全文获取类型
收费全文 | 274篇 |
免费 | 13篇 |
国内免费 | 30篇 |
专业分类
化学 | 300篇 |
力学 | 1篇 |
物理学 | 16篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 2篇 |
2020年 | 13篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 13篇 |
2015年 | 16篇 |
2014年 | 15篇 |
2013年 | 18篇 |
2012年 | 13篇 |
2011年 | 30篇 |
2010年 | 10篇 |
2009年 | 37篇 |
2008年 | 18篇 |
2007年 | 21篇 |
2006年 | 17篇 |
2005年 | 13篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 7篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1990年 | 1篇 |
排序方式: 共有317条查询结果,搜索用时 0 毫秒
211.
Novel functionalized indolines were synthesized from 2-(((N-aryl)amino)methyl)acrylates and formamides under ultrasonic irradiation for the first time. Aiming to develop a straightforward and easy-to-implement methodology for the synthesis of indolines, an instrumentation setup was designed, including ultrasound (US) equipment (Ultrasonic Horn; tip diameter of 12.7 mm, 20 kHz, maximum power of 400 W), an open reaction flask, and an inexpensive and green catalyst (1 mol%; FeSO4·7H2O; CAS: 7782–63–0) without the need for anhydrous conditions. The use of the sono-Fenton process in the presence of formamides and 2-(((N-aryl)amino)methyl)acrylates afforded a broad range of functionalized indolines within 60 s in high yields. Several experimental parameters of the ultrasound-assisted reaction were evaluated, such as amplitude (40–80%), sonication time (15–60 s), and pulsed ultrasonic irradiation. A 60 s silent reaction did not produce the desired indoline. The optimized conditions for US-mediated reactions allowed the production of functionalized indolines in high isolated yields (up to 99%, 60 s reaction, pulse ration 1 s:1 s, US amplitude 60 %). 相似文献
212.
The synthesis of various functionalized or spirobicyclic glutarimides by a novel tandem process has been disclosed. The reaction involves a base-catalyzed Michael addition of active methylene compounds to secondary conjugated amides, followed by intramolecular N-acylation of the carboxamido group. It provides a relatively general and simple access to useful synthetic intermediaries and potentially active pharmacological compounds. In addition, a novel group of spirobicyclic systems has been synthesized. 相似文献
213.
Jae-Won Ka 《Tetrahedron letters》2004,45(23):4519-4523
Functionalized azacryptands containing resorcinol derivatives such as orcinol (5-methylresorcinol), 3,5-dihydroxybenzoic acid (5-carboxyresorcinol), and methyl 3,5-dihydroxybenzoate (5-methoxycarbonylresorcinol) were synthesized by one-pot synthesis in the presence of potassium carbonate with moderately good yields for advanced photonic materials, such as optical amplifying and light-emitting materials, for the first time to our knowledge. 相似文献
214.
Reactions between a series of nonenolisable aldehydes and tris(dimethylsilyl)methyllithium, (HMe2Si)3CLi, are described. The Peterson reaction takes place readily to give vinylbis(silanes). Moreover, styrene and butyl acrylate 1:1 copolymer (P), prepared by use of α,α′-azobis(isobutyronitrile) (AIBN) as an initiator in toluene at 70 ± 1°C, was formylated via direct electophilic substitution by methyl dichloromethyl ether (Cl2CHOMe) in the presence of tin(IV) chloride (SnCl4) in nitrobenzene (PhNO2) as solvent. The reaction of (HMe2Si)3CLi with formyl groups on the side chains of the copolymer led to new macromolecules bearing vinylbis(silane) functional groups. 相似文献
215.
Functionalized graphenes have been utilized as electronic devices and energy materials. In the present paper, the effects of fluorine-termination of graphene edge on the structures and electronic states of graphene have been investigated by means of density functional theory (DFT) method. It was found that the ionization potential (Ip) and electron affinity of graphene (EA) are blue-shifted by the F-substitution. On the other hand, the excitation energy was red-shifted. The drastic change shows a possibility as electronic devices such as field-effect transistors. The drastic change of electronic states caused by the F-substitution of graphene edge was discussed on the basis of the theoretical results. 相似文献
216.
