全文获取类型
收费全文 | 943篇 |
免费 | 35篇 |
国内免费 | 23篇 |
专业分类
化学 | 841篇 |
晶体学 | 4篇 |
力学 | 20篇 |
数学 | 59篇 |
物理学 | 77篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 29篇 |
2021年 | 37篇 |
2020年 | 64篇 |
2019年 | 55篇 |
2018年 | 80篇 |
2017年 | 39篇 |
2016年 | 73篇 |
2015年 | 54篇 |
2014年 | 71篇 |
2013年 | 125篇 |
2012年 | 67篇 |
2011年 | 73篇 |
2010年 | 52篇 |
2009年 | 47篇 |
2008年 | 43篇 |
2007年 | 29篇 |
2006年 | 9篇 |
2005年 | 13篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 3篇 |
1999年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1976年 | 1篇 |
排序方式: 共有1001条查询结果,搜索用时 15 毫秒
61.
Zahra Talebpour Mehregan Safari Fatemeh Molaabaci Ali Alizadeh Hassan Y. Aboul-Enein 《Chromatographia》2010,72(7-8):707-712
A novel poly(methyl methacrylate–ethyleneglycol dimethacrylate–acrylic acid) film has been introduced for coating on stir bars to sorptive extraction (SBSE). The effects of different contents of porogen, monomer, cross-linker, modifier and initiator during the solvent or bulk polymerization step on the mechanical property and solvent resistant of prepared sorptive stir bars were investigated. The evaluation of results were caused to obtain the four prepared sorptive stir bars with good mechanical stability and excellent resistance to organic solvents. The extraction efficiency of these prepared sorptive stir bars were investigated by liquid desorption-liquid chromatography-ultraviolet detection (LD-LC-UV) using N-Nitrosodiphenylamine as target analyte. SBSE assays showed the sorptive stir bar that prepared using solution polymerization method had the better recovery for N-Nitrosodiphenylamine in water samples. This sorptive stir bar showed good linearity and acceptable recoveries, as well as advantages such as sensitivity, simplicity, low cost and high feasibility. Based on atomic force microscopy (AFM) results, the average pore size of optimum prepared stir bar using solvent polymerization method was obtained ~9 nm. The thermal gravity (TG) and differential scanning calorimetric (DSC) results showed this polyacrylate film has high thermal stability. 相似文献
62.
Mohammad-Saleh Zabihi Jahan Bakhsh Raoof Mahmoud Reza Sohrabi Sayed Reza Hosseini Fatemeh Farrash Bamoharram 《Journal of the Iranian Chemical Society》2016,13(11):2093-2101
Phosphotungstic acid (PWA) was used for accumulation of nickel ions at the carbon paste electrode for preparation of PWA-modified CPE (PWA/CPE). The PWA was evenly mixed with graphite powder and paraffin oil. Then, for preparation of Ni/PWA/CPE, Ni ions were included onto the PWA/CPE surface through immersion method at open circuit condition. The scanning electron microscopy (SEM), energy-dispersive spectroscopy and electrochemical methods were used to verify the prepared electrodes. The SEM images reveal that morphology of the CPE was influenced by PWA addition. Application of the Ni/PWA/CPE for methanol oxidation was explored by various electrochemical techniques. Electrochemical response of methanol oxidation at the surface of Ni/PWA/CPE was 2.5 times higher than that Ni/CPE. The obtained results indicated that the modified electrode exhibited high electrocatalytic activity toward methanol oxidation. Then, catalytic rate constant was found to be 8.25 × 104 cm3 mol ?1 s?1 using chronoamperometry method. Furthermore, the effects of several parameters, such as PWA loading, NiSO4 concentration, accumulation time and methanol concentration toward methanol oxidation at the surface of this modified electrode as well as stability, have been investigated. 相似文献
63.
