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   14230篇
  免费   1240篇
  国内免费   4419篇
化学   14724篇
晶体学   430篇
力学   529篇
综合类   146篇
数学   1721篇
物理学   2339篇
  2024年   130篇
  2023年   170篇
  2022年   379篇
  2021年   370篇
  2020年   427篇
  2019年   380篇
  2018年   369篇
  2017年   435篇
  2016年   495篇
  2015年   405篇
  2014年   670篇
  2013年   1106篇
  2012年   1445篇
  2011年   779篇
  2010年   648篇
  2009年   868篇
  2008年   989篇
  2007年   1059篇
  2006年   977篇
  2005年   959篇
  2004年   870篇
  2003年   721篇
  2002年   628篇
  2001年   502篇
  2000年   503篇
  1999年   470篇
  1998年   408篇
  1997年   363篇
  1996年   354篇
  1995年   344篇
  1994年   305篇
  1993年   221篇
  1992年   275篇
  1991年   204篇
  1990年   159篇
  1989年   118篇
  1988年   88篇
  1987年   64篇
  1986年   67篇
  1985年   48篇
  1984年   34篇
  1983年   19篇
  1982年   23篇
  1981年   11篇
  1980年   7篇
  1979年   3篇
  1978年   4篇
  1977年   5篇
  1972年   2篇
  1936年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
含C=N结构的过渡金属配合物具有抗肿瘤、抗细菌、抗癌等多种生物活性[1].亚胺金属配合物大多具有优异的光电性能和功能性,而且可以通过扩充配合物中心离子的种类、调整自由配体的结构及取代基效应、立体效应和溶剂效应等使其具有结构多样性和性质可调变性,是合成大环配合物、自组装分子及分子器件的重要原料,日益受到物理、化学和材料科学家的关注[2-11].  相似文献   
992.
采用微波辐射加热方法,将2,3-二苯基喹喔啉(DPQ)与水合三氯化铱(IrCl3•H2O)反应,合成了一种新型三环喹喔啉铱配合物[Ir(DPQ)3],通过元素分析,1H NMR和质谱方法对配合物结构进行了表征,并初步研究了配合物的吸收光谱和荧光光谱。结果表明,配合物Ir(DPQ)3在387和458nm处存在单线态1MLCT(金属到配体的电荷跃迁)和三线态3MLCT的吸收;在634nm 处有较强的金属配合物三线态的磷光发射。  相似文献   
993.
A polypyridyl nickel complex of [Ni(phen)(H2O)4]SO4?2H2O (phen = 1,10-phenanthroline) was synthesized and characterized by X-ray diffraction and IR spectroscopy. The results indicated that the central nickel ion is in a distorted octahedral geometry coordinated by two nitrogen atoms from 1,10-phenanthroline and four water molecules. The crystal data for this complex are: a=8.8797(18) Å, b=18.468(4) Å, c=22.081(4) Å, α=90°, β=90°, γ=90°, R 1=0.0533, and wR 2=0.2095. Electrochemical experiments showed that the complex could be reoxidized at a gold electrode under the precondition of electrolysis stripping. According to the results of cyclic voltammetry and coulometry, an electrochemical reaction mechanism was proposed. The DNA binding properties of the complex were further investigated by electronic absorption spectrophotometry and electrochemistry. The binding constant and the binding mode between the two species were estimated based on the spectroscopic and electrochemical results.  相似文献   
994.
The reaction of 2,6-diformyl-4-methylphenol, ethylenediamine and Cu(Ⅱ) in the proportion of 3:2:2 yields a new tetranuclear copper(Ⅱ) complex, [Cu2L]2(ClO4)2.2H2O(H3L= N,N'-bis(4-(3'-formyl-5'-methylsalicyclidene)iminoethyl)-4-methyl-2,6-bimethyliminophenol). The complex has been characterized by ES-MS, IR and X-ray diffraction analysis, and its crystal crystallizes in the triclinic system, space group P1 with a = 10.8673(11), b = 12.0829(12), c = 14.4834(15) А, α= 111.946(2), β= 105.828(2), γ = 99.583(2)°,V= 1618.5(3) А^3, Dc = 1.605 g/cm^3, Z = 2, Mr = 1564.26, F(000) = 800.0,μ(MoKa) = 1.460/mm, S = 1.063, R = 0.0612 and wR = 0.1163 for 6245 observed reflections (I 〉 2σ(I)). The complex is a dimer of dinuclear copper(Ⅱ) acylic enantiomorph subunit [Cu2L]ClO4.H_2O, held together by π…π weak coordination and hydrogen bonding interactions. In addition, the π…π interactions related to phenyl moieties as well as CH=N…π interactions were also found to stabilize the supramolecular architectures in the solid state.  相似文献   
995.
