全文获取类型
收费全文 | 44122篇 |
免费 | 2539篇 |
国内免费 | 1975篇 |
专业分类
化学 | 21707篇 |
晶体学 | 449篇 |
力学 | 2207篇 |
综合类 | 84篇 |
数学 | 10432篇 |
物理学 | 13757篇 |
出版年
2024年 | 60篇 |
2023年 | 322篇 |
2022年 | 565篇 |
2021年 | 601篇 |
2020年 | 651篇 |
2019年 | 650篇 |
2018年 | 1746篇 |
2017年 | 1938篇 |
2016年 | 1423篇 |
2015年 | 1312篇 |
2014年 | 1433篇 |
2013年 | 1823篇 |
2012年 | 4479篇 |
2011年 | 3737篇 |
2010年 | 2835篇 |
2009年 | 2418篇 |
2008年 | 1563篇 |
2007年 | 1527篇 |
2006年 | 1415篇 |
2005年 | 5116篇 |
2004年 | 4418篇 |
2003年 | 2725篇 |
2002年 | 888篇 |
2001年 | 583篇 |
2000年 | 390篇 |
1999年 | 422篇 |
1998年 | 331篇 |
1997年 | 265篇 |
1996年 | 225篇 |
1995年 | 183篇 |
1994年 | 226篇 |
1993年 | 149篇 |
1992年 | 294篇 |
1991年 | 249篇 |
1990年 | 226篇 |
1989年 | 191篇 |
1988年 | 144篇 |
1987年 | 87篇 |
1986年 | 76篇 |
1985年 | 65篇 |
1984年 | 50篇 |
1983年 | 37篇 |
1976年 | 89篇 |
1975年 | 44篇 |
1974年 | 48篇 |
1973年 | 55篇 |
1972年 | 41篇 |
1969年 | 41篇 |
1968年 | 40篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
103.
The determination of the sensitivity of the acoustical characteristics of vibrating systems with respect to the variation of the design parameters predicting these characteristics is a necessary and important step of the acoustic design and optimization process. Acoustic design sensitivity analysis includes the computation and evaluation of the sensitivity information required for this procedure. In this study, a boundary element code performing the sensitivity analysis of the acoustic pressure by using the matrix sensitivities with respect to different design variables has been developed. The effect of the precision of boundary element discretization on the acoustic pressure sensitivity is examined via this code. The formulation is applied to a multi-source system and the dimension sensitivity analysis of near field pressures of two-dilating-spherical source is performed. The last application is devoted to a real sound source: a washing machine sitting on the floor. Sensitivity of the field pressures to the machine’s dimensions (size), surface velocity and frequency is examined on the bases of the boundary element model of the machine and half-space condition. The impacts of these variables are compared; and a limiting speed for the machine responding both the acoustical and operational requirements is determined. 相似文献
104.
硅色敏器件对复色光色差辨识能力的数值分析 总被引:3,自引:2,他引:1
对复色光的光谱功率分布和色敏器件光谱响应的实验曲线进行了函数拟合,采用Mathematica 4.2计算了具有不同峰值波长和半高宽的高斯分布的复色光在色敏器件中产生的电流比.计算结果表明,待测复色光的峰值波长和半高宽变化对两种典型的色敏器件的输出信号影响的权重比分别为100:1和10:1。权重比说明色敏器件的输出电流比随峰值波长和半高宽的变化非常灵敏,但两者权重不同,其中峰值波长的变化影响更为显著,是影响复色光颜色变化的主要因素.数值分析的结果表明,硅双结色敏器件对复色光色差有良好的辨识能力.两种器件权重比的差异说明了器件制作工艺与其辨识能力的关系,为器件合理设计提供了理论依据. 相似文献
105.
We prove an existence theorem for a nonlinear integral equation being a Volterra counterpart of an integral equation arising in the traffic theory. The method used in the proof allows us to obtain additional characterization in terms of asymptotic stability of solutions of an equation in question. 相似文献
106.
107.
由于含时波包方法具有经典的直观又不乏量子力学的准确 ,选择含时波包方法来处理F +CH2 D2 →CH2 D/CHD2 +DF/HF反应 .把半刚性振转子 (SVRT)模型应用到该反应体系中 ,研究了两个通道中该反应从基态反应物开始在修正过的J1(MJ1)势能面上计算出来了反应几率、积分截面、速率常数 .反应几率随能量变化的图的数值结果给出了振荡结构 ,这些振荡结构是可以和动力学振荡联系起来的 .而这些振荡结构在积分截面随着能量变化的图中就被反应几率求和后的平均结果所掩盖了 .速率常数和实验结果的比较也得到了较好的结果 . 相似文献
108.
Jin Sun Yihu Song Qiang Zheng Hong Tan Jie Yu Hong Li 《Journal of Polymer Science.Polymer Physics》2007,45(18):2594-2602
The reinforcement and nonlinear viscoelastic behavior have been investigated for silica (SiO2) filled solution‐polymerized styrene butadiene rubber (SSBR). Experimental results reveal that the nonlinear viscoelastic behavior of the filled rubber is similar to that of unfilled SSBR, which is inconsistent with the general concept that this characteristic comes from the breakdown and reformation of the filler network. It is interesting that the curves of either dynamic storage modulus (G′) or loss tangent (tan δ) versus strain amplitude (γ) for the filled rubber can be superposed, respectively, on those for the unfilled one, suggesting that the primary mechanism for the Payne effect is mainly involved in the nature of the entanglement network in rubbery matrix. It is believed there exists a cooperation between the breakdown and reformation of the filler network and the molecular disentanglement, resulting in enhancing the Payne effect and improving the mechanical hysteresis at high strain amplitudes. Moreover, the vertical and the horizontal shift factors for constructing the master curves could be well understood on the basis of the reinforcement factor f(φ) and the strain amplification factor A(φ), respectively. The surface modification of SiO2 causes a decrease in f(φ), which is ascribed to weakeness of the filler–filler interaction and improvement of the filler dispersion. However, the surface nature of SiO2 hardly affects A(φ). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2594‐2602, 2007 相似文献
109.
110.
Using the Ward-Takahashi identity, on-shell condition, bound Dirac equation and off-shell expansion, a reduced version of half off-shell virtual photon nucleon vertex has been suggested. The vertex are decomposed into several different order terms: the on-shell terms, first and second off-shell terms. The off-shell behaviour of the form factors is discussed in the one meson loop model. Using the reduced vertex and parametrized off-shell form factors the quasielastic response functions are calculated for several nuclei at ¦q¦–kf and for56Fe at large ¦q¦ up to 1.14 GeV/c and at ?q2=0.9 (GeV/c)2. The Coulomb sums are evaluated and a comparison of the theoretical prediction with data is given. The off-shell electron nucleon cross section is calculated and compared with the “cc1” off-shell extrapolation. 相似文献