首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   126篇
  免费   4篇
化学   92篇
晶体学   3篇
数学   2篇
物理学   33篇
  2024年   2篇
  2023年   1篇
  2022年   2篇
  2021年   6篇
  2020年   5篇
  2019年   7篇
  2018年   5篇
  2017年   3篇
  2016年   5篇
  2015年   4篇
  2014年   14篇
  2013年   17篇
  2012年   13篇
  2011年   9篇
  2010年   3篇
  2009年   3篇
  2008年   6篇
  2007年   4篇
  2006年   4篇
  2005年   1篇
  2004年   1篇
  2002年   1篇
  2001年   3篇
  2000年   1篇
  1999年   1篇
  1991年   1篇
  1990年   1篇
  1985年   1篇
  1984年   2篇
  1981年   1篇
  1976年   1篇
  1974年   1篇
  1970年   1篇
排序方式: 共有130条查询结果,搜索用时 15 毫秒
21.
Some novel functionalized dihydropyrido[2,3-d]pyrimidine derivatives 4 were synthesized using a one-pot three-component reaction of 6-aminouracils 1, aryl aldehydes 2 and 3-cyanoacetyl indole 3 using InCl3 as catalyst.  相似文献   
22.
In this paper we investigate the holographic dark energy scenario in higher derivative gravity with a varying gravitational constant. We introduce a kind of energy density from higher derivative gravity which has role of the same as holographic dark energy. We obtain the exact differential equation , which determine the evolution of the dark energy density based on varying gravitational constant G. We also find out a cosmological application of our work by evaluating a relation for the equation of state of dark energy for low redshifts containing varying G correction.  相似文献   
23.
We study the possibility of generating deviations from tri-bimaximal (TBM) neutrino mixing to explain the non-zero reactor mixing angle within the framework of both type I and type II seesaw mechanisms. The type I seesaw term gives rise to the μτ   symmetric TBM pattern of neutrino mass matrix as predicted by generic flavor symmetry models like A4A4 whereas the type II seesaw term gives rise to the required deviations from TBM pattern to explain the non-zero θ13θ13. Considering extremal values of Majorana CP phases such that the neutrino mass eigenvalues have the structure (m1,−m2,m3)(m1,m2,m3) and (m1,m2,m3)(m1,m2,m3), we numerically fit the type I seesaw term by taking oscillation as well as cosmology data and then compute the predictions for neutrino parameters after the type II seesaw term is introduced. We consider a minimal structure of the type II seesaw term and check whether the predictions for neutrino parameters lie in the 3σ range. We also outline two possible flavor symmetry models to justify the minimal structure of the type II seesaw term considered in the analysis.  相似文献   
24.
Saikia  D.  Parnami  Sugam  Borah  J. P. 《JETP Letters》2022,116(7):444-448
JETP Letters - The magnetic properties of Co-doped CdS has been investigated by ab initio calculations using the GGA + U approximation. The study reveals the ferromagnetic ordering of Co-doped CdS...  相似文献   
25.
High-resolution proton-decoupled carbon-13 nuclear magnetic resonance relaxation parameters have been obtained as a function of temperature for a set of completely amorphous polymers, semicrystalline polymers, and a series of ethylene–vinyl acetate copolymers. With these samples the nature of the glass temperature, other postulated amorphous transitions, and the β transition were investigated. For the completely amorphous polymers, the average correlation times depend on temperature according to the Williams–Landel–Ferry relation. Spectral collapse occurs at temperatures whose ratio to Tg is in the range 1.2–1.4 and corresponds to a correlation time of about 10?7s. The loss of resolvable spectra is demonstrated to be a consequence of experimental methods and is not due to the occurrence of another amorphous transition. Both the methylene and methine carbons can be resolved for the ethylenevinyl acetate copolymers. Although the correlation time for the methylene carbon is continuous and resolvable through the β transition region, the methine branch-point resonance is lost. The implication of these results to the molecular nature of the β transition is discussed.  相似文献   
26.
A new series of Brønsted–Lewis acidic diethyldisulfoammonium chlorometallates, [DEDSA][FeCl4] and [DEDSA]2[Zn2Cl6], were synthesized as solid materials from the reaction of [(Et)2N(SO3H)2][Cl] ionic liquid with transition metal chlorides (FeCl3 and ZnCl2) at 80 °C in neat condition for 2 h. The chlorometallates were fully characterized using various spectroscopic and analytical techniques such as Fourier transform infrared, UV–visible and Raman spectroscopies, powder X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray and thermogravimetric analyses, Hammett acidity and elemental analyses. Their catalytic activity was studied as reusable heterogeneous catalysts for the three‐component synthesis of novel 14‐aryl‐7‐(N‐phenyl)‐14H‐dibenzo[a,j]acridines under solvent‐free conditions at 100 °C.  相似文献   
27.
Aza-Michael adducts are obtained in very good yields by the conjugate addition of aliphatic amines to α,β-unsaturated compounds using molecular iodine as catalyst in dichloromethane at room temperature. Aromatic amines were found to be reactive under reflux in toluene.  相似文献   
28.
Study of electron drift velocity caused by Etimes B motion is done with the help of a Mach probe in a dc cylindrical magnetron sputtering system at different plasma discharge parameters like discharge voltage, gas pressure and applied magnetic field strength. The interplay of the electron drift with the different discharge parameters has been investigated. Strong radial variation of the electron drift velocity is observed and is found to be maximum near the cathode and it decreases slowly with the increase of radial distance from the cathode. The sheath electric field, E measured experimentally from potential profile curve using an emissive probe is contributed to the observed radial variation of the electron drift velocity. The measured values of the drift velocities are also compared with the values from the conventional theory using the experimental values of electric and magnetic fields. This study of the drift velocity variation is helpful in providing a useful insight for determining the discharge conditions and parameters for sputter deposition of thin film.  相似文献   
29.
The functionalization of photocatalytic metal oxide nanoparticles of TiO2, ZnO, WO3 and CuO with amine-terminated (oleylamine) and thiol-terminated (dodecane-1-thiol) alkyl-chain ligands was studied under ambient conditions. A high selectivity was observed in the binding specificity of a ligand towards nanoparticles of these different oxides. It was observed that oleylamine binds stably to only TiO2 and WO3, whereas dodecane-1-thiol binds stably only to ZnO and CuO. Similarly, polar-to-nonpolar solvent phase transfer of TiO2 and WO3 nanoparticles could be achieved by using oleylamine, but not dodecane-1-thiol, whereas the opposite holds for ZnO and CuO. The surface chemistry of ligand-functionalized nanoparticles was probed by attenuated total reflectance (ATR)-FTIR spectroscopy, which enabled the occupation of the ligands at the active sites to be elucidated. The photostability of the ligands on the nanoparticle surface was determined by the photocatalytic self-cleaning properties of the material. Although TiO2 and WO3 degrade the ligands within 24 h under both UV and visible light, ligands on ZnO and CuO remain unaffected. The gathered insights are also highly relevant from an application point of view. As an example, because the ligand-functionalized nanoparticles are hydrophobic in nature, they can be self-assembled at the air-water interface to give nanoparticle films with demonstrated photocatalytic as well as anti-fogging properties.  相似文献   
30.
Selective benzene hydroxylation: A periodic mesoporous organosilica embedded with a vanadyl(IV) acetylacetonate complex has been synthesized through a co-condensation method. This system is a catalyst for direct hydroxylation of benzene to phenol, presenting a selectivity of 100?% towards the phenol formation as well as an excellent catalytic recyclability (see scheme).  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号