全文获取类型
收费全文 | 141篇 |
免费 | 10篇 |
国内免费 | 3篇 |
专业分类
化学 | 106篇 |
力学 | 16篇 |
数学 | 11篇 |
物理学 | 21篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 13篇 |
2012年 | 11篇 |
2011年 | 12篇 |
2010年 | 6篇 |
2009年 | 11篇 |
2008年 | 6篇 |
2007年 | 6篇 |
2006年 | 7篇 |
2005年 | 5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 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1980年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有154条查询结果,搜索用时 125 毫秒
1.
Toluene was methylated with methanol and disproportionated using catalysts containing different Pt contents (0.2, 0.4 and 0.6%) supported on H‐ZSM‐5 or H‐mordenite (H‐M) zeolites in a fixed‐bed flow‐reactor operated atmospherically at temperatures of 300–500 °C in a flow of hydrogen. Platinum dispersion in the zeolite supports and acid sites strength distribution were evaluated using hydrogen chemisorption (1:1 stoichiometry) and ammonia temperature programmed desorption (TPD) in a differential scanning calorimeter (DSC). Toluene methylation was much faster on all catalysts than toluene disproportionation (DISP). Both reactions were more accelerated using H‐ZSM‐5 containing catalysts than H‐M containing catalysts. The yield of xylenes, and in particular para‐xylene, was significantly influenced by the yield of trimethylbenzenes (TMBs) in product. The selectivities for para‐, ortho‐ and meta‐xylenes production were found largely dependent on the Pt content in the catalysts, particularly when supported on H‐ZSM5‐zeolite. However, using Pt/H‐M catalysts, these selectivities were not strictly controlled by Pt content in the catalysts. 相似文献
2.
The stabilization of polyolefins against γ-sterilization has been studied with single or binary additive system. The present attempt is to utilize synergistic mixtures of stabilizers which are approved for food contact applications. Ethylene-propylene (EP) copolymer has been melt-mixed with hindered amine stabilizers (HAS), phenolic antioxidants and organo-phosphites (hydroperoxide decomposer). Samples were sterilized with different doses of γ-radiation. Stabilization was characterized in terms of changes in the functional groups (oxidation products), tensile properties, yellowing and surface morphology by FTIR spectroscopy, Instron, colorimetry (reflectance) and scanning electron microscopy (SEM), respectively. Results were discussed by comparing the stabilizing efficiency of mixtures with and without phenol system. Among phenol containing systems, where we mostly observe discoloration due to the oxidation of hindered phenol and the combination of secondary HAS, tertiary HAS, organo-phosphite and hindered phenol exhibited improved stabilization efficiency than single or binary additive systems. The mixture of secondary HAS and tertiary HAS, has shown antagonistic effect of stabilization whereas their combination with organo-phosphite has exhibited synergistic effect of stabilization even at higher doses of γ-sterilization. The effects have been explained through the interaction between the stabilizers. 相似文献
3.
[reaction: see text]. Stereocontrolled synthesis of the ABC ring framework of zoanthenol has been achieved. Our studies show that a beta,beta-disubstituted enone can act as a good acceptor of arylpalladium intermediates in the formation of a congested benzylic quaternary carbon center through an intramoleculer Mizoroki-Heck reaction. The cis B/C ring system was stereoselectively converted to the trans-fused framework through a SmI2-promoted deoxygenation of the alpha-hydroxy ketone. 相似文献
4.
In this paper, we have investigated the motion of a heated viscoelastic fluid layer in a rectangular tank that is subjected to a horizontal periodic oscillation. The mathematical model of the current problem is communicated with the linearized Navier–Stokes equation of the viscoelastic fluid and heat equation together with the boundary conditions that are solved by means of Laplace transform. Time domain solutions are consequently computed by using Durbin's numerical inverse Laplace transform scheme. Various numerical results are provided and thereby illustrated graphically to show the effects of the physical parameters on the free-surface elevation time histories and heat distribution. The numerical applications revealed that increasing the Reynolds number as well as the relaxation time parameter leads to a wider range of variation of the free-surface elevation, especially for the short time history. 相似文献
5.
Youssef Ibrahim Moharram El-Hallag Ibrahim Shibl Selim Sameh Mahmoud 《Russian Journal of Electrochemistry》2021,57(6):644-653
Russian Journal of Electrochemistry - Generic products are not identical to their branded equivalents. They are typically off-patent. Therefore, this paper suggests a selective, reliable, and... 相似文献
6.
Journal of Thermal Analysis and Calorimetry - Numerical simulations for the convective transport due to triangular fins within an inclined trapezoidal enclosure that is filled by a nanofluid layer... 相似文献
7.
Nareman Harpy Abdel-Rahman Mohamed A. E. Sallam Abdelsattar M. El Dabour Sameh 《Physics of Particles and Nuclei Letters》2020,17(2):253-259
Physics of Particles and Nuclei Letters - Gamma spectrometry is applied for measurement of natural radioactivity by Hyper-pure germanium (HPGe) systems during the application of bioleaching optimum... 相似文献
8.
A new method for the preparation of 3-amino-2-quinoxalinecarbonitrile ( 1 ) was studied. A successful condensation reaction between bromomalononitrile and o-phenylenediamine in the presence of Lewis acid catalyst (AlCl3) was achieved to produce compound 1 . 相似文献
9.
Sameh E. Shaban Nagdya M. Ibrahiem Sayed A. El-mongy Elsayed E. Elshereafy 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(3):1219-1224
Ten ore samples, two unpurified yellow cake samples and natural uranyl nitrate hexahydrate sample were analyzed by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) method to verify source nuclear material. Samples represent source nuclear material as possible. All samples were scanned at ideal conditions; working distance = 10 mm, voltage = 30 kV, magnification value = × 100, spot size = 50 to screen samples for the presence of uranium and thorium, Also Hyper pure germanium (HPGe) gamma spectrometers were applied to estimate the uranium and thorium contents in Bq/kg (ppm). For the ore samples uranium-238 ranges from 1,049.23 Bq/kg (85.30 ppm) to 2,096.06 Bq/kg (170.41 ppm), uranium-235 ranges from 47.51 to 105.61 Bq/kg and thorium-232 ranges from 22.84 Bq/kg (5.65 ppm) to 41.78 Bq/kg (10.34 ppm). For the yellow cake samples and uranyl nitrate hexahydrate uranium-238 ranges from 42.99 Bq/kg (3.50 ppm) to 71,887.2 Bq/kg (5,844.49 ppm) and thorium-232 is 4.78 Bq/kg (1.83 ppm) and the other two samples are lower than the detection limit. 相似文献
10.