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排序方式: 共有491条查询结果,搜索用时 15 毫秒
151.
The solubilities of two fatty acids, namely hexadecanoic acid (palmitic acid) and octadecanoic acid (stearic acid) in supercritical carbon dioxide (SCCO2), were determined at T = (328 and 338) K from 12.8 MPa to 22.6 MPa. Three models, namely a thermodynamic model based on the Peng–Robinson equation of state with Kwak and Mansoori mixing rules, a model based on dilute solution theory proposed by Mendez-Santiago and Teja and a new reformulated Chrastil equation model, were used to correlate the solubilities. In all the models, the correlation constants are temperature independent. All the models successfully correlated the experimental results for the solubilities of hexadecanoic acid within 3%. 相似文献
152.
Hexakis(2-pyridyloxy)cyclotriphosphazene (L) is an efficient multisite coordination ligand which binds with transition metal ions to produce dinuclear (homo- and heterometallic) complexes [L(CuCl)(CoCl3)], [L(CuCl)(ZnCl3)], [L(CoCl)(ZnCl3)], and [L(ZnCl2)2]. In these dinuclear derivatives the cyclophosphazene ligand utilizes from five to six nitrogen coordination sites out of the maximum of nine available sites. Further, the spacer oxygen that separates the pyridyl moiety from the cyclophosphazene ring ensures minimum steric strain to the cyclophosphazene ring upon coordination. This is reflected in the near planarity of the cyclophosphazene ring in all the dinuclear derivatives. In the dinuclear heterobimetallic derivatives one of the metal ions [Cu(II) or Co(II)] is hexacoordinate and is bound by the cyclophosphazene in a eta5-gem-N5 mode. The other metal ion in these heterobimetallic derivatives [Co(II) or Zn(II)] is tetracoordinate and is bound in an eta(1)-N(1) fashion. In the homobimetallic derivative, [L(ZnCl2)2], one of the zinc ions is five-coordinate (eta3-nongem-N3), while the other zinc ion is tetracoordinate(eta2-gem-N2). The reaction of L with CuCl2 followed by Co(NO3)2.6H2O yields a trinuclear heterobimetallic complex [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)]. In the formation of this compound an unusual P-O bond cleavage involving one of the phosphorus-pyridyloxy bonds is observed. The molecular structure of [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)] reveals that each of the two the P-O-cleaved L' ligands is involved in binding to Cu(II) to generate the motif L'CuCl. Two such units are bridged by a Co(II) ion. The coordination environment around the bridging Co(II) ion contains four oxygen (two P-O units, one chelating nitrate) and two nitrogen atoms (pyridyloxy nitrogens). 相似文献
153.
Two-terminal thin films of poly(3-hexylthiophene) (P3HT) with a wide electrode separation (150 m) has been studied using current-voltage characteristics at different temperatures. Space-charge-limited conduction (SCLC) with high injection barriers (1.3 eV) has been observed at all temperatures in the low electric field regime. A possible transition from SCLC to injection-limited conduction (ILC) is reported. The experimental results have been compared with the disorder-controlled injection model proposed by Arkhipov et al. [V.I. Arkhipov, H. von Seggern, E.V. Emilianova, Appl. Phys. Lett. 83 (2003) 5074; V.I. Arkhipov, E.V. Emilianova, Y.-H. Tak, H. Bässler, J. Appl. Phys. 84 (1998) 848; V.I. Arkhipov, U. Wolf, H. Bässler, Phys. Rev. B 59 (1999) 7514]. 相似文献
154.
Chandrasekhar S Chandrashekar G Reddy MS Srihari P 《Organic & biomolecular chemistry》2006,4(9):1650-1652
A highly chemoselective conjugate reduction of electron-deficient Michael acceptors, including alpha,beta-unsaturated ketones, carboxylic esters, nitriles and nitro compounds with PMHS in the presence of catalytic B(C6F5)3 is described. 相似文献
155.
P. Chandrasekhar Reddy K. S. S. Prasad B. Rangamannar 《Journal of Radioanalytical and Nuclear Chemistry》1999,241(3):671-674
A rapid and sensitive substoichiometric radiochemical procedure has been developed for the extraction of cobalt with potassium
salts of ethyl, propyl, butyl, pentyl and benzyl xanthates. The relative extractabilities of the cobalt-xanthate complexes
into chloroform and carbon tetrachloride were studied. Substoichiometric quantification methods were developed in each case
and utilised to determine the cobalt content present in standard solutions as well as biological samples. 相似文献
156.
R. P. Tripathi H. C. Verma S. Chandrasekhar S. Ramaswamy 《Hyperfine Interactions》2008,186(1-3):153-160
The paper describes part of the study carried out on the iron bearing phases of china clays collected from different china clay reserves of the country. Chemical assays of the clays as well as the “panned” impurities were determined by standard methods and the rational mineral data was calculated from the composition. XRD and thermal analysis also were carried out to get the mineralogy of the samples. Mössbauer spectral studies were conducted on the iron rich phases separated from the clays by “panning” to get information on the different iron minerals present in these clays. It was observed that Mössbauer spectra of the impurities from the low iron containing clays were qualitatively much different from those of the impurities from the high iron containing clays. 相似文献
157.
Chandrasekhar V Nagendran S Gopal K Steiner A Zacchini S 《Chemical communications (Cambridge, England)》2003,(7):862-863
A 1:2 reaction of Ph3SnOSnPh3 1 with RfCOOH 2 leads to the formation of [Ph2Sn(OH)OC(O)(Rf)]2 3, by means of a facile Sn-C bond cleavage process. 相似文献
158.
Chandrasekhar AV Ramanaiah MV Reddy BJ Reddy YP Rao PS Ravikumar RV 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(9):2115-2121
The iron phosphate minerals satterlyite and gormanite have been investigated by EPR and optical absorption studies. The optical results indicate the presence of ferrous and ferric ions in both minerals. In gormanite the site symmetry of Fe(III) is near octahedral whereas in satterlyite it is tetragonally distorted. On the other hand, the Fe(II) ions are in tetragonally distorted octahedral site in both minerals. In satterlyite the EPR results indicate the presence of the ferric ion in a tetragonally distorted state together with a small percentage of Mn(II). Crystal field (Dq) and interelectronic parameters (B and C) are evaluated. 相似文献
159.
Guimarães CR Repasky MP Chandrasekhar J Tirado-Rives J Jorgensen WL 《Journal of the American Chemical Society》2003,125(23):6892-6899
The rate enhancement provided by the chorismate mutase (CM) enzyme for the Claisen rearrangement of chorismate to prephenate has been investigated by application of the concept of near attack conformations (NACs). Using a combined QM/MM Monte Carlo/free-energy perturbation (MC/FEP) method, 82% and 100% of chorismate conformers were found to be NAC structures in water and in the CM active site, respectively. Consequently, the conversion of non-NACs to NACs does not contribute to the free energy of activation from preorganization of the substrate into NACs. The FEP calculations yielded differences in free energies of activation that well reproduce the experimental data. Additional calculations indicate that the rate enhancement by CM over the aqueous phase results primarily from conformational compression of NACs by the enzyme and that this process is enthalpically controlled. This suggests that preferential stabilization of the transition state in the enzyme environment relative to water plays a secondary role in the catalysis by CM. 相似文献
160.