全文获取类型
收费全文 | 18457篇 |
免费 | 408篇 |
国内免费 | 1638篇 |
专业分类
化学 | 8810篇 |
晶体学 | 122篇 |
力学 | 183篇 |
综合类 | 188篇 |
数学 | 8075篇 |
物理学 | 3125篇 |
出版年
2023年 | 112篇 |
2022年 | 195篇 |
2021年 | 120篇 |
2020年 | 183篇 |
2019年 | 280篇 |
2018年 | 262篇 |
2017年 | 264篇 |
2016年 | 265篇 |
2015年 | 234篇 |
2014年 | 413篇 |
2013年 | 1249篇 |
2012年 | 745篇 |
2011年 | 842篇 |
2010年 | 714篇 |
2009年 | 1035篇 |
2008年 | 1191篇 |
2007年 | 1313篇 |
2006年 | 1053篇 |
2005年 | 935篇 |
2004年 | 873篇 |
2003年 | 626篇 |
2002年 | 464篇 |
2001年 | 486篇 |
2000年 | 1277篇 |
1999年 | 953篇 |
1998年 | 914篇 |
1997年 | 353篇 |
1996年 | 368篇 |
1995年 | 378篇 |
1994年 | 341篇 |
1993年 | 277篇 |
1992年 | 257篇 |
1991年 | 151篇 |
1990年 | 136篇 |
1989年 | 107篇 |
1988年 | 86篇 |
1987年 | 106篇 |
1986年 | 84篇 |
1985年 | 124篇 |
1984年 | 79篇 |
1983年 | 61篇 |
1982年 | 117篇 |
1981年 | 105篇 |
1980年 | 78篇 |
1979年 | 43篇 |
1978年 | 72篇 |
1977年 | 68篇 |
1976年 | 67篇 |
1975年 | 16篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Irina O. Zhuravel Oleg V. Zaremba Oleksandr S. Detistov Svitlana S. Kovalenko Valentin P. Chernykh 《合成通讯》2013,43(21):3778-3784
New 5-hydroxymethyl-8-methyl-3-(3-aryl-[1,2,4]oxadiazol-5-yl)-2H-pyrano-[2,3-c]pyridin-2-ones and their esters were synthesized. The structure of obtained compounds was determined through a complete 1H NMR analysis. 相似文献
992.
A facile and efficient synthesis of 14-aryl or alkyl-14H-dibenzo[a,j]xanthenes has been accomplished by treatment of β-naphthol with aryl or alkyl aldehydes catalyzed by 2-1′-methylimidazolium-3-yl-1-ethyl sulfate in ionic liquid [BMIM][BF4] at 80°C. The luminescence of products was studied in detail. 相似文献
993.
Thirupaiah Bade 《合成通讯》2013,43(20):2350-2354
The synthesis of 3-(2-(5-(benzylideneamino)-3-phenyl-1H-pyrazol-1-yl)thiazol-4-yl)-4-hydroxy-6-methyl-2H-pyran-2-one derivatives was achieved through a one-pot, four-component reaction involving condensation of 3-(2-bromoacetyl)-4-hydroxy-6-methyl-2H-pyran-2-one, thiosemicarbazide, phenacylcyanaide, and various aryl aldehydes in dry alcohol and few drops of acetic acid under reflux condition. This four-component reaction has some advantages such as ease of handling, good yields, and easy workup. All structures of newly prepared compounds were confirmed by analytical and spectral data. 相似文献
994.
《合成通讯》2013,43(18):3233-3241
Abstract A concise synthesis of (2E,4Z)-2,4-heptadien-1-ol and (2E,4Z)-2,4-heptadienal is presented. Commercially available (Z)-2-penten-1-ol was converted to ethyl-(2E,4Z)-2,4-heptadienoate by reaction with activated MnO2 and (carboethoxymethylene)triphenylphosphorane in the presence of benzoic acid as a catalyst. Ethyl-(2E,4Z)-2,4-heptadienoate was converted to (2E,4Z)-2,4-heptadien-1-ol with LiAlH4. The alcohol was partially oxidized to (2E,4Z)-2,4-heptadienal with MnO2. The title compounds are male-specific, antennally active volatile compounds from the Saltcedar leaf beetle, Diorhabda elongata Brulle (Coleoptera: Chrysomelidae) and have potential use in the biological control of the invasive weed saltcedar (Tamarix spp). 相似文献
995.
