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   5534篇
  免费   161篇
  国内免费   956篇
化学   2854篇
晶体学   2篇
力学   397篇
综合类   190篇
数学   1073篇
物理学   2135篇
  2022年   1篇
  2021年   3篇
  2020年   2篇
  2019年   1篇
  2016年   9篇
  2015年   27篇
  2014年   12篇
  2013年   59篇
  2012年   73篇
  2011年   988篇
  2010年   514篇
  2009年   547篇
  2008年   78篇
  2007年   88篇
  2006年   142篇
  2005年   318篇
  2004年   961篇
  2003年   554篇
  2002年   439篇
  2001年   339篇
  2000年   114篇
  1999年   103篇
  1998年   139篇
  1997年   91篇
  1996年   74篇
  1995年   48篇
  1994年   51篇
  1993年   201篇
  1992年   171篇
  1991年   113篇
  1990年   101篇
  1989年   102篇
  1988年   86篇
  1987年   7篇
  1986年   61篇
  1985年   8篇
  1984年   20篇
  1983年   2篇
  1982年   1篇
  1979年   1篇
  1936年   2篇
排序方式: 共有6651条查询结果,搜索用时 31 毫秒
71.
Two new compounds with microporous Co3[MnMo9O32].15H2O(1) and Cu3[MnMo9O32].15H2O(2) have been synthesized,and characterized by IR,element analysis,TG and single-crystal X-ray analysis.The structure analyses reveal that compounds 1 and 2 are isostructural.In crystal,the Waugh-type polyoxoanions [MnMo9O32]6-are connected by Co2+ or Cu2+ cations to a 3D open-framework,which possesses channels along the [1 2 2] direction of approximately 8.27 × 11.97 .The photocatalytic performances of compounds 1 and 2 for p...  相似文献   
72.
Rigid trigonal tris(3-pyridylduryl)borane L was synthesized through four steps in good overall yield from readily available 1,2,4,5-tetramethylbenzene and was used to construct two porous cadmium(II) complexes Cd(L)X2.G(X = Cl,Br;G = guset molecules),1(Cd(L)Cl2.EtOH.iPrOH.3H2O) and 2(Cd(L)Br2.MeOH.C7H8.3H2O),under mild reaction conditions.1 and 2 are isostructural and featured with 3D porous metal-organoboron framewoks with rtl topology,in which L acts as a 3-connected node while a dicadmium motif serves as...  相似文献   
73.
The optimized geometries of the three complexes between MeHn (Me=Na,Mg,Be;n=1 or 2) and SiH4 have been calculated at the B3LYP/6-311++g**,MP2/6-311++g(3df,3pd) and MP2/aug-cc-pvtz levels,respectively.The red-shift inverse hydrogen bonds (IHBs) based on Si-H,an electron donor,were reported.The calculated binding energies with basis set super-position error (BSSE) correction of the three complexes are-5.98,-8.65 and-3.96 kJ mol-1 (MP2/6-311++g(3df,3pd)),respectively,which agree with the results obtained via M...  相似文献   
74.
Nanocrystalline anatase TiO2 films with indium tin oxide(ITO) coated glass as the film substrate were fabricated through spin-coating technique. The TiO2 pastes were prepared with sodium dodecylbenzenesulfonate(DBS) modified TiO2 nanocrystals, synthesized by sol-hydrothermal processes in advance, together with different amounts of polyethylene glycol(PEG) macromolecules. The as-prepared films were mainly characterized by ultraviolet-visible (UV-Vis) spectroscopy, field emission scanning electron microscopy(...  相似文献   
75.
This paper studies the extraction and identification of ginsenoside Re from ginseng fruits and investigates the effect and mechanism of ginsenoside Re of protecting acute renal ischemia-reperfusion injury in rats.Having been smashed,the ginseng fruits were ultrasonically extracted twice with 95% ethanol for 30min each.Having been concentrated,the solution was dissolved with distilled water and separated by two-column chromatography,of which one was packed with macroporous resin D4020,and the other was packe...  相似文献   
76.
Soluble and ordered ladder like polyphenylsilsesquioxane was synthesized by a two-step sol-gel method including hydrolysis and polycondensation. The procedure was monitored by Fourier transform infrared spectroscopy and the presence of the ladder like structure was confirmed by X-ray techniques. 29Si NMR analysis shows a very narrow half peak width(δ<4) at δ -78.866 of the main chain unit C6H5SiO3/2 of polyphenylsilsesquioxane, indicating that the polyphenylsilsesquioxane has ordered ladder like structures ...  相似文献   
77.
The semi-conductive performances of hot growth film on 316L stainless steel were studied by means of electrochemical impedance spectroscopy(EIS) and Mott-Schottky analysis.The chemical compositions of the hot growth films were detected by X-ray photoelectron spectroscopy(XPS).The results show that the transfer resistance and film resistance increase with increasing temperature to 400℃,then they decrease sharply with further continuously increasing temperature.Formation time plays an important role in determ...  相似文献   
78.
The hydrothermal reaction of Zn(NO3)2·4H2O, cyclohexane-1,2,3,4,5,6-hexacarboxylic acid hydrate (H6LI·H2O, cis-conformation LI: a,e,a,e,a,e) and 2,2'-bpy yielded a new coordination polymer [Zn2(H2LII)(2,2'-bpy)]·2H2O(trans-conformation LII: e,e,e,e,e,e), which was characterized by single-crystal X-ray diffraction, elemental analysis, IR and XRPD(X-ray powder diffraction). This complex crystallized in the triclinic system, with P1 space group and parameters a=0.66922(5) nm, b=0.97291(8) nm, c=1.22184(9) nm, ...  相似文献   
79.
A series of new flavanone derivatives of farrerol was designed and synthesized as a potent inhibitor of vascular smooth muscle cells(VSMCs) vegetation according to a convenient method. The structures of all the synthesized compounds were confirmed by 1H NMR, 13C NMR and EIHR-MS. The biological activities of these compounds against VSMCs in vitro were evaluated. The assay results indicate that two compounds, 5,7-dihydroxy-6,8-dimethyl- 2-(2-nitrophenyl)chroman-4-one(7f) and 2,3-dibromo-4,5-dihydroxydiphenylm...  相似文献   
80.
The present paper covers the various photonic crystals(PhCs) structures mimicking real atom-lattice structures in electronic crystals by using the femtosecond laser-induced two-photon photopolymerization of SU-8 resin. The bandgap properties were investigated by varying the crystal orientations in <111>, <110> and <100> of diamond-lattice PhCs. The photonic stop gaps were present at λ=3.88 μm in <111> direction, λ=4.01 μm in <110> direction and λ=5.30 μm in <100> direction, respectively. In addition, defect...  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