全文获取类型
收费全文 | 1033篇 |
免费 | 57篇 |
国内免费 | 183篇 |
专业分类
化学 | 1197篇 |
晶体学 | 14篇 |
综合类 | 7篇 |
物理学 | 55篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 8篇 |
2021年 | 20篇 |
2020年 | 34篇 |
2019年 | 21篇 |
2018年 | 33篇 |
2017年 | 32篇 |
2016年 | 44篇 |
2015年 | 37篇 |
2014年 | 57篇 |
2013年 | 147篇 |
2012年 | 69篇 |
2011年 | 59篇 |
2010年 | 40篇 |
2009年 | 52篇 |
2008年 | 67篇 |
2007年 | 59篇 |
2006年 | 52篇 |
2005年 | 50篇 |
2004年 | 53篇 |
2003年 | 57篇 |
2002年 | 38篇 |
2001年 | 30篇 |
2000年 | 22篇 |
1999年 | 16篇 |
1998年 | 20篇 |
1997年 | 12篇 |
1996年 | 13篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 15篇 |
1992年 | 16篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1273条查询结果,搜索用时 250 毫秒
1.
Bohuai Xiao Jianqiao Dong Zhiye Wang Xu Wang Mingjun Sun Jing Guo Gongming Qian Yunchuan Li Shuai Chang 《Chemphyschem》2022,23(7):e202100833
One important prerequisite for the fabrication of molecular functional device strongly relies on the understanding the conducting behaviors of the metal-molecule-metal junction that can respond to an external stimulus. The model Lewis basic molecule 4,4′-(pyridine-3,5-diyl)dibenzonitrile (DBP), which can react with Lewis acid and protic acid, was synthesized. Then, the molecular conducting behavior of DBP, DBP-B(C6F5)3, and DBP-TfOH (DBP-B(C6F5)3, and DBP-TfOH were produced by Lewis acid and protonic acid treatment of DBP) was researched and compared. Given that their identical physical paths for DBP, DBP-B(C6F5)3, and DBP-TfOH to sustain charge transport, our results indicate that modifying the molecular electronic structure, even not directly changing the conductive physical backbone, can tune the charge transporting ability by nearly one order of magnitude. Furthermore, the addition of another Lewis base triethylamine (of stronger alkaline than DBP), to Lewis acid-base pair reverts the electrical properties back to that of a single DBP junction, that is constructive to propose a useful but simple strategy for the design and construction of reversible and controllable molecular device based on pyridine derived molecule. 相似文献
2.
A highly active multi‐usable palladium pyridylfluorene film‐based catalyst for C–C cross‐coupling reactions 下载免费PDF全文
The two terminal pyridyl nitrogen atoms of 2,7‐bis(4‐pyridyl)fluorene ( 1 ) were coordinated to Pd(II) ions to give self‐assembled, multilayer films using the layer‐by‐layer (LbL) method. The films were prepared by alternately dipping the substrate, pre‐coated with a polyethyleneimine layer, in aqueous solutions of PdCl2 and ethanol solutions of 1 . The resulting films were characterized using UV–visible absorption spectroscopy, atomic force microscopy (AFM), X‐ray photoelectron spectroscopy, scanning electron microscopy (SEM) and inductively coupled plasma atomic emission spectroscopy (ICP‐AES). UV–visible spectra and SEM images show almost uniform growth of the film in a near ideal LbL manner. AFM images show that nanostructured aggregates of Pd(II) complexes form on the surface. With an increase in the number of Pd(II)/ 1 bilayers, more particulate aggregates are distributed on the surface. When released from the substrate, the Pd(II) complex nanostructure shows high catalytic activity for Suzuki–Miyaura and Mizoroki–Heck cross‐coupling reactions. The catalyst loading is as low as 9.1 × 10?3 mol% Pd, as measured using ICP‐AES, and high turnover numbers of up to 1.08 × 104 are obtained. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
Jun-Jie Tian Zhao-Ying Yang Xin-Shen Liang Ning Liu Chen-Yu Hu Xian-Shuang Tu Xiang Li Prof. Dr. Xiao-Chen Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(42):18610-18614
Herein, we report that highly chemoselective and enantioselective reduction of 2-vinyl-substituted pyridines has been achieved for the first time. The reaction, which uses chiral spiro-bicyclic bisboranes as catalysts and HBpin and an acidic amide as reducing reagents, proceeds through a cascade process involving 1,4-hydroboration followed by transfer hydrogenation of a dihydropyridine intermediate. The retained double bond in the reduction products permits their conversion to natural products and other useful heterocyclic compounds by simple transformations. 相似文献
4.
5.
