全文获取类型
收费全文 | 202篇 |
免费 | 14篇 |
国内免费 | 4篇 |
专业分类
化学 | 152篇 |
晶体学 | 1篇 |
力学 | 12篇 |
数学 | 20篇 |
物理学 | 35篇 |
出版年
2022年 | 5篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 16篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 16篇 |
2014年 | 22篇 |
2013年 | 22篇 |
2012年 | 24篇 |
2011年 | 15篇 |
2010年 | 16篇 |
2009年 | 14篇 |
2008年 | 14篇 |
2007年 | 3篇 |
2006年 | 5篇 |
2005年 | 2篇 |
2004年 | 2篇 |
2003年 | 4篇 |
2001年 | 2篇 |
1993年 | 1篇 |
1989年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有220条查询结果,搜索用时 15 毫秒
1.
Molecular Diversity - This study describes the use of 3-aminotriazole, different aldehydes and N-methyl-1-(methylthio)-2-nitroethenamine as a ketene N,S-acetal in a three-component condensation for... 相似文献
2.
Shamsipur M Chaichi MJ Karami AR 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(3):511-517
The chemiluminescence arising from the reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO) with hydrogen peroxide in the presence of acriflavine has been studied. The relationship between the chemiluminescence intensity and concentrations of TCPO, H2O2, acriflavine and the base sodium salicylate are reported. The kinetic parameters for the peroxyoxalate-chemiluminescence (PO-CL) of acriflavine were evaluated from the computer fitting of the corresponding chemiluminescence intensity-time plots. 相似文献
3.
Urea-hydrogen peroxide (UHP) was used in the presence of maleic anhydride as mediator in a simple and convenient method for the oxidation in high yield of some thiols to the corresponding disulfides. Peroxymaleic acid formed in situ from the reaction of UHP with maleic anhydride has a key role in this oxidation. Performance of the reaction in various solvents showed that methanol was the solvent of choice at 0 oC. The products were isolated by simple filtration on silica gel. 相似文献
4.
Hossein Filian Alireza Kohzadian Masoud Mohammadi Arash Ghorbani-Choghamarani Amirali Karami 《应用有机金属化学》2020,34(6):e5579
In this research, a rapid, green and efficient protocol for synthesis of bis (pyrazolyl)methane derivatives in the presence of Pd(0)-guanidine@MCM-41 catalysts under solvent-free conditions by the following two methods has been reported: (i) via the one-pot pseudo five-component reaction among phenylhydrazine (2 equivalents), ethyl acetoacetate (2 equivalents) and aromatic aldehydes (1 equivalent); and (ii) the one-pot pseudo three-component reaction between 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (2 equivalents) and aromatic aldehydes (1 equivalent). Some advantages of this protocol include: green conditions, extremely short times, high efficiency, proper one-pot operation, generality of method, easy work-up and recyclability, and reusability of the catalyst up to five times without significant loss in catalytic activity. 相似文献
5.
Reaction pathways of ethylene and carbon monoxide on the singlet and triplet potential energy surfaces (PESs) have been calculated at B3LYP/6-311++G (3df, 3dp), G3B3 and CCSD(T)//B3LYP levels. Reaction mechanisms have been investigated by analysis of various structures. Suggested reaction mechanisms reveal that 3P3(CH2CHCHO) and 3P4(CH3CCHO) are thermodynamically stable adducts with the negative value in Gibbs free energies on the triplet PES. In addition, results show that one intersystem crossing exists between triplet and singlet PESs, which are obtained by scanning of the C–C bond length in 1IN3 and 3IN7 species. 相似文献
6.
A combination of molybdatophosphoric acid and NaNO2 in the presence of wet SiO2 was used as an effective oxidizing agent for the oxidation of 1,2‐dihydroquinolines to their corresponding quinoline derivatives in dichlomethane at room temperature with excellent yields. 相似文献
7.
The activity of [Pd(C6H4CH2 NH2‐κ2‐C‐N)PPh3MOBPPY]OTf complex, A (MOBPPY = 4‐methoxybenzoylmethylenetriphenyl‐ phosphoraneylide), was investigated in the Heck–Mizoroki C? C cross‐coupling reaction under conventional heating and microwave irradiation conditions. The complex is an active and efficient catalyst for the Heck reaction of aryl halides. The yields were excellent using a catalytic amount of [Pd(C6H4CH2 NH2‐κ2‐C‐N)PPh3MOBPPY]OTf complex in N‐methyl‐2‐pyrrolidinone (NMP) at 130 °C and 600 W. In comparison to conventional heating conditions, the reactions under microwave irradiation gave higher yields in shorter reaction times. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd. 相似文献
8.
As a first endeavor, a mixed differential quadrature (DQ) and finite element (FE) method for boundary value structural problems in the context of free vibration and buckling analysis of thick beams supported on two-parameter elastic foundations is presented. The formulations are based on the two-dimensional theory of elasticity. The problem domain along axial direction is discretized using finite elements. The resulting system of equations and the related boundary conditions are discretized in the thickness direction and in strong-form using DQM. The method benefits from low computational efforts of the DQ in conjunction with the effectiveness of the FE method in general geometry and systematic boundary treatment resulting in highly accurate and fast convergence behavior solution. The boundary conditions at the top and bottom surface of the beams are implemented accurately. The presented formulations provide an effective analysis tool for beams free of shear locking. Comparisons are made with results from elasticity solutions as well as higher-order beam theory. 相似文献
9.
Hassan Karami Amir Aminifar Hossein Tavallali Zeinol-Abedin Namdar 《Journal of Cluster Science》2010,21(1):1-9
CdO–ZnO nanocomposite was fabricated by a sol–gel pyrrolysis method based on the poly vinyl alcohol (PVA) polymeric network.
The prepared nanocomposite was carefully characterized using scanning electron microscopy, X-Ray dispersive energy analysis,
ICP-atomic emission spectroscopy, X-Ray diffraction, transmission electron microscopy and UV–visible spectroscopy. The structure,
composition, and morphology of this composite depend on a number of aspects: the amounts of cadmium salt, zinc salt, and PVA
in the initial solution, the solvent composition, and the pyrrolysis temperature. The obtained results showed that the nanocomposite
had excellent linear nanoclusters created from nanograins. Each nanograin was made of a CdO core, completely covered by ZnO
layers. Total diameter of each nanograin was 70–90 nm. 相似文献
10.
Mubasher Jamil K. Karami A. Sheykhi 《International Journal of Theoretical Physics》2011,50(10):3069-3077
Motivated by recent works (Saridakis in Phys. Lett. B 660:138, 2008; Sheykhi in Int. J. Mod. Phys. D 19(3):305, 2010), we investigate the new agegraphic model of dark energy in the framework of RS II braneworld. We also include the case of
variable gravitational constant G in our model. Moreover, we reconstruct the potential and the dynamics of the quintessence, tachyon, K-essence and dilaton
scalar field models according to the evolutionary behavior of the new agegraphic dark energy model in RS II braneworld cosmology
including varying G. 相似文献