全文获取类型
收费全文 | 622篇 |
免费 | 30篇 |
国内免费 | 11篇 |
专业分类
化学 | 523篇 |
晶体学 | 4篇 |
力学 | 4篇 |
数学 | 60篇 |
物理学 | 72篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 18篇 |
2021年 | 19篇 |
2020年 | 17篇 |
2019年 | 39篇 |
2018年 | 45篇 |
2017年 | 24篇 |
2016年 | 37篇 |
2015年 | 38篇 |
2014年 | 35篇 |
2013年 | 93篇 |
2012年 | 40篇 |
2011年 | 56篇 |
2010年 | 24篇 |
2009年 | 30篇 |
2008年 | 25篇 |
2007年 | 20篇 |
2006年 | 12篇 |
2005年 | 17篇 |
2004年 | 21篇 |
2003年 | 5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663条查询结果,搜索用时 15 毫秒
41.
Maha Chaieb Héla Habli Leila Mejrissi Attieh A Al‐Ghamdi Brahim Oujia Florent Xavier Gadéa 《International journal of quantum chemistry》2017,117(22)
An extensive diabatic investigation of the NaRb species has been carried out for all excited states up to the ionic limit Na‐Rb+. An ab initio calculation founded on the pseudopotential, core polarization potential operators and full configuration interaction has been used with an efficient diabatization method involving a combination of variational effective hamiltonian theory and an effective overlap matrix. Diabatic potential energy curves and electric dipole moments (permanent and transition) for all the symmetries Σ+, Π, and Δ have been studied for the first time. Thanks to a unitary rotation matrix, the examination of the diabatic permanent dipole moment (PDM) has shown the ionic feature clearly seen in the diabatic 1Σ+ potential curves and confirming the high imprint of the Na‐Rb+ ionic state in the adiabatic representation. Diabatic transition dipole moments have also been computed. Real crossings have been shown for the diabatic PDM, locating the avoided crossings between the corresponding adiabatic energy curves. 相似文献
42.
Leila Torkian Mostafa M. Amini Tayebeh Gorji Omid Sadeghi 《Arabian Journal of Chemistry》2019,12(7):1315-1321
In this study, multiwalled carbon nanotube (MWCNT) was modified by the pyridine group using a silane agent and characterized by infrared spectroscopy (IR), thermal analysis (TG/DTA), and elemental analysis (CHN) and scanning electron microscopy (SEM). The application of this sorbent was investigated in determination of lead ions in aqueous samples, using flame atomic absorption spectrometry (FAAS). Through this study, different parameters such as pH and sample flow rate on adsorption process and eluent concentration, volume and flow rate were optimized. The limit of detection (LOD), the relative standard deviation and the recovery of the method were 2 ng mL?1, 1.3% and 99.7%, respectively. Two standard reference materials (NIST 1571 and NIST 1572) were used to verify accuracy of this method. Finally, the sorbent was successfully applied for extraction and determination of low levels of Pb(II) ions in aqueous samples. 相似文献
43.
Novel and fast deep eutectic solvent (DES)-based homogeneous liquid–liquid microextraction (HLLME) was applied for the extraction of copper from vegetable samples followed by flame atomic absorption spectrometry (FAAS). 1,5-diphenyl carbazone (DPC) was used as the chelating agent, and a DES was used as the extraction media. The utilized DES was based on benzyl triphenyl phosphonium bromide and ethylene glycol in a 1:8?mole ratio. The phase separation phenomenon was occurred by changing of sample temperature. Several factors influencing the extraction efficiency were investigated and optimized. Under the optimized conditions, an enhancement factor of 64 was obtained. The limit of detection, based on three signal-to-noise ratio, and limit of quantification were found to be 0.13?µg L?1 and 5.0?µg L?1, respectively. The calibration curve was linear within the range of 5.0–250?µg L?1 with r2 > 0.9957. Intra- and inter-day relative standard deviations (%) of 2.1% and 2.6% were obtained at the concentration of 25?µg L?1. The accuracy of the proposed method was evaluated by analyzing a tomato leaves certified reference material and the results were to be in agreement with the certified value. Finally, the feasibility of the method was successfully confirmed by determination of copper in spinach, lettuce, broccoli, potato, carrot and parsley samples. 相似文献
44.
