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131.
本文考察了Fe-Fe50 wt.%Si扩散偶在1200℃ 无磁场以及稳恒磁场下扩散层生长规律. 利用真空浇注强制冷却技术制备Fe-Fe50 wt.%Si扩散偶, 将制备的扩散偶进行1200℃不同磁感应强度下的热处理. 对获得热处理后试样进行SEM与EDS线扫描分析, 结果表明, 无论无磁场还是稳恒磁场下Fe-Fe50 wt.%Si扩散偶均生成两个扩散层, 即FeSi相层和Fe-Si固溶体层, 并且发现0.8 T下的两个扩散层宽度均小于0 T磁场下试样. 按照抛物线规律, 计算了扩散偶中间扩散层的互扩散系数, 发现0.8 T磁场下FeSi相层和Fe-Si固溶体层的互扩散系数较无磁场下 分别降低了26.7%与34.1%. 通过对磁吉布斯自由能的计算, 发现0.8 T磁场对扩散激活能Q的影响不足以影响扩散过程. 但扩散过程中原子振动频率ν会受到磁场的影响, 进而影响扩散常数D0, 磁场对原子振动频率的影响可以用拉莫尔旋进理论进行解释.
关键词:
Fe-Fe50wt.%Si扩散偶
稳恒磁场
FeSi相
Fe-Si固溶体 相似文献
132.
In this paper, we try to propose a toy model, which follows the majority rule with the Fermi function, to uncover the role of the heterogeneous interaction between individuals in opinion formation. In order to do this, we define the impact factor IFi, says individual i, as the exponential function of its connectivity ki with the tunable parameter β. β also shows the public information that can be collected by individuals in the system. We realize our model in scale-free networks with mean connectivity 〈k〉. We find that much more public information (β>β2) and less public information (β<β1) cannot let either of the two opinions be the majority during the opinion formation. Furthermore, β1 is a constant and equal to −0.76(±0.04), and β2 decreases as a power-law function of the mean connectivity 〈k〉 of the network. Our work can provide some perspectives and tools to understand the diversity of opinion in social networks. 相似文献
133.
本文用分子动力学模拟研究了Ni熔体以不同冷速凝固后微观结构的演变规律, 并通过理论计算确定出了Ni熔体凝固后获得理想非晶的临界条件. 模拟结果发现冷速小于1011 K/s时, Ni 熔体凝固后形成晶态组织; 冷速在1011 K/s到1014.5 K/s之间时, Ni熔体凝固后形成由晶态结构与非晶态结构组成的混合组织. 冷速小于1010 K/s, Ni 熔体凝固后形成的晶态组织具有fcc结构; 冷速在1010 K/s到1014.5 K/s之间时, Ni熔体凝固后组织中的晶态由fcc和hcp结构层状镶嵌排列构成. 通过分析模拟结果和计算结果, 确定出了Ni熔体凝固后形成理想非晶的临界冷速为1014.5 K/s. 并发现Ni熔体中临界晶核(冷速等于1014.5 K/s)和亚临界晶核(冷速大于1014.5 K/s) 均由fcc和hcp组成层状偏聚结构, 这表明Ni熔体中生长的晶体、临界晶核和晶胚的结构是相同的.
关键词:
分子动力学模拟
晶体团簇
临界冷速
结构 相似文献
134.
Accurate attenuation correction is required in dedicated breast PET imaging systems for image artifact removal and quantitative studies. In this study, a method using only emission data based on consistency conditions is proposed for attenuation correction in breast PET imaging systems. The consistency conditions are exploited to evaluate the accuracy of the estimated attenuation distribution and find the appropriate parameters that yield the most consistent attenuation distribution with the measured emission data. We have proved the validity of the method with experimental investigations and single-patient studies using a dedicated breast PET. The results show that the method is capable of accurately estimating the attenuation distribution of a uniform attenuator from the experimental data with various relatively low activities. The results also show that in single-patient studies, the method is robust for the irregular boundary of breast tissue and provides a distinct improvement in image quality. 相似文献
135.
深入研究潘宁放电的物理机制, 研制了全三维高品质算法粒子模拟软件(PIC), 设计并添加了相应物理情景的蒙特卡罗碰撞模块(MCC), 并对电子、氢分子离子(H2+)、氢正离子(H+)、氢三正离子(H3+)同时进行了跟踪, 成功研制了全三维电磁PIC/MCC数值算法. 结合国内研究较热的潘宁放电模型, 对该算法进行模拟验证. 模拟结果显示: 采用有效的滤波算法能抑制电磁数值噪声, 电子能量呈麦克斯韦分布, 由于电子的径向漂移和加速导致离子源顶端H2+产量较大.
