全文获取类型
收费全文 | 198篇 |
免费 | 6篇 |
国内免费 | 3篇 |
专业分类
化学 | 149篇 |
力学 | 5篇 |
数学 | 27篇 |
物理学 | 26篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 13篇 |
2019年 | 5篇 |
2018年 | 12篇 |
2017年 | 7篇 |
2016年 | 23篇 |
2015年 | 4篇 |
2014年 | 14篇 |
2013年 | 18篇 |
2012年 | 12篇 |
2011年 | 6篇 |
2010年 | 14篇 |
2009年 | 6篇 |
2008年 | 8篇 |
2007年 | 13篇 |
2006年 | 9篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
排序方式: 共有207条查询结果,搜索用时 15 毫秒
1.
Ghodratollah Absalan Mohammad Soleimani Mozaffar Asadi Mohammad Bagher Ahmadi 《Analytical sciences》2004,20(10):1433-1436
A new ammonia optical sensor was designed using bis(acetylacetoneethylendiamine)tributylphosphin cobalt(III) tetraphenylborate complex, coated on transparent triacetylcellulose film as membrane. The change in the absorbance of the optode at the maximum wavelength of 408 nm was related to ammonia concentration in aqueous samples. A buffer solution with a pH of 9 (sodium borate-HCl) was used. The optode was fully regenerated in pH 2. The linear dynamic range for determination of ammonia was 3.3 x 10(-4) to 6.9 x 10(-3) mol l(-1) with a detection limit of 5.0 x 10(-5) mol l(-1) and a response time range of 4 - 6 min. This membrane was successfully applied for determination of ammonia in drinking water. 相似文献
2.
In this work, a simple and rapid analytical procedure was applied for simultaneous determination of folic acid (vitamin B0), thiamin (vitamin B1), riboflavin (vitamin B2) and pyridoxal (vitamin B6) based on the absorbance data in the pH range 2.0‐12.0 at 25 °C using parallel factor analysis (PARAFAC). The effect of the pH as the most important factor on the sensitivity of the determination was studied. The spectral data were recorded in 400‐650 nm intervals and a 2‐12 pH range for all four vitamins. The calibration set was constructed in the concentration ranges of 4‐22, 1‐20, 6‐26, and 4‐20 μg mL?;1 for B6,B2,B1 and B0, respectively. The root mean squares errors of prediction for the prediction set, (RMSEP), are 0.65, 0.63, 1.13 and 0.34 for B0,B1,B2 and B6, respectively. The recovery percent for the validation set are in the range of 90.6 to 107.0%. The effect of the experimental conditions and diverse species were discussed. The optimum values of these factors were searched according to the relative standard deviation of the prediction set of mixtures solutions. 相似文献
3.
The equilibrium constants and the thermodynamic parameters were spectrophotometrically measured for the 1:1 adduct formation of [Co(Salen)(PPh3)]ClO4.H2O, and [Co(7,7′-Me2Salen)(PPh3)]ClO4.H2O as acceptors, with P(OR)3 (R = methyl, ethyl, and i-propyl) as donors, in acetonitrile (CH3CN) and dimethylformamide (DMF) as solvents at constant ionic strength (I = 0.1 M NaClO4), and various temperatures (t = 10–50 °C). Our results revealed the following trends: stability of the cobalt(III) Schiff base complexes toward a given phosphite donor, [Co(7,7′-Me2Salen)(PPh3)]+ < [Co(Salen)(PPh3)]+; binding of the donors (phosphites) toward a given cobalt(III) Schiff base complex, P(OEt)3 > P(OMe)3 > P(O-iPr)3; influence of solvent on the stability of a given cobalt(III) Schiff base complex toward a given phosphite donor, CH3CN < DMF. 相似文献
4.
A chemically modified carbon paste electrode with 3,4-tetra pyridinoporphirazinatocobalt(II) (Co(3,4 tppa) was applied to the determination of free cyanide ion. The electrode has a linear range between 1.5 × 10−5 M and 1.0 × 10−2 M with a Nernstian slope of 60 ± 1.5 mV/decade and its detection limit is 9 × 10−6 M. The response time of electrode is 5 min. The proposed electrode was applied successfully for the determination of cyanide in commercially available spring water. Some anions, such as SCN−, I−, Cl−, Br− and oxalate that are usually serious interfering species for most of cyanide selective electrodes, did not have any interfering effect for this proposed electrode. 相似文献
5.
