全文获取类型
收费全文 | 7687篇 |
免费 | 169篇 |
国内免费 | 24篇 |
专业分类
化学 | 5782篇 |
晶体学 | 45篇 |
力学 | 70篇 |
数学 | 1115篇 |
物理学 | 868篇 |
出版年
2020年 | 77篇 |
2019年 | 73篇 |
2016年 | 147篇 |
2015年 | 146篇 |
2014年 | 114篇 |
2013年 | 258篇 |
2012年 | 244篇 |
2011年 | 324篇 |
2010年 | 183篇 |
2009年 | 192篇 |
2008年 | 293篇 |
2007年 | 301篇 |
2006年 | 274篇 |
2005年 | 306篇 |
2004年 | 285篇 |
2003年 | 231篇 |
2002年 | 199篇 |
2001年 | 112篇 |
2000年 | 103篇 |
1999年 | 110篇 |
1998年 | 109篇 |
1997年 | 129篇 |
1996年 | 129篇 |
1995年 | 124篇 |
1994年 | 112篇 |
1993年 | 123篇 |
1992年 | 109篇 |
1991年 | 108篇 |
1990年 | 85篇 |
1989年 | 109篇 |
1988年 | 119篇 |
1987年 | 105篇 |
1986年 | 113篇 |
1985年 | 138篇 |
1984年 | 107篇 |
1983年 | 109篇 |
1982年 | 112篇 |
1981年 | 100篇 |
1980年 | 107篇 |
1979年 | 96篇 |
1978年 | 88篇 |
1977年 | 85篇 |
1976年 | 82篇 |
1974年 | 95篇 |
1973年 | 86篇 |
1971年 | 75篇 |
1961年 | 141篇 |
1960年 | 195篇 |
1959年 | 102篇 |
1958年 | 115篇 |
排序方式: 共有7880条查询结果,搜索用时 15 毫秒
51.
Klaus Brodersen 《Fresenius' Journal of Analytical Chemistry》1958,161(5):370
Ohne Zusammenfassung 相似文献
52.
Optical resolution by counter-current distribution has been demonstrated on a preparative scale for two chiral ferrocene derivatives, e.g. 1.2-(α-oxotetramethylene)ferrocene (1), and 1.2-(α-butenylene)ferrocene (2), resp., in the system cyclohexane—(+)-diethyltartrate. The optical yields were 12 and 1%, resp., and are in good agreement with the values calculated from the partition coefficients of the enantiomers. The optical purity of1 could be increased to 40% by crystallization from cyclohexane. A resolution of1 with an optical yield of 14% was also possible by thin layer partition chromatography on silica gel using the same solvents. 相似文献
53.
Analytical and Bioanalytical Chemistry - 相似文献
54.
55.
Diphenylphosphorylazide N3P(O)(OPh)2 reacts with Pt(PPh3)3, Pt(PPh3)2(C2H4), trans-RhCl(CO)(PPh3)2, Ru(CO)3(PPh3)2, CoCl2(PPh3)2 and CuCl(PPh3)2 to give the azido complexes Pt(PPh3)2(N3)R, Pt(PPh3)2(N3)2R2, the urylene complex RhCl(PPh3)2(RNCONR) and the phosphine imine complexes Ru(CO)3(RPPh3)2, CoCl2(RNPPh3)2, CuCl(RNPPh3)2, respectively, (RP(O)(OPh)2). The oxidative addition of n-C6F13SO2N3 to Pt(PPh3)4 and Pt(PPh3)2(C2H4) affords the complexes Pt(PPh3)2(N3)R and Pt(PPh3)2(N3)2R2, respectively, (RSO2C6F13. The compounds are characterized by elemental analysis and by their IR spectra. 相似文献
56.
Thyagarajan S Shay DT Incarvito CD Rheingold AL Theopold KH 《Journal of the American Chemical Society》2003,125(15):4440-4441
Reaction of TpR,MeCo(I) dinitrogen complexes (R = iPr, tBu) with trimethylsilyl azide yields structurally characterized compounds that imply the formation of reactive intermediates of the type TpR,MeCo=NSiMe3. These cobalt imido species apparently abstract hydrogen from the 3-substituent of the Tp-ligand, leading to the formation of amido complexes accompanied by either Co-C bond formation (R = tBu) or C-C bond formation (R = iPr). 相似文献
57.
Klaus B. Wenzel 《Journal of computational chemistry》1982,3(2):191-207
It is shown that even the CPMET approximation for the contributions of fourfold excitations can be replaced by a more sophisticated method. Furthermore, an approximation is presented for the contributions of threefold excitations which are neglected in CPMET . Finally, it is described how the advantages of different CEPA methods can be united in a single CEPA scheme (called CEPA -U). The various approximations are discussed in terms of Slater determinants, and it is shown how the relatively large amount of details can be handled with the help of computer programs, i.e., how knowledge engineering can be successfully applied here. 相似文献
58.
Azomethine ylide 3 , generated by thermolysis of 3,4-diphenyl-Δ1-1,2,3-triazoline-5,5-dimethyldicarboxylate 1 , can be trapped by isonitriles to give 3-imino-1,4-diphenylazetidine-2,2-dimethyldicarboxylates 5 . The IR, 1H-NMR, 13C-NMR and mass spectral data of the new compounds are discussed. 相似文献
59.
Hans-Dietrich Stachel K. Klaus Harigel Hermann Poschenrieder Hans Burghard 《Journal of heterocyclic chemistry》1980,17(6):1195-1199
Alkyl cyanoacetate, malonate, acetoacetate and methylsulfonyl acetic acid ethyl ester are acylated by alkylidenazlactones. The acyl compounds easily form alkylideneteramic acids by condensations. The acylcyanoacetates 2 isomerize into aminopyrrolinones 3 via acid catalysis. 相似文献
60.
Klaus Burger Elisabeth Windeisen Elisabeth Heistracher Torsten Lange Abdel-Aleem H. Abdel-Aleem 《Monatshefte für Chemie / Chemical Monthly》2002,2(3):41-58
The synthesis of homochiral heterocyclic α-hydroxy acids starting from (S)- and (R)-malic acid using hexafluoroacetone as protecting and activating agent is described. The new compounds are useful building
blocks for peptide and depsipeptide modification. 相似文献