全文获取类型
收费全文 | 574篇 |
免费 | 41篇 |
国内免费 | 11篇 |
专业分类
化学 | 500篇 |
晶体学 | 4篇 |
力学 | 2篇 |
数学 | 51篇 |
物理学 | 69篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 18篇 |
2020年 | 16篇 |
2019年 | 38篇 |
2018年 | 47篇 |
2017年 | 25篇 |
2016年 | 37篇 |
2015年 | 36篇 |
2014年 | 34篇 |
2013年 | 82篇 |
2012年 | 38篇 |
2011年 | 51篇 |
2010年 | 24篇 |
2009年 | 29篇 |
2008年 | 26篇 |
2007年 | 17篇 |
2006年 | 11篇 |
2005年 | 17篇 |
2004年 | 22篇 |
2003年 | 4篇 |
2002年 | 14篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有626条查询结果,搜索用时 15 毫秒
121.
Nadia Mayoufi Didier Dalmazzone Walter Fürst Leila Elghoul Adel Seguatni Anthony Delahaye Laurence Fournaison 《Journal of Thermal Analysis and Calorimetry》2012,109(1):481-486
The phase behaviour of the system water?Ctri-n-butylmethylammonium chloride (TBMAC)?CCO2 was investigated by pressure-controlled differential scanning calorimetry in the range 0?C10?mol% TBMAC in water and at CO2 pressures ranging from 0 to 1.5?MPa. In the absence of CO2, an incongruent melting hydrate, which estimated composition corresponds to TBMAC·30H2O, crystallizes at temperatures below ?13.6?°C and forms with ice a peritectic phase at approximately 3.9?mol% TBMAC. In the presence of CO2 at pressures as low as 0.5?MPa, curves evidenced the presence of an additional phase exhibiting congruent melting at temperatures that are strongly pressure dependent and significantly higher than those of hydrates obtained without CO2. This new phase, whose enthalpy of dissociation and CO2 content increase slightly with CO2 pressure, was identified as a mixed semi-clathrate hydrate of TBMAC and CO2 of general formula: (TBMAC?+?xCO2)·30H2O. 相似文献
122.
Leila Bakhtiyari Fereshteh Moghimi Seyed Soheil Mansouri Ali Farsi Masoud M. Malek-Shah 《Research on Chemical Intermediates》2012,38(3-5):965-982
The production of metal concentrates during mineral processing of ferrous and non-ferrous metals involves a variety of highly corrosive chemicals which deteriorate common mild steel as the material of choice in the construction of such lines, through rapid propagation of localized pitting in susceptible parts, often in sensitive areas. This requires unscheduled maintenance and plant shut down. In order to test the corrosion resistance of different available materials as replacement materials, polarization and electrochemical impedance spectroscopy (EIS) tests were carried out. The EIS numerical outputs were then transformed into an equivalent electric circuit using Z-View software, and the predictive behavior was contrasted with actual performance after long-term immersion, depicted through SEM, EDS, XRD and weight change observations. Also, results of pits and cracks, obtained with climax software-enhanced polarization resistance, and reduced capacitance added to much diminished current densities, verified the acceptable performance of CK45 compared with high priced stainless steel substitutes with comparable operational life. Therefore, CK45 can be a suitable alternative in steel constructions which are exposed to super-alkaline and corrosive environments. 相似文献
123.
Hassan Valizadeh Esmail Vesally Leila Dinparast 《Journal of heterocyclic chemistry》2012,49(1):106-110
Facile synthesis of N‐(methyl and phenyl)‐Δ4‐isoxazolines via the reaction of (Z)‐N‐(methyl and phenyl)‐C‐arylnitrones with dimethyl acethylenedicarboxylate, DMAD, in ionic liquid is described. (Z)‐N‐methyl‐C‐arylnitrones afforded the high yield of N‐methyl‐Δ4‐isoxazolines 4a , 4b , 4c , 4d , 4e in ionic liquid, [bmim]BF4, at room temperature. However, the reaction of (Z)‐N‐phenyl‐C‐arylnitrones with DMAD afforded the mixtures of cis and trans isomers of related N‐phenyl‐Δ4‐isoxazolines ( 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j , 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j ) under these conditions. J. Heterocyclic Chem., (2012). 相似文献
124.
Luiz C. Dias Gustavo C. Monteiro Giovanni W. Amarante Leila S. Conegero Fernanda G. Finelli 《Tetrahedron letters》2012,53(6):707-709
An approach for the highly stereoselective synthesis of analogs of the macrolactone of isomigrastatin is described. Our optimized strategy is based on a very efficient lactone opening, a Wittig olefination reaction and a ring closing metathesis. The syntheses were accomplished in 10–11 steps and good overall yields. 相似文献
125.
Ange Polidori Bernard Pucci Leila Zarif Jean G. Riess Andr A. Pavia 《Macromolecular rapid communications》1996,17(4):229-238
Sugar-derived surfactants bearing a polymerizable acryloyl moiety on one of the branches of the double-chain hydrophobic tail were prepared. The non–ionic hydrophilic head and the biantennary hydrophobic tail were built on, respectively, an aspartic acid and a tris(hydroxymethyl)aminomethane core. Ultraviolet irradiation of aqueous dispersions of these surfactants above their transition phase temperature (Tc) was achieved. The morphology of self-assemblies produced in such a way were investigated by transmission electron microscopy. TEM photographs revealed that irradiation leads to the formation of unilamellar vesicles. Neither fibers nor tubules were detected in contrast to what was observed before polymerization. 相似文献
126.
