全文获取类型
收费全文 | 696篇 |
免费 | 111篇 |
国内免费 | 815篇 |
专业分类
化学 | 1361篇 |
晶体学 | 133篇 |
力学 | 9篇 |
综合类 | 13篇 |
物理学 | 106篇 |
出版年
2024年 | 4篇 |
2023年 | 10篇 |
2022年 | 18篇 |
2021年 | 28篇 |
2020年 | 27篇 |
2019年 | 38篇 |
2018年 | 43篇 |
2017年 | 43篇 |
2016年 | 48篇 |
2015年 | 51篇 |
2014年 | 103篇 |
2013年 | 160篇 |
2012年 | 86篇 |
2011年 | 140篇 |
2010年 | 126篇 |
2009年 | 113篇 |
2008年 | 107篇 |
2007年 | 88篇 |
2006年 | 81篇 |
2005年 | 70篇 |
2004年 | 53篇 |
2003年 | 64篇 |
2002年 | 28篇 |
2001年 | 26篇 |
2000年 | 8篇 |
1999年 | 11篇 |
1998年 | 15篇 |
1997年 | 1篇 |
1996年 | 14篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有1622条查询结果,搜索用时 234 毫秒
991.
One new sandwich-type tetra-nickel substituted polyoxotungsate,[Ni(trien)]4-[Ni4(H2O)2(HPW9O34)2]·4H2O(1,trien=triethylenetetramine),has been hydrothermally synthesized and characterized by IR,elemental analysis,TGA,and single-crystal X-ray diffraction analysis.Crystal data for 1:triclinic,space group P with a=13.279(3),b=13.816(3),c=14.494(4),α=95.403(1),β=113.173(4),γ=93.809(3)o,V=2418.0(10)3,Z=1 and Dc=3.861 g/cm3.X-ray crystallographic study shows that compound 1 is a relatively rare inorganic-organic hybrid polyoxo tungstate constructed from sandwich Ni-substituted polyoxo-anions and nickel complexes. 相似文献
992.
Two new transition metal compounds, [Mn(dpa)2(tmd)2]n (1, H2dpa = 4-hydroxy-phenyl-acetic acid, tmd = 4,4-trimethylenedipyridine) and [Co4(dpa)6(tmd)4(H2O)4]n·nH2O·nCl2 (2), have been synthesized by hydrothermal synthesis. Compound 1 crystallizes in the monoclinic system, space group P21/n with a = 9.828(3), b = 17.493(5), c = 11.616(4), β = 110.146(6)o, V = 1874.9(10)3, C42H42MnN4O6, Mr = 753.74, Z = 2, Dc = 1.335 g/cm3, μ = 0.406 mm–1, F(000) = 790, the final R = 0.1047 and wR = 0.2021 for 2698 observed reflections (I > 2σ(I)). Compound 2 crystallizes in the monoclinic system, space group P21/c with a = 11.7214(13), b = 17.1582(19), c = 24.625(3), β = 103.055(3)o, V = 4824.4(9)3, C100H104Cl2Co4N8O23, Mr = 2094.55, Z = 2, Dc = 1.443 g/cm3, μ = 0.809 mm–1, F(000) = 2180, the final R = 0.0550 and wR = 0.0673 for 4104 observed reflections (I > 2σ(I)). These complexes were characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. The structural analyses show that the two compounds are both one-dimensional chain structures. However, compounds 1 and 2 form threedimensional supramolecular structures by hydrogen bonds, respectively. 相似文献
993.
A novel complex ZnTPPL1·3DMF 1(TPP = tetraphenylporphyrin,L1 = N-(4-(9-carbazolyl) phenyl)-N,N-di(4-pyridyl)amine) was prepared by a hydrothermal method and characterized by elemental analysis,IR,and single-crystal X-ray diffraction analysis.Compound 1 crystallizes in triclinic,space group P1 with a = 13.3082(2),b = 14.3276(2),c = 18.6120(3) ,α = 109.853(1),β = 95.054(1),γ = 98.832(1)°,V = 3260.57(9) 3,Z = 2,Dc = 1.334 g/cm3,C81H69N11O3Zn,Mr = 1309.84,μ(MoKα) = 0.438 mm-1,F(000) = 1372,GOF = 1.159,the final R = 0.0482 and wR = 0.1479 for 12091 observed reflections(Ⅰ 2σ(Ⅰ)).Crystal structure analyses revealed that L1 utilizes one pyridyl N atom to bind Zn via axial coordination,affording a 1:1 complex.The binding constant was estimated to be 1.74(7) × 104 M-1 from electronic spectra measurements. 相似文献
994.
