全文获取类型
收费全文 | 211篇 |
免费 | 5篇 |
国内免费 | 42篇 |
专业分类
化学 | 241篇 |
晶体学 | 7篇 |
综合类 | 2篇 |
物理学 | 8篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 1篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 3篇 |
2014年 | 7篇 |
2013年 | 72篇 |
2012年 | 9篇 |
2011年 | 8篇 |
2010年 | 3篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2007年 | 10篇 |
2006年 | 9篇 |
2005年 | 13篇 |
2004年 | 11篇 |
2003年 | 13篇 |
2002年 | 3篇 |
2001年 | 7篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1980年 | 2篇 |
排序方式: 共有258条查询结果,搜索用时 31 毫秒
101.
Ahmad Shaabani Sajjad Keshipour Morteza Aghaei M. Hassan Khodabandeh Mansour Zahedi 《中国化学》2012,30(8):1893-1900
The zwitterionic intermediate generated from the reaction of triphenylphosphine with electron deficient acetylenic compounds was trapped by various NH acids. The synthesis resulted in a new class of highly functionalized heterocyclic compounds. Some of the reactions produced E and Z isomers. And the stability and transformation of them were studied by dynamic 1H NMR and density functional theory (DFT) calculations. 相似文献
102.
《Journal of Coordination Chemistry》2012,65(3-4):345-355
Abstract The triply chloro-bridged binuclear complex [Ru2Cl5(CO)(PPh3)3]·CH2Cl2, (PPh3 = triphenylphosphine), Mr = 1279.23, prepared from the precursor compound [RuCl3(PPh3)2DMA]·DMA (DMA = N,N′-dimethylacetamide) and crystallizes in the monoclinic space group P21/c. The structure was solved from 6994 independent reflections for which I > 3σ(I) by Patterson and difference Fourier techniques and refined to a final R = 0.042. The complex is formed by two Ru atoms bridged through three chloride anions. One Ru atom is further coordinated to two non-bridging Cl atoms and a triphenylphosphine ligand, whereas the other is bonded to two PPh3 ligands and a carbon monoxide molecule. The presence of RuIII was confirmed by EPR data. The absence of an intervalence charge-transfer transition (IT) in the near-infrared spectrum suggests that the binuclear complex is of a localized valence type. The IR spectrum shows a νCO band at 1964cm? and νRu-Cl bands at 328, 280 cm?1, corresponding to chlorides at terminal positions and 250, 225 cm?1 for the bridged ones. Two redox processes, RuII/RuII (E1/2 = -0.29 V) ← RuII/RuIII ← (E1/2 = 1.19 V) RuIII/RuIII, were observed by cyclic voltammetry. 相似文献
103.
Abstract The homogeneous hydrogenation of carbon dioxide into formate anion has been investigated in aqueous solution, using water soluble ruthenium(1I)-phosphine (meta-monosulphonated triphenylphosphine, TPPMS; and 1,3,5-triaza-7-phosphaadamantane, PTA) complexes as catalysts. These reactions take place in amine free medium under mild conditions, bicarbonate anion is more active than carbon dioxide in the reduction. The initial turnover frequenc of the reduction increases with increasing H2 pressure, as it was observed in situ by C and 'H NMR spectroscopy. High pressure FT-IR were used to find evidence for the formation of the catalytically active ruthenium hydride species. 相似文献
104.
Sayyed Mostafa Habibi‐Khorassani Malek Taher Maghsoodlou Ali Ebrahimi Marzyeh Mohammadi Mehdi Shahraki Elham Aghdaei 《Journal of Physical Organic Chemistry》2012,25(12):1328-1335
In the present work, the dynamic 1H NMR effects were investigated at variable temperatures within a particular phosphorus ylide involving a 2‐benzoxazolinone around the carbon–carbon single bond and also partial carbon–carbon double bond in two Z‐ and E‐rotational isomers. Activation and kinetic parameters including ΔH≠, ΔG≠, ΔS≠ and Ea were determined in accord with the dynamic 1H NMR data for three rotational processes. In addition, theoretical studies based upon rotation around the same bonds were investigated using ab initio and DFT methods at the HF/6‐31G(d,p) and B3LYP/6‐31G(d,p) levels of theory. Theoretical activation and kinetic parameters including ΔH≠, ΔG≠, ΔS≠ and Ea were calculated at 298 K and experimental temperatures for five rotational processes. These results (experimental and theoretical), taken together, indicate that the rotational energy barrier around the C = C double bond was considerably high and the observation of the two rotational isomers was impossible (seen as a single isomer) at the high temperatures, in this case rotation around the C = C bond was too fast on the NMR time scale. When the temperature was relatively low, the rate of rotation was sufficiently slow; therefore, observation of the two Z‐ and E‐isomers was possible. In addition, calculations at the HF/6‐31G(d,p) level of theory showed very favorable results in agreement with the experimental data on rotation around the C = C bond. While, B3LYP level using the 6‐31G(d,p) basis set was provided the reasonable data for the restricted rotations around the C–C and C–N single bond. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
105.
