全文获取类型
收费全文 | 183篇 |
免费 | 20篇 |
国内免费 | 15篇 |
专业分类
化学 | 194篇 |
晶体学 | 3篇 |
综合类 | 1篇 |
数学 | 1篇 |
物理学 | 19篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 2篇 |
2015年 | 12篇 |
2014年 | 10篇 |
2013年 | 23篇 |
2012年 | 15篇 |
2011年 | 15篇 |
2010年 | 9篇 |
2009年 | 10篇 |
2008年 | 9篇 |
2007年 | 6篇 |
2006年 | 10篇 |
2005年 | 5篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有218条查询结果,搜索用时 15 毫秒
1.
Poly(ortho‐phenylene ethynylene)s (PoPEs) have been synthesized via an in situ activation/coupling AB′ polycondensation protocol. The resulting polymers have been characterized by several analytical methods and are shown to have no structural defects. Although the Sonogashira–Hagihara polycondensation reaction is less efficient than for the preparation of the corresponding meta‐ and para‐linked polymers, presumably because of steric hindrance caused by the ortho substituents, the process can be accelerated by the use of microwave irradiation. Optical spectroscopy indicates solvent‐dependent conformational changes between extended transoid and helical cisoid conformations, providing the first experimental evidence for solvophobically driven folding of the PoPE backbone. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1619–1627, 2006 相似文献
2.
Huseyin Zengin Gulay Zengin Dennis W. Smith 《Journal of polymer science. Part A, Polymer chemistry》2006,44(24):6988-6996
This study focuses on the preparation, characterization, and optical properties of new bis(3,4‐diphenylethynylphenyl)phenylamine. This is the first nitrogen‐containing bis‐ortho‐diynylarene (BODA) monomer having a nitrogen atom as the spacer group. BODA monomers are usually prepared from common bisphenols, thereby providing great synthetic versatility and the opportunity to develop a wide array of novel polyarylene thermosets by varying the aromatic spacer group. The new bis(3,4‐bisphenylethynylphenyl)phenylamine was synthesized in five steps. This compound emits an intense blue color (λ = 438 nm) upon irradiation by UV light and may be suitable for use as an emitting layer in electroluminescent devices. Bis‐(3,4‐bisphenylethynylphenyl)phenylamine and its polymer have photoluminescence quantum yields 34 and 38%, respectively, and long excited‐state lifetimes of 3.2 and 3.6 ns, respectively. The structure of the monomer and its polymer were characterized using spectroscopic techniques including Ultraviolet–visible Spectrophotometer, Photoluminescence Spectrophotometer, Fourier Transform infrared spectroscopy, and Gel Permeation Chromatography. The polymerizations were studied by Differential Scanning Calorimeter. The amount of weight loss and the thermostability of the nitrogen‐containing polymer were determined from thermogravimetric analysis. The electrical conductivity of neat HCl‐doped BODA‐derived polymer film was measured according to the standard four‐point probe technique. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6988–6996, 2006 相似文献
3.
本文研究了邻位取代苯基氯化汞o-XC_6H_4HgCl(X=CH_3、H、Cl、Br、COOC_2H_5、NO_2)与HCl(NaI)在85%对氧陆圜水溶液中的质子分解反应,证明反应按S_El历程进行。视取代基不同,反应速度次序如下:CH_3>H>Cl>COOC_2H_5~Br>NO_2。从化学反应与紫外光谱的研究以及理论计算结果表明,p或π电子的邻位取代基对水原子有分子内配位,它对反应速度有重要影响。测定了15种p-、m-、o-取代苯基氯化汞在80%对氧陆圜水溶液中在40.0℃的质子分解反应的速度常数k_1,表明给电性取代基加速反应,吸电性取代基使反应减慢,这可以看作是反应中心在芳环上的芳基汞化合物的S_E1反应所具有的一个特点。 相似文献
4.
V. V. Dovlatyan K. A. Eliazyan V. A. Pivazyan A. P. Engoyan 《Chemistry of Heterocyclic Compounds》2003,39(9):1238-1241
We have carried out solvolysis of the previously described ethyl esters of 3-methyl(aryl)-4-methyl-2-thioxothiazoline-5-carboxylic acids, leading to the corresponding acids without breaking down the heterocycle. We synthesized a series of novel esters from the latter by treatment with dimethyl sulfate or reactive halides. Of these, only in the case of the ethyl ester of 3,4-dimethyl-2-thioxothiazoline-5-carboxylic acid did we obtain the hydrazinolysis product (the hydrazide), from which we synthesized novel hydrazones by treatment with aldehydes and ketones. 相似文献
5.
