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   9005篇
  免费   735篇
  国内免费   400篇
化学   3295篇
晶体学   34篇
力学   407篇
综合类   81篇
数学   2300篇
物理学   1964篇
无线电   2059篇
  2023年   73篇
  2022年   108篇
  2021年   130篇
  2020年   157篇
  2019年   194篇
  2018年   165篇
  2017年   206篇
  2016年   217篇
  2015年   197篇
  2014年   327篇
  2013年   400篇
  2012年   394篇
  2011年   541篇
  2010年   469篇
  2009年   609篇
  2008年   526篇
  2007年   468篇
  2006年   452篇
  2005年   335篇
  2004年   233篇
  2003年   260篇
  2002年   241篇
  2001年   184篇
  2000年   193篇
  1999年   161篇
  1998年   140篇
  1997年   104篇
  1996年   94篇
  1995年   58篇
  1994年   66篇
  1993年   51篇
  1992年   52篇
  1991年   48篇
  1990年   28篇
  1989年   32篇
  1988年   24篇
  1987年   24篇
  1985年   420篇
  1984年   282篇
  1983年   237篇
  1982年   211篇
  1981年   152篇
  1980年   118篇
  1979年   135篇
  1978年   77篇
  1977年   86篇
  1976年   88篇
  1975年   88篇
  1974年   118篇
  1973年   131篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
F. Estevan  P. Lahuerta  I. Solana 《Polyhedron》1985,4(11):1965-1967
This paper reports the reaction of Ag2(mnt) and [(NEt4)Ag(mnt)] (mnt2? = maleonitriledithiolate) with PPh3 and 1,2-bis(diphenylphosph  相似文献   
993.
The 195Pt and 13C chemical shifts (δPt and δc) are reported for platinum(II), platinum(IV) and class II mixed-valence complexes, with general formula [PtL4]X2, cis- and trans-PtL2X2, PtL2X4 and Pt2L4X6 (where L may be thiourea, 2-imidazolidine-thione, tetrahydro 2-pyrimidinethione, thiocaprolactam, pyridine-2-thione and tetramethylthiourea, and X may be Cl or Br). The 195Pt chemical shifts can be understood in view of 13C data in terms of variations of electronegativities and σ-donor abilities of ligands attached to platinum.  相似文献   
994.
Mixed complexes of Pb(II) with some carboxylate ions, viz. tartrate (tart2?), malonate (mal2?) and citrate (citr3?); and imidazole (im) have been studied polarographically at 25°C and at constant ionic strength μ = 2.0 (NaNO3) and at pH 6. The polarographic reduction of the complexes in each case is reversible and diffusion-controlled. Pb(II) forms a single mixed complex with tartrate and imidazole, viz [Pb(tart)(im)] with stability constant log β11 = 4.19; with mal2? and im, three mixed complexes, [Pb(mal)(im)], [Pb(mal)(im)2] and [Pb(mal)2(im)]2? with stability constants log β11 = 4.3, log β12 = 7.3 and log β21 = 5.5 respectively are formed. With citr3? and im a single mixed species, [Pb(citr)(im)]? with stability constant log β11 = 8.0 is formed. Various equilibria involved in the mixed systems have been discussed.  相似文献   
995.
996.
The reaction of LiA1H4 with CO2 or NaHCO3 at elevated temperatures has been investigated. Methane and ethylene are the primary products of each reaction. These molecules are probably the “explosive” reaction products formed when CO2 fire extinguishers are used on LiAlH4 fires.  相似文献   
997.
Ph3TeF is ionic and no evidence is obtained for a covalent form in solvents of relatively low polarity. By contrast significant covalent interaction is seen for Ph2(CH3)Te(OOCR)(R=Ph, o-CH3O·C6H4-, m-NO2·C6H4). Factors influencing the formation and stability of covalent forms of telluronium “salts” are discussed. Phenyl(methyl)telluronium-ortho-phthalate is shown to be a monomer in chloroform solution. The structure of the compound is discussed in relation to NMR and IR data and against the background of previous literature reports of both dimeric and monomeric diorganotellurium-ortho-phthalates.  相似文献   
998.
A pulse ultrasonic nebulizer system capable of reproducibly introducing small sample volumes into a flame for analysis by flame emission spectrometry i  相似文献   
999.
The action of Na2Fe(CO)4 with tin(IV) and germanium(IV) porphyrins affords metal(II) porphyrin complexes [(por)M(II)Fe(CO)4] (por = porphyrinate, M - Sn(II) or Ge(II)). The molecular structure of [(oep)Sn(II)Fe(CO)4] was solved by X-ray diffraction techniques. The molecular structure of [(oep)Sn(II)Fe(CO)4] was solved by X-ray diffraction techniques : the Sn coordination is square pyramidal with the iron in axial position (Sn-Fe = 2.492(1)Å) whereas the Fe coordination is trigonal bipyramidal. Mössbauer parameters provide convincing evidence for the formal zero oxidation state of the iron atom.  相似文献   
1000.
Substitution reactions take place following the photonic excitation of aqueous K4M(CN)8 (where M = Mo or W) in the presence of 1,10-phenanthroline and 2,2-?bipyridyl. Changes in absorbance with time show that the overall reaction is dependent on photochemical activation of potassium octacyanomolybdate(IV) and -tungstate(IV). The species [K2Mo(CN)4(OH)2(phen)], [K2W(CN)4(OH)2(phen)], [K2Mo(CN)4(OH)2(bipy)] and [K2W(CN)4(OH)2(bipy)] exist in solution. The final photosubstitution products [Mo(OH)3(CN)(phen)2] · 2H2O], [Mo(OH)3(CN)(bipy)2] · 3H2O, [W(OH)3(CN)(phen)2] · 2H2O and [W(OH)3(CN)(bipy)2] · H2O have been isolated in the solid state. Their IR spectra have been discussed. The quantum yield of the photosubstitution reactions has been determined and its variation with change of concentration of the complex as well as the H+ ion concentration has been studied.  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