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   3853篇
  免费   432篇
  国内免费   734篇
化学   4741篇
晶体学   98篇
力学   2篇
综合类   10篇
数学   1篇
物理学   167篇
  2024年   4篇
  2023年   26篇
  2022年   108篇
  2021年   156篇
  2020年   224篇
  2019年   172篇
  2018年   145篇
  2017年   148篇
  2016年   224篇
  2015年   186篇
  2014年   222篇
  2013年   320篇
  2012年   457篇
  2011年   245篇
  2010年   215篇
  2009年   235篇
  2008年   244篇
  2007年   246篇
  2006年   214篇
  2005年   182篇
  2004年   231篇
  2003年   157篇
  2002年   91篇
  2001年   76篇
  2000年   65篇
  1999年   83篇
  1998年   51篇
  1997年   47篇
  1996年   37篇
  1995年   30篇
  1994年   27篇
  1993年   23篇
  1992年   30篇
  1991年   14篇
  1990年   15篇
  1989年   6篇
  1988年   19篇
  1987年   5篇
  1986年   11篇
  1985年   4篇
  1984年   2篇
  1983年   2篇
  1982年   7篇
  1981年   4篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1973年   2篇
  1972年   2篇
排序方式: 共有5019条查询结果,搜索用时 15 毫秒
991.
992.
The synthesis and characterization of lanthanide(III) complexes with the Schiff-base hydrazone, o-hydroxyacetophenone-7-chloro-4-quinoline, (HL) are reported. The complexes were characterized by different physicochemical methods: mass spectrometry, 1H NMR, 13C NMR, and IR, UV-visible, molar conductance and magnetic studies. They have the stoichiometry [Ln(L)2(NO3)]·nH2O where Ln = La(III), Pr(III), Nd(II), Sm(III), Eu(III) and n = 1–3. The spectra of the complexes were interpreted by comparison with the spectrum of the free ligand. The Schiff-base ligand and its metal complexes were tested against one stain Gram +ve bacteria (Staphylococcus aureus), Gram ?ve bacteria (Escherichia coli), and Fungi (Candida albicans). The tested compounds exhibited high antimicrobial activities  相似文献   
993.
A ligand ipdp (ipdp?=?indeno[1′,2′?:?5,6]pyrazino[2,3-i]dipyrido[3,2-a?:?2′,3′-c]phenazine-8-one) and its ruthenium complexes, [Ru(L)2(ipdp)]2+ (L?=?bpy (2,2′-bipyridine), phen (1,10-phenanthroline)), have been synthesized and characterized by elemental analysis, electrospray mass spectra, and 1H NMR. The interaction between the complexes and calf thymus DNA (CT-DNA) has been investigated by spectroscopic methods and viscosity measurements. The results indicate that the complexes can bind to CT-DNA in an intercalative mode. In addition, both complexes promote the photocleavage of plasmid pBR322 DNA under irradiation. The mechanistic studies reveal that singlet oxygen 1O2 plays a significant role in DNA photocleavage.  相似文献   
994.
995.
The reaction of 2-thiazoline-2-thione (TZDSH) with SnR2Cl2 (R=Ph 1, Me 2, Bu 3) in dry ethanol in the presence of sodium ethoxide leads to [SnR2(C3H4NS2)2] (1, 2, and 3), respectively. Reaction between TZDSH and SnPh2Cl2 in dichloromethane and dry ethanol in an inert atmosphere produces [SnPh2Cl2(C3H5NS2)2] (4). The yields of the products were over 80%. These new complexes have been characterized by IR, UV-Vis, multinuclear (1H, 13C, and 119Sn) NMR spectroscopy, and mass spectrometry, as well as elemental analysis.  相似文献   
996.
The reactions of 2-PAMF with metal perchlorates [2-PAMF = (2-pyridylmethylamino)carbonylferrocene] yielded three coordination compounds, M(2-PAMF)2(CH3CH2OH)2(ClO4)2 (M = Co 1, Zn 2, and Cu 3), which were characterized by single crystal X-ray diffraction and IR spectroscopy. Compounds 1 and 2 have similar structures with six-coordinate metals in octahedral geometries. The CuII in 3 possesses a severely distorted octahedral geometry due to Jahn–Teller distortion. Adjacent molecules in the three compounds were linked by intermolecular hydrogen bonds to form a 1-D supramolecular chain.  相似文献   
997.
Four transition metal coordination compounds, {[Co(PPDA)(H2O)2]}n (1), {[Ni(HPPDA)2]}n (2), {[Cd(PPDA)(H2O)]?H2O}n (3), and {Zn(HPPDA)2(H2O)4}n (4), were synthesized by assembling transition metal salts with a semirigid ligand 4-(pyridin-3-yloxy)-phthalic acid (H2PPDA) under hydrothermal conditions. The compounds have been characterized by elemental analyses, IR spectra, TGA, powder X-ray diffraction, and single-crystal X-ray crystallography. Compound 1 exhibits a three-connected 2-D layered structure, 2 shows a (3,6)-connected 2-D layered structure, 3 displays a (3,6)-connected 2-D layered framework based on binuclear units, and 4 is a mononuclear structure, connected to generate a 3-D supramolecular architecture by hydrogen bonds. Compound 2 is thermally stable up to 300 °C. The magnetic properties of 1 and photoluminescent properties of 3 and 4 have been explored.  相似文献   
998.
999.
Three new compounds, [Cd(μ 3 -Hpdh)(μ2-Cl)] n (1), Mn(Hpdh)2(H2O)2 (2) and Zn(Hpdh)2 (H2O)2 (3) (H2pdh =?pyridine-2,3-dicarbo-2,3-hydrazide), have been synthesized and characterized by elemental analysis, IR spectra, TG and single-crystal X-ray diffraction. Under hydrothermal conditions, H2pdh is generated by an in situ acylation of H2pda (H2pda =?pyridine-2,3-dicarboxylic acid) with hydrazine hydrate. Complex 1 features a 2D layer structure constructed by a dinuclear Cd(II) building block. In complexes 2 and 3, hydrogen bonding interactions connect mononuclear structures into 3D supramolecular frameworks.  相似文献   
1000.
Reactions of Al(OPri)3 with LH2 =?[R′C(NYOH)CHC(R)OH] R=R′=CH3, Y =?(CH2)2 (L1H2); R =?CH3, R′ =?C6H5, Y =?(CH2)2 (L2H2); R =?R′ =?CH3, Y =?(CH2)3 (L3H2); R =?CH3, R′ =?C6H5, Y =?(CH2)3 (L4H2), in 1 : 2 molar ratio give mononuclear derivatives of aluminium AlLLH (1a1d). Equimolar reactions of AlLLH with M(OPri)3 (M =?Al and B) yield homo- and hetero-dinuclear derivatives AlLLM(OPri)2 (M=Al=2a2d M=B=3a3d). Reaction of 2a with L1H2 affords AlL1L1AlL1 (4). All these derivatives have been characterized by elemental analysis, molecular weight measurements and plausible structures have been suggested on the basis of IR, NMR [1H, 13C, 27Al and 11B] spectral data and FAB-mass studies of 2b and 3b. Schiff base L1H2 and its mononuclear derivative with aluminium (AlL1L1H) have been screened for their antibacterial activity against Escherischia coli and Bacillus subtilis.  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