全文获取类型
收费全文 | 233篇 |
免费 | 4篇 |
国内免费 | 9篇 |
专业分类
化学 | 230篇 |
物理学 | 16篇 |
出版年
2024年 | 2篇 |
2023年 | 26篇 |
2022年 | 3篇 |
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 11篇 |
2017年 | 7篇 |
2016年 | 1篇 |
2015年 | 1篇 |
2014年 | 11篇 |
2013年 | 18篇 |
2012年 | 5篇 |
2011年 | 11篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 11篇 |
2007年 | 14篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 15篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 6篇 |
1998年 | 10篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1972年 | 3篇 |
1969年 | 1篇 |
1968年 | 4篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有246条查询结果,搜索用时 46 毫秒
1.
The treatment of tertiary esters with triphenylphosphine and iodine under mild conditions gives the most stable alkene in good yield. Formates, acetates and trifluoroacetates were studied. 相似文献
2.
Absolute rate constants are reported for the addition of the 1‐[(tert‐butoxy)carbonyl]ethyl (= 2‐(1,1‐dimethylethoxy)‐1‐methyl‐2‐oxoethyl) radical .CHMeCO2(t‐Bu) to several cyclic and monosubstituted alkenes in MeCN as obtained by time‐resolved electron paramagnetic resonance (EPR). The activation energies for the addition of this alkyl radical are mainly governed by the addition enthalpy but are also substantially lowered by the ambiphilic effect and by relief of cyclic strain. 相似文献
3.
Proton-active substances react with certain electron-rich olefins with cleavage of the central C?C double bond to give compounds that can be formally regarded as insertion products of nucleophilic carbenes. If they satisfy certain structural conditions, they isomerize with β elimination to give open-chain compounds. Both CH-acidic compounds and compounds containing NH or OH groups can undergo this reaction. The mechanisms are discussed, and the importance of the intermediate products to biochemistry (thiamine, tetrahydrofolic acid) is indicated. 相似文献
4.
Summary Gas chromatographic retention indices for 47 C5 to C8 alkenes on OV-101 dimethylsilicone at 50 and 70 °C were determined within a standard deviation of 0.3i.u. Data obtained on
OV-101 are compared with those measured on squalane. The comparison of the retention index and dl/dT values from both columns
is presented as linear regression equations with correlation coefficients greater than 0.98. 相似文献
5.
2-Iodoaniline reacts with α,β-unsaturated carbonyl compounds in DMF at 100 °C in the presence of a catalytic amount of a palladium catalyst along with a base to afford the corresponding quinolones or quinolines in moderate to good yields. 相似文献
6.
Mhamed Lemhadri Touriya Zair Maurice Santelli 《Journal of organometallic chemistry》2007,692(11):2270-2281
The Heck reaction of aryl halides with functionalised alk-1-enes should be a powerful method for the synthesis of functionalised (E)-1-arylalk-1-ene derivatives. The major problem of this reaction is the palladium-catalysed migration of the carbon-carbon double bond along the alkyl chain when there are no substituents on the C3 carbon of the alk-1-enes. We observed that for the arylation of ethyl pent-4-enoate, ethyl 2-methylpent-4-enoate or dimethyl allylmalonate this migration could be partially or completely controlled using appropriate reaction conditions. The ramification on the alkyl chain and the substituents on the aryl halide have also an important influence on this migration. Moreover, the cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane/1/2[PdCl(C3H5)]2 system catalyses this reaction with a wide range of aryl bromides using very high ratio substrate/catalyst in good yields. 相似文献
7.
8.
In 1959, Horner showed that metalated alkyldiphenylphosphane oxides react with aldehydes or ketones to give alkenes. With this reaction, the diphenylphosphoryl (Ph2PO) group made its entrance into synthetic organic chemistry. In the thirty-six years since that date, extensive research has shown that this olefination, the Horner–Wittig reaction, has unique properties that make it much more than simply the phosphane oxide cousin of the more famous phosphorus-based olefinations—the Wittig reaction (based on phosphonium salts) and the Wadsworth–Emmons reaction (based on phosphonate esters). Early work on the Horner–Wittig reaction concentrated on the reactivity of phosphane oxides and the regioselectivity of their reactions, but more recently the power of the Ph2PO group to control the stereochemistry of alkenes, and to produce “on demand” either stereoisomer in high stereochemical purity, has emerged. From the study of these stereocontrolled Horner–Wittig reactions arose the realization that the Ph2PO group is useful not only for the control of the two-dimensional stereochemistry of alkenes, but also of three-dimensional stereochemistry in general. After a brief introduction to phosphane oxide chemistry, this review will examine the Horner–Wittig reaction, in both its original and “stereocontrolled” varieties. From there, we will move on to an account of the stereoselective construction of molecules containing the Ph2PO group, concentrating on the stereochemical directing effects of the Ph2PO group and on the role of its unique combination of attributes—steric bulk, electronegativity, and Lewis basicity—in controlling these reactions. Finally, we will present what is intended as a practical guide to this chemistry, covering the type of functionalized alkenes that have been made with the help of the Ph2PO group and giving guidelines that we hope will help the organic chemist to make the most of the chemistry the Ph2PO group has to offer. 相似文献
9.
Behaviour of water-soluble dinuclear rhodium complexes in the hydroformylation reaction of oct-1-ene
The biphasic hydroformylation reaction of oct-1-ene, has been investigated by using the water-soluble dinuclear complex [Rh2(μ-StBu)2(CO)2(TPPTS)2] as precursor. Addition of ethanol as a cosolvent dramatically improved the yields but the good regioselectivity in linear aldehyde observed for neat oct-1-ene—water systems (97%) decreased to 83% (for 22% ethanol w/w). It is shown that the dinuclear framework cannot be maintained, that the mononuclear complex [RhH(CO)(TPPTS)3] is formed, and that thiol and significant amounts of [Rh2(μ-StBu)2(CO)4] move into the organic phase. This reaction from the dinuclear species requires the simultaneous presence of water and carbon monoxide. Introduction of the water-soluble thiol HS(CH2)3NMe2 in the bridging positions affords the complex [Rh2(μ-S(CH 2)3NHMe2)2(CO)2(TPPTS)2]Cl2 which can be kept in the aqueous hase but has a low level of catalytic activity. 相似文献
10.
Kiyoshi Tanemura 《Tetrahedron letters》2018,59(49):4293-4298
Silica gel-mediated hydrochlorination of unactivated alkenes using 35% hydrochloric acid under organic solvent-free conditions proceeded to give the corresponding chlorides in good yields. Hydrobromination or hydriodination using 47% hydrobromic acid or 55% hydriodic acid afforded the corresponding halides, respectively. Silica gel could be recycled five times without any significant loss of activities. 相似文献