The vinylidenebis(diphenylphosphine) (vdpp) reacts with CuBr to give a tetranuclear complex, [Cu4(μ3-Br)2(μ2-Br)2(μ2-vdpp)2(CH3CN)2]·(CH3CN)2 1. The title complex has crystallo- graphically imposed centrosymmetry and presents a CuaBr4 core with distorted stair-like structure. All copper(I) atoms in 1 assume distorted tetrahedral coordination geometry. The distance of 2.7745(11) A between the two copper centers indicates the presence of ligand-supported Cu…Cu interactions. Crystal data for 1: C_60H_56Br_4Cu_4N_4P_4, Mr= 1530.77, triclinic, space group P1, a = 11.6593(9), b = 11.7181(9), c = 13.8711(11) А, a = 110.1020(10), β = 102.0050(10), γ = 109.8040(10)°, V = 1557.5(2) А^3, Z = 1, Dc = 1.632 g/cm^3, F(000) = 760, λ= 0.71073А, T = 298(2) K, 2θmax = 50.04°,μ= 4.056 mm^-1, S = 1.181, R = 0.0507 and wR = 0.1025.  相似文献   
996.
Under given conditions, two complexes of [Ni(H20)2BEDA]·2H2O 1 and [Ni(Py)2- BEDA]·6H2O 2 (BEDA = bis(3-methoxy-2-pyridyl)ether-6,6′-dicarboxylic acid) have been synthesized and characterized by elemental analysis and X-ray single-crystal diffraction. Crystal data for 1: C14H18NiN2O11, monoelinic C2/c, a = 14.3844(17), b = 12.9900(15), c = 9.6309(11) A, β = 104.3350(10)°, V= 1743.5(4) A3, Z = 4, Dc= 1.711 g/cm^3, F(000) = 928, μ = 1.179 mm^-1, Mr= 449.01, the final R = 0.0228 and wR = 0.0625. Crystal data for 2: C24H32NiN4O13, triclinic P1, a = 9.423(2), b = 11.863(3), c = 13.089(3) A, α = 91.511(3), β = 92.465(3), γ = 100.696(2)°, V = 1435.6(6) A^3, Z = 2, Dc= 1.488 g/cm^3, F(000) = 672, μ = 0.748 mm^-1, Mr= 643.25, the final R = 0.0400 and wR = 0.0975. Interestingly, in the two complexes, lattice water molecules dominate its crystal structures. Therefore, extensive intermolecular hydrogen bonds assemble 1 and 2 into 2D extended sheets and a 3D open framework, respectively. Furthermore, water molecules present in 2 are associated to form water clusters.  相似文献   
997.
A new metal-organic complex [Mn2(PDC)2(bipy)2(H2O)2] (H2PDC = 2,4-pyridine-dicarboxylic acid, bipy = 2,2′-bipyridine) 1 has been hydrothermally synthesized and structurally characterized by elemental analysis, IR spectrum, TG and single-crystal X-ray diffraction. The compound crystallizes in triclinic, space group P ^-1 with a = 7.376(3), b = 9.990(4), c = 11.950(5) A^°, α= 75.217(5), β = 78.052(5), γ = 70.655(5)°, V = 796.0(5)A^°3, C34HE6Mn2N6O10, Mr = 788.49, De = 1.645 g/cm^3,μ(MoKa) = 0.866 mm^-1, F(000) = 235, Z = 1, the final R = 0.0425 and wR = 0.0700 for 1971 observed reflections (I 〉 2σ(I)). In the crystal structure, the manganese atom is six-coordinated by two carboxylate oxygen atoms from two different PDC ligands, one aqua ligand, and three nitrogen atoms from 2,2′-bipy and PDC ligands, giving a distorted octahedral geometry. It exhibits a three-dimensional supramolecular network defined by O-H…O hydrogen-bonding interactions.  相似文献   
998.
