全文获取类型
收费全文 | 536篇 |
免费 | 25篇 |
国内免费 | 76篇 |
专业分类
化学 | 334篇 |
晶体学 | 1篇 |
力学 | 36篇 |
综合类 | 14篇 |
数学 | 116篇 |
物理学 | 136篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 15篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 19篇 |
2015年 | 10篇 |
2014年 | 23篇 |
2013年 | 57篇 |
2012年 | 52篇 |
2011年 | 45篇 |
2010年 | 34篇 |
2009年 | 25篇 |
2008年 | 50篇 |
2007年 | 22篇 |
2006年 | 32篇 |
2005年 | 26篇 |
2004年 | 25篇 |
2003年 | 13篇 |
2002年 | 12篇 |
2001年 | 9篇 |
2000年 | 18篇 |
1999年 | 11篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有637条查询结果,搜索用时 15 毫秒
131.
132.
133.
A facile synthesis of novel 1,2,6,7-tetrahydro-3H-pyrazolo[4,3-c]pyridine-3,4(5H)-diones has been achieved. The operationally simple procedure, using readily available intermediates, allows for rapid derivatisation of the pharmacophore with alkyl, aryl and heteroaryl substituents. 相似文献
134.
The bismuth-catalyzed oxidative condensation of aldehydes with 2-aminobenzamide under aerobic conditions is reported using ethanol as the solvent. Good to excellent isolated yields (68–95%) of the corresponding 2-substituted quinazolinones were obtained under mild reaction conditions with excellent functional group tolerance. The quinazolinones were further functionalized to afford N-allylated quinazolinones, 2-aminopyridine derivatives, and annulated polyheterocyclic compounds via transition-metal catalyzed reactions. 相似文献
135.
N-substituted oxindoles were obtained through a facile KOH/DMSO promoted intramolecular cyclization of o-bromophenylacetamides in good yields. Furthermore, isoindigo derivatives were readily synthesized through sequential intramolecular cyclization, oxidation and condensation of o-bromophenylacetamide in the presence of copper (II) acetate monohydrate, iodobenzene diacetate and KOH/DMSO. This method provides a convenient synthesis of a range of oxindoles and symmetrical biologically important (E)-bisindole-2-ones using o-bromophenylacetamide as sole starting material. The reaction mechanism is elucidated in light of the control experiment results. 相似文献
136.
We report molecular dynamics studies on the effect of CCD– (chlorinated cobalt-dicarbollide) anions on the Eu3+ lanthanide cation extraction by a calix[4]arene-CMPO ligand L, focusing on the water–‘oil’ interface, where ‘oil’ is modelled by chloroform. The free L ligand and its EuL3+ complex are found to adsorb and to concentrate at the interface, but are too hydrophilic to be extracted. Addition of CCD– anions in diluted conditions (either covalent linked to L or as separated CCD– H3O+ ions) also leads to adsorption of these species at the interface. However, at high concentrations, CCD– anions saturate the interface and promote the extraction of EuL3+ to the oil phase. Another important feature concerns the uncomplexed Eu(CCD)3 salt: accumulation of CCD– anions at the interface creates a negative potential which attracts the hydrated Eu3+ ions, therefore facilitating their complexation by interfacial ligands. These features allow us to better understand the synergistic effect of lipophilic anions in the assisted liquid-liquid extraction of trivalent M3+ lanthanide or actinide cations. To cite this article: B. Coupez, G. Wipf, C. R. Chimie 7 (2004).
Résumé
Synergie due aux anions dicarbollides lors de l’extraction d’ions lanthanides M3+ par des calix[4]arènes : simulations de dynamique moléculaire à l’interface eau–« huile ». Nous étudions par simulations de dynamique moléculaire l’effet de synergie dû aux anions CCD– (cobalt-dicarbollides) lors de l’extraction de Eu3+ par un calix [4]arène L, en se focalisant sur l’interface eau–« huile », l’huile étant modélisée par du chloroforme. On montre que le ligand L et son complexe EuL3+ s’adsorbent à l’interface, mais sont trop hydrophiles pour être extraits. L’addition d’anions CCD– (qu’ils soient sous la forme d’ions CCD– H3O+ séparés ou greffés de façon covalente au calixarène) conduit aussi à l’adsorption de ces espèces à l’interface. Cependant, aux plus fortes concentrations, les anions CCD– saturent l’interface et induisent l’extraction du complexe EuL3+ vers l’huile. Un autre résultat remarquable concerne les sels Eu(CCD)3 : l’accumulation des anions CCD– à l’interface y crée un potentiel négatif, ce qui attire les cations Eu3+ et facilite ainsi leur complexation par des ligands à l’interface. Ces résultats permettent de mieux comprendre l’effet de synergie dû aux anions CCD– lors de l’extraction d’ions lanthanides ou actinides M3+ et, d’une manière générale, ce qui se passe à l’interface entre l’eau et des liquides non miscibles. Pour citer cet article : B. Coupez, G. Wipf, C. R. Chimie 7 (2004). 相似文献137.
α,α-二乙酰基二硫缩烯酮和芳醛的缩合反应研究 总被引:4,自引:0,他引:4
在碱性条件下,α,α-二乙酰基二硫缩烯酮和芳醛的缩合反应受烷硫基的影响.α,α-二乙酰基二苄硫缩烯酮1和芳醛3缩合生成单面缩合脱乙酰基产物α-肉桂酰基二苄硫缩烯酮4;α,α-二乙酰基环二硫缩烯酮2和芳醛3缩合生成双面缩合产物α,α-二肉桂酰基环二硫缩烯酮5. 相似文献
138.
Dienone- and tetrahydropyrone- esters undergo Nazarov-type cyclisation using trimethylsilyltriflate.
Cyclopentenone esters have been synthesized via a Nazarov cyclisation of the corresponding ,′-dienone esters or tetrahydro-γ-pyrone esters employing trimethylsilyltriflate at room temperature. The dienone esters were synthesised by a short two-step acylation-Knoevenagel sequence. 相似文献
139.
合成了不对称冠醚方酸碲碳菁染料和对称冠醚方酸碲碳菁染料,并探讨了对称冠醚方酸碲碳菁的合成方法及反应条件,提出了其可能的反应机理。 相似文献
140.
A novel column made through the condensation reaction of TiO2 nanoparticles (TiO2 NPs) with silanol groups of the fused-silica capillary is described. EOF measurements under various buffer constitutions were used to monitor the completion of reactions. The results indicated that the EOF was dependent on the interactions between buffers and the bonded TiO2 NPs. With formate/Tris buffer, EOF reversal at pH below 5 and cathodic EOF at pH above 5 were indicated. The pI of the bonded TiO2 NPs was found at approximately ph 5. Only cathodic EOF was illustrated by substituting the mobile phase with either glutamate or phosphate buffer. It was elucidated that both glutamate and phosphate buffer yield a negative charge layer on the surface of TiO2 NPs attributable to the formation of a titanium complex. The CEC performance of the column was tested with angiotensin-type oligopeptides. Some parameters that would affect the retention behavior were investigated. The interactions between the bonded phases and the analytes were explicated by epitomized acid-base functional groups of the oligopepetides and the speciation of the surface oxide in different pH ranges. The average separation efficiencies of 3.1 x 10(4) plates/m is readily achieved with a column of 70 cm (50 cm) x 50 mum ID under an applied voltage of 15 kV, phosphate buffer (pH 6.0, 40 mM), and UV detection at 214 nm. 相似文献