A new method for multi-component synthesis of 1,4-dihydropyridine derivatives (1,4-DHPs) in the presence of meglumine supported on multiwalled carbon nanotubes (MWCNTs@meglumine) as a new heterogeneous, highly efficient and reusable catalyst was investigated. The reaction was performed under ultrasonic irradiation in EtOH at room temperature. A new, highly efficient heterogeneous catalyst, short reaction times, high to excellent yield of products, and safe and clean conditions are the advantages of the presented method. 相似文献
45.
Evolved Gas Analysis‐Mass Spectrometry to Identify the Earliest Organic Binder in Aegean Style Wall Paintings 下载免费PDF全文
Dr. Ravit Linn Dr. Ilaria Bonaduce Dr. Georgia Ntasi Prof. Leila Birolo Prof. Assaf Yasur‐Landau Prof. Eric H. Cline Dr. Austin Nevin Dr. Anna Lluveras‐Tenorio 《Angewandte Chemie (International ed. in English)》2018,57(40):13257-13260
An organic binder was identified in the painted fragments from the Canaanite palace of Tel Kabri, Israel. Recently dated to the late 18th century B.C.E. by 14C, Tel Kabri is the most ancient of the Eastern Mediterranean sites in which Aegean style paintings have been found. The application of pigments was suspected to be using an organic binding medium, particularly for the Egyptian Blue pigment. Samples of blue paint were examined using evolved gas analysis‐mass spectrometry (EGA‐MS) in order to overcome the analytical challenges imposed by highly degraded aged proteinaceous materials. Egg was identified as the binder based on the presence of hexadecanonitrile and octadecanonitrile, confirming the use of a secco painting technique. Lysozyme C from Gallus gallus was detected by proteomics analysis, confirming the presence of egg. To our knowledge, this is the earliest use of egg as a binder in Aegean style wall paintings. 相似文献
46.
Parisa Pazhooh Roushan Khoshnavazi Leila Bahrami Elham Naseri 《Journal of the Iranian Chemical Society》2018,15(8):1775-1783
New nanocomposites containing sandwich-type polyoxometalate of [(PW9O34)2(HOSnIVOH)3]12? (P2W18Sn3) loaded onto Ln-doped TiO2 (Nd, Sm, Dy, Tb) nanoparticles were synthesized and their catalytic activities were assessed. The Ln–TiO2 nanoparticles and Ln–TiO2/P2W18Sn3 nanocomposites were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction, field emission scanning electron microscope, energy dispersive analysis of X-rays spectra and diffuse reflectance spectra. The photocatalytic efficiency of the Ln–TiO2 and Ln–TiO2/P2W18Sn3 were examined in the photodegradation of methyl orange and methylene blue solutions. It was revealed through different characterization techniques that the P2W18Sn3 was successfully loaded on the lanthanide-doped anatase phase TiO2 nanoparticles and the particles diameter were relatively 20–30 nanometers. It was revealed that doping by the lanthanide ions followed by loading of polyoxometalates improves the photocatalytic performance of TiO2 effectively. The effects of operational parameters and the kinetics of photocatalytic degradation under UV light were discussed. The prepared nanocomposites were stable and could be easily separated from the reaction system. 相似文献
47.