王天维 《无机化学学报》2009,25(12):2189-2192
The title linear trinuclear complexes, [Fe3L2(CH3COO)2](L=bis-(salicylidene)-1,3-diaminopropane (salpd) (1) and L=bis-(salicylidene)-1,4-diaminobutane (salbd) (2) were synthesized simply using solvothermal method in methanol and were characterized by X-ray single crystal diffraction. [Fe3L2(CH3COO)2](1) was obtained using salicylaldehyde, 1,3-diaminopropane and Fe(CH3COO)2·4H2O via the above method with monoclinic crystal system and space group of P21/c, and lattice parameters of a=0.945 0(8) nm, b=1.037 0(8) nm, c=1.830 5(14) nm, β=94.357(16)°. The [Fe3L2(CH3COO)2](2) was obtained using1,4-diaminobutane instead of 1,3-diaminopropane while keeping the other conditions the same as that for synthesis of [Fe3L2(CH3COO)2] (1). The [Fe3L2(CH3COO)2](2) was in monoclinic crystal system and space group of P21/c, and lattice parameters of a=0.919 0(5) nm, b=1.675 6(9) nm, c=1.270 0(7) nm, β=95.126(11)°. CCDC: 754930, 1; 754931, 2.  相似文献   
999.
A novel bridged binuclear Cu(II) complex with mixed ligands, di-μ-(2-aminopyridine(N,N′))-bis[(2,6-pyridinedicarboxylate)aquacopper(II)] tetrahydrate, formulated as [Cu(μ-ap)(dipic)(H2O)]2·4H2O (1) (dipic = 2,6-pyridinedicarboxylate, ap = 2-aminopyridine), has been synthesized and characterized by elemental, spectral (IR and UV–Vis.), thermal analysis, magnetic measurements and single crystal X-ray diffraction analysis. The central Cu(II) ion resides on a centre of symmetry in a distorted square-pyramid coordination environment comprising of two N atoms, one from dipic and one from the ap ring, two carboxylate O atoms from dipic, and one O atom from water. Intermolecular N–HO and O–HO hydrogen bonds and π–π stacking interactions seem to be effective in the stabilization of the crystal structure. The free ligands and the complex were also evaluated for their antimicrobial and radical scavenging activities (DPPH = 1,1-diphenyl-2-picrylhydrazyl hydrate) using in vitro microdilution methods. Antimicrobial screening of the free ligands and their complex showed that the free ligands and the complex possess antifungal activity against Candida sp.  相似文献   
1000.
The eco-friendly synthesis, spectroscopic (IR, MS, 1H and 13C NMR) study and biological (cytostatic, antiviral) activity of sodium and potassium benzeneazophosphonate complexes, obtained by reaction in the solid state under microwave irradiation of the alkali salts of ethyl [α-(4-benzeneazoanilino)-N-benzyl]phosphonic acid and [α-(4-benzeneazoanilino)-N-4-methoxybenzyl]phosphonic acid with crown ethers containing 18-membered (dibenzo-18-crown-6 and bis(4′-di-tert-butylbenzo)-18-crown-6), 24-membered (dibenzo-24-crown-8) and 30-membered (dibenzo-30-crown-10) macrocyclic rings, have been described. The simple work-up solvent free reaction is an efficient green procedure for the formation of mononuclear crown ether complexes in which the sodium/potassium ion is bound to oxygen atoms of the macrocycle and the phosphonic acid oxygen. The free crown ethers, alkali benzeneazophosphonate salts and their complexes were evaluated for their cytostatic activity in vitro against murine leukemia L1210, murine mammary carcinoma FM3A and human T-lymphocyte CEM and MT-4 cell lines, as well as for their antiviral activity against a wide variety of DNA and RNA viruses. The investigated compounds showed no specific antiviral activity, whereas all the free crown ethers and their complexes demonstrated cytostatic activity, which was especially pronounced in the case of bis(4′-di-tert-butylbenzo)-18-crown-6 and its complexes.  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