全文获取类型
收费全文 | 13980篇 |
免费 | 641篇 |
国内免费 | 827篇 |
专业分类
化学 | 14463篇 |
晶体学 | 154篇 |
力学 | 6篇 |
综合类 | 27篇 |
数学 | 170篇 |
物理学 | 628篇 |
出版年
2023年 | 106篇 |
2022年 | 274篇 |
2021年 | 318篇 |
2020年 | 441篇 |
2019年 | 367篇 |
2018年 | 299篇 |
2017年 | 309篇 |
2016年 | 383篇 |
2015年 | 287篇 |
2014年 | 358篇 |
2013年 | 836篇 |
2012年 | 1467篇 |
2011年 | 549篇 |
2010年 | 471篇 |
2009年 | 672篇 |
2008年 | 767篇 |
2007年 | 912篇 |
2006年 | 714篇 |
2005年 | 682篇 |
2004年 | 643篇 |
2003年 | 545篇 |
2002年 | 439篇 |
2001年 | 373篇 |
2000年 | 375篇 |
1999年 | 351篇 |
1998年 | 310篇 |
1997年 | 316篇 |
1996年 | 333篇 |
1995年 | 340篇 |
1994年 | 230篇 |
1993年 | 206篇 |
1992年 | 171篇 |
1991年 | 115篇 |
1990年 | 68篇 |
1989年 | 56篇 |
1988年 | 52篇 |
1987年 | 45篇 |
1986年 | 38篇 |
1985年 | 29篇 |
1984年 | 36篇 |
1983年 | 15篇 |
1982年 | 28篇 |
1981年 | 19篇 |
1980年 | 22篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1977年 | 13篇 |
1976年 | 7篇 |
1974年 | 8篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Ibragimov A. G. Khafizova L. O. Zagrebel"naya I. V. Parfenova L. V. Sultanov R. M. Khalilov L. M. Dzhemilev U. M. 《Russian Chemical Bulletin》2001,50(2):292-296
A new method for the synthesis of dialkyl(ethyl)alanes by the reaction of EtAlCl2 with -olefins in the presence of Mg and a catalytic amount of Cp2TiCl2 (Ti(OPri)4, Ti(OBun)4) in THF was developed. 相似文献
992.
Zupančič M. Cerc Korošec R. Bukovec P. 《Journal of Thermal Analysis and Calorimetry》2001,65(3):787-795
The thermal behaviour of Mg(II), Zn(II) and Co(II) compounds of ciprofloxacin was studied by thermogravimetry (TG) and differential
thermal analysis (DTA) in order to determine or to confirm some structural characteristics of substances. The complexes decompose
in two steps: dehydration and pyrolytic decomposition of the anhydrous complexes to form metal oxide or metal fluoride. The
dehydration process of one magnesium(II) compound takes place in two steps suggesting a marked difference in the bonding of
water molecules. The different bonding mode of the ciprofloxacin molecules in both magnesium compounds leads to different
residues of the thermal decompositions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
993.
Mészáros Szécsényi K. Leovac V. M. Jaćimović Ž. K. Češljević V. I. Kovács A. Pokol G. 《Journal of Thermal Analysis and Calorimetry》2001,66(2):573-581
The synthesis of copper(II) chloride complexes with 3,5-dimethylpyrazole, 1-carboxamidine-3,5-dimethylpyrazole, 5-amino-4-carboxamide-1-phenylpyrazole
and 4-acetyl-3-amino-5-methylpyrazole is described. The compounds are characterized by elemental analysis, FT-IR spectroscopy,
thermal methods, magnetic moment and molar conductivity measurements. Thermal decomposition of the dichloro-(3,5-dimethylpyrazole)-copper(II)
complex results in an unstable intermediate with a stochiometric composition. The decomposition of the other compounds is
continuous.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
994.
Liliana N. Trevani Jenene C. Roberts Peter R. Tremaine 《Journal of solution chemistry》2001,30(7):585-622
The spectra of copper(II)–ammonia solutions in 2 mol-kg–1 NH4NO3(aq) were recorded as a function of pH with a new UV–visible flow cell, capable of operating at conditions up to 325°C and 300 bars. Equilibrium constants for the formation of copper(II)–ammonia complexes Cu(NH3)n
2+, 1 n 4, from 30 to 150°C were determined by evolving factor analysis and nonlinear least-squares regression. Measurements at higher temperatures were limited by thermal decomposition of NH4NO3(aq). The formation constants of Cu(NH3)n
2+ decrease with temperature, consistent with extrapolations of literature data from measurements below 100°C. Measurements above 150°C were carried out in 0.5 mol-kg–1 CF3SO3H (aq), at the very high ammonia concentrations required to avoid the precipitation of CuO(s). The spectra are consistent with Cu(NH3)4
2+ as the predominant species, based on extrapolations of peak maxima and molar absorptivities from lower temperatures. Shifts in the spectra of Cu2+ and the Cu(NH3)n
2+ species to higher wavelength and increases in molar absorbance with increasing temperature are discussed in terms of the structure of the complexes. 相似文献
995.