Fatma M. Abdel-Gawad Yousry M. Issa Hussein M. Fahmy Hanan M. Hussein 《Mikrochimica acta》1998,130(1-2):35-40
Three simple, quick and sensitive spectrophotometric methods are described for the determination of ciprofloxacin. The methods are based on the reaction of this drug as ann-electron donor with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 7,7,8,8,-tetracyanoquinodimethane (TCNQ) andp-chloranil (CL) as -acceptors to give highly coloured complex species. The coloured products are quantitated spectrophotometrically at 460, 843 and 550 nm for DDQ, TCNQ and CL, respectively. Optimization of the different experimental conditions is described. Beer's law is obeyed in the concentration ranges 5–50, 1.5–15 and 20–200 g ml–1 ciprofloxacin, but the concentration ranges for best accuracy are 10–48, 2.5–15 and 35– 195 g ml–1 of drug for DDQ, TCNQ and CL, respectively. The relative standard deviations are less than 1.5%. Applications of the suggested methods to ciprofloxacin tablets are presented and compared with the USP method. The stability constants of the 11 DDQ and CL complexes were 1.086 × 104 and 2.581 × 104 lmol–1, respectively, whereas for the 12 TCNQ complex it was 3.62 × 1081. mol–1. 相似文献
6.
7.
Thanner H. Krempl P. W. Selic R. Wallnöfer W. Worsch P. M. 《Journal of Thermal Analysis and Calorimetry》2003,71(1):53-59
Quartz-homeotypic gallium (ortho-) phosphate, GaPO4, is of special interest for resonator applications asking for temperature compensated cuts with higher electro-mechanical coupling than quartz and operational temperatures up to 970°C. The crystal microbalance technique, well known for quartz (QCM) which can be used only at moderate temperatures, can now be extended to much higher temperatures using GaPO4 crystals, benefiting from all three advantages mentioned above. Two different experiments were done to demonstrate the advantages of a crystal microbalance based on GaPO4. First, the GaPO4 resonator was used for film thickness determination and compared with a commercial QCM. This experiment demonstrated that the measuring range can be extended by using GaPO4 resonators instead of quartz. The second experiment demonstrates the possibility for thermogravimetric analysis up to 720°C by using a new concept for resonator mounting.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
8.
V. B. Vol'eva T. I. Prokofeva A. I. Prokofev I. S. Belostotskaya N. L. Komissarova V. V. Ershov 《Russian Chemical Bulletin》1995,44(9):1720-1724
The interaction of 3,6-di-tert-butyl-ortho-benzoquinone (1) and 3,5-di-tert-butyl-ortho-benzoquinone (2) with NH3 in water—alcohol medium and with (NH4)2CO3 in a solid phase has been studied. Redox processes with participation of a nucleophile of the medium take place for1, while2 reacts with NH3 at the carbonyl group with transformation of the quinone imide. The mechanism of redox transformation of1 has been proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1789–1793, September, 1995.This work was carried out with financial support from the Russian Foundation for Basic Research (Project No. 94-03-08653). 相似文献
9.
我们在研究 9-氧代桉烷 - 4-烯 - 3 -酮类化合物的 2 ,3 -二氯 - 5 ,6 -二腈基 - 1 ,4-苯醌 (DDQ)脱氢反应时[1] ,发现 1 4-降桉烷 - 4,1 1 -二烯 - 3 ,9-二酮及其 1 0 - Epimer在 DDQ脱氢条件下发生迁移重排反应 ,生成酚类化合物 .反应式如下 :DDQ脱氢反应已被详细研究 ,并被广泛地用于有机合成中 [2~ 5] ,但这种脱氢重排反应尚未见文献报道 .为了深入研究该反应 ,提出可能的重排机理 .我们参照文献 [6~ 1 0 ]方法 ,用 MVK和 EVK与相应的 2 -甲基 - 1 ,3 -二酮进行 Robinson成环反应 ,合成了一系列具有类似结构的化合物 ,并与 DD… 相似文献
10.
Y. E. Kuznetsov N. L. Sukhov F. V. Pichugin B. G. Ershov 《Russian Chemical Bulletin》1996,45(12):2816-2819
Reactions ofmyo-inositiol hexa-O-nitrate with ammonia and primary amines yield tetrahydroxy-1,4-benzoquinone derivatives,viz., its tetraammonium salt and its diimines, respectively. Reactions with secondary and tertiary amines give salts of rhodizonic acid, which are converted into salts of croconic acid under certain conditions. The reactions with secondary amines involve intermediate formation of radical species, which were dectected by ESR spectroscopy. A scheme for the chemical transformations ofmyo-inositol hexa-O-nitrate under the action of amines was proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2962–2967, December, 1996. 相似文献