2, 4-Bis-(4-methoxyphenyl)-1, 3, 2, 4-dithiadiphosphetane-2, 4-disulfide [Lawesson reagent (LR)] 1 reacts with p-quinone monoimine- 2a to give the novel benzo-1,3,2-oxathiaphosphol-5-(methanesulfonamido)-2-(4-methoxyphenyl)-2-sulfide 4 . On the other hand, the reaction of 2b and 3 with LR 1 leads to the formation of the benzo- and the naphtho-1,3,2-dithiaphosphol-5 -(benzenesulfonamido)- 2- (4-methoxyphenyl) -2-sulfide 5 , 6 . Thiation of 2a , 2b , and 3 with P4S10 yields phenoxathiin derivatives 8a , 8b , and 9 , respectively. The identity of the new products is established from analytical and spectroscopic evidence. 相似文献
127.
A new heterogeneous nanocatalyst [MWCNTs@TEPA/Co (II)] was successfully prepared using multiwall carbon nanotubes (MWCNTs) as a suitable and efficient support for covalent anchoring of tetraethylene pentaamine (TEPA)/Co (II). The new heterogeneous catalyst was prepared through an easy and applicable method, and characterized by various techniques such as Fourier transform-infrared, thermogravimetric analysis, energy-dispersive X-ray spectroscopy, mapping, field emission-scanning electron microscopy, inductively coupled plasma-optical emission spectrometry and Brunauer−Emmett−Teller. Synthesized catalyst was used efficiently for the preparation of dihydropyrimido [4,5-b]quinolinetrione derivatives via the four-components reaction of barbituric acid, dimedone, aryl aldehyde and amines under thermal conditions. The nanostructure catalyst was easily recovered by filtration and reused several times without noticeable loss of its catalytic activity. Low amounts of catalyst (0.005 g), short reaction times and green conditions are some merits of the presented method. 相似文献
128.
Mohammad Ali Kamyabi Fatemeh Soleymani-Bonoti Leila Taheri Ahmad Morsali Hassan Hosseini-Monfared 《应用有机金属化学》2020,34(5):e5562
Oxygen reduction at the polarized water/1,2-dichloroethane (DCE) interface catalyzed by a Cu (II) coordination polymer (Cu–pol) was studied with two lipophilic electron donors ferrocene (Fc) and tetrathiafulvalene (TTF). The results of the ion transfer voltammetry and two-phase shake flask experiments suggest proceeding of the catalytic reaction as proton-coupled electron transfer reduction of oxygen to hydrogen peroxide and water. In this process, while the protons supplied from the aqueous phase, the electrons provided from the organic phase by the weak electron donor, Fc. The O2 molecule takes a superoxide structure with Cu–pol which resulted to hydrogen peroxide or water on reduction. Furthermore, the results revealed that the apparent rate constant of TTF + Cu-pol is higher than that of Fc + Cu-pol system due to the faster kinetic reaction of TTF with respect to Fc. 相似文献
129.
Glauco F. Bauerfeldt Leila M. M. de Albuquerque Graciela Arbilla Edilson C. da Silva 《Journal of Molecular Structure》2002,580(1-3):147-160
The competitive unimolecular reactions of formaldehyde, H2CO→H2+CO; H2CO→trans-HCOH and H2CO→H+HCO, were comparatively studied under the direct dynamics formalism, using Density functional and ab initio levels of theory. In addition, the geometric isomerization trans-HCOH→cis-HCOH was evaluated. Calculated reaction path properties were used in the determination of Rice–Ramsperger–Kassel–Marcus microcanonical rate coefficients. The reaction dynamics was evaluated for each individual process based on the nuclear displacements in the reaction path and normal coordinate analysis. Our results found are in very good agreement with experimental barrier heights and quantum yields trends. 相似文献
130.
A. Antony Muthu Prabhu Madi Fatiha Nouar Leila T. Anantha Raj Inmaculada Navarro-González Maria Jesús Periago Maria Josefa Yáñez-Gascón Horacio Pérez-Sánchez 《Journal of solution chemistry》2018,47(3):409-429
The interactions of the neurotransmitter dopamine (DA) with β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was characterized using UV–visible, 2D fluorescence, 3D fluorescence, FT–IR, PXRD and SEM techniques. PM3, PM7 and DFT methods were used to optimize the structures of the inclusion complexes in the gas phase. The absorbance and fluorescence intensities of DA increased in the presence of CDs in aqueous solution. The binding energy, HOMO–LUMO energy gap and Mulliken atomic charges were computed for the inclusion complexes. NBO analysis revealed a greater number of intermolecular hydrogen bonds in DA:HP-β-CD. Experimental and theoretical results suggested that the DA molecule is deeply embedded in the cavities of both CDs. 相似文献