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131.
Myron H. Miller DeLyle Eastwood Martha Schulz Hendrick 《Spectrochimica Acta Part B: Atomic Spectroscopy》1984,39(1):13-56
Experimental data and theoretical criteria are used to critically review existing models for analyte emission enhancement in the 3-electrode d.c. plasma (DCP). The analytical zone is characterized as a non-optically thin recombining plasma in partial thermodynamic equilibrium (PTE). Spectrochemical excitation the authors ascribe largely to: (1) argon resonance line radiative transport; (2) inversion of optically pumped argon states; (3) inversion of analyte populations by Franck-Condon collisions with argon; (4) energy cascading in analytes via a multitude of channels. Adding an easily ionized element (EIE): (1) induces additional resonance line radiative transfer; (2) raises electron densities in cooler, analyte-rich plasma margins; (3) locally increases argon optical absorption cross sections via Stark broadening; (4) redistributes ohmic heating. Coupling between the proposed mechanisms is non-linear. Relationships between radiative transfer and collisional redistribution and (1) background suppression by EIE and (2) analyte emission enhancement by helium are also examined. Similarities between DCP and inductively coupled plasma (ICP) excitation mechanisms are noted and practical implications are addressed. 相似文献
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134.
Dr. Heinz Berner Gerhard Schulz Hellmuth Reinshagen 《Monatshefte für Chemie / Chemical Monthly》1977,108(1):233-242
Some syntheses of [9](2,4)pyrrolophane are described. 相似文献
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136.
The Diterpene Pleuromutilin(1) reacts with orthoformicacid-trimethylester at room temperature almost quantitatively to give the 11-keto-3-methylester 2 with AB-trans-configuration. This conversion is shown to occur through a 1,5-hydride-shift between C3 and C11. Treatment of 2 with Lewis acid (ZnCl2) initiated a retro-1,5-hydride-shift which resulted in the formation of Pleuromutilin(1). Mechanistic aspects and structure assignments, which are based on chemical and spectroscopic (1H- and 13C-NMR) data are discussed. 相似文献
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139.
The gas phase infrared spectra of monoisotopic H3Si35Cl and H3Si37Cl have been studied in the region near 2200 cm?1 with a resolution of 0.012 and 0.04 cm?1, respectively, and rotational fine structure for ΔJ = ±1 branches has been resolved. In addition, some information on ν3 + ν4 of H3Si35Cl near 2750 cm?1 has been obtained. ν1 and ν4 are weakly coupled by Coriolis x, y resonance, , only the upper states K′ = 2, l = 0 and K′ = 1, l = ?1 being substantially affected. Local perturbation due to rotational l(±1, ±1)-type resonance with ν3 + ν5+1 + ν6+1 and ν3 + ν5+1 + ν6?1 is revealed in the ΔK = +1 and ?1 branches, respectively. From a fit of the experimental line positions, standard deviations of 1.4 and 3.8 × 10?3 cm?1, respectively, to a model with five interacting levels conventional excited state parameters and interaction constants have been obtained. In the fundamentals are ν1, and ν4, , respectively. Q branches of the “hot” band (ν3 + ν4) ? ν3 and of ν4 of the 29Si and 30Si species have been detected. 相似文献
140.
Isotope studies to the sorption behavior of atmospheric sulfate in humus layers of scots pine ecosystems 总被引:1,自引:0,他引:1
The sorption potential for SO4(2-) in humus layer samples from field sites along a deposition gradient was determined experimentally in batch experiments. The Freundlich equation was used to quantify the sorption of added SO4(2-) in humus layer samples and to determine site-dependent sorption parameters. SO4(2-) sorption in humus layers is a concentration-dependent process. The linearity of isotherms reveals that SO4(2-) is reversibly bound in the organic surface layer, as long as soil solution concentrations remain above 26 to 44 mg SO4(2-) L(-1). Natural isotope variations of sulfur in SO4(2-) were analysed to investigate the degree of sorption of dissolved atmospheric and added SO4(2-). Both sulfate species differed significantly in their isotope composition. The pattern of delta34S values for SO4(2-) in all equilibrium solutions confirm the findings from sorption isotherms, showing a close relationship between the sulfur isotope ratios of SO4(2-) in soil solutions and the amount of SO4(2-) sorbed at the humus layer matrix. Stored atmospheric SO4(2-) in humus layers is released at sites where sulfate concentration in throughfall drops below 26 mg SO4(2-) L(-1). Concentration of soluble Fe decreased with increasing sulfate sorption, thus supporting the assumption that active Fe for example is important. Iron probably stabilizes the reactive surface of humus complexes and therefore has a positive influence on the SO4(2-) sorption in humus layers. 相似文献