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   3687篇
  免费   661篇
  国内免费   414篇
化学   2693篇
晶体学   37篇
力学   472篇
综合类   40篇
数学   534篇
物理学   986篇
  2024年   13篇
  2023年   60篇
  2022年   170篇
  2021年   163篇
  2020年   194篇
  2019年   179篇
  2018年   142篇
  2017年   166篇
  2016年   216篇
  2015年   174篇
  2014年   222篇
  2013年   320篇
  2012年   261篇
  2011年   269篇
  2010年   224篇
  2009年   214篇
  2008年   201篇
  2007年   206篇
  2006年   188篇
  2005年   169篇
  2004年   162篇
  2003年   184篇
  2002年   121篇
  2001年   91篇
  2000年   69篇
  1999年   53篇
  1998年   53篇
  1997年   54篇
  1996年   33篇
  1995年   40篇
  1994年   33篇
  1993年   15篇
  1992年   14篇
  1991年   17篇
  1990年   14篇
  1989年   9篇
  1988年   11篇
  1987年   6篇
  1986年   6篇
  1985年   5篇
  1984年   4篇
  1983年   5篇
  1982年   2篇
  1981年   2篇
  1979年   2篇
  1978年   1篇
  1977年   1篇
  1963年   1篇
  1959年   1篇
  1936年   1篇
排序方式: 共有4762条查询结果,搜索用时 17 毫秒
991.
A one dimensional coordination polymer, [(C7H18N)(Ag2I3)]n((C7H18N)+=Methyltriethylammonium) has been successfully synthesized and characterized by X-ray single-crystal diffraction method. Structure analysis shows that the compound consists of organic cations(Methyltriethylammonium) and inorganic anion chains (Ag2I3)n-. The inorganic moiety consists of AgI4 tetrahedron, which shares the same edges with adjacent AgI4 tetrahedrons to form one-dimensional infinite double chains along a-axis. There exists weak interaction among Ag…Ag atoms in the crystal. Anion chains are surrounded by Methyltriethylammonium cations. Anion chains and cations are in combination with each other by static attracting forces in the crystal to form so-called organic-inorganic hybrid structure. According to the crystal structure data, quantum chemistry calculation with DFT on B3LYP level was used to reveal the electronic structure of title compound. CCDC: 254288.  相似文献   
992.
Organically-modified silicate-phosphate and silicate-phosphite copolymers were prepared through nonaqueous acid–base reaction. The inductive effect of the organic substituent of the starting materials such as organically-modified chlorosilane and phosphorous acid on the acid–base reaction was investigated by 31P NMR measurement and ab initio molecular orbital calculation. The condensation reaction takes place by nucleophilic addition of phosphate ion (or phosphite ion) to chlorosilane through SN2 mechanism to form silicate-phosphate (or phosphite) network. The reactivity of the acid–base pair can be controlled by changing the inductive effect of the organic substituents on the starting materials.  相似文献   
993.
Summary. Two novel compounds, [Co(phen)3]2V4O12·phen·22H2O (1) and [Ni(phen)3]2 V4O12·phen·22H2O (2), were prepared from KVO3–1,10-phenanthroline (phen)–Co(NO3)2, resp. NiCl2–H2O reaction systems. The compounds 1 and 2 are isomorphous and crystallize in triclinic system, space group P-1. Their crystal structures are formed by two types of layers parallel to 001: a cationic one consisting of [MII(phen)3]2+ ions and an anionic one containing the cyclic V4O12 4– anions. The solvate phenanthroline and crystal water molecules are located in the cationic and anionic layers, respectively. The IR spectra of 1 and 2 are consistent with the presence of the cyclic V4O12 4– anions in the complexes.Received November 13, 2002; accepted (revised) February 3, 2003 Published online June 2, 2003  相似文献   
994.
995.
