全文获取类型
收费全文 | 161篇 |
免费 | 4篇 |
专业分类
化学 | 146篇 |
晶体学 | 1篇 |
数学 | 2篇 |
物理学 | 16篇 |
出版年
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2018年 | 1篇 |
2017年 | 6篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 7篇 |
2012年 | 5篇 |
2011年 | 10篇 |
2010年 | 1篇 |
2009年 | 5篇 |
2008年 | 8篇 |
2007年 | 10篇 |
2006年 | 7篇 |
2005年 | 20篇 |
2004年 | 9篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1994年 | 2篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有165条查询结果,搜索用时 31 毫秒
81.
Reactions of metallic Ba with benzofuranol (dbbfoH) or diethylene glycol give homoleptic and homonuclear complexes Ba(dbbfo)(2)(dbbfoH)(2).3dbbfoH and Ba{O(CH(2)CH(2)O)(2)}{O(CH(2)CH(2)OH)(2)}(2) (60-89%). Both compounds and formerly described Ba{O(CH(2)CH(2)O)(2)Me}(2) react with Al(CH(3))(3) to yield trinuclear heterobimetallic low-coordinated barium compounds with structure and geometry depending on the reaction stoichiometry and crystallization procedure. 相似文献
82.
The electronic spectrum of the confacial bioctahedral complex Cs(3)Mo(2)Br(9) has been investigated by single-crystal absorption, Zeeman, and MCD spectroscopies. A total of seven distinct band regions were resolved and assigned to transitions essentially within the t(2)(2)t(2)(2) configuration that arises when the pair of t(2)(z)() orbitals in the t(2)(3)t(2)(3) configuration is decoupled by strong Mo-Mo sigma bonding. The excited state separations, and in particular the orbital g values, are sensitive to Mo-Mo pi bonding and show clearly that the pi bonding is weaker in the bromide than in the chloride complex. 相似文献
83.
Surman J. Majda D. Rafalska-Łasocha A. Kuśtrowski P. Chmielarz L. Dziembaj R. 《Journal of Thermal Analysis and Calorimetry》2001,65(2):445-450
K-promoted hematite catalysts for ethylbenzene dehydrogenation were studied by thermal analysis (TG/DTG) and high-temperature
XRD. The formation of potassium ferrite (K2Fe2O4), considered to be a catalytically active phase, was observed during calcination of the Ce-promoted catalysts. A linear correlation
of the catalytic activity and the temperature of potassium ferrites formation was found.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
84.
Hanafi H. Zoorob Mohamed A. Ismail Lucjan Strekowski 《Journal of heterocyclic chemistry》2001,38(2):359-363
A sodium derivative of 1,3‐dimefhylbarbituric acid or 1,3‐diethyl‐2‐thiobarbituric acid undergoes an efficient monoacylation at C5 by the reaction with ω‐chloroalkanoyl chloride or diacid dichloride in the presence of pyridine in tetrahydrofuran. A nucleophilic displacement of the chlorine in a 5‐chloroacetyl‐bartiburate can be accomplished by using a one‐pot procedure. By contrast, a similar transformation of a 5‐(chlorobutanoyl)barbituric acid requires intramolecular cyclization in the presence of a nonnucleophilic base followed by treatment with a nucleophile of the resultant 5‐[4,5‐dihydro(3H)‐2‐furylidene]barbiturate. 相似文献
85.
W Buchowicz B Herbaczyńska LB Jerzykiewicz T Lis S Pasynkiewicz A Pietrzykowski 《Inorganic chemistry》2012,51(15):8292-8297
A new hexanuclear cyclopentadienylnickel carbide cluster (NiCp)(6)(μ(6)-C) (1) was obtained through the thermolysis of the alkene complex [NiCp(CH(3))(η(2)-CH(2)═CHC(4)H(9))] (4). The X-ray molecular structure of 1 (monoclinic; P2(1)/c; Ni-C(carbide) = 1.767(4)-2.109(4) ?) reveals a highly deformed octahedral arrangement of nickel atoms with two octahedron edges opened (Ni-Ni bonding distances = 2.410(1)-2.623(1) ?, Ni···Ni nonbonding distances = 3.107(2) and 3.108(2) ?). Cluster 1 is the first example of a homoleptic, cyclopentadienylnickel carbide cluster. Moreover, (13)C-labeling studies proved that the carbido ligand in cluster 1 originated from the Ni-bound methyl group. This transformation requires a triple C-H bond activation in the methyl group, which has not been observed so far for late transition metal compounds. 相似文献
86.
