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231.
P. T. Callaghan P. J. Back D. H. Chaplin H. R. Foster G. V. H. Wilson 《Hyperfine Interactions》1985,22(1-4):39-45
A novel extension of the Single or Adiabatic Fast Passage NMR/ON technique is described. Its principal advantages in extracting the mode magnitudes and distribution widths of weak nuclear electric quadrupole splittings much less than the magnetic inhomogeneous broadening are its simplicity and generality requiring no assumptions on the degree of adiabaticity of the nuclear spin motion during sweep through the quadrupolar split subresonances. The technique is applied to a concentrated single crystal sample of60CoFe which failed to yield a well resolved mid passage signal to conventional single passage NMR/ON. The result is an asymmetric frequency distribution of quadrupole frequencies with a mode value of P=3e2qQ/4I (2I-1)=+4.5 ±1.0 kHz and half maxima of +2.5 kHz and +7.0 kHz. 相似文献
232.
233.
(+/-)-Bakkenolide A was prepared in five steps from ethyl 4-benzyloxyacetoacetate by sequential alkylations with tiglyl bromide nd cis-5-bromo-1,3-pentadiene, followed by an intramolecular Diels-Alder reaction as the key step. The known 7-epibakkenolide A and novel 10-epi- and 7,10-diepibakkenolide A stereoisomers were obtained as minor byproducts. 相似文献
234.
235.
The decomposition of ethanol vapour induced by infrared radiation from a pulsed HF-laser has been studied as a function of pressure. At high pressures, above 10 torr, the main primary processes appear to be:C2H5OH → H2 + CH3CHO,C2H5OH → C2H4 + H2O,C2H5OH → CH3 + CH2OHin a ratio of 3:2:1 which is independent of pressure. At low pressures the process yielding C2H4 and H2O becomes dominant. The results suggest that the high pressure behaviour involves a “thermal” decomposition with collisional processes dominating, whereas at low pressures the decomposition is due to multiple photon absorption which at the lowest pressures approaches a collision-free unimolecular decomposition. 相似文献
236.
Andersen DL Back TG Janzen L Michalak K Pharis RP Sung GC 《The Journal of organic chemistry》2001,66(21):7129-7141
Ten novel compounds, each consisting of two subunits and a linker, were designed with the aid of molecular modeling to resemble the natural steroidal phytohormone brassinolide. The mimetics were synthesized and subjected to the rice leaf lamina inclination bioassay to test for brassinosteroid activity. Most of the mimetics displayed very weak or no bioactivity, but two were strongly active when coapplied with the auxin indole-3-acetic acid (IAA), which synergizes the activity of brassinosteroids. Thus, 1-(4,6 alpha,7 alpha-trihydroxy-5,6,7,8-tetrahydronaphthyl)-2-(6 alpha',7 alpha'-dihydroxy-5',6',7',8'-tetrahydronaphthyl)ethyne (4) and (E)-1,2-bis[trans-(4a alpha,8a beta)-4-oxo-6 alpha,7 alpha-dihydroxy-4a,5,6,7,8,8a-hexahydro-(3H)-naphthyl]ethylene (11) showed exceptional activity at doses as low as 0.01 ng and 0.001 ng/plant, respectively. These compounds are the first biologically active nonsteroidal brassinolide mimetics. 相似文献
237.
1,2-Oxaselenolane Se-oxide is a novel cyclic seleninate ester that functions as a remarkably efficient glutathione peroxidase mimetic by catalyzing the reduction of tert-butyl hydroperoxide to tert-butyl alcohol in the presence of benzyl thiol. The seleninate ester can be conveniently generated in situ by oxidation of allyl 3-hydroxypropyl selenide with tert-butyl hydroperoxide. Its catalytic activity surpasses that of several other known GPx mimetics containing cyclic selenenamide structures, which were also tested for comparison. 相似文献
238.
β-(Phenylseleno)vinyl sulfones are readily available from the selenosulfonation of acetylenes and undergo efficient, stereoselective substitution of the phenylseleno moiety by the alkyl group of alkyl (phenylseleno) cuprates. 相似文献
239.
lida Bonfada Gelson Manzoni de Oliveira Davi Fernando Back Ernesto Schulz Lang 《无机化学与普通化学杂志》2005,631(5):878-881
Chloridrate of pyridoxine (vitamin B6) reacts with UO2(NO3)2·6H2O in acetonitril containing triethylamine to give the complex salt [UO2(PN)2(H2O)]Cl2. The structure of the novel compound was analyzed by single crystal X‐ray diffraction affording the centrosymmetric triclinic space group . In [UO2(PN)2(H2O)]2+ two zwitterionic pyridoxine molecules complex the uranium atom in a planar manner with a water molecule achieving the coordination of a semi planar pentagon. The two uranyl oxo ligands set the axis of a distorted pentagonal bipyramide. The ability of vitamin B6 pyridoxine to react with UO22+ allowing the chelation of one uranium atom represents a very specific model of assimilation of uranium by living beings. It could also explain the serious damages caused by heavy or radioactive metals like uranium since their complexation “in vivo” by enzymatic systems like pyridoxal phosphate‐containing enzymes would lead to a modification of the prosthetic groups of the metalloenzymes with loss of their catalytic activities. 相似文献
240.