全文获取类型
收费全文 | 215篇 |
免费 | 8篇 |
专业分类
化学 | 189篇 |
力学 | 4篇 |
数学 | 1篇 |
物理学 | 29篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 7篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 12篇 |
2012年 | 16篇 |
2011年 | 21篇 |
2010年 | 8篇 |
2009年 | 11篇 |
2008年 | 10篇 |
2007年 | 16篇 |
2006年 | 21篇 |
2005年 | 17篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 7篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
排序方式: 共有223条查询结果,搜索用时 15 毫秒
81.
Elier Hernando Dr. Rafael R. Castillo Dr. Nuria Rodríguez Dr. Ramón Gómez Arrayás Prof. Dr. Juan C. Carretero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(43):13854-13859
A practical copper‐catalyzed direct nitration of protected anilines, by using one equivalent of nitric acid as the nitrating agent, has been developed. This procedure features mild reaction conditions, wide structural scope (with regard to both N‐protecting group and arene substitution), and high functional‐group tolerance. Dinitration with two equivalents of nitric acid is also feasible. 相似文献
82.
83.
New photopolymerizable holographic recording material based on polyvinylalcohol and 2-hydroxiethylmethacrylate (HEMA) 总被引:2,自引:0,他引:2
S. Blaya L. Carretero R.F. Madrigal M. Ulibarrena A. Fimia 《Applied physics. B, Lasers and optics》2002,74(6):603-605
We have developed a new polyvinylalcohol-based photopolymeric holographic recording material. The recording is obtained by
the copolymerization of acrylamide and 2-hydroxiethylmethacrylate (HEMA). Diffraction efficiencies near 70% are obtained with
exposures of ≈65 mJ/cm2 in materials of 110-μm thickness. The addition of HEMA increases the thickness of the film, which results in improved storage
capacity for holographic optical storage.
Received: 7 March 2002 / Published online: 2 May 2002 相似文献
84.
85.
Moreno A Pregosin PS Veiros LF Albinati A Rizzato S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(18):5617-5629
PGSE diffusion, 19F, 1H HOESY and 13C NMR studies for a series of [Ru(Cp*)(eta6-arene)][PF6] (1) salts are presented. The solid-state structure of [Ru(Cp*)(eta6-fluorobenzene)][PF6] (1 c) is reported. The extent of the ion pairing and the relative positions of the ions are shown to depend on the arene. For the solvent dichloromethane, new and literature PGSE data for PF6(-) salts of transition-metal, inorganic, and organic salts are compared. Taken together, these new results show that the charge distribution and the ability of the anion to approach the positively charged positions (steric effects due to molecular shape) are the determining factors in deciding the amount of ion pairing. DFT calculations of the charges in four salts of type 1, as well as in a variety of other salts, using a natural population analysis (NPA), support this view. This represents the first attempt, using experimental data, to understand, correlate, and partially explain the various degrees of ion pairing in a widely different collection of salts. 相似文献
86.
Salvador González A Gómez Arrayás R Rodríguez Rivero M Carretero JC 《Organic letters》2008,10(19):4335-4337
Both cyclic and acyclic silyl dienol ethers participate efficiently in the asymmetric vinylogous Mannich reaction of N-2-thienylsulfonylimines catalyzed by copper(I) complexes of Fesulphos ligands. This procedure displays wide imine and nucleophile versatility, high enantiocontrol, and complete gamma-regioselectivity in most cases examined. The mild sulfonamide deprotection allows the resulting products to be readily transformed into optically active delta-lactams or 5-hydroxy-2-piperidone derivatives. 相似文献
87.
Junting Wang Fernando Gordillo Gámez Jose Marín-Beloqui Aitor Diaz-Andres Dr. Xiaohe Miao Prof. David Casanova Prof. Juan Casado Dr. Junzhi Liu 《Angewandte Chemie (International ed. in English)》2023,62(10):e202217124
Incorporating non-hexagonal rings into polycyclic conjugated hydrocarbons (PCHs) can significantly affect their electronic and optoelectronic properties and chemical reactivities. Here, we report the first bottom-up synthesis of a dicyclohepta[a,g]heptalene-embedded PCH ( 1 ) with four continuous heptagons, which are arranged in a “Z” shape. Compared with its structural isomer bischrysene 1 R with only hexagonal rings, compound 1 presents a distinct antiaromatic character, especially the inner heptalene core, which possesses clear antiaromatic nature. In addition, PCH 1 exhibits a narrower highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gap than its benzenoid contrast 1 R , as verified by experimental measurements and theoretical calculations. Our work reported herein not only provides a new way to synthesize novel PCHs with non-alternant topologies but also offers the possibility to tune their electronic and optical properties. 相似文献
88.
The ‘pseudo-total’ contents and the chemical fractionation pattern of eight toxic elements (As, Cd, Co, Cu, Cr, Ni, Pb and Zn) have been determined in 12 soil samples collected around a coal-fuelled power plant (Velilla del Río Carrión, Spain) by using, respectively, the US-EPA 3051 norm and the modified BCR (SM&T) chemical fractionation procedure. The ‘pseudo-total’ dataset has been analyzed by classical two-way principal component analysis (PCA) finding a PC accounting for the metal ‘pollution’ of the area. On the other hand, the three-dimensional (samples × metals × fractions) X array obtained after application of the modified BCR SM&T procedure, has been studied by matrix augmentation (MA-PCA) and three-way principal component analysis (3-PCA) using PARAFAC and TUCKER3 models. Whereas both MA-PCA and PARAFAC originated two-factor models biased towards the different chemical fractionation of the samples, the best TUCKER3 model [1, 2, 2] takes into account simultaneously both the ‘pseudo-total’ contents and the chemical fractionation of the soil samples. Therefore, the TUCKER3 originated a better representation of the global environmental impact caused by the power plant, and the plotting of the soil samples loadings, A1, in the physical space allowed to locate the most potentially hazardous areas. 相似文献
89.
90.