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221.
In the field of room acoustics, it is popular belief that the early and late reflections contribute to auditory source width (ASW) and listener envelopment (LEV), respectively. However, some papers have demonstrated results not necessarily in agreement with the belief. In this paper, a hypothesis is proposed to clarify the essentials of ASW and LEV from point of view of the auditory phenomenon. The hypothesis is that the components of reflections under and beyond the upper limit of validity for the law of the first wavefront contribute to ASW and LEV, respectively. Two experiments were performed to evaluate the hypothesis. In the first experiment, the results showed directly that the components of reflections under the upper limit of validity for the law contribute to ASW. In the second experiment, four kinds of threshold were measured to evaluate the relation between the effect and LEV: image-splitting which corresponds to the upper limit of validity for the law, LEV, reverberation perception, and reverberation disturbance. The results showed that the threshold of image-splitting coincides with the that of LEV. This suggests that the components of reflections beyond the upper limit of validity for the law contribute to LEV. In conclusion, it seems that the results of experiments shown in this paper favor the hypothesis. 相似文献
222.
Acoustic plane progressive waves incident on a sphere immersed in a nonviscous fluid exert a steady force acting along the
direction of wave motion. It is shown here that when an elastic gold sphere is coated with a polymer-type (polyethylene) viscoelastic
layer, this force becomes a force of attraction in the long wavelength limit. Kinetic, potential and Reynolds stress energy
densities are defined and evaluated with and in the absence of absorption in the layer. Without absorption, the mechanical
energy density counteracts the Reynolds stress energy density, which causes a repulsive force. However, in the case of absorption,
the attractive force is predicted to be a physical consequence of a mutual contribution of both the mechanical and the Reynolds
stress energy densities. This condition provides an impetus for further designing acoustic tweezers operating with plane progressive
waves as well as fabricating polymer-coated gold particles for specific biophysical and biomedical applications. 相似文献
223.
224.
海洋水色水温扫描仪(COCTS)是中国海洋水色系列卫星上的主遥感器,主要用于探测我国及全球部分海域的海洋水色和水温环境信息.大气漫射透射比计算是COCTS大气校正的必需过程,直接影响COCTS大气校正和水色信息反演的精度.提出了基于加倍法解大气-海洋耦合矢量辐射传输方程的大气漫射透射比精确计算方法,通过与SeaWiFS精确大气漫射透射比查找表计算结果的比较,结果表明计算相对误差小于1.5%,而当观测天顶角小于60°时,计算相对误差小于0.5%,可以用来生成COCTS的精确大气漫射透射比查找表.在此基础上,生成了专门针对COCTS的精确大气漫射透射比查找表. 相似文献
225.
水面下的波浪--海洋内波 总被引:13,自引:0,他引:13
讨论了海洋中因温度、盐度非均匀引起的分层结构.内波因恢复力小比表面波有较大振幅和较低频率.在地球上,内波以不同形式(如:内潮,内孤立波等)发生在层结、洋流和地形合适的大陆边缘地带.内波活动是海洋结构的安全隐患、水下声道的背景噪声源和深水混合的“搅拌器”,我们考察了内波在海洋工程、海洋环境和水声探测中的各种应用. 相似文献
226.
浮游植物的吸收和散射特性:理论模型 总被引:5,自引:0,他引:5
利用Mie理论模型对不同粒径分布和复折射率的浮游植物吸收和散射特性进行了模拟计算。在550nm波长处,直径<10μm的颗粒对总的散射系数贡献最大,单位体积浓度的散射系数随着折射率实部n的增大呈有规律的地增加。对给定的n值来说,随着微分粒径分布参数j值的增大而增加,折射率实部n对单位色素浓度的吸收系数ap*(λ)的影响很小,对bp*(λ)影响相对较大。折射率虚部n′对单位色素浓度的吸收系数ap*(λ)的影响很大,对bp*(λ)的影响相对较小。微分粒径分布参数j对ap*(λ)和bp*(λ)的影响都很大,ap*(λ)随j值的减小而减小的主要原因是因为大颗粒“打包效应”引起的吸收减弱,而bp*(λ)随j值的增大而增大的主要原因是因为小粒径颗粒对散射的贡献。 相似文献
227.
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229.
This paper presents the applicability of an explicit time-domain finite element method (TD-FEM) using a dispersion reduction technique called modified integration rules (MIR) on room acoustics simulations with a frequency-independent finite impedance boundary. First, a dispersion error analysis and a stability analysis are performed to derive the dispersion relation and the stability condition of the present explicit TD-FEM for three-dimensional room acoustics simulations with an infinite impedance boundary. Secondly, the accuracy and efficiency of the explicit TD-FEM are presented by comparing with implicit TD-FEM using MIR through room acoustics simulations in a rectangular room with infinite impedance boundaries. Thirdly, the stability condition of the explicit TD-FEM is investigated numerically in the case with finite impedance boundaries. Finally, the performance of the explicit TD-FEM in room acoustics simulations with finite impedance boundaries is demonstrated in a comparison with the implicit TD-FEM. Although the stability of the present explicit TD-FEM is dependent on the impedance values given at boundaries, the explicit TD-FEM is computationally more efficient than the implicit method from the perspective of computational time for acoustics simulations of a room with larger impedance values at boundaries. 相似文献
230.