Dissociation equilibria of 4‐(2‐pyridylazo) resorcinol (PAR) in aqueous micellar solutions were determined spectrophotometrically at 25 °C and at the constant ionic strength I = 0.1 M KNO3. For this purpose, the effect of nonionic (Brij‐35, Triton X‐100, Triton X‐114, Triton X‐405), and anionic (SDS) surfactants on the absorption spectra of PAR at different pH values was studied. Results show that the pKa values and pure spectra of each species of PAR are influenced by percentages of a neutral and an anionic surfactant such as Brij‐35, Triton X‐100, Triton X‐114, Triton X‐405 and SDS, respectively, added to the solution of this reagent. 相似文献
6.
Batool Akhlaghinia Mozafar Asadi Elham Safaee Mozhgan Heydarpoor 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2099-2104
Alcohols and phenols are protected with hexamethyldisilazane in the presence of N,N′,N′,N?-tetramethyletra-2,3-pyridinoporphyrazinato copper (II) in good-to-excellent yields at room temperature. 相似文献
7.
8.
Saleh Ashrafi Okhtay Jahanbakhsh Davood Alizadeh Behrooz Salehpour 《Central European Journal of Physics》2013,11(5):560-567
Compton scattering tomography is widely used in numerous applications such as biomedical imaging, nondestructive industrial testing and environmental survey, etc. This paper proposes the use of the genetic algorithm (GA), which utilizes bio-inspired mathematical models, to construct an image of the insides of a test object via the scattered photons, from a voxel within the object. A NaI(Tl) scintillation detector and a 185 MBq 137Cs gamma ray source were used in the experimental measurements. The obtained results show that the proposed GA based method performs well in constructing images of objects. 相似文献
9.
A. S. Tabrizi M. Asadi G. Xie G. Lorenzini C. Biserni 《Journal of Engineering Thermophysics》2014,23(1):27-38
In this paper, the ball valve performance is numerically simulated using an unstructured CFD (Computational Fluid Dynamics) code based on the finite volume method. Navier-Stokes equations in addition to a transport equation for the vapor volume fraction were coupled in the RANS solver. Separation is modeled very well with a modification of turbulent viscosity. The results of CFD calculations of flow through a ball valve, based on the concept of experimental data, are described and analyzed. Comparison of the flow pattern at several opening angles is investigated. Pressure drop behind the ball valve and formation of the vortex flow downstream the valve section are also discussed. As the opening of the valve decreases, the vortices grow and cause higher pressure drop. In other words, more energy is lost due to these growing vortices. In general, the valve opening plays very important roles in the performance of a ball valve. 相似文献
10.
Seyyed Mahmoud Mousavi Hamed Tavakoli Mohammad Samadfam Fatemeh Semnani Zahra Asadi Hamid Sepehrian 《Research on Chemical Intermediates》2013,39(3):951-959
Adsorption and recovery of uranium by nanoporous MCM-41 from aqueous solutions (synthetic solution and uranium conversion facility liquid waste) were investigated by use of a fixed-bed column (1.2 cm diameter and 3.0 cm height). Adsorption was carried out at flow rates 0.2 and 0.5 mL min?1, which correspond to retention times of 10 and 6 min. The maximum breakthrough capacity for uranium ions was achieved by use of nanoporous MCM-41 at the optimum pH of 3.6 and flow rate 0.2 mL min?1 (61.95 μg g?1). The Thomas and Yan models were applied to the experimental data, by use of linear regression, to determine the characteristics of the column for process design. The breakthrough curves calculated from the models were in good agreement with the experimental data. The elution behavior of uranium on nanoporous MCM-41 was studied with different eluents; the results showed that 0.1 M HCl is good eluent for uranium recovery. The regenerated column could be used in a multitude of adsorption–desorption cycles. 相似文献