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   2929篇
  免费   173篇
  国内免费   240篇
化学   704篇
晶体学   30篇
力学   167篇
综合类   18篇
数学   1476篇
物理学   947篇
  2024年   4篇
  2023年   30篇
  2022年   48篇
  2021年   72篇
  2020年   61篇
  2019年   63篇
  2018年   57篇
  2017年   87篇
  2016年   67篇
  2015年   83篇
  2014年   98篇
  2013年   231篇
  2012年   106篇
  2011年   156篇
  2010年   114篇
  2009年   171篇
  2008年   180篇
  2007年   231篇
  2006年   175篇
  2005年   167篇
  2004年   139篇
  2003年   135篇
  2002年   134篇
  2001年   92篇
  2000年   88篇
  1999年   113篇
  1998年   111篇
  1997年   82篇
  1996年   45篇
  1995年   32篇
  1994年   27篇
  1993年   17篇
  1992年   27篇
  1991年   16篇
  1990年   9篇
  1989年   12篇
  1988年   13篇
  1987年   7篇
  1986年   5篇
  1985年   5篇
  1984年   8篇
  1982年   5篇
  1981年   4篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
  1977年   2篇
  1975年   2篇
  1973年   1篇
  1969年   2篇
排序方式: 共有3342条查询结果,搜索用时 15 毫秒
921.
A novel coordination polymer {[Zn(ts-gln)(bipy)]3H2O}n (ts-glnH2=N-p-toly-sulfonyl-glutamine,bipy=2,2-bipyridine) has been prepared and structurally characterized by X-ray diffraction method. It crystallizes in orthorhombic,space group P212121 with a=8.2622(5),b=16.6244(10),c=18.2807(10) ,V=2510.9(3) 3,C22H28N4O8SZn,Mr=573.91,Z=4,Dc= 1.518 g/cm3,μ(MoKa)=1.115 mm-1,F(000)=1192,the final R=0.0262 and wR=0.0662 for 5691 independent reflections with Rint=0.0240. The zinc(Ⅱ) atom is coordinated by N(3) and N(4) atoms of a bipy molecule,two carboxylate O(1) and O(2A) and amino N(1) atoms of ts-gln ligands,resulting in a square-pyramidal geometry. The title complex consists of an infinite zigzag chain of zinc(Ⅱ) ions linked by the carboxylate of N-p-tolysulfonyl-glutamine.  相似文献   
922.
Two novel complexes {[Zn(IM4py)2(tp)(H2O)]·2H2O}n 1 and {[Cd(IM4py)2(tp)- (H2O)]·1.25H2O}n 2 (IM4py = 2-(4'-pyridinyl)-4,4,5,5-tetramethylimidazoline-1-oxyl and tp = terephthalate dianion) have been synthesized and characterized by elemental analyses, IR spectrum and single-crystal X-ray diffraction. Crystal data for complex 1: monoclinic, space group C2/c, a = 20.648(7), b = 12.130(4), c = 14.036(4) , β = 106.351(5)o, C32H42N6O9Zn, Mr = 720.09, V = 3373.3(2) 3, Z = 4, Dc = 1.418 g/cm3, μ(MoKα) = 0.790 mm-1, F(000) = 1512, the final R = 0.0407 and wR = 0.0894 for 3480 independent reflections with Rint = 0.0432. Crystal data for complex 2: monoclinic, space group C2/c, a = 21.332(6), b = 12.063(3), c = 14.246(4) , β = 106.704(4)o, C32H40.50N6O8.25Cd, Mr = 753.60, V = 3511.2(2) 3, Z = 4, Dc = 1.426 g/cm3, μ(MoKα) = 0.679 mm-1, F(000) = 1554, the final R = 0.0419 and wR = 0.0961 for 3627 independent reflections with Rint = 0.0440. The framework structures of complexes 1 and 2 are 3-D networks via the hydrogen bonds among 1-D chains. The notable characteristics of the two complexes are that the coordination polyhedron of Zn(II) adopts a rare distorted five-coordinate square pyramidal geometry in 1, and the Cd(II) complex exhibits an unusual distorted seven-coordinate pentagonal bipyramid in 2.  相似文献   
923.