Mediated by samarium diiodide, 1-(benzotriazole-1-yl)alkyl esters 1 underwent cross-coupling with aldehydes or ketones to afford β-(benzotriazole-1-yl)alcohols 2 exclusively with the selective removal of acyloxy over benzotriazolyl. 相似文献
996.
AbstractHerein, we describe a one-pot synthesis of some novel 2-(3-alkyl/aryl-5-trifluoromethylpyrazol-1-yl)-4-(coumarin-3-yl)thiazoles (6) involving the reaction of 3-alkyl/aryl-5-hydroxy-5-trifluoromethyl-4,5-dihydropyrazole-1-thiocarboxamides (3) with 3-bromoacetylcoumarins (5) in the presence of sodium carbonate in ethanol. Reaction of 3 with 5 in the absence of sodium carbonate, however, resulted in the formation of 2-(3-alkyl/aryl-5-hydroxy-5-trifluoromethyl-4,5-dihydropyrazol-1-yl)-4-(coumarin-3-yl)thiazoles, which were subsequently dehydrated to 6 by refluxing in ethanol in the presence of sodium carbonate. The structure of the synthesized compounds (6) was confirmed by infrared (IR), mass, 1H NMR, and 13C NMR spectra and elemental analysis data. Newly synthesized compounds (6) showed moderate to good activity against Gram-positive bacteria. 相似文献
997.
Justin R. Denton 《合成通讯》2013,43(5):770-776
A protocol has been developed to purify 9-(trifluoroacetyl)anthracene from anthracene, the major impurity associated in its synthesis. The protocol utilizes a chemoselective thermal Diels–Alder reaction, employing maleic anhydride as the dienophile. The resulting Diels–Alder adduct can then be removed by extractive workup followed by recrystallization to give 9-(trifluoroacetyl)anthracene with ≥99% chemical purity. 相似文献
998.
A short, practical, and efficient preparation of 2-(indol-3-yl)pyridine derivatives via a one-pot procedure of 3-cyanoacetylindole, chalcones, and ammonium acetate under microwave irradiation was described. All these compounds were obtained in good yield, and their structures were confirmed by 1H NMR, infrared, and elementary analysis. 相似文献
999.
Jarosław Sławiński Aneta Pogorzelska Beata Żołnowska Tomasz Laskowski Paweł Sowiński 《Tetrahedron》2013
3-Amino-1,1-dioxopyrido[4,3-e]-1,4,2-dithiazine has been synthesized and applied to the synthesis of 3-amino-2-(4-thioxo-1,4-dihydropyridin-3-ylsulfonyl)guanidine. The reaction of the aminoguanidine with the appropriate 1,2-diarylethane-1,2-diones afforded 2,3-diaryl-9,9-dioxo-1H-9-thia-1,4,4a,7,10-pentaazaphenanthrene-2-ol derivatives. The structure of these compounds, which represent a novel heterocyclic ring system, was confirmed on the basis of elemental analysis and spectroscopic data including COSY, NOESY, ROESY, HSQC, and HMBC. 相似文献
1000.
Synthesis of 2-cinnamoyl-1-styryl-3,4-diarylcyclopentanol via cyclodimerization of 1,5-diaryl-1,4-pentadien-3-one mediated by zinc was carried out in good yields at room temperature in NH4Cl (aq.) and tetrahydrofuran under ultrasonic irradiation. In comparison with conventional methods, the main advantages of the present procedure are shorter reaction time and better yields. 相似文献