Pyrimidine and thienopyrimidine derivatives play a very important role in organic chemistry because of their wide applications as bioactive compounds with multiple biological activities. However, a literature survey revealed that the merger of different groups in the thieno[2,3‐d]pyrimidine heterocyclic ring enhances its antibacterial, antifungal and anti‐inflammatory activities. This encouraged us to prepare a new series of thieno[2,3‐d]pyrimidine heterocyclic compounds and to test them as antimicrobial and anti‐inflammatory agents. These compounds have shown remarkable activity toward fungi, bacteria, and inflammation. Thus, these compounds have been prepared by the chloroacylation of 5‐amino‐4‐phenyl‐2‐(p‐tolylamino)thieno[2,3‐d] pyrimidine‐6‐carboxamide ( 4 ) using chloroacetyl chloride under neat condition to afford the target compound ( 6 ), which was used as precursor for the synthesis of a number of bioactive compounds. Thus reaction of the chloromethylpyrimidine derivative ( 6 ) with triphenylphosphine in dry benzene gave the corresponding ((4‐oxo‐9‐phenyl‐7‐(p‐tolylamino)‐3,4‐dihydropyrimido[4′,5′:4,5]thieno[2,3‐d]pyrimidin‐2‐yl)methyl) triphenylphosphonium chloride ( 7 ). Compounds 8a – 8c and 9a – 9c were obtained by the reaction of 7 with some selected aromatic aldehydes and ketones in methanol and sodium methoxide under Wittig reaction condition. The structures of the all new synthesized compounds were established on the basis of their analytical and spectral data (IR, 1H NMR, 13C NMR, and MS). 相似文献
106.
Vladimir F. Mironov Andrey V. Nemtarev Olga V. Tsepaeva Mudaris N. Dimukhametov Igor A. Litvinov Alexandra D. Voloshina Tatiana N. Pashirova Eugenii A. Titov Anna P. Lyubina Syumbelya K. Amerhanova Aidar T. Gubaidullin Daut R. Islamov 《Molecules (Basel, Switzerland)》2021,26(21)
It has been shown for a wide range of epoxy compounds that their interaction with triphenylphosphonium triflate occurs with a high chemoselectivity and leads to the formation of (2-hydroxypropyl)triphenylphosphonium triflates 3 substituted in the 3-position with an alkoxy, alkylcarboxyl group, or halogen, which were isolated in a high yield. Using the methodology for the disclosure of epichlorohydrin with alcohols in the presence of boron trifluoride etherate, followed by the substitution of iodine for chlorine and treatment with triphenylphosphine, 2-hydroxypropyltriphenylphosphonium iodides 4 were also obtained. The molecular and supramolecular structure of the obtained phosphonium salts was established, and their high antitumor activity was revealed in relation to duodenal adenocarcinoma. The formation of liposomal systems based on phosphonium salt 3 and L-α-phosphatidylcholine (PC) was employed for improving the bioavailability and reducing the toxicity. They were produced by the thin film rehydration method and exhibited cytotoxic properties. This rational design of phosphonium salts 3 and 4 has promising potential of new vectors for targeted delivery into mitochondria of tumor cells. 相似文献
107.
108.
本文研究了三苯基磷(PPh3)对以AgSt为银源的亲水型PTG材料照相性能的影响:PTG材料的感光度随PPh3用量不同而变化,PPh3用量相对较少时,感光度随PPh3用量增加而提高;PPh3用量增加到一定程度,感光度达到极大值;进一步增加PPh3用量,感光度反而随PPh3用量增加而下降.据分析结果推测,在PPh3用量较少时,PPh3的作用主要是打开AgSt二聚体的八元环而生成一种中间配合物,该中间体对热显影有促进作用;在PPh3用量较多时,PPh3的作用主要是与AgSt作用生成稳定的四元环配合物,该配合物对热显影有抑制作用.PPh3的引入也会影响光敏元中潜影的形成效率,有利于提高感光度. 相似文献
109.
Single-crystal X-ray structures of four nickel dithiocarbamate complexes, the homoleptic mixed-organic bis-dithiocarbamates Ni[S2CN(isopropyl)(benzyl)]2, Ni[S2CN(ethyl)(n-butyl)]2, and Ni[S2CN(phenyl)(benzyl)]2, as well as the heteroleptic mixed-ligand complex NiCl[P(phenyl)3][(S2CN(phenyl)(benzyl)], were determined. A slightly distorted square-planar nickel coordination environment was observed for all four complexes. The organic residues adopt conformations to minimize steric interactions. Steric effects also may determine puckering, if any, about the nickel and nitrogen atoms, both of which are planar or nearly so. A trans-influence affects the Ni-S bond distances. Nitrogens interact with the CS2 carbons with a bond order near two; the other substituents on nitrogen display transoid conformations. There are no strong intermolecular interactions, consistent with prior observations of the volatility of nickel dithiocarbamate complexes. A preliminary thermolysis study of the homoleptic species results in production of 1?:?1 nickel sulfide phases, indicating the potential utility of these species as “single-source” precursors. 相似文献
110.
Tris(triphenylphosphine)nickel(0) (A) and a zerovalent pyridine–nickel complex (B) have been used as reagents for the coupling reaction of 3-, 6- and 8-bromoquinolines: 3,3′-, 6-6′- and 8,8′- Biquinolines were obtained in quantitative yields when A was used as the coupling reagent. B gave always a mixture of the n,n′ -biquinoline and substitution products. A mechanism can be outlined to explain the coupling reaction of bromoquinolines using zerovalent nickel complexes. 相似文献