全文获取类型
收费全文 | 102篇 |
免费 | 6篇 |
专业分类
化学 | 67篇 |
数学 | 19篇 |
物理学 | 22篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 10篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 11篇 |
2012年 | 6篇 |
2011年 | 12篇 |
2010年 | 2篇 |
2009年 | 5篇 |
2008年 | 4篇 |
2007年 | 2篇 |
2006年 | 2篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1968年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有108条查询结果,搜索用时 15 毫秒
11.
Ruthenium‐Catalyzed Reductive Methylation of Imines Using Carbon Dioxide and Molecular Hydrogen
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Kassem Beydoun Ghazi Ghattas Katharina Thenert Prof. Dr. Jürgen Klankermayer Prof. Dr. Walter Leitner 《Angewandte Chemie (International ed. in English)》2014,53(41):11010-11014
The use of the well‐defined [Ru(triphos)(tmm)] catalyst, CO2 as C1 source, and H2 as reducing agent enabled the reductive methylation of isolated imines, as well as the direct coupling of amines with aldehydes and the subsequent reductive methylation of the in situ formed imines. The method, which afforded the corresponding N‐methyl amines in very good to excellent yields, was also used for the preparation of the antifungal agent butenafine in one step with no apparent waste, thus increasing the atom efficiency of its synthesis. 相似文献
12.
Andy K. W. Ma Ali A. Alghamdi Kassem Tofailli Nicholas M. Spyrou 《Journal of Radioanalytical and Nuclear Chemistry》2012,291(2):353-357
Early detection of the red palm weevils (RPW) is a major challenge in agriculture among all kinds of palm trees due to the
nature of the insect and the difficulty to trace them through their life stages associated with the tree life. Many methods
have been applied for the weevil detection such as X-ray diffraction techniques, fluoroscopy and ultrasound. On the other
hand, the idea of tomography has been used for other purposes such as the determination of the age of the tree and for applied
environmental studies. Such technology can also reveal the weevil in principle. In this study, we explore the use of X-ray
CT for weevil detection with the Monte Carlo method. A model of the stem of a palm tree is developed for simulations. MCNPX
is chosen to carry out the simulations for the radiography tally in the code. The tally records the 2D data of the X-ray beams
irradiating the tree model. An iterative reconstruction method for cone beam CT is applied to obtain the 3D slices of the
tree model. We are exploring the minimum number of projection angles and the detectability of the weevil. We shall also report
the sensitivity of weevil detection using X-ray CT with a large set of simulations with different weevil sizes and tree diameters. 相似文献
13.
A. H. Galmed A. K. Kassem H. Von Bergmann M. A. Harith 《Applied physics. B, Lasers and optics》2011,102(1):197-204
Metals and metal alloys are usually employed as interconnections to guide electrical signals between components into the very
large scale integrated (VLSI) devices. These devices demand higher complexity, better performance and lower cost. Thin film
is a common geometry for these metallic applications, requiring a substrate for rigidity. Accurate depth profile analysis
of coatings is becoming increasingly important with expanding industrial use in technological fields. A number of articles
devoted to LIBS applications for depth-resolved analysis have been published in recent years. In the present work, we are
studying the ability of femtosecond LIBS to make depth profiling for a Ti thin film of thickness 213 nm deposited onto a silicon
(100) substrate before and after thermal annealing. The measurements revealed that an average ablation rates of 15 nm per
pulse have been achieved. The thin film was examined using X-Ray Diffraction (XRD) and Atomic Force Microscope (AFM), while
the formation of the interface was examined using Rutherford Back Scattering (RBS) before and after annealing. To verify the
depth profiling results, a theoretical simulation model is presented that gave a very good agreement with the experimental
results. 相似文献
14.
Diagnosis of lubricating oil by evaluating cyanide and carbon molecular emission lines in laser induced breakdown spectra 总被引:1,自引:0,他引:1
I.Y. Elnasharty A.K. Kassem M. Sabsabi M.A. Harith 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(8):588-593
To prevent engine failure it is essential to change lubricating oil regularly before it loses its protective properties. It is also necessary to monitor the physical and chemical conditions of the oil to reliably determine the optimum oil-change intervals. The present work focuses on studying evolution of the cyanide (CN) and carbon (C2) molecular spectral emission lines in the laser induced breakdown spectra of lubricating oil as a function of its consumption. The intensities of these molecular bands have been taken as indicator of engine oil degradation at certain mileage. Furthermore, the percentage of decay of CN and C2 integral intensity values at the corresponding mileage was calculated in order to relate it to the degree of consumption of the motor oil. Such percentage decay of the CN and C2 integral intensities have been found to increase gradually with increasing mileage which is accompanied with increasing depletion of engine oil. The results of using LIBS technique in the present measurements proved that it is possible to have a direct, straightforward and easy method for prediction of lubricating oil degree of consumption. This may facilitate scheduling the proper time and/or mileage intervals for changing the oil to avoid any possibility of engine failure. 相似文献
15.