A new organic-inorganic hybrid sandwich-type arsenotungstate[H2dap]2H2[Ni(dap)2] [Ni(dap)2(H2O)2][Ni4(H2O)2(B-α-AsVW9O34)2]·8H2O 1 (dap = 1,2-diaminopropane) has been synthesized by the reaction of Na6[AsIII2W21O69(H2O)]·nH2O, NiCl2·6H2O and dap under hydro- thermal conditions and structurally characterized by elemental analysis, IR spectroscopy, thermo- gravimetric analysis and single-crystal X-ray diffraction. 1 crystallizes in the monoclinic space group P21/n with a = 13.5133(19), b = 19.043(3), c = 17.647(2) , β = 102.585(2)°, V = 4432.0(11) 3, T = 296(2) K, Z = 2, μ = 25.350 mm–1, GOOF = 1.058, R = 0.0353 and wR = 0.0838. The molecular unit of 1 consists of two diprotonated [H2dap]2+ cations, two protons, one four-coordinate [Ni(dap)2]2+ cation, one six-coordinate [Ni(dap)2(H2O)2]2+ cation, one classic tetra-NiII substituted sandwich-type [Ni4(H2O)2(B-α-AsVW9O34)2]10– polyoxoanion and eight lattice water molecules. Furthermore, some reported different types of transition-metal substituted sandwich-type poly- oxoanions are summarized and compared. 相似文献
995.
Two new coordination polymers,[Co(BYBA)2(4,4'-bpy)(H2O)2]·H2O (1) and [Zn(BYBA)2(4,4'-bpy)] (2) (4,4'-bpy=4,4'-bipyridine,BYBAH= 2-benzoylbenzoic acid),have been synthesized by hydrothermal conditions and characterized by single-crystal X-ray diffraction,elemental analyses,IR spectra and fluorescence spectrum.Crystal data for 1:C38H32CoN2O9,Mr= 719.59,monoclinic,space group P2/c,a=22.981(2),b=11.4438(11),c=12.9327(12),β=94.642(1)°,V=3390.0(5)3,Z=4,Dc=1.410 g/cm3,F(000)=1492,R=0.0488 and wR=0.1201;and those for 2:C38H26ZnN2O6,Mr=672.00,triclinic,space group P1,a=8.7032(10),b=11.4882(13),c=16.872(2),α=107.146(1),β=99.055(1),γ=90.851(2)°,V=1588.5(3)3,Z= 2,Dc=1.405 g/cm3,F(000)=692,R=0.0409 and wR=0.0894.Complex 1 exhibits 1D polymeric chains which are linked into a 2D sheet by π···π interactions.Complex 2 is composed by 1D zigzag chains connected through C-H···π stacking interactions to generate a 2D layer. 相似文献
996.
997.
A novel supramolecular compound,{[2-(2-pyridyl)benzimidazoleH2]2·[BiCl6]·Cl},was synthesized by the hydrothermal reaction of o-phenylenediamine and α-pyridinecarboxylic acid with BiCl3 in 6.0 mol·L-1 HCl solution,and characterized by elemental analysis,IR,X-ray single-crystal diffraction and photoluminescence spectroscopy.The crystal (C24H22N6Cl7Bi,Mr= 851.61) belongs to the triclinic system,space group P1 with a =7.2887(18),b =9.548(2),c= 12.469(3),α=85.306(4),β=82.814(4),γ=71.349(4)°,Z=1,V=814.9(3)3,Dc=1.735 g/cm3,μ(MoKα)=6.007 mm-1,F(000)=410,R=0.0307 and wR=0.0787.The bismuth ion and six chlorine ions construct a distorted octahedral configuration.The three-dimensional supramolecular network is built from electrostatic attractions,hydrogen bonds and π-π interaction between the BiCl6 anion,Cl anion and [2-(2-pyridyl)benzimidazoleH2] cation.The photoluminescence spectroscopy study shows that the title compound has a blue fluorescent emission at 450 nm in the solid state. 相似文献
998.
999.
以氨水和盐湖盛产的水氯镁石为原料经过两步反应制备碱式氯化镁。第一步,水氯镁石和氨水反应制备氢氧化镁;第二步,利用氢氧化镁和水氯镁石,通过水热反应得到了具有纤维形貌、结晶较好的碱式氯化镁。应用化学分析、XRD、SEM和FIIR等手段对产物进行测试与表征。化学分析结果表明产物组成为5Mg(OH)2·MgCl2·3H2O。将得到的5Mg(OH)2·MgCl2·3H2O和碱式氯化镁系列标准XRD图对照,未有较好的匹配,且结合化学分析和已报道碱式硫酸镁具有5Mg(OH)2·MgSO4·3H2O物相,因而推测其为新物相;SEM图中5Mg(OH)2·MgCl2·3H2O纤维直径约为0.4 μm,平均长度大于24 μm,长径比大于60;FTIR图谱中3 419 cm-1附近出现了氢键的O-H伸缩振动吸收峰,1 635 cm-1附近出现了游离水中H-O-H的弯曲振动吸收峰。水热合成的5Mg(OH)2·MgCl2·3H2O和常压下的产物相比直径较小,晶形更完整,强度更高。 相似文献
1000.
纳米片组装的Zn_2SnO_4空心八面体分级结构的制备与发光性能(英文) 总被引:1,自引:0,他引:1
以乙酸锌、四氯化锡、氢氧化钠为原料,在200℃用L-赖氨酸辅助合成纳米片组装的锡酸锌(Zn2SnO4)空心八面体分级结构。采用XRD、FESEM、TEM、HRTEM等对样品进行了表征,结果表明产物为立方相的Zn2SnO4,单个八面体的棱长在1~2μm,并且表面以及棱上长有许多尺寸在200~400nm的纳米片。此外,结果还表明,氢氧化钠和L-赖氨酸的加入量对八面体形状的形成起到了决定性的作用。产物的室温光致发光谱图说明所制备的产物在500~600nm有很强的发光性能。 相似文献