Seyyedeh Fatemeh Mousavi Zinatossadat Hossaini Faramarz Rostami-Charati Navabeh Nami 《Journal of heterocyclic chemistry》2020,57(11):3868-3881
In this research, synthesis of pyrrolo isoquinoline derivatives in excellent yields was performed using the multicomponent reaction of isoquinoline, alkyl bromides, 2-hydroxyacetophenone, or its derivatives, dimethyl carbonate as a green reagent and KF/clinoptinolite nanoparticles as a catalyst in the aqueous media at 80°C. The Punica granatum peel water extract was used as the green media for the synthesis of PG-KF/clinoptilolite nanoparticles in high yield. The PG-KF/clinoptilolite nanoparticles show a significant basic catalytic role in these reactions in preparing the product in high yield and used for several times. In addition, for studying the antioxidant ability of some of the synthesized compounds, diphenyl-picrylhydrazine (DPPH) radical trapping and power of ferric reduction tests are employed. The short time of the reaction, high yields of the product, easy separation of the catalyst and products are some of the advantages of this procedure. 相似文献
64.
Mark Edgar Dee Hayward Fatemeh Zeinali Shahzad Riaz George W. Weaver 《Magnetic resonance in chemistry : MRC》2020,58(2):170-185
A simple to use nuclear magnetic resonance analysis method has been tested on complex 1H, 19F, and 13C multiplets. This open-source line-shape analysis method analysis of total lineshape (ANATOLIA)1 provides some significant advantages over traditional assign-iterate methods of NMR spectral analysis by avoiding false minima and progressing optimisation to the global minimum. The target molecules are 1-perfluorotol-4-yl-2-perfluorotol-4-yl-oxymethyl-1H-benzimidazole (molecule-I) and 1-tetrafluoropyrid-4-yl-2-tetrafluoropyrid-4-yl-thio-1H-benzimidazole (molecule-II) which were produced as part of a family of fluorinated drug scaffolds prepared for anticancer and antiparasitic screening. Spectra display significant second-order effects with 1H Δδ = 3.68 and 4.67 Hz for the aromatic hydrogen “triplets”, with 19F 4JAA', 4JBB', 4JXX', and 4JYY' coupling constants range from +4.8 to −14.0 Hz and for 13C-isotopomers 19F Δδ of up to 111.56 Hz. A spin-system of six coupling nuclei (HaHbHcHd FYFY') was analysed in 12 s, a spin-system of nine coupling fluorine nuclei (AA'BB'CCC-YY') was analysed within 2 min, and 10 coupling nuclei (XX'YY'ZZZ-BB'-Hd) was optimised in 6 min using a laptop computer. ANATOLIA was also robust enough to be able to yield accurate spectral values from inaccurate input values. In both compounds, a fluorine–fluorine coupling constant was identified between the two fluoro-aromatic rings (FBB' and FYY') of +4.05 and +4.67 Hz and attributed to a through-space interaction. Ab initio structure optimisations and coupling constant calculations provided useful input data for spectral analysis. A modern 19F nuclear magnetic resonance spectrum of perfluorotoluene (octafluorotoluene) and analysis from 1975 was used as a test data set to assess ANATOLIA. 相似文献
65.
Farrokh Gharib Ali Shamel Fatemeh Jaberi Ali Farajtabar 《Journal of solution chemistry》2013,42(5):1083-1095
The solvatochromic properties of the free base and the protonated 5,10,15,20-tetrakis(4-trimethyl-ammonio-phenyl)-porphine tetratosylate (TTMAPP) were studied in pure water, methanol, ethanol, 2-propanol, and their corresponding aqueous mixtures. The correlation of the empirical solvent polarity scale (E T) values of TTMAPP with composition of the solvents were analyzed by the solvent exchange model of Bosch and Roses to clarify the preferential solvation of the probe dyes in the binary mixed solvents. The solvation shell composition effects in preferential solvation of the solute dyes were investigated in terms of both solvent–solvent and solute–solvent interactions and also the local mole fraction of each solvent composition was calculated in the cybotactic region of the probe. The effective mole fraction variation may provide significant physicochemical insights in the microscopic and molecular level of interactions between TTMAPP species and the solvent components and, therefore, can be used to interpret the solvent effect on kinetics and thermodynamics of TTMAPP. 相似文献
66.
