) spectrum were rather well correlated with the effective distances calculated for the X-ray structure and molecular mechanics structures calculated in vacuo and water, although they are slightly better correlated with molecular mechanics structure in vacuo than with the other structures. From the changes of the chemical shifts of several CTS protons with increasing ethanol concentration, it was suggested that adsorption sites of ethanol on the plate structure of CTS are protons B2 and B4 (site B) in the concave face side and protons A1 and A2 (site A) in the convex back side. The binding constants for sites A and B are 0.0061 and 0.0176 M(-1), respectively. These binding constants are much smaller than a value of 4.1 M(-1) for the ethanol-alpha-cyclodextrin complex. 相似文献
18.
Koichiro Fukuda Tomoyuki Iwata Takashi Orito 《Journal of solid state chemistry》2005,178(12):3662-3666
The structural disorder in Ba0.6Sr0.4Al2O4 (space group P6322) was investigated by X-ray powder diffraction and selected-area electron diffraction (SAED). The initial structural model was determined using direct methods, and it was further modified by the combined use of Rietveld method and maximum-entropy method (MEM). MEM-based pattern fitting method was subsequently applied, resulting in the final reliability indices of Rwp=9.61%, Rp=6.96%, RB=1.40% and S=1.25. The electron density distribution was satisfactorily expressed by the split-atom model in which the strontium/barium and oxygen atoms were split to occupy the lower symmetry sites. The diffuse scattering in SAED was mainly attributable to the positional disorder of oxygen atoms. 相似文献
19.
Preparation of peptide thioester is essential for native chemical ligation and block condensation. Our novel methodology involves conversion of the carboxylic acid of a peptide into a thioester using p-toluenesulfonyl isocyanate, followed by alkylation, then thiol substitution. Our methodology can also be used for the preparation of glycopeptide thioesters. Furthermore, it is possible to carry out the reaction as a sequential peptide chemical ligation. 相似文献
20.