Cell shape and spreading of stromal (mesenchymal) stem cells cultured on fibronectin coated gold and hydroxyapatite surfaces 总被引:1,自引:0,他引:1
Dolatshahi-Pirouz A Jensen TH Kolind K Bünger C Kassem M Foss M Besenbacher F 《Colloids and surfaces. B, Biointerfaces》2011,84(1):18-25
In order to identify the cellular mechanisms leading to the biocompatibility of hydroxyapatite implants, we studied the interaction of human bone marrow derived stromal (mesenchymal) stem cells (hMSCs) with fibronectin-coated gold (Au) and hydroxyapatite (HA) surfaces. The adsorption of fibronectin was monitored by Quartz Crystal Microbalance with Dissipation (QCM-D) at two different concentrations, 20 μg/ml and 200 μg/ml, and the fibronectin adsorption experiments were complemented with antibody measurements. The QCM-D results show that the surface mass uptake is largest on the Au surfaces, while the number of polyclonal and monoclonal antibodies directed against the cell-binding domain (CB-domain) on the fibronectin (Fn) is significantly larger on the (HA) surfaces. Moreover, a higher number of antibodies bound to the fibronectin coatings formed from the highest bulk fibronection concentration. In subsequent cell studies with hMSC's we studied the cell spreading, cytoskeletal organization and cell morphology on the respective surfaces. When the cells were adsorbed on the uncoated substrates, a diffuse cell actin cytoskeleton was revealed, and the cells had a highly elongated shape. On the fibronectin coated surfaces the cells adapted to a more polygonal shape with a well-defined actin cytoskeleton, while a larger cell area and roundness values were observed for cells cultured on the coated surfaces. Among the coated surfaces a slightly larger cell area and roundness values was observed on HA as compared to Au. Moreover, the results revealed that the morphology of cells cultured on fibronectin coated HA surfaces were less irregular. In summary we find that fibronectin adsorbs in a more activated state on the HA surfaces, resulting in a slightly different cellular response as compared to the fibronectin coated Au surfaces. 相似文献
16.
Abd El-Moneim Anwar Mohamed Mohamed Abd El-Hady Kassem Mohamed Abd Allah El-Hadidy 《Applied Mathematical Modelling》2011,35(9):4127-4139
This paper investigates a search problem for a brownian target motion on one of n-intersected real lines in which any information of the target position is not available to the searchers all the time. We have n-searchers start searching for the target from the origin that is the intersection point of these lines. Each of the searchers moves continuously along his line in both directions of the starting point. The purpose of this paper is to formulate a search model and find the condition under which the expected value of the first meeting time between one of the searchers and the target is finite. Also, we show the existence of the optimal search plan which minimizes the expected value of the first meeting time and find it. 相似文献
17.
Chiraz Youssef Hamed Ben Ammar Mohamed Belhouchet Kassem Beydoun Ridha Ben Salem Henri Doucet Pierre H. Dixneuf 《Journal of heterocyclic chemistry》2011,48(5):1126-1131
2‐(Arylidene)cyanomethylbenzoxazoles have been prepared in water from benzoxazole‐2‐ylacetonitriles. Using multi‐component reactions, a variety of heterocycles containing benzoxazole and nitrile functionality has been prepared. J. Heterocyclic Chem., (2011). 相似文献
18.
Summary The direct-current resistivity, β, and Hall coefficient,R
H, of lightly dopedn-type InP samples were measured at temperatures (T) down to 12K and magnetic fields up to 4.8 kG. A sharp exponential increase in β, asT was decreased, was observed for temperatures below 80 K. The Hall coefficient showed a similar trend,i.e. R
H increased sharply asT was reduced below 80 K. This is attributed to the freeze-out of conduction electrons onto their donor sites. The donor activation
energy,E
d, calculated from the temperature dependence of the resistivity, was less than the theoretical prediction. An enhanced dielectric
constant would be a possible candidate for such behaviour. The initial decrease in β (asT is reduced) recorded in the higher-temperature region is due to impurity scattering probably combined with lattice scattering.
The authors of this paper have agreed to not receive the proofs for correction. 相似文献
19.
Summary: The good swelling and high loading of poly(vinyl alcohol)-graft-poly(ethylene glycol) (PVA-g-PEG) resins proved to be effective for performing supported proline-catalyzed aldol reactions stereoselectively in a wide range of polar non-protic, protic and non-polar solvents as well as in neat substrate. The catalysts could be recovered by filtration and recycled, without significant loss of activity. The use of poly(vinyl alcohol)-graft-poly(ethylene glycol) matrix improved the solubility of the proline-derived catalysts and expanded the scope of permissible solvents for performing selective aldol chemistry. 相似文献
20.
El-Kady Mohamed Abbas Eman M. H. Salem Marwa S. Kassem Asmaa F. M. Abd El-Moez Sherein I. 《Research on Chemical Intermediates》2016,42(4):3333-3349
Research on Chemical Intermediates - 1,3-Thiazol derivatives have been synthesized via reaction of 1-(1-(5,6-dimethoxy-2-oxobenzo[d]thiazol-3(2H)-yl)propan-2-ylidene)-4-substituted... 相似文献