全文获取类型
收费全文 | 123篇 |
免费 | 6篇 |
国内免费 | 11篇 |
专业分类
化学 | 87篇 |
晶体学 | 1篇 |
数学 | 31篇 |
物理学 | 21篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 5篇 |
2013年 | 9篇 |
2012年 | 8篇 |
2011年 | 7篇 |
2010年 | 4篇 |
2009年 | 7篇 |
2008年 | 6篇 |
2007年 | 3篇 |
2006年 | 8篇 |
2005年 | 9篇 |
2004年 | 12篇 |
2003年 | 8篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1985年 | 1篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有140条查询结果,搜索用时 15 毫秒
1.
2.
A new series of thiophene‐ and furan‐containing chromophores with a chiral prolinol donor and a sulfone acceptor has been synthesized. The UV‐vis absorptions, second‐order nonlinear optical properties, and X‐ray crystal structures are described. 相似文献
3.
The three new lignanoids 1 – 3 and the five new phyllocladane diterpenoids 7 – 11 were isolated from the leaves of Callicarpa furfuraceae, together with two known lignanoids, lariciresinol ( 4 ) and (+)‐sesamin ( 5 ), and five known diterpenoids, 17‐norphyllocladane‐3,16‐dion ( 6 ), calliterpenone ( 12 ), calliterpenone 17‐acetate ( 13 ), (3β,16α)‐phyllocladane‐3,16,17‐triol ( 14 ), and (3β,16α)‐phyllocladane‐3,16,17‐triol 17‐acetate ( 15 ). Their structures were established by spectral‐data interpretation. 相似文献
4.
Tian Xiu-Zhi Yang Rui Ma Jia-Jia Ni Yong-Hao Deng Hai-Bo Dai Lei Tan Jiao-Jun Zhang Mei-Yun Jiang Xue 《高分子科学》2022,40(7):789-798
Chinese Journal of Polymer Science - Antistatic and strength properties are of vital importance for polyurethane rubber used in moving parts of many industrial instruments. Herein, polyurethane was... 相似文献
5.
Haplotypic variation within and among the Ascaris populations representing six provinces in China was investigated. Mitochondrial DNA regions in the cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 1 (nad1) genes were amplified by PCR from total genomic DNA samples (n > 720) from Ascaris individuals from humans and pigs, and subjected to mutation scanning and subsequent selective sequencing. For the cox1, ten different electrophoretic profiles were recorded for human Ascaris, and the same number for pig Ascaris, one of them being common to both host species. For the nad1, 11 different profiles were detected for human Ascaris, and 15 for pig Ascaris. Having defined all haplotypes (20 for pcox1 and 26 for pnad1) by sequencing, their frequencies were estimated in each of the two host species and each of the six provinces. For each mitochondrial region, the frequency of the different haplotypes varied considerably, depending on host species and geographical origin. Analysis of the sequence data (representing all haplotypes for each mitochondrial locus) by F-statistics indicated restricted gene flow between human Ascaris and pig Ascaris, and supported the conclusions from previous molecular epidemiological investigations that pigs are not a significant source of Ascaris infection in humans in endemic regions. 相似文献
6.
WANG LiTao HE Chen LIU Yang ZHAO SuoQi ZHANG YaHe XU ChunMing CHUNG Keng H. SHI Quan 《中国科学:化学(英文版)》2013,56(7):863-873
A vacuum topped Canadian oilsands bitumen (VTB) was subjected to solvent precipitation and subsequently characterized by elemental analysis, gel permeation chromatograph (GPC), 1 H-NMR spectroscopy and negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Effects of experimental conditions such as solvent types (n-C5 , n-C6 , and n-C7 ), solvent purity, and solvent washing time on asphaltenes yields, bulk composition, and molecular composition of detectable heteroatom compounds in ESI source were determined. Elemental nitrogen and sulfur were enriched in asphaltenes while elemental oxygen had comparable content in maltenes and asphaltenes. Molecular composition of asphaltenes varies with separation conditions. The N1 and O1 species identified by ESI FT-ICR MS were enriched in maltenes. The O2 species exhibited two different double bond equivalents (DBE) distributions and solubility in normal paraffin solvents, indicating two types of molecular structures. Multi oxygen atom containing compounds mainly detected in asphaltenes. Compound class distributions are similar for maltenes derived from n-C5 , n-C6 , and n-C7 , as well as for asphaltenes. The cyclic paraffin impurities in normal paraffin solvents had a significant influence on asphaltenes yields and heteroatom molecular composition. A portion of neutral N1 species and acidic O2 species adsorbed on asphaltenes could be dissolved by increasing washing time. Cautions should be exercised when interpreting the properties and composition of asphaltenes obtained with different experimental conditions. 相似文献
7.
