全文获取类型
收费全文 | 307134篇 |
免费 | 18491篇 |
国内免费 | 9472篇 |
专业分类
电工技术 | 13203篇 |
技术理论 | 24篇 |
综合类 | 16026篇 |
化学工业 | 49499篇 |
金属工艺 | 17573篇 |
机械仪表 | 17280篇 |
建筑科学 | 19623篇 |
矿业工程 | 7998篇 |
能源动力 | 7446篇 |
轻工业 | 16834篇 |
水利工程 | 4805篇 |
石油天然气 | 16894篇 |
武器工业 | 1647篇 |
无线电 | 33765篇 |
一般工业技术 | 42495篇 |
冶金工业 | 15300篇 |
原子能技术 | 2483篇 |
自动化技术 | 52202篇 |
出版年
2024年 | 993篇 |
2023年 | 3806篇 |
2022年 | 6484篇 |
2021年 | 9096篇 |
2020年 | 7079篇 |
2019年 | 6014篇 |
2018年 | 20072篇 |
2017年 | 19902篇 |
2016年 | 15959篇 |
2015年 | 9416篇 |
2014年 | 11462篇 |
2013年 | 13451篇 |
2012年 | 17172篇 |
2011年 | 24322篇 |
2010年 | 21252篇 |
2009年 | 17871篇 |
2008年 | 18767篇 |
2007年 | 19283篇 |
2006年 | 12446篇 |
2005年 | 11896篇 |
2004年 | 8314篇 |
2003年 | 7338篇 |
2002年 | 5983篇 |
2001年 | 4973篇 |
2000年 | 5599篇 |
1999年 | 6489篇 |
1998年 | 5483篇 |
1997年 | 4480篇 |
1996年 | 4233篇 |
1995年 | 3508篇 |
1994年 | 2823篇 |
1993年 | 1972篇 |
1992年 | 1547篇 |
1991年 | 1249篇 |
1990年 | 934篇 |
1989年 | 741篇 |
1988年 | 547篇 |
1987年 | 336篇 |
1986年 | 278篇 |
1985年 | 196篇 |
1984年 | 139篇 |
1983年 | 114篇 |
1982年 | 124篇 |
1981年 | 98篇 |
1980年 | 70篇 |
1968年 | 47篇 |
1966年 | 43篇 |
1965年 | 48篇 |
1955年 | 64篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Shuang Shao Yong Liu Chun-Shui Xu Ying-Xuan Xu Bin Wu Xiao-Shu Zeng Xian-Feng Lu Xiang-Jie Yang 《金属学报(英文版)》2015,(1):7-14
The microstructure and mechanical properties of Mg–6Zn–1Y and Mg–6Zn–3Y(wt%) alloys under different cooling rates were investigated. The results show that the second dendrite arm spacing(SDAS) of Mg–6Zn–1Y and Mg–6Zn–3Y is reduced by 32 and 30% with increasing cooling rates(Rc) from 10.2 to 23 K/s, which can be predicted using a empirical model of SDAS=68 R 0:45:45cand SDAS=73 R 0c, respectively. The compressive strength of both alloys increases with increasing the cooling rate, which is attributed to the increase of volume fraction(Vf) of secondary phases under high cooling rate. The interaction of the cooling rate and component with SDAS has been theoretically analyzed using interdependence theory. 相似文献
32.
33.
主要分析国产电牵引采煤机控制系统中PLC电源故障,介绍输入回路、输出回路故障的分析、判断及排除方法。 相似文献
34.
35.
A new constitutive equation of thermoelasticity for crystals is presented based on the interatomic potential and solid mechanics at finite temperature. Using the new constitutive equation, the calculations for crystal copper and graphene are carried out under different loading paths at different temperatures. The calculated results are in good agreement with those of the previous thermoelasticity constitutive equation based on quantum mechanics, which clearly indicates that our new constitutive equation of thermoelasticity is correct. A lot of comparisons also show that the present theory is more concise and efficient than the previous thermal stress theory in the practical application. 相似文献
36.
37.
38.
本文通过径流还原计算和绘制降水径流深相关图的方法,对天然年径流系列的一致性进行了分析,并通过实例验证了该方法可使水文资料系列更具代表性。 相似文献
39.
Based on the current spin density functional theory, a theoretical model of three vertically aligned semiconductor quantum dots is proposed and numerically studied. This quantum dot molecule (QDM) model is treated with realistic hard-wall confinement potential and external magnetic field in three-dimensional setting. Using the effective-mass approximation with band nonparabolicity, the many-body Hamiltonian results in a cubic eigenvalue problem from a finite difference discretization. A self-consistent algorithm for solving the Schrödinger-Poisson system by using the Jacobi-Davidson method and GMRES is given to illustrate the Kohn-Sham orbitals and energies of six electrons in the molecule with some magnetic fields. It is shown that the six electrons residing in the central dot at zero magnetic field can be changed to such that each dot contains two electrons with some feasible magnetic field. The Förster-Dexter resonant energy transfer may therefore be generated by two individual QDMs. This may motivate a new paradigm of Fermionic qubits for quantum computing in solid-state systems. 相似文献
40.
Shunkang Liu 《Journal of Infrared, Millimeter and Terahertz Waves》2003,24(5):629-638
The pill-box and block RF windows for millimeter wave (MMW) tubes are presented. The pill-box window is suitable for broadband MMW tubes. And the block window can be used for high power tubes in short MMW. The equivalent circuits for two windows are given. To reach better match characteristics in wider operating bandwidth, the optimum design methods for pill-box and block window in MMW tubes are described in this paper. The testing results show that the theoretic computation is fast and useful accuracy. The design methods possess references value to designer for MMW tubes. 相似文献