全文获取类型
收费全文 | 195篇 |
免费 | 19篇 |
国内免费 | 29篇 |
专业分类
化学 | 226篇 |
晶体学 | 2篇 |
物理学 | 15篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 15篇 |
2013年 | 14篇 |
2012年 | 16篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 18篇 |
2008年 | 15篇 |
2007年 | 14篇 |
2006年 | 7篇 |
2005年 | 8篇 |
2004年 | 14篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有243条查询结果,搜索用时 31 毫秒
21.
Novel cationic palladacycles based on benzylidene-2,6-diisopropylphenylimines were prepared via C-H activation using Pd(CH3CN)2Cl2 as metal precursor. The complexes were fully characterized by IR and NMR spectroscopy, mass spectrometry and elemental analysis. The cationic palladacycles were found to be active catalysts for the polymerization of phenylacetylene producing largely trans-cisoidal PPA. 相似文献
22.
<正>A new practical method for the synthesis of unsymmetrical ureas was achieved by reaction of phenylurea with primary and secondary amines under neutral and mild condition in very good yields.The reaction took place in refluxing dioxane and does not require any catalyst or additives. 相似文献
23.
The complex [Pt(9S3)(SbPh3)(Ph)](PF6) forms directly from [Pt(9S3)(SbPh3)2](PF6)2 during the room temperature crystallization of the latter in nitromethane. The crystal structure shows a five-coordinate Pt(II) center containing the tridentate thiacrown ligand, a Sb donor from the triphenylstibine ligand, and a σ-coordinating phenyl group. The phenyl group forms via Sb-C bond cleavage from one of the SbPh3 ligands in the bis complex. 相似文献
24.
Optimized structures and photophysical properties of mer- and fac-Alq3 have been generated by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Investigating the substitution effect in the Alq3 derivatives, the role of the electron-donating (CH3- and NH2-) and electron-withdrawing (F-, CN-, NO2- and phenyl-) groups with 2- to 7-substitution have been analyzed. According to the calculation results, the 4- and 5- substituted Alq3 exhibit an apparent spectral shift relative to the non-substituted Alq3. The HOMO, LUMO, Eg (the energy gap between LUMO and HOMO), (maximum absorption wavelength) and f (the relative oscillator strength) of mer-Alq3 with the 4- or 5-phenyl substitution on the quinoline ligand in the ground electronic state were calculated by using the DFT/B3LYP/6-31G(d) and TD-DFT methods. 5-phenyl substituted mer-Alq3 with an electron-donating substituent showed an increase in the π-delocalization as compared to the 4-phenyl substituted mer-Alq3 derivatives. Similarly, 4-phenyl substituted mer-Alq3 with electron-withdrawing substituents also exhibits increased π-delocalization in the pyridine ring as compared to the non-substituted Alq3. Replacing the CH group at the 4, 5 and 4,5 positions of the quinoline ligand of mer-Alq3 with the aza group (nitrogen atom) gives three Alq3 analogous: AlX3, Al(NQ)3 and Al(NX)3; the calculated energy gap Eg of these derivatives decreases in the order Al(NQ)3>Al(NX)3>AX3. Four quinoline with group III metals Mq3 complexes were investigated for the photophysical properties; the calculated energy gap Eg decreases in the order Tlq3>Inq3>Gaq3>Alq3. The photophysical properties of 4-hydroxy-8-methyl-1,5-naphthyridine (mND) chelated with group III metals (MmND3 complexes) were investigated also; their calculated Eg have the opposite order as those of Mq3 complexes. 相似文献
25.
Synthesis,characterization, and metal complexes of polyacetylenes with pendant 2,2′‐bipyridyl groups
Jos Vicente Juan Gil‐Rubio Natalia Barquero 《Journal of polymer science. Part A, Polymer chemistry》2005,43(14):3167-3177
5‐Ethynyl‐2,2′‐bipyridine ( 1 ; bpyC≡CH) polymerized in the presence of catalytic amounts of [RhF(COD)(PPh3)] or [Rh(μ‐OH)(COD)]2 (COD = 1,5‐cyclooctadiene) in 74–91% yields. In contrast, [Rh(μ‐X)(NBD)]2 (X = Cl or OMe; NBD = norbornadiene) did not catalyze the polymerization of 1 or gave low yields of the polymer. The obtained polymer, poly(5‐ethynyl‐2,2′‐bipyridine) [ 2 ; (bpyC?CH)n], was highly stereoregular with a predominant cis–transoidal geometry. Random copolyacetylenes containing the 2,2′‐bipyridyl group with improved solubility in organic solvents were obtained by the treatment of a mixture of 1 and phenylacetylene ( 3 ) or 1‐ethynyl‐4‐n‐pentyl‐benzene with catalytic amounts of [RhF(COD)(PPh3)]. A block copolymer of 1 and 3 was prepared by the addition of 1 to a poly(phenylacetylene) containing a living end. The reaction of 2 with [Mo(CO)6] produced an insoluble polymer containing [Mo(CO)4(bpy)] groups, whereas with [RuCl2(bpy)2] or [Ru(bpy)2(CH3COCH3)2](CF3SO3)2, it gave soluble metal–polymer complexes containing [Ru(bpy)3]2+ groups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43:3167–3177, 2005 相似文献
26.