The mass spectra of a series of N‐aryl α,β‐unsaturated γ‐lactams were studied. Besides the molecular ion, the three characteristic fragments such as [M+‐29], [M+‐55], and [M+‐82] were commonly found in a series of N‐Aryl α,β‐unsaturated γ‐lactams in EI/MS. Further more the mechanism for the interpretation of these fragments is also de scribed. 相似文献
8.
牛血清白蛋白与有机小分子偶氮磺Ⅲ、溴偶氮磺Ⅲ相互作用的研究 总被引:1,自引:0,他引:1
本文研究了在不同酸度下.偶氮磺、溴偶氮磺Ⅲ与牛血清白蛋白的作用情况,用光度法求出了不同条件下偶氮磺Ⅲ、溴偶氮磺Ⅲ与牛血清白蛋白的结合个数,并用三种不同的方法相互对照.证明偶氮磺Ⅲ、溴偶氮磺Ⅲ在牛血清白蛋白上有两类不同接合部位。利用Forster非幅射转移理论确定了有机小分子在牛血清白蛋白上的结合位置并对反应机理作了初步讨论。 相似文献
9.
Keng Lung Lee Joey Feld Dr. Paul Hume Prof. Tilo Söhnel Dr. Erin Leitao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(2):815-824
A series of ammonium monosubstituted H-phosphonate salts were synthesized by combining H-phosphonate diesters with amines in the absence of solvent at 80 °C. Variation of the ester substituent and amine produced a range of ionic liquids with low melting points. The products and by-products were analyzed by spectroscopic and spectrometric techniques in order to get a better mechanistic picture of the dealkylation and formal dearylation observed. For dialkyl H-phosphonate diesters, (RO)2P(O)H (R=alkyl), the reaction proceeds via direct dealkylation with the reactivity increasing in the order R=iPr<Et<Me corresponding to DFT calculated activation enthalpies of 22.6, 20.8, and 17.9 kcal mol−1. For the diphenyl H-phosphonate diesters, (PhO)2P(O)H, the dearylation was found to proceed via phenol-assisted formation of a 5-coordinate intermediate, (PhO)3PH(OH), from which P(OPh)3 and water were eliminated. The presence of an equivalent of water then facilitated the formation of P(OH)2OPh and the amine, R'NH2, subsequently abstracted a proton from it to yield [(PhO)PH(O)O]-[R'NH3]+. 相似文献
10.
Ali Mohammad Akbar Mirza Aminul Huq Keng See Tho Wai Butcher Raymond J. 《Transition Metal Chemistry》2003,28(2):241-245
Condensation of 2,6-diacetylpyridine (dap) with S-methyldithiocarbazate (smdtc) in a 1:2 molar ratio yields a bicondensed pentadentate Schiff base (H2dapsme) which reacts with K2MCl4 (M = PdII, PtII) giving stable complexes of empirical formula, [M(dapsme)] · 0.5Me2CO. These complexes have been characterized by a variety of physico-chemical techniques. Condensation of dap with smdtc in a 1:1 molar ratio also yields the bicondensed Schiff base (H2dapsme) as the major product, but a mono-condensed one-armed Schiff base (Hmdapsme) is also obtained as a minor product. The latter reacts with K2PdCl4 in an EtOH–H2O mixture yielding a crystalline complex of empirical formula, [Pd(mdapsme)Cl], the crystal structure of which has been determined by X-ray diffraction. The complex has a distorted square-planar structure in which the ligand is coordinated to the palladium(II) ion as a uninegatively charged tridentate chelating agent via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom; the oxygen atom of the acetyl group does not participate in coordination. 相似文献