Hassan Ali Zamani Rahimi Fatemeh Naghavi‐Reyabbi Fatemeh Arvinfar Ali Imani Alihossien Reza Ganjali Mohammad Faridbod Farnoush Salavati‐Niasari Masoud 《中国化学》2011,29(7):1523-1528
A poly(vinyl chloride) (PVC) membrane sensor for holmium ions was fabricated based on N‐[(Z)‐1‐(2‐thienyl)‐ methylidene]‐N‐[4‐(4‐{[(Z)‐1‐(2‐thienyl)methylidene]amino} phenoxy)phenyl] amine (TPA) as a new ion carrier, acetophenon (AP) as plasticizing solvent mediator and sodium tetraphenyl borate (NaTPB) as an anion excluder. The electrode shows a good selectivity towards Ho3+ ions respect to other inorganic cations, including alkali, alkaline earth, transition and heavy metal ions. The constructed sensor displays a Nernstian behavior (19.5±0.3 mV/decade) over the concentration range of 1.0×10−6 to 1.0×10−2 mol·L−1 with the detection limit of the electrode being 4.6×10−7 mol·L−1 and very short response time (ca. 5 s). It has a useful working pH range of 3.2–9.8 for at least 8 weeks. The electrode was successfully applied as an indicator electrode for the potentiometric titration of a Ho3+ solution with EDTA and holmium determination in some alloys. The proposed sensor accuracy was studied by the determination of Ho3+ in mixtures of three different ions. 相似文献
67.
Majid M. Heravi Hamideh Alinejhad Fatemeh Derikvand Hossein A. Oskooie Bita Baghernejad Fatemeh F. Bamoharram 《合成通讯》2013,43(14):2033-2039
We report here two simple methods for the synthesis of benzo[c]acridine derivatives from three-component, one-pot condensation of 1-naphthylamine, dimedone, and a variety of substituted aldehydes in the presence of a catalytic amount of NH2SO3H or H6P2W18O62 · 18H2O under solvent-free conditions at 120 °C or in refluxing ethanol. 相似文献
68.
Majid M. Heravi Fatemeh Nahavandi Samaheh Sadjadi Hossein A. Oskooie Fatemeh F. Bamoharram 《合成通讯》2013,43(4):498-503
Reaction of aldehydes and 4-hydroxycoumarin in the presence of catalytic amount of silica-supported Preyssler nanoparticles led to synthesis of bis-coumarins in excellent yields. 相似文献
69.
Lida Jahanian Hassan Ali Zamani Fatemeh Joz-Yarmohammadi Hossien Behmadi Mohammad Reza Abedi 《Russian Journal of Electrochemistry》2017,53(5):435-442
The sufficient amounts of bis(salicylaldehyde) thiocarbohydrazone (STCH) as a lipophilic selective element (3%, w/w), sodium nitrobenzene (NB) as a plasticizer (64%, w/w), tetraphenyl borate (NaTPB) as an anionic additive (3%, w/w), and poly vinyl chloride (PVC) as a polymeric matrix (30%, w/w) was employed to form a PVC membrane of a new Pr3+ ions selective sensor to apply as an indicator electrode in analytical applications. The best electrode response was observed in the slope (19.5 ± 0.7 mV per decade) over a wide concentrations from lower (1.0 × 10?6 mol L–1) to higher (1.0 × 10?2 mol L–1) of Pr3+ ion solution with a detection limit of 8.5 × 10–7 mol L–1. This electrode showed the fast response time about 10 second for praseodymium ion concentration range of 1.0 × 10–6 to 1.0 × 10–2 mol L–1, in the pH range of 2.3–7.9. The matched potential method was applied to study the selectivity of electrode toward Pr3+ ions in comparison with many common cations. The results showed the negligible disturbance of all other cations on the proposed praseodymium(III) electrode. The making sensor has been employed successfully as an indicator electrode in the potentiometric titration of praseodymium(III) solution with EDTA at pH 6.0. Moreover the applicability of the sensor was studied in determination of Pr3+ ion in mixtures of different ions. 相似文献
70.
Majid M. Heravi Samaheh Sadjadi Sodeh Sadjadi Hossein A. Oskooie Fatemeh F. Bamoharram 《Ultrasonics sonochemistry》2009,16(6):718-720
Bis(indolyl)alkanes have been synthesised in excellent yields in the presence of catalytic amount of silica-supported Preyssler nano particles as green, reusable and efficient catalyst under ultra sonic irradiation. 相似文献