全文获取类型
收费全文 | 1940篇 |
免费 | 54篇 |
国内免费 | 4篇 |
专业分类
化学 | 1598篇 |
晶体学 | 4篇 |
力学 | 13篇 |
数学 | 230篇 |
物理学 | 153篇 |
出版年
2024年 | 2篇 |
2023年 | 13篇 |
2022年 | 69篇 |
2021年 | 104篇 |
2020年 | 66篇 |
2019年 | 56篇 |
2018年 | 44篇 |
2017年 | 37篇 |
2016年 | 80篇 |
2015年 | 83篇 |
2014年 | 73篇 |
2013年 | 154篇 |
2012年 | 136篇 |
2011年 | 136篇 |
2010年 | 106篇 |
2009年 | 86篇 |
2008年 | 113篇 |
2007年 | 107篇 |
2006年 | 104篇 |
2005年 | 91篇 |
2004年 | 88篇 |
2003年 | 55篇 |
2002年 | 53篇 |
2001年 | 25篇 |
2000年 | 20篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 15篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1936年 | 2篇 |
1927年 | 2篇 |
1924年 | 2篇 |
1923年 | 1篇 |
排序方式: 共有1998条查询结果,搜索用时 31 毫秒
991.
992.
Reinhold Tacke Rüdiger Bertermann Christian Burschka Simona Dragota 《无机化学与普通化学杂志》2004,630(12):2006-2012
Morpholinium meso‐bis[citrato(3‐)‐O1, O3, O6]silicate (meso‐ 5 ) and racemic morpholinium bis[citrato(4‐)‐O1, O3, O6]silicate (rac‐ 6 ) were synthesized by treatment of tetramethoxysilane with citric acid and morpholine (molar ratio 1:2:2 and 1:2:4, respectively). Treatment of tetramethoxysilane with (S)‐malic acid and tri(n‐propyl)amine or tri(n‐butyl)amine (molar ratio 1:3:2) yielded tri(n‐propyl)ammonium (Λ, S, S, S)‐mer‐tris[malato(2‐)‐O1, O2]silicate ((Λ, S, S, S)‐mer‐ 7 ) and tri(n‐butyl)ammonium (Λ, S, S, S)‐mer‐tris[malato(2‐)‐O1, O2]silicate ((Λ, S, S, S)‐mer‐ 8 ). The hexacoordinate silicon compounds meso‐ 5 ·2MeOH, rac‐ 6 ·1.73MeOH, (Λ, S, S, S)‐mer‐ 7 , and (Λ, S, S, S)‐mer‐ 8 ·2MeCN were structurally characterized in the solid state by single‐crystal X‐ray diffraction and VACP/MAS NMR spectroscopy (13C, 15N, 29Si). Upon dissolution in water at 20 °C, spontaneous hydrolysis of the λ6Si‐silicate anions was observed. 相似文献
993.
Marco Bandini Alfonso Melloni Simona Tommasi Achille Umani‐Ronchi 《Helvetica chimica acta》2003,86(11):3753-3763
A new class of α,β‐unsaturated S‐(1,3‐benzoxazol‐2‐yl) thioesters of type 2 have been synthesized and effectively employed as electrophiles in the stereoselective alkylation of indoles. The combination of electronic as well as steric properties of such Michael acceptors allowed us to carry out Friedel? Crafts alkylations of various substituted indoles in the presence of a catalytic amount (20 mol‐%) of chiral cationic [PdII(Tol‐binap)] complexes. With the optimized catalytic system (PdCl2(MeCN)2/Tol‐binap/AgSbF6), the desired β‐indolyl‐substituted thioderivatives 4 were obtained in good yield, with an enantiomeric excess (ee) of up to 86%. The remarkable versatility of the enantiomerically enriched thioesters 4 was demonstrated by quantitatively transforming them into optically active β‐indolyl esters and amides under mild conditions. With this stereoselective, catalytic Friedel? Crafts reaction, we open up the way towards new α,β‐unsaturated compounds that could be suitable candidates for the preparation of a number of optically active β‐substituted carboxylic compounds. 相似文献
994.
We report a method for the synthesis of 9-N-alkyl-8-arylsulfoxyl adenines and 9-N-alkyl-8-arylsulfonyl adenines. The approach starts with a tandem one-pot reaction that by using Mitsunobu conditions converts 8-arylsulfanyl adenines to the corresponding iminophosphorane protected 9-N-alkyl-8-arylsulfanyl adenines. These compounds were further subjected to selective OXONE®/alumina mediated oxidation followed by deprotection of the amine leading to the desired sulfoxides and sulfones. 相似文献
995.
A study of the addition of boron enolates of methyl ketones to trans α,β-aziridine aldehydes is reported. The reaction proceeds with excellent anti stereoselectivity furnishing functionalized products, capable of other controlled transformations, some of which are described. 相似文献
996.
Ring-opening hydrofluorination of enantiomerically pure (2S,3S)-3-arylglycidyl ethers (aryl = phenyl, 4-trifluoromethylphenyl) by boron trifluoride-diethyl ether under mild conditions provides β-fluoro alcohols in good yield in a stereospecific manner with complete regiocontrol. 相似文献
997.
The optical transmission and the electric power was simultaneously recorded for the binary compensated cholesteric mixture cholesteryl chloride + cholesteryl nonanoate (70:30 molar). The values of the critical voltages U1 and U2 (at which the planar texture changes into a conic focal one, and the cholesteric-nematic transition take place) at different temperatures were obtained. The temperature dependence of the anchoring constant is determined. 相似文献
998.
Gabriela Chaves 《Mathematische Zeitschrift》1997,226(1):67-84
Sans résumé
Received 11 July 1994; in final form 1 November 1995 相似文献
999.
Kuminek G Stulzer HK Tagliari MP Oliveira PR Bernardi LS Rauber GS Cardoso SG 《Journal of AOAC International》2011,94(6):1785-1790
An HPLC method was developed and validated for the simultaneous determination of buclizine, tryptophan, pyridoxine, and cyanocobalamin in pharmaceutical formulations. The chromatographic separation was carried out on an RP-C18 column using a mobile phase gradient of methanol, 0.015 M phosphate buffer (pH 3.0), and 0.03 M phosphoric acid at a flow rate of 1.0 mL/min and UV detection at 230, 280, and 360 nm, respectively, for buclizine, tryptophan, pyridoxine, and cyanocobalamin. The method validation yielded good results with respect to linearity (r>0.999), specificity, precision, accuracy, and robustness. The RSD values for intraday and interday precision were below 1.82 and 0.63%, respectively, and recoveries ranged from 98.11 to 101.95%. The method was successfully applied for the QC analysis of buclizine, tryptophan, pyridoxine, and cyanocobalamin in tablets and oral suspension. 相似文献
1000.
Procopio EQ Rojas S Padial NM Galli S Masciocchi N Linares F Miguel D Oltra JE Navarro JA Barea E 《Chemical communications (Cambridge, England)》2011,47(42):11751-11753
The highly porous and robust [Ni(8)(OH)(4)(OH(2))(2)(4,4'-(buta-1,3-diyne-1,4-diyl)bispyrazolato)(6)](n) MOF can be used as a proof of concept for the incorporation and release of the non-conventional [Ru(p-cymene)Cl(2)(pta)] RAPTA-C metallodrug. 相似文献