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81.
Alberico E Baumann W de Vries JG Drexler HJ Gladiali S Heller D Henderickx HJ Lefort L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(45):12683-12695
The mechanism of the asymmetric hydrogenation of methyl (Z)-2-acetamidocinnamate (mac) catalysed by [Rh(MonoPhos)(2)(nbd)]SbF(6) (MonoPhos: 3,5-dioxa-4-phosphacyclohepta[2,1-a:3,4-a']dinaphthalen-4-yl)dimethylamine) was elucidated by using (1)H, (31)P and (103)Rh NMR spectroscopy and ESI-MS. The use of nbd allows one to obtain in pure form the rhodium complex that contains two units of the ligand. In contrast to the analogous complexes that contain cis,cis-1,5-cyclooctadiene (cod), this complex shows well-resolved NMR spectroscopic signals. Hydrogenation of these catalyst precursors at 1 bar total pressure gave rise to the formation of a bimetallic complex of general formula [Rh(MonoPhos)(2)](2)(SbF(6))(2); no solvate complexes were detected. In the dimeric complex both rhodium atoms are ligated to two MonoPhos ligands but, in addition, each rhodium atom also binds to one of the binaphthyl rings of a ligand that is bound to the other rhodium metal. Upon addition of mac, a mixture of diastereomeric complexes [Rh(MonoPhos)(2)(mac)]SbF(6) is formed in which the substrate is bound in a chelate fashion to the metal. Upon hydrogenation, these adducts are converted into a new complex [Rh(MonoPhos)(2){mac(H)(2)}]SbF(6) in which the methyl phenylalaninate mac(H)(2) is bound through its aromatic ring to rhodium. Addition of mac to this complex leads to displacement of the product by the substrate. No hydride intermediates could be detected and no evidence was found for the involvement at any stage of the process of complexes with only one coordinated MonoPhos. The collected data suggest that the asymmetric hydrogenation follows a Halpern-like mechanism in which the less abundant substrate-catalyst adduct is preferentially hydrogenated to phenylalanine methyl ester. 相似文献
82.
Fischer C Kohrt C Drexler HJ Baumann W Heller D 《Dalton transactions (Cambridge, England : 2003)》2011,40(16):4162-4166
Three novel trinuclear rhodium hydride complexes of the type {[Rh(PP*)H](3)(μ(2)-H)(3)(μ(3)-H)}[BF(4)](2) containing diphosphines Tangphos, t-Bu-BisP* and Me-DuPHOS have been synthesised. The new compounds are very stable. Their structures have been characterized by X-ray analysis in the solid state and by NMR-spectroscopic investigations in solution. 相似文献
83.
Brown MA Fujimori Y Ringleb F Shao X Stavale F Nilius N Sterrer M Freund HJ 《Journal of the American Chemical Society》2011,133(27):10668-10676
The nucleation and electronic structure of vapor-deposited Au on hydroxylated MgO(001) surfaces has been investigated under ultrahigh vacuum conditions. Hydroxylated MgO(001) surfaces with two different hydroxyl coverages, 0.4 and 1 monolayer, respectively, were prepared by exposure to water (D(2)O) at room temperature. Scanning tunneling microscopy experiments show significantly higher gold particle densities and smaller particle sizes on the hydroxylated MgO surface as compared to gold deposited on clean MgO(001). Infrared spectroscopy and X-ray photoelectron spectroscopy experiments were performed to reveal details about the initial nucleation of gold. Gold atoms are found to chemically interact with a specific type of hydroxyl groups on the MgO surface, leading to the formation of oxidized gold particles. The enhanced adhesion of Au particles, which is due to the formation of strong Au-O interfacial bonds, is responsible for the observed higher stability of small Au clusters toward thermal sintering on hydroxylated MgO surfaces. The results are compared to similar studies on Au/TiO(2)(110) model systems and powder samples prepared by the deposition-precipitation route. 相似文献
84.
Dipole moments and static dipole polarizabilities are calculated for neon and the molecules HF, H2O, NH3, CH4 and CO from SCF and correlated wavefunctions. The construction of appropriate gaussian-type basis sets is discussed and the convergence of the correlation contributions to the polarizability is analysed. The effect of vibrational averaging is also investigated. The polarizabilities as obtained from the coupled electron pair approximation (CEPA) with the most extended basis sets differ from experimental values by less than 1·5 per cent in all cases. The calculated polarizability anisotropies appear to be correct to about 5–15 per cent. The correlation contributions to the polarizabilities are found to vary from 3 to 12 per cent. 相似文献
85.
Hans-Joachim Timpe Steffen Neuenfeld 《Journal of polymer science. Part A, Polymer chemistry》1993,31(6):1347-1353
Styrene can be photopolymerized with methanolic solutions of safranine T(STH+) in the absence of any additives. Under these conditions the monomer acts as an electron donor for the excited singlet state of STH+, and after electron transfer an initiating semireduced STH+ radical is produced. The experimentally determined monomer exponent of α = 2 indicates additional deactivation reactions of the primary radicals. The polymerization rate depends on the dye concentration also in those regions, in which all light is already absorbed. Presumably, this dependence is caused by a comproportionation reaction between STH+ and substituted leuco-safranine T formed in the course of polymerization. © 1993 John Wiley & Sons, Inc. 相似文献
86.
87.
Hans-Joachim Kowalsky 《Archiv der Mathematik》1957,8(5):336-339
Ohne Zusammenfassung 相似文献
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