全文获取类型
收费全文 | 201篇 |
免费 | 9篇 |
国内免费 | 54篇 |
专业分类
化学 | 259篇 |
晶体学 | 3篇 |
物理学 | 2篇 |
出版年
2023年 | 6篇 |
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 15篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 36篇 |
2012年 | 8篇 |
2011年 | 8篇 |
2010年 | 12篇 |
2009年 | 5篇 |
2008年 | 13篇 |
2007年 | 14篇 |
2006年 | 16篇 |
2005年 | 7篇 |
2004年 | 11篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
排序方式: 共有264条查询结果,搜索用时 15 毫秒
71.
72.
合成了含氮、磷四元不饱和化合物. 反应可能是通过phosphinidene对P—C=N的1,3环加成反应过程进行的. 相似文献
73.
随着组合化学的迅速发展, 兼容固相合成和溶液相合成优点的液相合成方法已成为实现组合化学的一条重要途径. 综述了近年来聚乙二醇为可溶性聚合物载体支载的杂环化合物库的研究, 并展望了其今后的发展方向. 相似文献
74.
The anionic tripodal N-heterocyclic carbene (C3N2H3)3BH- first prepared by Fehlhammer, together with three neutral variants, (C3N2H3)3CH, (C3N2H3)3P, and (C3N2H3)3SiH, have been studied using quantum chemical methods. Isodesmic reactions are used to deduce that the phosphine-bridgehead species in particular has a large-resonance stabilization energy. All the podands undergo substantial conformational change on excitation to the lowest triplet electronic state, with effective localization of the excitation on one of the heterocyclic rings, dearomatizing it. On monoprotonation of the ground states, three of these species display intramolecular C-H...Ccarbene hydrogen bonding: The nature and strength of these interactions is explored using model (intermolecularly hydrogen-bonded) complexes, isodesmic reactions, and GIAO calculations of chemical shifts. One surprising result is that C-H...Ccarbene hydrogen bonds involving ethenic hydrogens can be almost as strong as those involving the imidazolium proton (first identified by Arduengo). The case of the monoprotonated carbon bridgehead species is in particular intriguing. It is stabilized by a competitive Ccarbene...N interaction of sufficient strength to override the C-H...Ccarbene bonding motif observed in the other structures. 相似文献
75.
3-氯-4-氰基-5-取代苯氧基异噻唑的合成及生物活性 总被引:1,自引:0,他引:1
有些醚化合物如早期出现的商品化品种草枯醚、间草醚等二苯醚类除草剂 ,其结构相对简单、在土壤中易于降解且易于合成 ,因而引起了人们的广泛[1 - 3] 兴趣。最近的研究表明很可能从异噻唑杂环中找到生物活性独特的新型化合物[4] 。为此 ,我们设计合成了含异噻唑杂环的醚类化合物3a~ 3k ,合成路线见下图 .所有产物经1 HNMR、IR和元素分析证实 ,并对大部分化合物的除草活性和杀菌活性进行了测定。1 实验部分所有溶剂为分析纯 ,用前经纯化处理。试剂为化学纯或分析纯。硅胶为青岛海洋化工厂产品。元素分析用YanacoCHNCOR… 相似文献
76.
A. Wallace Cordes Robert C. Haddon Richard T. Oakley 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4-5):673-684
The use of neutral π-radicals as building blocks for molecular conductors holds both appeal and challenge. Such systems obviate the need for counterions, as charge transfer is not required to generate charge carriers. Essentially an array of π-radicals should function like atoms in an elemental metal, e.g., sodium, affording a half-filled energy band. Most radicals, however, tend to dimerize, and even when association can be suppressed the resulting low bandwidth W, coupled with a high on-site Coulomb repulsion U, leads to a Mott insulating state. We are pursuing the design and synthesis of stable heterocyclic thiazyl radicals, with a view to generating stable, crystalline materials with a high W/U ratio. The search for these new radicals, the molecular analogues of sodium, is the subject of this presentation. 相似文献
77.
Ming Zhang 《应用有机金属化学》2010,24(4):269-284
The C? H functionalization strategy has received substantial attention because of its economic, sustainable and environmentally benign features. Most reports are on palladium, rhodium or ruthenium catalysis, and reports on copper catalysis are relatively fewer. Recently, many reports on copper‐catalyzed/mediated C? H functionalization have been published. Copper salts bear properties of cheapness and relatively low toxicity. This review introduces an advance on copper‐catalyzed/mediated aromatic C? H functionalization. The content includes aromatic ring C? H bond functionalization and heteroaromatic C? H bond functionalization forming new carbon–carbon or carbon–heteroatom bonds. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
78.
79.
Donald Craig Mark J. Ford Richard S. Gordon James A. Stones Andrew J. P. White David J. Williams 《Tetrahedron》1999,55(52):828-15066
Intramolecular Diels-Alder reactions of cyclohexane-1,2-dicarboxylic anhydride-derived diester-tethered trienes are described. The stereoselectivities of most of the cycloaddition processes studied may be rationalised in terms of an preferred ‘inside’-oriented diene giving rise to an endo-transition state. 相似文献
80.
A simple and clean synthesis of 3,5-dicyano-1,2-dihydropyrid-2-ones by a one-pot three-component reaction of malononitrile, aromatic aldehydes and 2-cyanoacetamide or 2-cyanothioacetamide has been achieved in an aqueous solution with potassium carbonate as a base under microwave irradiation without a phase transfer reagent. This protocol has the advantages of short reaction time (5-8 min) and convenient work-up. 相似文献