In this work, a solidified floating organic drop microextraction was developed based on a vesicular supramolecular solvent consisting of decanoic acid and quaternary ammonium. The method was used for preconcentration of trace amount of cadmium in different rice samples followed by flow-injection analysis–flame atomic absorption spectrometry. Several parameters affecting the extraction efficiency including pH, concentration of 1-(2-pyridylazo)-2-naphthol as the chelating agent, sample and extraction solvent volume, stirring rate, extraction time, salt effect, and interfering ions were investigated and optimized. Under the optimum conditions, a preconcentration factor of 84 was achieved. LOD and LOQ were found to be 0.09 and 0.31 µg L?1, respectively. The calibration curve was linear within the range of 5.0–700 µg L?1 (r2?>?0.9978). Intra- and inter-day precisions (RSD% n?=?3) were estimated 2.7 and 3.9% at the concentration of 20 µg L?1, respectively. The accuracy of the method was successfully validated by analysis of an SRM-1643f standard reference material. Relative recoveries were achieved within the range of 93–107% elucidating suitability of the method for determination of cadmium in rice samples. 相似文献
48.
In the present work, gel polymer electrolytes (GPEs) were prepared using poly(methyl methacrylate) (PMMA), lithium perchlorate (LiClO4) and dimethylacetamide as a plasticizer. Solution-casting technique was used to fabricate GPEs containing different weight percentage of PMMA. The degree of crystallinity of GPE samples was studied by X-ray diffraction (XRD) analysis. Fourier transform infrared (FT-IR) spectroscopy was applied to study the level of interactions between lithium salt and PMMA in the prepared GPEs. Electrochemical properties were studied by electrochemical impedance spectroscopy, linear sweep voltammetry and DC polarization techniques. Lithium ion conductivity of GPEs was determined by calculating the bulk resistance of polymer electrolytes from Nyquist plot. Increasing PMMA content of GPEs resulted in an improvement in the electrochemical potential window from 4.2 to 4.5 V. The highest lithium transference number (0.42) and also the best electrochemical properties were obtained for GPE containing 0.75 M LiClO4 and 10 wt% PMMA. Scanning electron microscopy images of the optimized GPE showed a porous and heterogeneous surface structure which is desirable for application in Li-ion batteries. 相似文献
49.
The tandem catalysis system including the trimerization catalyst of CrCl3/SNS (SNS = bis-(2-pentylsulfanyl-ethyl)-amine) (Cat 1) and the copolymerization catalyst Cat 2 of Cr/SiO2 (Grace 643) has been prepared and used to the synthesis of branched polyethylene. The optimum polymerization conditions were found to be as follows: chromium concentration 0.2 wt %, ethylene pressure 23 bar, solvent hexane, polymerization temperature 90°C, co-catalyst triethylaluminum. The optimally prepared polyethylene was characterized thermally and morphologically. Appearance of α and γ hydrogens in ethylene-1-hexene copolymer confirms the presence of branches in polyethylene backbone. 相似文献
50.
Leila Irannejad Seyed Javad Ahmadi Sodeh Sadjadi Mojtaba Shamsipur 《Journal of the Iranian Chemical Society》2018,15(1):111-119
Metal-free electrocatalysts for oxygen reduction reaction (ORR) are key to the development of efficient, durable, and low-cost alternatives to noble-metal-based electrocatalysts in fuel cell cathodes. In recent years, many efforts are directed to the metal-free catalyst based on heteroatom-doped graphene. In this work, we demonstrate that the graphene surface can be converted into the catalyst for the oxygen reduction by chemical functionalization. In this context, we first synthesized malononitrile-functionalized graphene oxide. Amidoximation of nitrile group and reduction in graphene oxide were then carried out by hydroxylamine in one step. The electrochemical behavior of functionalized graphene-modified electrode for the reduction in oxygen was studied. The results showed that the electrocatalyst fabricated by this method exhibited striking catalytic activities in alkaline solution. In alkaline solution, this catalyst showed a competitive activity to the commercial Pt catalyst via four-electron transfer pathway with better ORR selectivity and stability. In addition, this metal-free electrocatalyst exhibited tolerance to methanol crossover effect. Based on its outstanding performance, this functionalized graphene electrocatalyst showed the promising prospect of a metal-free catalyst for fuel cell with much lower cost than currently used Pt/C catalyst. 相似文献