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21.
It was found that the chemical ionization mass spectra of the enantiomers of some α-amino acids and α-hydroxy acids could be definitely distinguished when a chiral compound, l-amyl alcohol, was used as a component of the reagent gases. The relative abundances of some characteristic ions produced through ion-molecule reactions in the gas phase were much higher in the D isomers than in the L isomers. The results were highly reproducible. This approach proved to be a convenient way for the detection of the chirality of these compounds by chemical ionization mass spectrometry. 相似文献
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An algorithm was developed with optimizable parameters to match sounds from individual insects in grain by cross-correlating signals from an acoustic sensor array. The algorithm was optimized in a series of trials conducted in the sample chamber of an Acoustic Location ‘Fingerprinting’ Insect Detector (ALFID). The sample chamber was filled with uninfested wheat, except for a single kernel, which was infested with an immature rice weevil. This kernel was placed at a known location in the sample chamber. With analysis parameters optimized, the algorithm successfully detected the single insect in 100% of the trials. The algorithm's capability to count multiple insects was assessed by combining signals in data files collected from single insects into a set that represented sounds from a pair of insects. In these analyses, the algorithm correctly detected the two insects in 100% of combinations three sensor spacings apart, 100% of combinations two sensor spacings apart, and 70% of combinations one sensor spacing apart. Based on these results and the dimensions of the ALFID sampling chamber, the algorithm has a 90% probability of identifying two randomly located insects producing sounds in a wheat sample. 相似文献
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We demonstrate and characterize a cryogenic buffer gas-cooled molecular beam source capable of producing bright beams of free radicals and refractory species. Details of the beam properties (brightness, forward velocity distribution, transverse velocity spread, rotational and vibrational temperatures) are measured under varying conditions for the molecular species SrF. Under typical conditions we produce a beam of brightness 1.2 × 10(11) molecules/sr/pulse in the X(2)Σ(+)(v = 0, N(rot) = 0) state, with 140(m/s) forward velocity and a rotational temperature of ≈ 1 K. This source compares favorably to other methods for producing beams of free radicals and refractory species for many types of experiments. We provide details of construction that may be helpful for others attempting to use this method. 相似文献
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Threshold photoelectron photoion coincidence (TPEPICO) has been used to study the sequential photodissociation reaction of internal energy selected 1,2-diiodoethane cations: C(2)H(4)I(2)(+) → C(2)H(4)I(+) + I → C(2)H(3)(+) + I + HI. In the first I-loss reaction, the excess energy is partitioned between the internal energy of the fragment ion C(2)H(4)I(+) and the translational energy. The breakdown diagram of C(2)H(4)I(+) to C(2)H(3)(+), i.e., the fractional ion abundances below and above the second dissociation barrier as a function of the photon energy, yields the internal energy distribution of the first daughter, whereas the time-of-flight peak widths yield the released translational energy in the laboratory frame directly. Both methods indicate that the kinetic energy release in the I-loss step is inconsistent with the phase space theory (PST) predicted two translational degrees of freedom, but is well-described assuming only one translational degree of freedom. Reaction path calculations partly confirm this and show that the reaction coordinate changes character in the dissociation, and it is, thus, highly anisotropic. For comparison, data for the dissociative photoionization of 1,3-diiodopropane are also presented and discussed. Here, the reaction coordinate is expected to be more isotropic, and indeed the two degrees of freedom assumption holds. Characterizing kinetic energy release distributions beyond PST is crucial in deriving accurate dissociative photoionization onset energies in sequential reactions. On the basis of both experimental and theoretical grounds, we also suggest a significant revision of the 298 K heat of formation of 1,2-C(2)H(4)I(2)(g) to 64.5 ± 2.5 kJ mol(-1) and that of CH(2)I(2)(g) to 113.5 ± 2 kJ mol(-1) at 298 K. 相似文献
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过去的CO2置换甲烷水合物的微观机理研究,主要集中在客体分子(CH4、CO2)之间的交换、占据状态,孤立地研究分解过程或生成过程,忽视主体-客体之间的作用、主体分子(H2O)的空位辅助和客体分子的多重竞争通道。本文基于水合物分解的过冷水及其水空位辅助,以及水合物生成的串滴链及其客体分子竞争的研究,进一步评论水合物CH4-CO2置换的双重机理。然后,对微观机理的动态性和未来研究的相关问题进行讨论。通过综述和评论,文章得出以下初步结果:过冷水通过水空位推动客体分子的跳跃、扩散,实现置换过程的自组装;CO2分子在分解前沿形成一个有序结构的CO2串滴链,其动态性伴随水的组织到获取包合物笼的结构,以及非晶形包合物转变成晶形包合物的生长过程;CO2和CH4在中晶穴中必然产生竞争,并且存在多种竞争类型;成核过程中,不稳定簇导致竞争结构,且有多重竞争通道。最后,结果表明水合物的CH4-CO2置换机理具有双重性,即主体分子的空位辅助和客体分子的竞争,是分解过程和生成过程的自然统一。 相似文献
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We demonstrate deceleration of a beam of neutral strontium monofluoride molecules using radiative forces. Under certain conditions, the deceleration results in a substantial flux of detected molecules with velocities ?50 m/s. Simulations and other data indicate that the detection of molecules below this velocity is greatly diminished by transverse divergence from the beam. The observed slowing, from ~140 m/s, corresponds to scattering ?10(4) photons. We also observe longitudinal velocity compression under different conditions. Combined with molecular laser cooling techniques, this lays the groundwork to create slow and cold molecular beams suitable for trap loading. 相似文献