Krzysztof Kurzak Iwona Kuźniarska-Biernacka Barbara Kurzak Julia Jezierska 《Journal of solution chemistry》2001,30(8):709-731
As a part of our general interest in the UV-Vis spectroscopy of multidentate mixed-donor ligands, the (salicylideneethylenediamine)Cu(II) complex has been prepared and characterized by elemental analyses, solubility in common solvents, molar conductivities, and ultraviolet (UV), and visible (Vis) spectroscopy. The combined results of spectrophotometric measurements and EPR spectra, as well as known the X-ray structure for solids, were used to determine the structure of the investigated complex in solutions. The spectra of [Cu(salen)] (H2salen = salicylideneethylenediamine), were measured in various solvents at room temperature, resolved by Gaussian analysis, and angular overlap model (AOM) treated in C
2v symmetry. Because of overparametrization problems, the bis(salicylaldehyde)Cu(II) complex has been characterized and AOM treated. The results of this have been used for AOM studies of [Cu(salen)]. The effect of the solvents upon the - and -bonding ligand abilities is discussed. 相似文献
996.
Eugenijus Urnezius Kin-Chung Lam Arnold L. Rheingold John D. Protasiewicz 《Journal of organometallic chemistry》2001,630(2):193-197
The new terminal phosphinidene complex [Cp2Zr=PDmp(PMe3)] (Dmp=2,6-Mes2C6H3; 1) was prepared in 81% yield by the reaction of [Li(Et2O)][P(H)Dmp] with [Cp2Zr(Me)Cl] in the presence of excess PMe3. Compound 1 reacts with Ph2PCl to produce selectively the sterically congested triphosphane DmpP(PPh2)2 (2) and [Cp2ZrCl2] in high yields. The structure of 2 obtained by X-ray diffraction analysis of a single crystal reveals phosphorus–phosphorus bond lengths of 2.251(2) and 2.234(2) Å and a PPP bond angle of 105.46(6)°. 相似文献
997.
Ekkehard Lindner Ulf Kehrer Manfred Steimann Markus Strbele 《Journal of organometallic chemistry》2001,630(2):3021-274
A series of novel heterobimetallic crown ether-like polyoxadiphosphaplatinaferrocenophanes cis-[1,1′-Fc(CH2O(CH2CH2O)nCH2CH2PPh2)2]PtCl2 (n=1–3) (4a–c) was synthesized in good yield by cyclization of the bis(phosphine) ligands 1,1′-Fc(CH2O(CH2CH2O)nCH2CH2PPh2)2 (n=1–3) (3a–c) and (PhCN)2PtCl2 under high dilution conditions in CH2Cl2. The bisphosphines 3a–c are obtained by reaction of the corresponding diols 1,1′-Fc(CH2O(CH2CH2O)nCH2CH2OH)2 (n=1–3) (1a–c) with: (i) CH3SO2Cl in CH2Cl2 and (ii) LiPPh2 in THF. Although the X-ray crystal structure of 4a shows that the cavity is large enough for the encapsulation of small metal cations, inclusion experiments of 4a–c with Group 1 cations, and Mg2+, or NH4+ in solution applying NMR titration and cyclovoltammetric methods reveal no evidence for the formation of host–guest complexes for 4a,b. In the case of 4c only the addition of Na+ or K+ leads to an insignificant effect. 相似文献
998.
《Polyhedron》2001,20(28):306-3306
Five new complexes of composition [Cu(dpt)Ni(CN)4] (1) (dpt=dipropylenetriamine), [Cu(dien)Ni(CN)4]·2H2O (2) (dien=diethylenetriamine), [Cu(N,N′-dimeen)Ni(CN)4]·H2O (3) (N,N′-dimeen=N,N′-dimethylethylenediamine), [Cu(N,N-dimeen)Ni(CN)4]·H2O (4) (N,N-dimeen=N,N-dimethylethylenediamine) and [Cu(trimeen)Ni(CN)4] (5) (trimeen=N,N,N′-trimethylethylenediamine) have been obtained by the reactions of the mixture of Cu(ClO4)2·6H2O, appropriate amine and K2[Ni(CN)4] in water and have been characterized by IR and UV–Vis spectroscopies and magnetic measurements. The crystal structure of [Cu(dpt)Ni(CN)4] (1) has been determined by single-crystal X-ray analysis. The structure of 1 consists of a one-dimensional polymeric chain ---Cu(dpt)---NC---Ni(CN)2---CN---Cu(dpt)--- in which the Cu(II) and Ni(II) atoms are linked by CN groups. The nickel atom is four coordinate with four cyanide-carbon atoms (two cyano groups are terminal and two cyano groups (in cis fashion) are bridged) in a square-planar arrangement and the copper atom is five coordinate with two cyanide-nitrogen and three dpt-nitrogen atoms, in a distorted square-pyramidal arrangement. The temperature dependence of magnetic susceptibility (2–300 K) was measured for compound 1. The magnetic investigation showed the presence of a very weak antiferromagnetic interaction (J=−0.16 cm−1) between the copper atoms within each chain through the diamagnetic Ni(CN)4 2− ions. 相似文献
999.
1000.
长链烷基二苯基膦—铑配合物催化烯烃氢甲酰化反应研究 总被引:1,自引:0,他引:1
研究了烷基二苯基膦-铑配合物RhCl(CO0(n-C8H17PPh2)2(1)和RhCl(Co)(n-C12H25PPh2)2(2)对1-辛烯氢甲酰化反应的催化性能。结果表明,配合物1比2具有更高的催化活性,而配合物2对生成正构醛的选择性更好;当催化剂浓度或膦/铑比增加时,配合物2催化成正构醛的选择性呈下降趋势,显示出与以PPh3为配体时的不同的性能。 相似文献