A novel complex Zn(phen)(m-CBA)2(H2O) with m-chlorobenzoic acid (m-CBA), 1,10-phenanthroline (phen) and zinc chloride has been hydrothermally synthesized and characterized. Crystal data for this complex: triclinic, space group P1, a = 0.8361(5), b = 1.2455(7), c = 1.3107(7) nm, α = 115.637(8), β = 91.014(9), γ = 104.857(8)o, V = 1.1763(11) nm3, Dc = 1.623 g/cm3, Z = 2, F(000) = 584, GOOF = 1.078, the final R = 0.0453 and wR = 0.1192. Structure analysis shows that the zinc ion coordinates with two nitrogen atoms of one 1,10-phenanthroline molecule, three oxygen atoms from two m-chlorobenzoic acid molecules and one water molecule, giving a distorted square-pyramidal coordination geometry. The cyclic voltametric behavior of the complex was also investigated.  相似文献   
924.
A new mononuclear Co(Ⅱ) complex, [Co(hmz)2(H2O)4]·2H2O, has been synthesized by the reaction of Co(CH3COO)2·4H2O with 1-(4-hydroxyphenyl)-5-mercaptotetrazole (Hhmz). It crystallizes in the monoclinic system, space group P21/n with a = 13.502(5), b = 6.718(3), c = 13.972(6) (A), β = 117.532(4)°, V = 1123.9(8) (A)3, Z = 2, M r = 553.45, F(000) = 570, Dc = 1.635 g/cm3, μ = 1.008 mm-1, the final R = 0.0272 and wR = 0.0684 for 2194 observed reflections (Ⅰ> 2σ(Ⅰ)). The Co(Ⅱ) is six-coordinated by two nitrogen atoms from two hmz-1 ligands and four water molecules, forming an octahedral geometry. The intermolecular hydrogen bonding and offset-panel π-π stacking interactions between the adjacent molecules extend the compound into a three- dimensional supramolecular framework. The title compound emits strong blue fluorescent light (λem(max) = 427 nm) at room temperature and is red-shifted compared with free ligand Hhmz (λem(max) = 342 nm).  相似文献   
925.
李薇  李昶红  杨颖群  匡云飞 《结构化学》2007,26(9):1057-1060
One novel complex Mn2(phen)2(p-CBA)4(H2O) has been hydrothermally syn- thesized from p-chlorobenzoic acid (p-CBA), 1,10-phenanthroline (phen) and anhydrous man- ganese(Ⅱ) sulfate and then characterized. Crystal data for this complex: monoclinic, space group C2/c, with a = 2.3416(3), b = 1.5604(2), c =1.5605(2) nm, β = 121.048(2)o, V = 4.8849(12) nm3, Dc = 1.510 g/cm3, Mr = 555.26, Z = 8, μ = 0.798 mm-1, F(000) = 2256, GOOF = 1.032, the final R = 0.0393 and wR = 0.0816. The crystal structure shows that two neighboring manganese(Ⅱ ) ions are linked together by two bridge-chelating p-chlorobenzoic groups and one bridging water molecule, forming a cage structure with the Mn–Mn bond distance of 0.3512 nm. Each manganese(Ⅱ ) ion is coordinated by two nitrogen atoms of one 1,10-phenanthroline molecule and four oxygen atoms from three p-chlorobenzoic acid anions and one water molecule, giving a distorted octahedral coordination geometry. The cyclic voltammetric behavior of the complex was also investigated.  相似文献   
926.
The title complex (C26H18CuN2O6, Mr=517.96) has been synthesized by the reaction of α-furanacrylic acid with 1,10-phenanthroline (phen) in the solvent mixture of water and methanol. Crystal data: monoclinic, space group C2/c with a=2.2927(4), b=1.01248(18), c=1.05061(18) nm, β=111.188(3)°, V=2.274(7) nm3, Dc=1.513 g/cm3, Z=4, F(000)=1060,μ=1.007mm-1, R=0.0320 and wR=0.0781. The crystal structural analysis shows that the copper atom is coordinated with four oxygen atoms from two α-furacrylic acids and two nitrogen atoms from 1,10-phenanthroline, giving a distorted octahedral coordination geometry. The result of electrochemical analysis shows that the electron transfer in the electrode reaction is quasi-reversible.  相似文献   
927.
