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   147篇
  免费   38篇
  国内免费   51篇
化学   89篇
晶体学   4篇
力学   1篇
综合类   3篇
数学   67篇
物理学   72篇
  2022年   5篇
  2021年   12篇
  2020年   15篇
  2019年   5篇
  2018年   8篇
  2017年   6篇
  2016年   17篇
  2015年   19篇
  2014年   25篇
  2013年   24篇
  2012年   15篇
  2011年   24篇
  2010年   8篇
  2009年   18篇
  2008年   8篇
  2007年   5篇
  2006年   7篇
  2005年   6篇
  2004年   5篇
  2003年   2篇
  2002年   2篇
排序方式: 共有236条查询结果,搜索用时 31 毫秒
1.
The authors present some new criteria for oscillation and asymptotic behavior of solutions of thirdorder nonlinear differential equations with a sublinear neutral term of the form ■where z(t) = x(t)+∫a~b p(t, ξ)x~γ(τ(t, ξ)) dξ, 0 < γ ≤ 1. Under the conditions∫t0~∞ r-1/α(t)dt = ∞ or∫t0~∞ r-1/α(t)dt <∞. The results obtained here extend, improve and complement to some known results in the literature. Examples are provided to illustrate the theorems.  相似文献   
2.
本文首先讨论调截断和Bergman空间 $b_{n}^{2}$ 上拟齐次函数为符号的Toeplitz算子的有限秩乘积问题,其次考察两个以拟齐次函数为符号的Toeplitz算子的换位子与半换位子的有限秩问题.  相似文献   
3.
对BL代数的(∈,∈∨q)-模糊滤子理论作系统研究。首先,在BL代数中引入(∈,∈∨q)-模糊对合滤子和(∈,∈∨q)-模糊结合滤子两类新概念,获得了这两类(∈,∈∨q)-模糊滤子的几个等价刻画。其次,详细讨论了BL代数中各类(∈,∈∨q)-模糊滤子间的关系,证明了一个模糊集为(∈,∈∨q)-模糊布尔(关联)滤子当且仅当它既是(∈,∈∨q)-模糊正关联滤子又是(∈,∈∨q)-模糊对合滤子。最后,以直观图示的方式对BL代数中各类(∈,∈∨q)-模糊滤子间关系进行了总结。  相似文献   
4.
曹洪玉 《结构化学》2015,34(3):441-446
A new dinuclear iron(Ⅲ) complex has been synthesized and structurally characterized by X-ray crystallography: [FeⅢ2(L)(C6H5COO)(SO4)(CH3OH)2]·CH3CN·CH3OH(1, H3 L = N,N'-bis(salicylidene)-1,3-diamino-2-propanol). Complex 1 belongs to orthorhombic space group Pna21 with a = 11.4400(8), b = 22.9705(2), c = 12.5712(9) , V = 3303.5(4) 3, Z = 4, F(000) = 1576, Dc = 1.531 g·cm–3, Mr = 761.36, μ = 1.007 mm–1, S = 1.014, the final R = 0.0505 and wR = 0.1018. The crystal packing is stabilized by intermolecular O–H···O hydrogen bonds, forming an extended one-dimensional chain structure. The temperature dependence of magnetic susceptibility measurement shows that antiferromagnetic interaction is propagated between the metal centers. Fit as dinuclear arrangement gave parameters of J = 19.7 cm-1, g = 1.89 and R2 = 0.9999.  相似文献   
5.
掺杂是调控金刚石性能的一种重要手段。本文采用温度梯度法,在5.6 GPa、1 312 ℃的条件下,选用Fe3P作为磷源进行磷掺杂金刚石大单晶的合成。金刚石样品的显微光学照片表明,随着Fe3P添加比例的增加,金刚石晶体的颜色逐渐变深,包裹体数量逐渐增加,晶形由板状转变为塔状直至骸晶。金刚石晶形的变化表明Fe3P的添加使生长金刚石的V形区向右偏移,这是Fe3P改变触媒特性的缘故。红外光谱分析表明,Fe3P的添加使金刚石晶体中氮含量上升,这说明磷的进入诱使氮原子更容易进入金刚石晶格中。激光拉曼光谱测试表明,随着Fe3P添加比例的增加,所合成的掺磷金刚石的拉曼峰位变化不大,其半峰全宽(FWHM)值变大,这说明磷的进入使得金刚石晶格畸变增加。XPS测试结果显示,随着Fe3P添加比例的增加,金刚石晶体中磷相对碳的原子百分含量也会增加,这意味着添加Fe3P所合成的金刚石晶体中有磷存在。  相似文献   
6.