Szemik-Hojniak A Deperasiñska I Jerzykiewicz L Sobota P Hojniak M Puszko A Haraszkiewicz N van der Zwan G Jacques P 《The journal of physical chemistry. A》2006,110(37):10690-10698
The crystal structure of 2-butylamino-6-methyl-4-nitropyridine N-oxide (2B6M) was resolved on the basis of X-ray diffraction. Solid 2B6M occurs in the form of a doubly hydrogen-bonded dimer with squarelike hydrogen-bonding network composed of two intra- (2.556(2) A) and two intermolecular (2.891(2) A) N-H...O type hydrogen bonds. The molecule thus has both a protonable and a deprotonable group that led us to investigate the possibility of an excited-state proton transfer (ESIPT) reaction in different solvents by means of experimental absorption, steady state, and time-resolved emission spectroscopy. The results were correlated with quantum mechanical TD-DFT and PM3 calculations. Experimental and theoretical findings show the possibility of an ESIPT reaction in polar solvents. It is demonstrated that in particular the emission spectra of 2B6M are very sensitive to solvent properties, and a large value of the Stokes shift (about 8000 cm(-1)) in acetonitrile is indicative for an ESIPT process. This conclusion is further supported by time-resolved fluorescence decay measurents that show dual exponential decay in polar solvents. Vertical excitation energies calculated by TD-DFT reproduce the experimental absorption maxima in nonpolar solvents well. The majority of electronic transitions in 2B6M is of pi --> pi* character with a charge shift from the electron-donating to the electron-accepting groups. The calculations show that, due to the charge redistribution on excitation, the acidity of the amino group increases significantly, which facilitates the proton transfer from the amino to the N-oxide group in the excited state. 相似文献
87.
Lucjan Strekowski Koen Van Aken Yuri Gulevich 《Journal of heterocyclic chemistry》2000,37(6):1495-1499
A number of 3,4,5,6‐tetrahydro‐1H‐azepino[5,4,3‐cd]indole derivatives have been synthesized starting with methyl indole‐4‐carboxylate functionalized at the 3 position. 相似文献
88.
Lucjan Piela 《中国科学:化学(英文版)》2014,57(10):1383-1392
Electrons are believed to avoid one another in space (correlation) due to the Coulomb repulsion and/or the Pauli exclusion principle. It is shown, using examples of two-electron systems, that indeed the mean electron-electron distance increases in case of the ground electronic state as compared to the independent electron model. It is demonstrated however that there exist excited states, often of low energy, in which the electrons, while having a lot of free physical space (with nuclei being absent), choose to be close to each other in their motion (“anticorrelation”), as if they mutually attracted one another. The source of this effect, quantummechanical in nature, is the orthogonality of the eigenfunctions, that forces the electronic wave functions to differ widely, even at the price of short electron-electron distances. There are also excited states with a mixed behaviour, with complex and often intriguing correlation-anticorrelation patterns. 相似文献
89.
Stability and Reactivity of the Active Assemblies in Modified Graphites Characterized by TPD and TPH
Chmielarz L. Dziembaj R. Jamrozik J. Kargulewicz I. Makowski W. 《Journal of Thermal Analysis and Calorimetry》1999,55(3):867-875
Synthetic graphites, as prepared and modified by sulphonation or acetylation, were doped by Fe-, Co-, Ni- and Ca-nitrates.
Temperature Programmed Desorption (TPD) and Temperature Programmed Hydrogenation (TPH) were applied to characterize thermal
stability and reactivity of the active assemblies formed on the matrix surface. The functional groups lowered the reactivity
of the graphites. Thermally less stabile carboxylic groups decomposed with formation of secondary groups giving more reactive
material. Fe containing as well as sulphonated graphites showed a much lower reactivity than the others. Synergistic effects
of Co/Ca and Ni/Ca were confirmed in the graphite materials.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
90.
Oxazinopurines were obtained in high yield by the reaction of 8-bromotheophylline with morpholinomethyl-, piperidinomethyl- or indolinomethyl-substituted oxiranes without isolation of the intermediate oxazolo[2,3-f]purine. 相似文献