全文获取类型
收费全文 | 68721篇 |
免费 | 11596篇 |
国内免费 | 8356篇 |
专业分类
化学 | 36701篇 |
晶体学 | 805篇 |
力学 | 2862篇 |
综合类 | 431篇 |
数学 | 5116篇 |
物理学 | 20294篇 |
无线电 | 22464篇 |
出版年
2024年 | 294篇 |
2023年 | 1564篇 |
2022年 | 2047篇 |
2021年 | 2683篇 |
2020年 | 2613篇 |
2019年 | 2684篇 |
2018年 | 2235篇 |
2017年 | 2217篇 |
2016年 | 3008篇 |
2015年 | 3326篇 |
2014年 | 4047篇 |
2013年 | 4991篇 |
2012年 | 5999篇 |
2011年 | 6025篇 |
2010年 | 4503篇 |
2009年 | 4520篇 |
2008年 | 5007篇 |
2007年 | 4307篇 |
2006年 | 4212篇 |
2005年 | 3570篇 |
2004年 | 2708篇 |
2003年 | 2178篇 |
2002年 | 2153篇 |
2001年 | 1784篇 |
2000年 | 1437篇 |
1999年 | 1412篇 |
1998年 | 1087篇 |
1997年 | 935篇 |
1996年 | 923篇 |
1995年 | 777篇 |
1994年 | 679篇 |
1993年 | 539篇 |
1992年 | 464篇 |
1991年 | 385篇 |
1990年 | 303篇 |
1989年 | 223篇 |
1988年 | 159篇 |
1987年 | 113篇 |
1986年 | 142篇 |
1985年 | 114篇 |
1984年 | 64篇 |
1983年 | 68篇 |
1982年 | 48篇 |
1981年 | 42篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1957年 | 8篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
使用Monte Carlo模拟的方法得出了随机粗糙表面,在Kirchhoff近似的基础上,利用数值分析的方法分析了一维随机粗糙表面的散射特征,得出了一维随机粗糙表面散射分布曲线,我们还考虑了遮蔽效应的影响,并且讨论了Kirchhoff近似的有效性。 相似文献
72.
Shi Wei Zhao Xuefeng Ma Conghui Management of the National Development Reform Commission 《中国通信》2008,(3)
After the new round of restructuring of Chinese telecom sector,it's pressing to formulate and implement asymmetric regulation policies so as to shape an effectively competitive market structure in a relatively short term.This paper reviewed the asymmetric regulation policies and practices carried out in foreign telecom market,and then according to the specific situations of Chinese telecom market,proposed the principles and corresponding policies for establishing an asymmetric regulation system fit for Chin... 相似文献
73.
Wang Qing-Lun Zhao Bin Liao Dai-Zheng Yan Shi-Ping Cheng Peng Jiang Zong-Hui 《Transition Metal Chemistry》2003,28(3):326-330
The copper(II) complex Na2[Cu(pba)] · 6H2O has been synthesized and its structure determined. It consists of a novel two-dimensional network of [Cu(pba)]2– anions connected to each other through the sodium ion as a bridge. Spectroscopic and magnetic properties have been measured and a spin distribution calculation has been carried out with the GAUSSIAN-94. Theoretical calculations indicate the rather larger spin density on nitrogen atoms should be responsible for the satellite lines appearing beside the main hyperfine coupling signs of copper(II). The antiferromagnetic interaction may be due to the intermolecular interaction and/or different copper(II) ions through the Na+ bridge in the same layer. 相似文献
74.
75.
A new stochastic method of reconstructing porous media 总被引:1,自引:0,他引:1
We present a new stochastic method of reconstructing porous medium from limited morphological information obtained from two-dimensional
micro- images of real porous medium. The method is similar to simulated annealing method in the capability of reconstructing
both isotropic and anisotropic structures of multi-phase but differs from the latter in that voxels for exchange are not selected
completely randomly as their neighborhood will also be checked and this new method is much simpler to implement and program.
We applied it to reconstruct real sandstone utilizing morphological information contained in porosity, two-point probability
function and linear-path function. Good agreement of those references verifies our developed method’s powerful capability.
The existing isolated regions of both pore phase and matrix phase do quite minor harm to their good connectivity. The lattice
Boltzmann method (LBM) is used to compute the permeability of the reconstructed system and the results show its good isotropy
and conductivity. However, due to the disadvantage of this method that the connectivity of the reconstructed system’s pore
space will decrease when porosity becomes small, we suggest the porosity of the system to be reconstructed be no less than
0.2 to ensure its connectivity and conductivity. 相似文献
76.
77.
Characterizations of Tb:Zn2SiO4 films on silicon wafer prepared by sol-gel dip-coating and solid-phase reaction 下载免费PDF全文
Terbium-doped Zn_2SiO_4 films were successfully prepared on Si wafers by a simple sol-gel dip-coating and solid-phase reaction method of ZnO and SiO_2. X-ray diffraction (XRD) and UV-Vis absorption results revealed that films processed below 850℃ were ZnO in wurzite structure, and films processed above 850℃ were Zn_2SiO_4 in wellimite structure. Photoluminescence measurements of the Tb-doped Zn_2SiO_4 films showed two strong emission bands at 490 and 545nm. The photoluminescence lifetime was 4.6ms. 相似文献
78.
79.
空时分集技术的最大优点在于在不增加带宽的情况下可以提高系统的可靠性,是目前移动通信的研究热点.常模算法是一种性能优良的码分多址(CDMA)盲多用户检测技术,能确保判决信号与实际传送信号之间的差错较小,误码率性能良好.文中提出将标准线性受限常模算法(LCCMA)与空时分组码(STBC)相结合,设计出一种收敛快、能够改善系统性能的基于2-空时分组码的多用户接收机. 相似文献
80.