全文获取类型
收费全文 | 8395篇 |
免费 | 954篇 |
国内免费 | 636篇 |
专业分类
化学 | 971篇 |
晶体学 | 15篇 |
力学 | 906篇 |
综合类 | 175篇 |
数学 | 5128篇 |
物理学 | 2790篇 |
出版年
2024年 | 6篇 |
2023年 | 96篇 |
2022年 | 143篇 |
2021年 | 169篇 |
2020年 | 222篇 |
2019年 | 205篇 |
2018年 | 204篇 |
2017年 | 312篇 |
2016年 | 325篇 |
2015年 | 203篇 |
2014年 | 459篇 |
2013年 | 610篇 |
2012年 | 519篇 |
2011年 | 458篇 |
2010年 | 386篇 |
2009年 | 522篇 |
2008年 | 543篇 |
2007年 | 540篇 |
2006年 | 478篇 |
2005年 | 435篇 |
2004年 | 383篇 |
2003年 | 378篇 |
2002年 | 345篇 |
2001年 | 302篇 |
2000年 | 243篇 |
1999年 | 235篇 |
1998年 | 199篇 |
1997年 | 179篇 |
1996年 | 164篇 |
1995年 | 128篇 |
1994年 | 81篇 |
1993年 | 66篇 |
1992年 | 60篇 |
1991年 | 46篇 |
1990年 | 44篇 |
1989年 | 33篇 |
1988年 | 31篇 |
1987年 | 33篇 |
1986年 | 26篇 |
1985年 | 35篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 13篇 |
1979年 | 21篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1936年 | 3篇 |
排序方式: 共有9985条查询结果,搜索用时 15 毫秒
131.
132.
Recoil proton tracks in nuclear emulsion are counted by scanning them using strip, square or circular field of view of optical microscope. In this paper, the overestimate due to the edge effects in counting recoil proton tracks at different neutron energies produced from the T(d,n)4He reaction has been determined by measuring the true track density in NTA film. The overestimate has also been calculated using the measured value of the mean projected track length (L) in the film. The percentage of measured overestimates has been compared with those obtained by calculation and the results agree reasonably well. Fading effect in NTA film has been studied and found to be 22% more in the summer than in the winter season. A great reduction in fading rate could be achieved if the films are desiccated and sealed in highly pure dry nitrogen maintained at an over-pressure of 1000 Pa to reduce water vapour ingress. After the edge effect correction, the sensitivity of NTA film has been calculated from (1.72±0.08)×10−3 tracksn−1 to (1.97±0.16)×10−3 tracksn−1 in the neutron energy ranges from 15.91 to 18.88 MeV. The response was found to be from 0.24±0.02 trackscm−2 permSv to 0.26±0.01 trackscm−2 permSv in the same energy range. 相似文献
133.
134.
Another generalization of the Mitrinovic-Djokovic inequality is proved by elementarymeans. 相似文献
135.
具有离散参数齐次随机场的线性预测(V) 总被引:1,自引:1,他引:0
本文提出并研究下列四类线性预测问题:2(n0),6(n0),5(NO,n0)及3(N0,n0).不仅求出了它们的预测误差,而且也求出了它们的预测值.因而不仅推广了而且也改进了[2-5]中的结果.本文还给出了场{X(m,n)}的一个新形式的表示式. 相似文献
136.
本文建立了解二阶双曲型方程的一种新数值方法一再生核函数法.利用再生核函数,直接给出每个离散时间层上近似解的显式表达式.此方法的优点是:计算格式绝对稳定,且可显式求解;利用显式表达式,可实现完全并行计算等文中对近似解的收敛性和稳定性进行了理论分析,并给出数值算例. 相似文献
137.
提出了一种用于修正光学神经网络硬件系统误差的虚拟神经网络模型,光学实验结果表明该网络能够有效地消除硬件系统误差对实验结果的影响。 相似文献
138.
Qiji J. Zhu 《Set-Valued Analysis》1998,6(2):171-185
Several different basic tools are used for studying subdifferentials. They are a nonlocal fuzzy sum rule in (Borwein et al., 1996; Zhu, 1996), a multidirectional mean value theorem in (Clarke and Ledyaev, 1994; Clarke et al., 1998), local fuzzy sum rules in (Ioffe, 1984, 1990) and an extremal principle in (Kruger and Mordukhovich, 1980; Mordukhovich, 1976, 1980, 1994). We show that all these basic results are equivalent and discuss some interesting consequences of this equivalence. 相似文献
139.
Dorina Mitrea Heather Rosenblatt 《Mathematical Methods in the Applied Sciences》2006,29(12):1349-1361
We prove a rather general mean‐value formula in the theory of elasticity, which expresses the value of the displacement at the centre of a sphere in terms of certain combinations of integral averages over the sphere itself of the traction and the displacement. We also establish the corresponding converse to this mean‐value formula under minimal smoothness assumptions on the displacement. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
140.
THE LARGE TIME BEHAVIOR OF SPECTRAL APPROXIMATION FOR A CLASS OF PSEUDOPARABOLIC VISCOUS DIFFUSION EQUATION 总被引:1,自引:0,他引:1
尚亚东 《数学物理学报(B辑英文版)》2007,27(1):153-168
The asymptotic behavior of the solutions to a class of pseudoparabolic viscous diffusion equation with periodic initial condition is studied by using the spectral method. The semidiscrete Fourier approximate solution of the problem is constructed and the error estiation between spectral approximate solution and exact solution on large time is also obtained. The existence of the approximate attractor AN and the upper semicontinuity d(AN,A)→0 are proved. 相似文献