全文获取类型
收费全文 | 413篇 |
免费 | 6篇 |
国内免费 | 21篇 |
专业分类
化学 | 399篇 |
数学 | 35篇 |
物理学 | 6篇 |
出版年
2024年 | 1篇 |
2023年 | 35篇 |
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 15篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 30篇 |
2013年 | 25篇 |
2012年 | 10篇 |
2011年 | 28篇 |
2010年 | 22篇 |
2009年 | 26篇 |
2008年 | 37篇 |
2007年 | 27篇 |
2006年 | 35篇 |
2005年 | 18篇 |
2004年 | 26篇 |
2003年 | 4篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 8篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有440条查询结果,搜索用时 31 毫秒
1.
Yuliya V. Rassukana Kateryna O. Davydova Anatolii D. Sinitsa 《Tetrahedron letters》2004,45(20):3899-3902
Hydrophosphoryl nucleophilic agents add to the CN bond of N-sulfonyltrichloroacetimidoylphosphonates to give unstable C,C-diphosphorylated adducts, which undergo competitive 1,2-C → N phosphorotropic rearrangement and dehydrochlorination with the formation of aza-Perkow reaction products, C,N-diphosphorylated dichlorovinylsulfonamides. This is the first reliably identified case of an aza-Perkow transformation for acid phosphites and their initial nucleophilic attack at the C atom of the azomethine bond in the aza-substrates. 相似文献
2.
Wolfgang Kirmse 《Angewandte Chemie (International ed. in English)》1997,36(11):1164-1170
Alkenylidenes R2C?C: (= alkylidene carbenes) undergo regio- and stereoselective intramolecular C? H insertion reactions that are excellently suited for the synthesis of cyclopentenes. The 1, 2-shifts occurring with R?H and R?Ar are useful for the preparation of alkynes. Alkenylidenes are efficiently generated from carbonyl compounds by diazomethylation, from vinyl halides by α-elimination, from alkynyliodonium salts by addition of nucleophiles, and from alkynes by retro-1, 2-shifts. Specific applications of the various methods, particularly in the synthesis of natural products, are discussed. 相似文献
3.
S.V. Astashkin F.A. Sukochev 《Journal of Mathematical Analysis and Applications》2007,336(2):1231-1258
We catalogue all Marcinkiewicz function and sequence spaces with the Banach-Saks property and present necessary and sufficient conditions for a wide subclass of spaces to possess the p-Banach-Saks property, 1<p<∞. We apply our results to several open problems. 相似文献
4.
Blandine Clique 《Tetrahedron letters》2004,45(6):1195-1197
4-Aryloxymethyl-3-pyrrolines and their isomeric pyrrolidines--assembled via a one-pot, three-component coupling of propargylic amines, vinyl sulfones, and phenols--may be elaborated further to provide an easy access to 2,4-disubstituted pyrrole-3-carboxylates and 3,4-disubstituted pyrrolidin-2-ones. The latter were prepared by means of an unprecedented rearrangement process involving hydrogenolysis of 2-aryl pyrrolidine-3-carboxylates, whereas the pyrrole carboxylates arose from aromatization of the corresponding pyrrolines. 相似文献
5.
Reaction of the vicinal diols of steroids1, 5, 7, 10, 13, and16 with TPP/DEAD yields both regio-and stereospecifically the oxosteroids2, 6, 8, 11, 14, and15 by displacement of an axial hydrogen and extrusion ofTPPO besides the cholest-4-en-6-ols9 and12 and the cyclic carbonate3. 16, 17-androstandiol16 gives only the cyclic carbonate17. The different structures of the carbohydrates withcis-diol arrangement19 and21 lead exclusively to cyclic carbonates20 and22 in moderate yields. Treatment of1 with TPP/DEAD/HN3 affords 3-azido-2-hydroxycholestane4 in addition to the above mentioned2. 相似文献
6.
将取代色满酮(1)与芳肼反应生成的腙与HNCO发生[3+2]环加成反应,加成产物(2)经氧化得到偕偶氮异氰酸酯(3).化合物3在HBF4的催化下发生环化-重排反应,得到新颖的三环系2-氧代-1,2,4-三唑并[3,2-d][1,5]苯并氧氮杂化合物5a~5g. 相似文献
7.
Acyclic nitrones react with dimethyl acetylenedicarboxylate (DMAD) to give stable isoxazolines, from which the ones that contain electron-donating aromatic rings at the C3 position (R1) were shown to undergo unprecedented fragmentation at room temperature, giving the R1-aldehyde and inseparable product mixtures, probably due to the formation of highly reactive species such as iminocarbenes. Attempts to convert the isoxazolines to the corresponding stable azomethine ylides, by refluxing in toluene, again led to the same product mixtures as above (e.g., the room temperature decomposition). Isoxazolines when reacted with methoxide at room temperature afforded highly functionalised diastereomeric mixtures. Also, isoxazolines, when reacted with propylamine, gave the corresponding amides regioselectively, all of which were more stable than the parent isoxazolines. 相似文献
8.
The introduction of a 5-trimethylsilyl group on the least hindered face of the diene thebaine was anticipated to favor attack by dienophiles from the alternate face, but only gave rise to a rearrangement product when treated with 3-butene-2-one at 110 °C. Reaction with the more reactive benzoquinone at lower temperature gave rise to a very slow reaction from the same face as the silyl group, indicating that a trimethylsilyl group does not sufficiently hinder this face to achieve reaction at the other face. 相似文献
9.
A new type of rearrangement of 3-unsubstituted-2-acyl substituted indole phenylhydrazones with formation of a quinoline ring under acid catalysed conditions was observed. 相似文献
10.
Bismuth triflate was found to be an efficient catalyst for the Claisen rearrangement of allyl naphthyl ethers. The reaction proceeds smoothly with a catalytic amount of bismuth triflate (20 mol %) to afford the corresponding ortho-allyl naphthol in moderate to good yields in most cases. 相似文献