关键词:
潘宁离子源
高品质算法
粒子模拟/蒙特卡罗 相似文献
136.
针对相关声呐接收阵元实际坐标与设计坐标不一致引起的测速误差,提出阵元坐标估计算法,以提高相关声呐的测速准确度。基于混响时空相关函数模型,对相关测速声呐时空相关函数特性进行了理论分析,提出了选择用延时0处的数据空间相关函数与理论空间相关函数进行阵元坐标估计的局域最小二乘拟合算法,并采用序列二次规划法解决了阵元坐标估计算法的最优化问题。海上试验数据的处理结果表明,该算法可以对阵元坐标进行有效估计,使用估计的阵元坐标后,相关测速声呐测速准确度提高了67%。 相似文献
137.
138.
It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, both
by measuring the diffusion coefficient of tagged particles or by NMR studies. Recent experiments have also demonstrated that
the glass transition temperature of thin polymer films can be shifted as compared to the same polymer in the bulk. We propose
here first a thermodynamical model for van der Waals liquids, which accounts for experimental results regarding the bulk modulus
of polymer melts and the evolution of the density with temperature. This model allows us to describe the density fluctuations
in such van der Waals liquids. Then, by considering the thermally induced density fluctuations in the bulk, we propose that
the 3D glass transition is controlled by the percolation of small domains of slow dynamics, which allows to explain the heterogeneous
dynamics close to T
g. We show then that these domains percolate at a lower temperature in the quasi-2D case of thin suspended polymer films and
we calculate the corresponding glass transition temperature reduction, in quantitative agreement with experimental results
of Jones and co-workers. In the case of strongly adsorbed films, we show that the strong adsorption amounts to enhance the
slow domains percolation. This effect leads to 1) a broadening of the glass transition and 2) an increase of T
g in quantitative agreement with experimental results. For both strongly and weakly adsorbed films, the shift in T
g is given by a power law, the exponent being the inverse of that of the correlation length of 3D percolation.
Received 21 March 2000 and Received in final form 4 December 2000 相似文献
139.
Upgrade of beamline BL08B at Taiwan Light Source from a photon‐BPM to a double‐grating SGM beamline 下载免费PDF全文
Jih‐Young Yuh Shan‐Wei Lin Liang‐Jen Huang Hok‐Sum Fung Long‐Life Lee Yu‐Joung Chen Chiu‐Ping Cheng Yi‐Ying Chin Hong‐Ji Lin 《Journal of synchrotron radiation》2015,22(5):1312-1318
During the last 20 years, beamline BL08B has been upgraded step by step from a photon beam‐position monitor (BPM) to a testing beamline and a single‐grating beamline that enables experiments to record X‐ray photo‐emission spectra (XPS) and X‐ray absorption spectra (XAS) for research in solar physics, organic semiconductor materials and spinel oxides, with soft X‐ray photon energies in the range 300–1000 eV. Demands for photon energy to extend to the extreme ultraviolet region for applications in nano‐fabrication and topological thin films are increasing. The basic spherical‐grating monochromator beamline was again upgraded by adding a second grating that delivers photons of energy from 80 to 420 eV. Four end‐stations were designed for experiments with XPS, XAS, interstellar photoprocess systems (IPS) and extreme‐ultraviolet lithography (EUVL) in the scheduled beam time. The data from these experiments show a large count rate in core levels probed and excellent statistics on background normalization in the L‐edge adsorption spectrum. 相似文献
140.
从离散的角度研究带边界的1+1维经典标量场和Dirac场的正则量子化问题. 与以往不同的是, 这里将时间和空间两个变量同时进行变步长的离散, 应用变步长离散的变分原理, 得到离散形式的运动方程、边界条件和能量守恒的表达式. 然后, 根据Dirac理论, 将边界条件当作初级约束, 将边界条件和内在约束统一处理. 研究表明, 采用此方法, 不仅在每个离散的时空格点上能够建立起Dirac括号, 从而可以完成该模型的正则量子化;而且, 该方法还保持了离散情况下的能量守恒. 相似文献