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61.
本文详细分析和讨论了结构分析的并行有限元方法—并行预处理共轭梯度法(以下简称PPCG法)。着重讨论了基于自带存储器的多处理机系统的并行预处理算法问题,并由此提出了两种PPCG法:PPCG1和PPCG2法。这两种方法适用于以单道剖分(one-way dissection)的子结构法为基础的并行分析。由于这种剖分法产生的结构刚度矩阵具有箭头形状,可独立地消除各子结构的内部自由度,并且不会在刚度矩阵中产生新的非零元素,因此很适合具有较多处理机的并行机系统对复杂结构进行的并行分析。 相似文献
62.
翼型与风洞侧壁交接角区分离流动研究 总被引:1,自引:0,他引:1
运用Navier-Stokes数值模拟对翼型模型试验时风洞侧壁和翼型模型结合部拐角区黏型分离流动进行模拟,并将简单代数湍流模型扩展用于机翼/风洞侧壁拐角区流动.计算格式在空间上采用中心有限体积离散,在时间上采用多步Runge-Kutta时间步长格式进行积分.结果显示,在翼型模型风洞试验时,模型/侧壁拐角区、模型表面、侧壁表面和模型后形成复杂的黏性分离流动和二次分离,对实验结果产生很大的影响. 相似文献
63.
In this paper the analytical solutions of the impact of a particle on Timoshenko beams with four kinds of different boundary
conditions are obtained according to Navier's idea, which is further developed. The initial values of the impact forces are
exactly determined by the momentum conservation law. The propagation of the longitudinal and transverse waves along the beam,
especially, the effects of boundary conditions on the characteristics of the reflected waves, are investigated in detail.
Some results are compared with those by MSC/NASTRAN. 相似文献
64.
Stacking fault tetrahedra (SFTs) are volume defects that typically form by the clustering of vacancies in face-centred cubic (FCC) metals. Here, we report a dislocation-based mechanism of SFT formation initiated from the semi-coherent interfaces of Cu–Al nanoscale multilayered metals subjected to out-of-plane tension. Our molecular dynamics simulations show that Shockley partials are first emitted into the Cu interlayers from the dissociated misfit dislocations along the Cu–Al interface and interact to form SFTs above the triangular intrinsic stacking faults along the interface. Under further deformation, Shockley partials are also emitted into the Al interlayers and interact to form SFTs above the triangular FCC planes along the interface. The resulting dislocation structure comprises closed SFTs within the Cu interlayers which are tied across the Cu–Al interfaces to open-ended SFTs within the Al interlayers. This unique plastic deformation mechanism results in considerable strain hardening of the Cu–Al nanolayered metal, which achieves its highest tensile strength at a critical interlayer thickness of ~4 nm corresponding to the highest possible density of complete SFTs within the nanolayer structure. 相似文献
65.
Xiaodong Xu Lifen Zhang Jian Zhou Jun Wang Jinghua Yin Jinliang Qiao 《Journal of Macromolecular Science: Physics》2015,54(1):32-44
The thermal behaviors of glycidyl methacrylate (GMA)-grafted polypropylene (PP) (PP-g-GMA) with two different grafting degrees, namely, GPP1 and GPP2, were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray diffraction (WAXD), dynamic mechanical analysis (DMA), and thermogravimetrical analysis (TGA). DSC results suggested that the GMA grafted PP exhibited higher crystallization temperature Tc, higher melting temperature Tm, and higher crystallinity compared with the neat PP. The isothermal crystallization kinetics was analyzed with the Avrami equation and the total crystallization activation energy was calculated. It was concluded that the crystallization processes of PP and the grafted PP were controlled by nucleation and the values of the crystallization activation energy of PP and the grafted PP were almost identical. POM results suggested that the GMA grafted PP exhibited smaller spherulites size compared with the neat PP. WAXD patterns indicated that the neat PP encouraged the formation of γ phase, compared with the grafted PP, during the crystallization process. DMA results showed that melt grafting did not induce a clear effect on the γ-transition and β-transition of the amorphous phase but resulted in a decrease in mobility of the PP chains in the crystals. TGA curves suggested that the melt grafting slightly improved the thermal stability of PP. 相似文献
66.
铜锌锡硫薄膜材料组成元素储量丰富, 环境友好, 成本低廉, 成为最具前景的薄膜材料之一. 目前, Cu2ZnSn(S, Se)4 (CZTSSe)薄膜太阳电池的最高转换效率已经达到12.6%. 本文总结了Cu2ZnSnS4 (CZTS)的发展历史, 依次介绍了CZTS薄膜材料的结构特性、光学特性、电学特性、界面特性和Na对CZTS 薄膜的影响, 详细介绍了CZTS薄膜的制备方法及器件应用的最新研究进展, 总结了目前CZTS薄膜太阳电池发展中存在的问题, 展望了今后的研究方向. 相似文献
67.
68.
基于有效介质理论研究了石墨烯/介质周期结构的电磁性质, 研究发现这种复合结构的等频面在太赫兹和远红外波段为双曲线, 可用来实现石墨烯基双曲色散特异材料. 通过改变石墨烯的费米能级、介质层厚度和单元结构中石墨烯的层数, 可很容易地调节双曲色散存在的频段. 由于等频面的双曲色散特性, 石墨烯基双曲色散特异材料在远低于截止频率的范围内, 对斜入射的电磁波具有负的能量折射率和正的相位折射率, 并支持局域体等离子体模式. 基于衰减全反射结构, 研究了体等离子体的激发, 探索了体等离子体在可调的光学反射调制器中的应用. 相似文献
69.
Development of Two‐Channel Phosphorescent Core–Shell Nanoprobe for Ratiometric and Time‐Resolved Luminescence Imaging of Intracellular Oxygen Levels 下载免费PDF全文
70.
Wen Wang Yuqing Qiao Li He Ludovic Dumée Lingxue Kong Minshou Zhao Weimin Gao 《Ionics》2015,21(8):2119-2125
LiFe1???x Sm x PO4/C cathode materials were synthesized though a facile hydrothermal method. Compared with high-temperature solid-phase sintering, the method can allow for the fabrication of low Sm content (2 %), a scarce and expensive rare earth element, while the presence of an optimized carbon coating with large amount of sp2-type carbon sharply increases the material’s electrochemical performance. The high-rate dischargeability at 5 C, as well as the exchange current density, can be increased by 21 and 86 %, respectively, which were attributed to the fine size and the large cell parameter a/c as much. It should be pointed out that the a/c value will be increased for the LiFePO4 Sm-doped papered by both of the two methods, while the mechanism is different: The value c is increased for the front and the value a is decreased for the latter, respectively. 相似文献