27.
Ping He Sha‐Sha Tian Yan Xu He Yu Yan‐Nan Ji Hua‐Jie Zhu Jian‐Heng Li 《Helvetica chimica acta》2015,98(6):819-822
Three new phenyl ether derivatives, 3‐hydroxy‐5‐(3‐hydroxy‐5‐methylphenoxy)benzoic acid ( 1 ), 3,4‐dihydroxy‐5‐(3‐hydroxy‐5‐methylphenoxy)benzoic acid ( 2 ), 3‐[3‐hydroxy‐5‐(hydroxymethyl)phenoxy]‐5‐methylphenol ( 3 ), and three known compounds 4 – 6 were obtained from the fermentation broth of Aspergillus carneus HQ889708, which was isolated from sea water from South China Sea. The structures of compounds 1 – 3 were established on the basis of spectroscopic methods including ESI‐MS and NMR. Compounds 4 – 6 were reported before as synthesized products, herein, they are reported from nature for the first time. 相似文献
28.
4,4-Dimethylcyclopenta[2,1-b:3,4-b′]dithiophene derivatives bearing trimethyl-, dimethylphenyl-, diphenylmethyl-, or triphenyl-silyl moieties were synthesized. The introduction of the silyl moieties onto cyclopenta[2,1-b:3,4-b′]dithiophene induced fluorescent emission as well as the bathochromic shift of wavelength at the maximum absorption and fluorescence. It was found that the larger number of phenyl group on silyl moiety resulted in the higher fluorescence quantum yield. 相似文献
29.
Gomes AG Azevedo AM Aires-Barros MR Prazeres DM 《Journal of chromatography. A》2011,1218(48):8629-8637
Plasmid DNA (pDNA) is purified directly from alkaline lysis-derived Escherichia coli (E. coli) lysates by phenyl boronate (PB) chromatography. The method explores the ability of PB ligands to bind covalently, but reversibly, to cis-diol-containing impurities like RNA and lipopolysaccharides (LPS), leaving pDNA in solution. In spite of this specificity, cis-diol free species like proteins and genomic DNA (gDNA) are also removed. This is a major advantage since the process is designed to keep the target pDNA from binding. The focus of this paper is on the study of the secondary interactions between the impurities (RNA, gDNA, proteins, LPS) in a pDNA-containing lysate and 3-amino PB controlled pore glass (CPG) matrices. Runs were designed to evaluate the role of adsorption buffer composition, feed type (pH, salt content), CPG matrix and sample pretreatment (RNase A, isopropanol precipitation). Water was chosen as the adsorption buffer over MgCl(2) solutions since it maximised pDNA yield (96.2±4.9%) and protein removal (61.3±3.0%), while providing for a substantial removal of RNA (65.5±3.5%) and gDNA (44.7±14.1%). Although the use of pH 3.5 maximised removal of impurities (~75%), the best compromise between plasmid yield (~96%) and RNA clearance (~60-70%) was obtained for a pH of 5.2. Plasmid yield was maximal (>96%) when the concentration of acetate and potassium ions in the incoming lysate feed were 1.7 M and 1.0 M, respectively. The pre-treatment of lysates with RNase A deteriorated the performance since the resulting oligoribonucleotides lack the cis-diol group at their 3' termini. Overall, the results support the idea that charge transfer interactions between the boron atom at acidic pH and electron donor groups in the aromatic bases of nucleic acids and side residues of proteins are responsible for the non-specific removal of gDNA, RNA and proteins. 相似文献
30.
The suitability of ormosils as photonic materials was investigated. Vinyl and phenyl silicates were synthesised below 100°C. A detailed assignment of mid-infrared vibrational absorption bands is given. This allowed assignment of overtone and combination bands in the near-infrared region and an assessment of residual water contamination, which is low and can be expelled by evacuation. These ormosils have low intrinsic and extrinsic optical absorption in the visible spectral region and at useful wavelengths in the near-infrared. 相似文献