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21.
The microwave-assisted synthesis of 5-amino-3-aralkoxy(methoxy)amino-1,2,4-oxadiazoles starting from N1-aralkoxy-(methoxy)-N3-cyano-O-phenylisoureas and hydroxylamine is described. N1-Aralkoxy(methoxy)-N3-cyano-O-phenylisoureas are readily accessible by treatment of diphenyl N-cyanimidocarbonate with O-substituted hydroxylamines. 相似文献
22.
Wilfried A. Knig Detlef Icheln Torsten Runge Ingo Pforr Adolf Krebs 《Journal of separation science》1990,13(10):702-707
Transferring the site of specific substitution of dipentylated cyclodextrins with methyl or acyl residues from the secondary 3-hydroxyl group to the primary 6-hydroxyl group was expected to provide new information on the mechanism of chiral recognition. The 3-position points towards and the 6-position points away from the cyclodextrin cavity which via inclusion complex formation is supposed to play a major role in chiral separation. The “inverse” 6-O-acyl-2,3-di-O-pentyl-cyclodextrins displayed almost no enantioselectivity but the corresponding 6-O-methyl derivatives are a versatile supplement to the chiral capillary GC phases nowadays available. Among the compounds that could be enantiomerically resolved are alcohols, amino acids, alkyl halides, bicyclic ethers, acetals, olefins, other hydrocarbons and chiral pharmaceuticals. 相似文献
23.
On the Reactions of CH3OCl, CF3OCl, CF3OF, and CF3OH with the Superacid System HF/MF5 (M = As, Sb). Preparation and Characterization of CH3OCl(H)+MF6? and CF3OCl(H)+MF6? The preparation of the chlorine oxoniumsalts CH3OCl(H)+MF6? and CF3OCl(H)+MF6? by protonation of CH3OCl and CF3OCl in the superacid solution of HF/MF5 (M = As, Sb) is described. However CF3OF and CF3OH have not been protonated under the same conditions. In the case of CF3OH the formation of F2CO · MF5 is observed. The novel compounds are characterized by nmr- and vibrational spectroscopy. 相似文献
24.
Dalvit C Mongelli N Papeo G Giordano P Veronesi M Moskau D Kümmerle R 《Journal of the American Chemical Society》2005,127(38):13380-13385
NMR-based binding and functional screening performed with FAXS (fluorine chemical shift anisotropy and exchange for screening) and 3-FABS (three fluorine atoms for biochemical screening) represents a potential alternative approach to high-throughput screening for the identification of novel potential drug candidates. The major limitation of this method in its current status is its intrinsic low sensitivity that limits the number of tested compounds. One approach for overcoming this problem is the use of a cryogenically cooled (19)F probe that reduces the thermal noise in the receiver circuitry. Sensitivity improvement in the two screening techniques achieved with the novel cryogenic (19)F probe technology permits an increased throughput, detection of weaker binders and inhibitors (relevant in a fragment-based lead discovery program), detection of slow binders, and reduction in protein and substrate consumption. These aspects are analyzed with theoretical simulations and experimental quantitative performance evaluation. Application of 3-FABS combined with the cryogenic (19)F probe technology to rapid screening at very low enzyme concentrations and the current detection limits reached with this approach are also presented. 相似文献
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The bimetallic cluster ion PtAu+ activates methane in the gas-phase, yielding the carbene PtAuCH2+ which further reacts with ammonia under C-N coupling. In contrast, neither Pt2+ nor Au2+ mediates C-N bond formation. This example demonstrates how bond activation in the gas phase can be tuned by cooperative effects in bimetallic clusters. 相似文献
28.
Pentafluorethyl Sulfurtrifluoride: Synthesis and Reactions By oxidation of (C2F5S?)2 ( 1 ) with AgF2 at 0°C a mixture of C2F5SF3 ( 2 ) and C2F5SF5 ( 3 ) besides C2F5S(O)F ( 4 ) is formed. With elemental fluorine only 3 is isolated, an intermediate in this reaction is (C2F5SF4?)2 ( 5 ). At ?40 to ?30°C the mixture of 2, 3 and 4 was reacted with TASF and AsF5, to give TAS+ C2F5SF4? ( 6 ), TAS+ C2F5S(O)F2? ( 7 ) and C2F5SF2+AsF6? ( 8 ), respectively. While 6 and 7 decompose rapidly in solution even at low temperatures, of thermally stable 8 the solid state structure was determined by x-ray diffraction. 相似文献
29.
Laurent De Windt Detlef W. M. Hofman Lorenzo Pisani Enrico Clementi 《International journal of quantum chemistry》1995,53(2):131-147
The Coulomb–Hole–Hartree–Fock method introduced by E. Clementi in the early 1960s and reparametrized more recently by S. Chakraworty and E. Clementi to compute the correlated electronic energy in atomic systems, is here extended to compute molecules. The new parametrization is obtained empirically by fitting first and second atomic ionization potentials from He to Ca and a few diatomic molecules. The present formulation makes use of either one or more determinants in order to ensure proper dissociation products, following the early proposal of G.C. Lie and E. Clementi in the context of density functional computations for molecular systems. The new formulation is tested against the dissociation energies of a large number of molecules and it is found satisfactory. © 1995 John Wiley & Sons, Inc. 相似文献
30.
Joseph Schwarz Detlef Schrder Helmut Schwarz Christoph Heinemann Jan Hruk 《Helvetica chimica acta》1996,79(4):1110-1120
State-of-the-art ab initio studies demonstrate that the reaction Pd+ + CH3I → PdCH2I+ + H. is endothermic by ca. 20 kcal/mol, which translates into a bond dissociation energy (BDE) of ca. 83 kcal/mol for the Pd+? CH2I bond. This figure is in agreement with an experimental bracket of 68 kcal/mol < BDE(Pd+? CH2I) < 92 kcal/mol. Based on these findings, the previously studied Pd+/CH3I system was re-investigated, and double-resonance experiments demonstrate that the formation of PdCH2I+ occurs stepwise via PdCH as a reactive intermediate. Further, ion/molecule reactions of PdCH2I+ with unsaturated hydrocarbons are studied, which reveal the formation of carbon–carbon bonds in the gas phase. 相似文献