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   146篇
  免费   8篇
化学   83篇
力学   1篇
数学   5篇
物理学   65篇
  2020年   2篇
  2019年   2篇
  2018年   7篇
  2017年   3篇
  2016年   2篇
  2015年   2篇
  2014年   4篇
  2013年   6篇
  2012年   13篇
  2011年   7篇
  2010年   5篇
  2009年   6篇
  2008年   10篇
  2007年   7篇
  2006年   3篇
  2005年   4篇
  2004年   6篇
  2003年   5篇
  2002年   6篇
  2001年   3篇
  2000年   6篇
  1999年   8篇
  1998年   1篇
  1997年   2篇
  1996年   3篇
  1995年   2篇
  1994年   6篇
  1993年   6篇
  1992年   2篇
  1991年   1篇
  1986年   2篇
  1985年   4篇
  1984年   2篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1977年   1篇
  1976年   1篇
排序方式: 共有154条查询结果,搜索用时 15 毫秒
51.
Journal of Solid State Electrochemistry - In this work, we report the electrochemical polymerization of novel low bandgap hybrid polymer films based on 3,4-ethylenedioxythiophene containing...  相似文献   
52.
53.
A 1D coordination polymer of manganese(III) with a hydrazone‐based ligand, [Mn2(L)(μ‐OCH3)2(OHCH3)2]n ( 1 ), was synthesized and characterized by elemental analyses and spectroscopic methods {H4L = bis[(2‐hydroxynaphthalen‐1‐yl)methylene]adipohydrazide}. The crystal structure of 1 was determined by X‐ray crystallography. The two dianionic domains of the ligand adopt trans configuration, and each coordinates in a tridentate mode via the O, N, O′‐donor atoms to a MnIII ion forming a dinuclear compound. The methoxy ligands provide an asymmetric bridge between two central manganese atoms, which lead to the formation of a 1D coordination polymer. A 2D supramolecular structure is formed by hydrogen bonding interactions between the 1D chains. Although the methoxy ligands are labile, the polymer preserves its oligonuclearity in the solution. Temperature‐dependent magnetic susceptibility studies proved the presence of a weak antiferromagnetic interaction between manganese(III) ions with J = –3.2 cm–1, which results from axial distortion of the manganese coordination environment. Compound 1 showed catalase‐like activity in disproportionation of H2O2.  相似文献   
54.
55.
The conductivity of styrene‐butadiene‐styrene block copolymers containing different amounts of extraconductive carbon black (CB) was investigated as a function of the mold temperature. The composites exhibited reduced percolation thresholds (between 1.0 and 2.0 vol % CB). The dynamic mechanical analysis characterization revealed that the glass‐rubber‐transition temperatures of both segments were not affected by the CB addition, although the damping of the polybutadiene phase displayed a progressive drop with an increase in the CB concentration. The normalized curves of tan δ/tan δmax (where tan δ represents the value of the loss tangent at any measurement temperature and tan δmax represents the loss tangent peak value at the corresponding temperature Tmax) versus T/Tmax (where T is the temperature and Tmax is the maximum temperature), corresponding to both polystyrene and polybutadiene phases as well as the activation energy related to the glass‐rubber‐transition process, did not present any significant change with the addition of CB. The dielectric analysis revealed the presence of two relaxation peaks in the composite containing 1.5 vol % CB, the magnitude of which was strongly influenced by the frequency, being attributed to interfacial Maxwell‐Wagner‐Sillars relaxations caused by the presence of different interfaces in the composite. The mechanical properties were not affected by the presence of CB at concentrations of up to 2.5 vol %. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2983–2997, 2003  相似文献   
56.
Structural studies on the electron doped Ca1−xYxMnO3 are presented. At 300 K, orthorhombic O-phase was observed in all cases, associated to low electric resistivity and high Curie–Weiss temperature. For samples with x>0.07, structural phase transitions to more distorted orthorhombic and monoclinic phases were found at T<170K. In these phases only weak ferromagnetic interactions were observed.  相似文献   
57.
For the characterization of deposit layers on AISI 316L surfaces in high purity water systems, operating up to 80 °C Mössbauer spectroscopy (ME), scanning electron microscopy (SEM), X-ray fluorescence (XRF) and X-ray photoelectron spectroscopy (XPS) are used. Austenitic steel particles were identified on the surfaces of systems not properly cleaned before start-up. Long exposition of austenitic surfaces to high purity water promotes the build-up, composed by trivalent iron and chromium oxidehydroxides and oxide. The oxidehydroxide phase is located mainly at the solid-water interface, whereas oxide phase is in direct contact with metal. Spheroid-like morphology of particles in these layers and the lack of metal attack suggest that coagulation and crystallization processes are the way for oxide production from existing dissolved species.  相似文献   
58.
Antonio Leyva 《Tetrahedron》2008,64(10):2348-2358
A new method for the synthesis of dienes and enynes containing chiral 1,2-diols is described. The strategy is based on the Pd-catalysed cross-coupling reactions of a series of vinyl and alkynyl asymmetric butanediacetal-protected building blocks. After the coupling, removal of the protecting group leads to the desired functionalised dienes and enynes.  相似文献   
59.
The experimental UV/vis absorption spectrum of ortho-nitrobenzaldehyde (o-NBA) has been assigned by means of MS-CASPT2/CASSCF, TD-DFT, and RI-CC2 theoretical computations. Additional information on the nature of the absorbing bands was obtained by comparing the o-NBA spectrum with that of related compounds, as, e.g., nitrobenzene and benzaldehyde. For wavelengths larger than approximately 280 nm, the absorption spectrum of o-NBA is dominated by a series of weak n pi* absorptions from the NO2 and CHO groups. These weak transitions are followed in energy by a more intense band, peaking at 250 nm and arising from charge transfer pi pi* excitations involving mainly benzene and nitro orbitals. Finally, the most intense band centered at 220 nm has its origin in the overlap of two different absorptions: the first one localized in the NO2 substituent and the second one arising from a charge transfer excitation involving the NO2 and the CHO fragments, respectively.  相似文献   
60.
o-Nitrobenzaldehyde is photolabile because of an irreversible phototautomerization, whereas comparable aromatic compounds function as photoprotectors because the tautomerization is reversible. In this experimental and theoretical study we track down the cause of this difference to the electronic changes that occur during the tautomerization.  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