Maximilian Baur Nina K. Mast Jan P. Brahm Rosa Habé Tobias O. Morgen Stefan Mecking 《Angewandte Chemie (International ed. in English)》2023,62(45):e202310990
Polyethylenes endowed with low densities of in-chain hydrolyzable and photocleavable groups can improve their circularity and potentially reduce their environmental persistency. We show with model polymers derived from acyclic diene metathesis polymerization that the simultaneous presence of both groups has no adverse effect on the polyethylene crystal structure and thermal properties. Post-polymerization Baeyer–Villiger oxidation of keto-polyethylenes from non-alternating catalytic ethylene-CO chain growth copolymerization yield high molecular weight in-chain keto-ester polyethylenes (Mn≈50.000 g mol−1). Oxidation can proceed without chain scission and consequently the desirable materials properties of HDPE are retained. At the same time we demonstrate the suitability of the in-chain ester groups for chemical recycling by methanolysis, and show that photolytic degradation by extended exposure to simulated sunlight occurs via the keto groups. 相似文献
217.
Solid-phase extraction (SPE) of trace elements before their analysis has become a conventional pretreatment step of analytes because of their frequent low concentrations in numerous samples. Additionally, interfering compounds often accompagny analytes of interest, thus requiring a clean-up step. The preconcentration step and/or matrix removal can be efficiently improved by chemometric approaches allowing obtention of reliable results. Single variable approach is often used but is time and cost consuming, and may be the source of mistakes; multivariable approach allows to overcome these problems and increases the probability of global optimum finding.In order to obtain a set of experimental conditions for the selective extraction of Al(III) in water samples, onto a modified organic support (salicylic acid grafted on XAD-4), a multicriteria approach (response surface methodology) has been applied. The extraction method was optimized by the aid of a factorial design and a uniform shell Doehlert design for six variables: sample percolation flow rate, trace metal amount, sample volume, concentration and volume of HCl used for elution of aluminium. Results demonstrate the synergic effects of four factors and allow us to define working ranges for each parameter tested. The designed SPE procedure was then sucessfully applied to synthetic and real samples, issued from a potable water treatment unit. 相似文献
218.
Gerhard Erker 《Journal of organometallic chemistry》2007,692(6):1187-1197
Group 4 metallocene complexes can form adducts or condensation products with a variety of typical biogenic molecules. In this account, examples are presented and discussed for the reactions of zirconocene or titanocene complexes with suitably protected/deprotected carbohydrate derivatives. Some methodological developments are shown for the attachment of aminoacid or peptide derived functional groups at the Cp-rings of the Group 4 bent metallocenes. Eventually, the reactions of methylzirconocene- and methyltitanocene cations with a series of short oligopeptides are discussed that lead to the formation of primary κO-adducts followed by O,N,O-chelate complex formation with methane evolution. The dynamic features of some such systems are discussed. 相似文献
219.
Jun Zhang Weiguo Cao Liping Song Qun Qian Min Shao 《Journal of fluorine chemistry》2009,130(5):488-8228
l-Proline-catalyzed reaction of ethyl 4,4,4-trifluoroacetoacetate, cinnamaldehyde and anilines provide a novel method for preparation of ethyl-6-(arylamino)-2-hydroxy-4-phenyl-2-(trifluoromethyl)tetrahydro-2H-pyran-3-carboxylate derivatives in good yields. The reaction was conducted by initial Michael addition, followed by intra-molecular cyclization under mild conditions. The structure of a typical ethyl-2-hydroxy-4-phenyl-6-(m-tolylamino)-2-(trifluoromethyl)tetrahydro-2H-pyran-3-carboxylate (4h) was confirmed by XRD analysis. A plausible mechanism is presented. 相似文献
220.
Aïcha Arfaoui 《Tetrahedron》2009,65(25):4904-4907
A regioselective coupling of ethyl 2-(bromomethyl)-3-cyanoacrylate and primary amines is described to give ethyl 2-[(alkylamino)(cyano)methyl] acrylates in good yields. Whereas the conversion of allyl bromide in the presence of TEAF leads to the first synthesis of ethyl 3-cyano-2-(hydroxymethyl) acrylate. 相似文献