全文获取类型
收费全文 | 233篇 |
免费 | 13篇 |
国内免费 | 37篇 |
专业分类
化学 | 232篇 |
力学 | 3篇 |
综合类 | 1篇 |
数学 | 23篇 |
物理学 | 24篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 14篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 3篇 |
2017年 | 10篇 |
2016年 | 5篇 |
2015年 | 19篇 |
2014年 | 13篇 |
2013年 | 21篇 |
2012年 | 21篇 |
2011年 | 15篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 15篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 3篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 15篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1993年 | 1篇 |
1990年 | 2篇 |
排序方式: 共有283条查询结果,搜索用时 31 毫秒
71.
We have developed a general and highly efficient method for the preparation of diverse [small omega]-formyl-[small alpha],[small beta]-unsaturated carbonyl compounds and optimized the conditions for the intramolecular Baylis-Hillman reactions of these compounds to provide various biologically important polycyclic compounds. 相似文献
72.
73.
Xiuling Xu Xiuli Zhuang Xuesi Chen Xinri Wang Lixin Yang Xiabin Jing 《Macromolecular rapid communications》2006,27(19):1637-1642
Summary: Uniform core‐sheath nanofibers are prepared by electrospinning a water‐in‐oil emulsion in which the aqueous phase consists of a poly(ethylene oxide) (PEO) solution in water and the oily phase is a chloroform solution of an amphiphilic poly(ethylene glycol)‐poly(L ‐lactic acid) (PEG‐PLA) diblock copolymer. The obtained fibers are composed of a PEO core and a PEG‐PLA sheath with a sharp boundary in between. By adjusting the emulsion composition and the emulsification parameters, the overall fiber size and the relative diameters of the core and the sheath can be changed. A mechanism is proposed to explain the process of transformation from the emulsion to the core‐sheath fibers, i.e., the stretching and evaporation induced de‐emulsification. In principle, this process can be applied to other systems to prepare core‐sheath fibers in place of concentric electrospinning and it is especially suitable for fabricating composite nanofibers that contain water‐soluble drugs.
74.
75.
With characteristic of structural integrity and high surface area, nanoporous gold (NPG) prepared by dealloying method is
proposed to be a highly sensitive catalyst for glucose electrooxidation. It can be found that a-NPG which obtained by electrochemical
corrosion method has the highest sensitivity for glucose electrooxidation among the three studied samples. Under alkaline
conditions, the catalytic current density of a-NPG is over 1.5 times and 17 times higher than that of f-NPG (prepared by free
corrosion) and poly-Au electrode, respectively. Using a-NPG sample for glucose detection, the obtained minimum sensible concentration
are 413 nM in alkaline media and 1 μM in neutral solutions. The a-NPG electrode also shows stable recovery and reproducibility
characteristics. These results indicate that NPG may work as an efficient electrode material for electrochemical sensors and
a promising catalyst for alkaline glucose fuel cells. 相似文献
76.
Jianyu Dong Xiuling Chen Fangyan Ji Lixin Liu Lebin Su Min Mo Jian‐Sheng Tang Yongbo Zhou 《应用有机金属化学》2021,35(1)
A simple and direct aerobic oxidative esterification reaction of arylacetonitriles with alcohols/phenols is achieved in the presence of a copper salt and molecular oxygen, which produces a broad range of aryl carboxylic acid esters in good to high yields. Copper salt plays multiple roles in the transformation, which allows the oxygenation of C? H bond, cleavage of inert C? C bond, and formation of C? O bond in one pot without the assistance of any of the acids, bases, ligands, and so on. The reaction provides a simple, direct, and efficient protocol towards functionalized esters, especially aryl benzoates, from readily available starting materials. 相似文献
77.
Cp*Co(III)-catalyzed direct C-H amidation of azines has been developed. This conversion could proceed smoothly in the absence of external oxidants, acids or bases, with excellent regioselectivity and broad functional group tolerance. CO2 was released as the sole byproduct, thus providing an environmentally benign amidation process. The products obtained are important intermediates in organic synthesis. 相似文献
78.
Lianmei Chen Xiuling Cui Haitao Cheng Xiaopei Chen Maoping Song Mingsheng Tang Donghui Wei Yangjie Wu 《应用有机金属化学》2012,26(9):449-454
Rigid N‐(substituted)‐2‐aza‐[3]‐ferrocenophanes L1 and L2 were easily synthesized from 1,1 ‐dicarboxyaldehydeferrocene and the corresponding amines. Ligands L1 and L2 were characterized by 1H NMR, 13C NMR and single‐crystal X‐ray crystallography. The coordination abilities of L1 and L2 with metal ions such as Cu2+, Mg2+, Ni2+, Zn2+, Pb2+ and Cd2+ were evaluated by cyclic voltammetry. The electrochemical shift (ΔE1/2) of 125 mV was observed in the presence of Cu2+ ion, while no significant shift of the Fc/Fc + couple was observed when Mg2+, Ni2+, Zn2+, Pb2+, Cd2+ metal ions were added to the solution of L1 in the mixture of MeOH and H2O. Moreover, the extent of the anodic shift of redox potentials was approximately equal to that induced by Cu2+ alone when a mixture of Cu2+, Mg2+, Ni2+, Zn2+, Pb2+ and Cd2+ was added to a solution of L1. Ligand L1 was proved to selectively sense Cu2+ in the presence of large, excessive first‐row transition and late‐transition metal cations. The coordination model was proposed from the results of controlled experiments and quantum calculations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
79.
N‐methyliminodiacetic acid as a simple and highly efficient ligand for palladium‐catalyzed Suzuki–Miyaura cross‐coupling of aryl chlorides 下载免费PDF全文
A simple, air‐stable, inexpensive and easily prepared molecule, N‐methyliminodiacetic acid (MIDA), is reported as a ligand for palladium‐catalyzed Suzuki–Miyaura cross‐coupling reaction of phenylboronic acid with aryl chlorides. The yield of the corresponding Suzuki coupling reaction is up to around 90% at both high temperature of 80°C and room temperature under ambient atmosphere. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
80.
In the reaction of 4-methoxypyridine derivatives with alkyl iodides in the presence or absence of solvent, not only the pyridinium ions but also the related 1-methylpyridones are produced. The presence of solvent favors the formation of the 1-methylpyridone. Electron withdrawing groups on the pyridine ring also favor this conversion. A possible mechanism is presented. 相似文献