The title compound 2-(((6-chloropyridin-3-yl)methyl)thio)-5-(pyridin-4-yl)-1,3,4-thiadiazole 5(C26H18Cl2N8S4) was synthesized, and its structure was confirmed by 1H NMR, MS and elemental analyses and X-ray diffraction. It crystallizes in the triclinic system, space group P1 with a = 9.452(4), b = 12.335(4), c = 13.017(5) A, α = 90.624(5), β = 110.541(5), γ =104.879(4)°, Dc = 1.561 g/cm3, Z = 2, V = 1364.9(9) A3, F(000) = 656, the final R = 0.0300 and w R = 0.0635 for 4206 observed reflections with I 2σ(I). The preliminary biological test showed that the title compound has activities against Stemphylium lycopersici(Enjoji) Yamamoto, Fusarium oxysporum. sp. cucumebrium, and Botrytis cinerea with inhibitory activities to be 9.82%, 44.44% and 20.00%, respectively. 相似文献
6.
《Mendeleev Communications》2023,33(2):180-183
A simple one-step synthesis of (NHC)2NiCl2 complexes containing bulky N-heterocyclic carbene (NHC) ligands relies on the C–H metallation of N,N'-diaryl-substituted azolium salts, NHC-precursors, with NiCl2Py2 in the presence of Cs2CO3 and pyridine. This procedure allows one to implement all synthetic manipulations in air. 相似文献
7.
Dmytro I. Sierov Illia V. Dzhulai Kateryna I. Siryk Kostiantyn V. Shvydenko Tetiana I. Shvydenko Prof. Dr. Kostiantyn Nazarenko Prof. Dr. Aleksandr Kostyuk Oleksandr S. Liashuk Prof. Dr. Oleksandr O. Grygorenko 《European journal of organic chemistry》2023,26(34):e202300538
A systematic study on the SnAr reaction of halogenated fluoropyridines and (hetero)aliphatic nitrile anions as an approach to the synthesis of functionalized pyridines bearing a (cyclo)alkyl or saturated heterocyclic substituent by is described. The scope of the method was demonstrated on a wide range of (hetero)aliphatic nitriles (including three- to six-membered cycloalkane derivatives and N-, O-, S-containing saturated heterocycles) and all isomeric halogenated 2-and 4-fluoropyridines. High chemo- and regioselectivity (i. e., exclusive substitution of the fluorine atom), as well as excellent scalability of the proposed reaction sequence were demonstrated (up to 450 g for the arylation step or up to 77 g of cycloalkylpyridine over two steps in a single run). The utility of the synthesized products was illustrated in the additional functional group transformations resulting in synthetically valuable pyridine-containing building blocks. 相似文献
8.
Synthesis and magnetic properties of organic multilayer films based on the layer‐by‐layer assembly 下载免费PDF全文
Two polymers containing pyridine rings were prepared by free‐radical polymerization and confirmed by Fourier transform infrared and 1H NMR spectra. The preparation of four multilayer films that were obtained by self‐assembly of the polymer and the transition metal neutralized polyelectrolyte on PE substrate was described. UV–vis spectra and atomic force microscopy images were applied to characterize these films and indicate the uniform assembling process. The driving force for building up the multilayer films was identified by infrared spectroscopy to be the coordination interaction. The magnetic behavior was examined as a function of magnetic field strength at 30 kOe and as a function of temperature (5–300 K). All films display strong soft ferromagnetic properties and higher than those of the bulk materials. The magnetic results show that the layer‐by‐layer self‐assembling approach is beneficial to the ordered alignment of adjacent paramagnetic spins and induces better magnetic phenomena. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
9.
Preparation and thermal characterization of poly(2‐vinylpyridine) copolymers coordinated to Cr nanoparticles 下载免费PDF全文
In this study, polystyrene‐block‐poly(2‐vinylpyridine), PS‐b‐P2VP, polyisoprene‐block‐poly(2‐vinylpyridne), PI‐b‐P2VP and poly(methyl metacrylate)‐block‐poly(2‐vinylpyridine), PMMA‐b‐P2VP, coordinated to Cr metal were synthesized and characterized by Fourier transform infrared, transmission electron microscopy and direct pyrolysis mass spectrometry techniques. Both thermal degradation mechanism and thermal stability of P2VP blocks were affected by the coordination of Cr nanoparticles to nitrogen of pyridine rings. Thermal decomposition of P2VP blocks was started by loss of pyridine units leaving an unsaturated and/or crosslinked polymer backbone that degraded at relatively high temperatures. Incorporation of Cr metal did not noticeably influence thermal behavior of PS and PI blocks. However, increase in thermal stability of PMMA block was detected and associated with inhibition of the interactions between carbonyl groups of MMA chains with nitrogen atom of pyridine ring as a consequence of coordination to metal. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
10.