传统的沸石和分子筛微孔晶体材料是指以硅酸盐、硅铝酸盐、磷铝酸盐和无机金属磷酸盐为骨架的晶体材料.近年来,利用刚性和热稳定性较好的有机分子(如芳香多酸和多碱)和金属离子作为结构单元制备出了新型的无机一有机杂化微孔晶体材料.这类晶体材料能够在去除孔道中的溶剂分  相似文献   
996.
有机-无机杂化分离膜研究进展   总被引:1,自引:0,他引:1  
有机-无机杂化膜材料结合了有机膜材料和无机膜材料的优良性能,已成为分离膜材料研究的一个热点。本文以有机、无机组分间相互作用类型对其进行分类,着重介绍组分间以化学键相结合的有机-无机杂化膜的优良特性,总结了影响此类杂化膜结构和性能的主要因素,概括了它在膜分离中的应用,提出了目前研究工作中存在的不足,并做出了简要的述评。  相似文献   
997.
Organic/Inorganic hybrid systems present a promising alternative for the creation of high-performance materials due to their biphasic structure that imparts multifunctional properties. The sol-gel process which initiated with the synthesis of inorganic glasses has now become a synthetic route for organic-inorganic assemblies due to several advantages such as mild processing conditions and the freedom to play with the structures of precursors. This versatility of the low-temperature sol-gel process provides an opportunity to engineer both the phases resulting in a synergistic combination or entirely new set of properties fruitful for different applications. This review highlights the several pathways for synthesis of silica particles, the interfacial modification and the classification of hybrid materials based on the method of incorporation of an inorganic moiety in the organic matrix along with the structure-property relationship, and the characterization to develop a fundamental understanding of the process. The nature of bonding between the two different species greatly affects the hybrid nanostructure and thus, the bulk properties of the system. In particular, acrylate/silica system has been focused due to its distinctive properties such as transparency, gloss, and strength that find large-scale application in the field of coatings, plastics and rubbers.Abbreviations: °: Degree; °C: Degree Celsius; 1H NMR: Proton nuclear magnetic resonance; A°: Angstrom; AHAS: N-(3-acryloxy-2-hydroxyl propyl)-3-amino-propyltriethoxysilane; AIBA: 2,2′-Azobis(2-methylpropionamidine) dihydrochloride; AIBN: 2,2′-Azobis(2-methylpropionitrile); Al: Aluminium; APDMES: Aminopropyldimethylethoxysilane; APTES: 3-Aminopropyltriethoxysilane; ATRP: Atom transfer radical polymerization; CERAMERS: Ceramically Modified Monomers; CTAB: Cetyltrimethylammonium bromide; DFMA: Dodecafluoroheptyl methacrylate; DMF: Dimethylformamide; DPSD: Diphenylsilanediol; FESEM: Field Emission Scanning Electron Microscope; FTIR: Fourier-transform infrared spectroscopy; GPTMS: 3-Glycidoxypropyltrimethoxysilane; HDTMS: Hexadecyltrimethoxysilane; HEMA: 2-Hydroxyethyl methacrylate; HLB: Hydrophilic-Lyophilic Balance; HMDS: Hexamethyldisilazane; HPC: Hydroxypropyl Cellulose; IPN: Interpenetrating Network; KPS: Potassium persulfate; LCST: Lower critical solution temperature; McPTMS: 3-Mercaptopropyltrimethoxysilane; MOI: 2-(methacryloyloxy)ethyl isocyanate; MPEGMA: Monomethoxy-capped poly(ethylene glycol) methacrylate; MPTMS: 3-methacryloxypropyltrimethoxysilane; MTC: 2-(methacryloyl) ethyltrimethylammonium chloride; MTES: Methyltriethoxysilane; MTMS: Methyltrimethoxysilane; NMP: Nitroxide-Mediated Polymerization; ORMOCERs: Organically Modified Ceramics; ORMOSILs: Organically Modified Silica; OTES: Octyltriethoxysilane; OTMS: Octadecyltrimethoxysilane; PAA: Poly(acrylic acid); PDMS: Polydimethylsiloxane; PEO-PPO-PEO: Poly (ethylene oxides)-b-poly (propylene oxides)-b-poly (ethylene oxides); PHPS: Perhydropolysilazane; PMMA: Poly(methyl methacrylate); POSS: Polyhedral Oligomeric Silsesquioxane; PTMO: Poly(tetramethylene oxide); PTMS: Phenyltrimethoxysilane; PTMS: Phenyltrimethoxysilane; PVP: Poly (vinylpyrrolidone); RAFT: Reversible addition- fragmentation chain transfer; Si: Silicon; Sn: Tin; Ta: Tantalum; TBN: 4-(triethoxysilyl)butyronitrile; TEM: Transmission Electron Microscopy; TEMED: N,N,N′,N′-tetramethylethylenediamine; TEOS: Tetraethoxysilane; Tg: Glass-Transition Temperature; THF: Tetrahydrofuran; Ti: Titanium; TMOS: Tetramethoxysilane; UV: Ultraviolet; VTES: Vinyltriethoxysilane; VTMS: Vinyltrimethoxysilane; Zr: Zirconium
  • Highlights
  • Advantages of hybrid systems over the conventional materials

  • Discusses the fundamental aspects of sol-gel chemistry

  • Focusses on a detailed classification of hybrid polymers

  • Covers different synthetic strategies, properties, and applications in diverse fields

  相似文献   
998.
A new cyano-bridged Gadolinium-Iron complex {[Gd(DMF)3(DMSO)(H2O)3](μ-CN)[Fe(CN)5]}·2H2O (DMF=N,N-dimethylformamide; DMSO=dimethylsulfoxide) was synthesized by the grinding reaction method. It crysta-llizes in the triclinic, space group P1 with cell parameters: a=0.90363(2) nm, b=1.250 78(3) nm, c=1.41303(1) nm, α=93.174(1)°, β=94.406(1)°, γ=91.817(2)°, and V=1.588 87(5) nm3, Dc=1.582 g·cm-3, Z=2, Mr=756.72, F(000)=760, μ=2.645 mm-1. The slightly distorted square-antiprism eightfold-coordinated Gd(Ⅲ) and the approxi-mately oriented octahedrally sixfold-coordinated Fe(Ⅲ) are linked by a cyano-bridge group to construct a dinuclear compound. The {[Gd(DMF)3(DMSO)(H2O)3](μ-CN)[Fe(CN)5]} species are held together via hydrogen bonds to form a three-dimensional framework. The Gd(Ⅲ)-Fe(Ⅲ) interaction is antiferromagnetic. CCDC: 223430.  相似文献   
999.
A polyoxometalate‐based inorganic–organic hybrid compound [CoII(2, 2′‐bpy)2]2[Mo8O26] ( 1 ) was synthesized by hydrothermal methods and structurally characterized by IR spectrum, TG analysis and X‐ray diffraction. The compound crystallizes in the monoclinic system, space group P21/n, a = 10.0681(2), b = 16.4467(2), c = 15.7838(3) Å, β = 100.046(1)°, V = 2573.52(8) Å3, Z = 2. The structure of 1 is built up from β‐[Mo8O26]4? subunits covalently linked via [CoII(2, 2′‐bpy)2]2+ fragments into a infinite 1D {[CoII(2, 2′‐bpy)2]2[Mo8O26]} polymer.  相似文献   
1000.
含倍半硅氧烷的杂化聚合物   总被引:25,自引:0,他引:25  
从杂化材料的形成方式 ,说明含倍半硅氧烷类杂化材料是基于化学键合作用形成的分子内杂化体系 ,是一类新型高性能的有机_无机杂化材料。介绍了倍半硅氧烷的结构、合成方法及性能特点 ,重点阐述了多面齐聚倍半硅氧烷类杂化聚合物的性能特点及其发展趋势。  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