A new metal-organic coordination complex [Zn(H2BPTC)(phen)2]n·3nH2O (BPTC =3,3',4,4'-benzophenone tetracarboxylate, phen = 1,10-phenanthroline) 1 has been obtained from hydrothermal reaction and characterized by elemental analysis, IR, TG and single-crystal X-ray diffraction. In compound 1, the zinc cation is hexa-coordinated with two carboxylate oxygen atoms from one H2BPTC ligand and four nitrogen atoms from two different phen ligands, showing a slightly distorted octahedral geometry. Crystal data: C41H30N4O12Zn, Mr = 836.06, monoclinic,P21/c, a = 14.2714(9), b = 16.9386(10), c = 15.0151(9) (A),β = 101.3420(10)°, V= 3558.8(4) (A)3, Dc= 1.560 g/cm3,μ(MoKα) = 0.766 mm-1, F(000) = 1720, Z = 4, R = 0.0439 and wR = 0.1157 for 4123observed reflections with I > 2σ(I).  相似文献   
928.
在苯溶液中,将2-(2-甲酰基苯氧基)乙酸与二正丁基氧化锡进行脱水反应,获得二正丁基锡二2-(2-甲酰基苯氧基)乙酸酯(1),并经过元素分析、1H NMR和IR及晶体结构测试技术进行了结构表征。结果表明,晶体属于C2/c空间群,晶胞参数:a=3.324 6(7)nm,b=0.484 54(10)nm,c=2.214 7(5)nm,β=131.373(2)°,V=2.677 3(9)nm3,Z=4,F(000)=1 208,Dc=1.467 g/cm3,μ=0.999 mm-1,R1=0.048 8,wR2=0.104 8。结构单元内包含1个独立分子,形成以六配位锡为中心的斜梯形双棱锥构型;分子间的Sn O(0.346 8 nm)配位作用,中心锡原子为八配位,构成以锡为中心的扭曲的六方双锥构型的一维链状桥环化合物。杀菌活性顺序为:化合物1>二丁基氧化锡>2-(2-甲酰基苯氧基)乙酸。  相似文献   
929.
在B3LYP/6-31G(d)水平上研究了B炸药的主要成分--2,4,6-三硝基甲苯(TNT)与环三亚甲基三硝胺(RDX)分子间的相互作用, 得到了10种TNT+RDX的全优化构型. 讨论了稳定构型在几何参数、稳定性、红外光谱和电荷分布上的差异. 借助自然键轨道(NBO)理论揭示了TNT与RDX分子间相互作用的本质, 主要由氢键所贡献. 分子间相互作用能在-3.930~-14.652 kJ•mol-1之间, 经基组叠加误差(BSSE)校正, 相互作用能顺序为VI>III>V>IV>X>I>IX>II>VII>VIII. 对全优化构型进行了热力学性质的分析, 探讨了由单体分子形成混合体系的热力学性质的变化, 结果发现, 形成分子间氢键是个放热过程. 运用Kamlet-Jacobs方程基于理论密度(ρ)估算了混合体系TNT+RDX的爆轰性质爆速(D)和爆压(p), 与文献值进行比较表明理论计算方法和结果是可靠的.  相似文献   
930.
Based on detailed in situ attenuated total‐reflection–surface‐enhanced IR reflection absorption spectroscopy (ATR‐SEIRAS) studies of the methanol oxidation reaction (MOR) on Ru/Pt thin film and commercial Johnson–Matthey PtRu/C, a revised MOR enhancement mechanism is proposed in which CO on Pt sites is irrelevant but instead Pt‐Ru boundary sites catalyze the oxygen insertion reaction that leads to the formation of formate and enhances the direct reaction pathway.  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