Research on Chemical Intermediates - The structure and racemization mechanism of l-aspartic acid (l-ASP) and l-ASP-intercalated layered double hydroxide (l-ASP-LDH, with intercalated...  相似文献   
7.
Four D–π–A bipolar molecules with n-butyl-1,8-naphthalimide (BNI) fragments as acceptors, acetylenes as π-spacers, and different aromatic groups as donors have been designed to explore their optical, electronic, and charge transport properties as charge transport and luminescent materials for organic light-emitting diodes (OLEDs). The frontier molecular orbitals (FMOs) and local density of states analysis have turned out that the vertical electronic transitions of absorption and emission are characterized as intramolecular charge transfer (ICT). The calculated results show that their optical and electronic properties are affected by the different donors of the bipolar molecules. Our results suggest that D–π–A 1,8-naphthalimide derivatives with donors triphenylamine (1), 1-nitrobenzene (2), anisole (3), and 4-phenylbenzo[c][1,2,5]thiadiazole (4) fragments are expected to be promising luminescent materials. Furthermore, 24 are expected to be promising candidates for both electron and hole transport materials as well as potential ambipolar charge transport material, whereas BNI and 1 can serve as hole transfer materials only. We have also predicted the mobility of 4 with better performance in three different space groups. On the basis of investigated results, we proposed a rational way for the design of charge transport and/or luminescent materials simultaneously.  相似文献   
8.
Two cobalt(II) and cadmium(II) complexes, [Co(H2DMOPhIDC)2(H2O)2] ? 2H2O (H3DMOPhIDC = 2-(3,4-dimethoxyphenyl)-1H-imidazole-4,5-dicarboxylic acid) (I), [Cd(H2MOPhIDC)2-(Phen)] ? C2H5OH (H3MOPhIDC = 2-(3-dimethoxyphenyl)-1H-imidazole-4,5-dicarboxylic acid, Phen = 1,10-phenanthroline) (II), have been hydro(solvo)thermally synthesized by employing two kinds of organic ligands, H3DMOPhIDC or H3MOPhIDC, respectively. The molecular structures of I and II have been characterized by IR spectra, elemental analyses and single-crystal X-ray diffraction (CIF files CCDC nos. 935845 (I), 935846 (II)). Both complexes show three-dimensional supramolecular structures supported by intermolecular H-bonds. Furthermore, the thermogravimetric and photoluminescent properties of two complexes have been investigated as well.  相似文献   
9.
In the present paper, we introduce some new subclasses of meromorphic starlike,convex, close-to-convex and quasi-convex functions of β-reciprocal in terms of the linear operator using subordination. We obtain the coefficient estimates, convolution properties, integral preserving properties and inclusion relationships of the classes. The results presented here include several results as their special cases.  相似文献   
10.
《Comptes Rendus Chimie》2015,18(12):1289-1296
The structural, electro-optical and charge-transport properties of compound trans-3-(3,4-dimethoxyphenyl)-2-(4-nitrophenyl)prop-2-enenitrile (DMNPN) were studied using quantum chemical methods. The neutral, cation and anion molecular geometries were optimized in the ground state using density functional theory (DFT) at the restricted and unrestricted B3LYP/6-31G** level of theory. The excited state geometries were optimized by applying time-dependent DFT at the TD-B3LYP/6-31G** level of theory. The absorption and fluorescence wavelengths were calculated at the TD-CAM-B3LYP/6-31G** and TD-LC-BLYP/6-31G** levels of theory. The distribution pattern of the charge densities on the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) are discussed. Intramolecular charge transfer was observed from the dimethoxyphenyl to (nitrophenyl)prop-2-enenitrile moieties. The detailed charge-transport behavior of the DMNPN molecule is investigated based on its ionization potential, electron affinity, hole and electron reorganization energies, hole and electron-transfer integrals, and hole and electron intrinsic mobilities. The total/partial densities of states and structure–property relationship are discussed in detail. The higher computed hole intrinsic mobility than electron intrinsic mobility reveals that DMNPN is an efficient hole-transport material.  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