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71.
72.
针对聚合物熔体流动过程中黏性耗散现象的理论教学不足, 在双料筒毛细管流变仪基础上研制了聚合物熔体黏性耗散测量装置并进行实验. 根据绝热边界条件径向温度分布方程, 对实验结果进行理论分析计算. 组织学生学习POLYFLOW 软件, 利用其可视化功能对黏性耗散引起的温度场变化进行数值模拟, 并与理论计算结果对比分析. 通过让学生自己动手, 改变了理论模式教学, 对加深黏性耗散知识的理解起到积极的作用. 相似文献
73.
74.
结构动力模型修正方法的比较研究及评估 总被引:33,自引:0,他引:33
在实际工程中,由结构动力模型得到的计算值与通过试验获得的测量值间往往存在偏差,为了能够精确预测结构的动力响应,依据测量信息修正存在的动力模型是非常必要的.对现有几种有效的用于结构动力模型修正的理论方法(包括基于敏感性分析的矩阵型法、基于神经网络算法的参数型法和基于遗传优化算法的方法)做了详细的综述;介绍了这些方法的步骤和研究进展;并分析了这些动力模型修正方法在工程运用中存在的一些实际问题,如不完整的模态测量值、模型修正的鲁棒性、模型修正的计算效率和收敛性等.最后,通过对一实际的五层钢框架的动力模型修正,比较了这几种方法的优缺点,提出了今后需要解决的问题. 相似文献
75.
76.
内切轧制是新的高温超导Bi2223/Ag带材加工方法.本文采用内切轧制进行高温超导Bi2223/Ag多芯带材加工实验,研究不同压下率(εh)的中间形变对带材组织、结构和性能的影响.研究结果表明,内切轧制中带材的形变属于两向延伸、一向压缩形变,其宽展延伸十分明显,随εh增加而增大;XRD分析结果表明,内切轧制中εh变化对带材相组成、Bi2223相含量和织构度影响不显著;SEM观察和Ic测试表明,εh的增加使带材致密性增强并提高Ic,但是这种作用一定程度上因银超界面而受到抑制. 相似文献
77.
Numerical analysis of plasma arc physical characteristics under additional constraint of keyhole 下载免费PDF全文
The physical characteristics of a plasma arc affect the stability of the keyhole and weld pool directly during keyhole plasma arc welding(KPAW). There will be significant change for these characteristics because of the interaction between the keyhole weld pool and plasma arc after penetration. Therefore, in order to obtain the temperature field, flow field, and arc pressure of a plasma arc under the reaction of the keyhole, the physical model of a plasma arc with a pre-set keyhole was established. In addition, the tungsten and base metal were established into the calculated domain, which can reflect the effect of plasma arc to weld pool further. Based on magneto hydrodynamics and Maxwell equations, a two-dimensional steady state mathematical model was established. Considering the heat production of anode and cathode, the distribution of temperature field, flow field, welding current density, and plasma arc pressure were solved out by the finite difference method. From the calculated results, it is found that the plasma arc was compressed a second time by the keyhole. This additional constraint results in an obvious rise of the plasma arc pressure and flow velocity at the minimum diameter place of the keyhole, while the temperature field is impacted slightly. Finally, the observational and metallographic experiments are conducted, and the shapes of plasma arc and fusion line agree with the simulated results generally. 相似文献
78.
With the help of the ab initio full-potential
linearized augmented plane wave (FPLAPW) method, calculations of
the electronic structure and linear optical properties are carried
out for red HgI2 and yellow HgI2. It is found that
the red HgI2 has a direct gap of 1.22834 eV and the yellow
HgI2 has an indirect gap of 2.11222 eV. For the red
HgI2, the calculated optical spectra are qualitatively in agreement with the
experimental data. Furthermore, the origins of the
different peaks of ε 2 (ω ) are discussed. Our
calculated anisotropic dielectric function of the red HgI2 is
a nice match with the experimental results. Our calculated results
are able to reproduce the overall trend of the experimental
reflectivity spectra. Although no comparable experimental and
theoretical results are available, clearly, the above proves the
reliability of our calculations, suggesting that our calculations
should be convincing for the yellow HgI2. Finally, the
different optical properties are discussed. 相似文献
79.
利用第一性原理系统地研究了RbH2PO4晶格优化结构、总的和分的态密度、电荷密度分布。我们发现氧原子和Rb, H原子的杂化形成了两种离子群,在铁电相离子键和PO4四面体的耦合强度比顺电相更强。结果,通过P-O 和 H-O的距离改变电荷密度的再分布和PO4四面体的顺序旋转导致了铁电性的产生。两种类型粒子群的运动和自动成型畴壁导致了可以观测的焦热电流。 相似文献
80.
In the littlest Higgs model with T-parity, the heavy photon (A_H) is supposed to be a possible dark matter (DM) candidate. The direct proof of the validity of this model is to produce the heavy photon at an accelerator. In this paper, we study the production rate of e~+ e~- → AH AH at the international e~+ e~- linear collider (ILC) in the littlest Higgs model with T-parity, and show the distributions of the transverse momenta of A H . The numerical results indicate that the heavy photon production rate could reach the 10~-1 fb level at some parameter space, so this could be a good chance to observe the heavy photon via the pair production process with high luminosity at the ILC (500 fb~-1). We know that DM is composed of weakly interacting massive particles, so the interactions with standard model particles are weak. How to detect heavy photons at a collider and distinguish them from other DM candidates are discussed in the final section of the paper. 相似文献