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41.
恒星氦燃烧阶段3α反应和12C(α,γ)16O反应相互竞争,两者的反应率共同决定了氦燃烧结束后12C与16O的丰度比,该比值是大质量恒星后继演化以及伴随的元素核合成过程的初始条件。目前,氦燃烧12C(α,γ)16O反应起始T9=0.2处,天体物理模型要求的反应率的精确度要低于10%,然而尚未有实验或理论给出满足要求的结果。最为直接和可靠地获取12C(α,γ)16O反应率的方法,就是尽可能往低能区测量其天体物理S因子,然后通过理论外推到感兴趣的能区。为此基于经典的R-矩阵理论,建立了适用于低能核反应的多道、多能级的约化R-矩阵理论来拟合几乎所有可用的16O系统的实验数据。配合使用协方差统计和误差传播理论,拟合外推得到了客观的、内部自恰的和唯一性好的12C(α,γ)16O反应天体物理S因子。总的外推S因子STOT(0.3 MeV)=162.7±7.3 keV·b,理论上首次给出达到恒星演化与元素核合成模型的最低要求的S因子。基于计算给出的全能区的S因子,数值积分给出了温度位于0.04 6 T9 6 10的12C(α,γ)16O天体物理反应率。在T9=0.2处,推荐的反应率为(7.83 ±0.35)×10-15 cm3mol-1s-1。During stellar helium burning, the rates of 3α and the 12C(α,γ)16O reaction, in competition with one another, determine the relative abundances of 12C and 16O in a massive star. The abundance ratio is the beginning condition of the following nucleosynthesis and star evolution of massive stars, which are extremely sensitive to the rate of 12C(α,γ)16O reaction at T9=0.2. The most direct and trustworthy way to obtain the reaction rate of the 12C(α,γ)16O reaction is to measure the S factor for that reaction to as low energy as possible, and to extrapolate to energies of astrophysical interest. Based on a new multilevel and multichannel reduced R-matrix theory for applications in nuclear astrophysics, we have obtained an accurate and self-consistent astrophysical S factor of 12C(α,γ)16O, by a global fitting for almost all available experimental data of 16O system, with the coordination of covariance statistics and error-propagation theory. The extrapolated S factor of 12C(α,γ)16O was obtained with a recommended value STOT (0.3 MeV)=162.7±7.3 keV·b. And the reaction rates of 12C(α,γ)16O for stellar temperatures between 0.04 6 T9 6 10 are provided. At T9=0.2, the reaction rate is (7.83 ±0.35)×10-15 cm3mol-1s-1, where stellar helium burning occurs. 相似文献
42.
The scaling behaviour of fluctuation for a download network we investigated a few years ago based upon Zhang's Econophysics web page is presented. A power law scaling, namely σ~〈f〉^α exists between the dispersion a and average flux 〈f〉 of the download rates. The fluctuation exponent α is neither 1/2 nor 1, which were claimed as two universal fluctuation classes in previous publication, while it varies from 1/2 to 1 with the time window in which the download data are accumulated. The crossover behaviour of fluctuation exponents can be qualitatively understood by the external driving fluctuation model for a small-size system or a network traffic model which suggests congestion as the origin. 相似文献
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用动力学模型计算10.6MeV/u 84Kr(27Al,准裂变)反应的裂变时间 总被引:1,自引:0,他引:1
用单体耗散模型对10.6MeV/u 84Kr在27Al上引起的准裂变反应进行了计算,结果表明该准裂变反应的准裂变时间大于200×10-22s.发现对本反应系统,准裂变的出现至少需要8MeV/u阈能. 相似文献
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We present a systematic analysis of two-pion interferometry for the central Au+Au collisions at √SNN=3, 5, 7, 11, 17, 27, 39, 62, 130 and 200 GeV/c with the help of a multiphase transport (AMPT) model. Emission source-size radius parameters Rlong, Rout, Rside and the chaotic parameter A are extracted and compared with the experimental data. Transverse momentum and azimuthal angle dependencies of the HBT radii are also discussed for central Au+Au collisions at 200 GeV/c. The results show that the HBT radii in central collisions do not change much above 7 GeV/c. For central collisions at 200 GeV/c, the radii decrease with the increasing of transverse momentum PT but are not sensitive to the azimuthal angle. These results provide a theoretical reference for the energy scan program of the RHIC-STAR experiment. 相似文献
49.
Investigation on the deformation of Ne and Mg isotope chains within relativistic mean-field model
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Ne and Mg isotope chains are investigated based on constrained calculations in the framework of a deformed relativistic mean-field (RMF) model with the NL075 parameter set. The calculated quadrupole deformation and binding energy are compared with other theoretical results as well as the available experimental data. It shows that the calculated deformations of Ne and Mg with the NL075 are more accurate than those obtained with the NL-SH. It is predicted that ^19,29,32Ne and ^20,31Mg maybe have a triaxial deformation and ^25-28Ne and ^27-30Mg exhibit a shape coexistence probably. The closure effect of neutron number N=8 for ^20Mg is predicted to be very weak. 相似文献
50.
使用LUCIAE3.0模型模拟了SPS能区Pb+Pb和C+C在不同能量(Elab=20—200A GeV)和不同中心度下的重离子碰撞.并通过逐个事件的粒子温度涨落提取出了相应粒子的热容,发现对于同一碰撞系统,单位发射粒子的热容随碰撞能量的升高而下降直至饱和,随着碰撞参数b的增大而减小,而且发现单位发射粒子的热容具有随粒子质量的变大而变大的关系.同时还发现不同碰撞系统中同一种粒子具有相同的单位发射粒子热容,并给出了相应的解释. 相似文献