全文获取类型
收费全文 | 22496篇 |
免费 | 2133篇 |
国内免费 | 975篇 |
专业分类
电工技术 | 1228篇 |
综合类 | 1077篇 |
化学工业 | 3689篇 |
金属工艺 | 1495篇 |
机械仪表 | 1697篇 |
建筑科学 | 1326篇 |
矿业工程 | 655篇 |
能源动力 | 828篇 |
轻工业 | 1535篇 |
水利工程 | 312篇 |
石油天然气 | 998篇 |
武器工业 | 117篇 |
无线电 | 3021篇 |
一般工业技术 | 3618篇 |
冶金工业 | 1240篇 |
原子能技术 | 195篇 |
自动化技术 | 2573篇 |
出版年
2024年 | 78篇 |
2023年 | 436篇 |
2022年 | 668篇 |
2021年 | 1099篇 |
2020年 | 820篇 |
2019年 | 677篇 |
2018年 | 823篇 |
2017年 | 787篇 |
2016年 | 808篇 |
2015年 | 930篇 |
2014年 | 1139篇 |
2013年 | 1388篇 |
2012年 | 1482篇 |
2011年 | 1645篇 |
2010年 | 1414篇 |
2009年 | 1395篇 |
2008年 | 1262篇 |
2007年 | 1059篇 |
2006年 | 1006篇 |
2005年 | 877篇 |
2004年 | 667篇 |
2003年 | 651篇 |
2002年 | 605篇 |
2001年 | 510篇 |
2000年 | 475篇 |
1999年 | 494篇 |
1998年 | 472篇 |
1997年 | 368篇 |
1996年 | 339篇 |
1995年 | 279篇 |
1994年 | 223篇 |
1993年 | 147篇 |
1992年 | 116篇 |
1991年 | 81篇 |
1990年 | 80篇 |
1989年 | 66篇 |
1988年 | 47篇 |
1987年 | 36篇 |
1986年 | 33篇 |
1985年 | 23篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
142.
日本国家计量研究院(National Research Laboratory of Metrology)540kN静重式力基准机中的振荡分量主要是由于砝码的摆动引起的。本文对砝码的动态特性做了详细的分析,给出了其摆动的轨迹图,并对由于砝码摆动引起的相对不确定度进行了评估。提出了一类采用传感器并联的叠加系统(以下称叠加系统)输出的力值信号来评估砝码动态特性的信号处理方法。它对研究静重式测力机砝码摆动提供了有效的分析方法。 相似文献
143.
在2007年夏天一个难得凉爽的日子,我采访了思维严谨、幽默风趣的山西焦煤集团总经理柴久茂。听他解读的企业安全观,既科学实在,又引人深思,很受启发。如果每一个煤炭企业的带头人都有如此理性的安全发展观,那么我国煤矿的真正安宁和谐就会加快实现。 相似文献
144.
分段线性材料桁架的位移灵敏度 总被引:2,自引:1,他引:1
本文推导了分段线性材料桁架结构的位移对截面积的灵敏度,并给出三杆桁架实例。指出了在材料性质发生突变处位移对截面积的灵敏度不连续、位移等值面不光滑:讨论了,采用准则法求解优化问题时的灵敏度计算和迭代公式,旨在指出文献中的错误。 相似文献
145.
J.Z. Wu S.H. Yoo T. Aytug A. Gapud B.W. Kang S. Wu W. Zhou 《Journal of Superconductivity》1998,11(1):169-171
The effect of Na- and Li-doping in Hg-based cuprates has been studied. It has been found that superconductivity can be achieved in samples containing small amount of Na or Li. While little change is found in the crystalline structure, the formed superconducting phase have the onset Tc typically above 140 K and zero-resistance Tc up to 136K. More interestingly, the processing temperature for the doped Hg-1223 can be reduced significantly to near 700 °C which is promising for thin films growth on many technologically compatible substrates. 相似文献
146.
The importance of the misframe times for DS1 frame synchronization has often been addressed in designing and using network elements and mediation units. By extending the work of J. H. Eu and W. W. Rollins (1991), Markov chain first passage time analysis is used to derive higher moments of the misframe times in both random and burst error environments. This methodology is of great value in evaluating frame synchronization techniques for digital transmission systems. By experimenting with several out-of-frame detection schemes and reasonable values for bit error ratio (BER), it is shown that misframe times are always approximately exponentially distributed for all schemes 相似文献
147.
Beckwith-Wiedemann syndrome (BWS) comprises of a number of childhood abnormalities, often associated with one or more tumors. Thirty-eight patients were investigated to determine clinical and/or biological signs associated with a tumor presence. Our patients exhibited a higher incidence of tumor development (21%) than that previously reported, underlying the care with which such patients should be followed, when particular clinical features are observed: visceromegaly affecting three organs (liver, kidney, spleen), and also family history with sign of BWS such as macroglossia, omphalocele, hemihypertrophy, embryonic tumor), high body weight at birth (> or = +2 standard deviations and diastasis recti. 相似文献
148.
本文根据光传输理论导出介导消光系数,折射率与介质电磁参数,光波频率,电偶极子浓度及迁移率等的关系,分析了光激发与增加气敏介质的氧吸附的规律,结合实验说明气敏薄膜的光学变化机制。 相似文献
149.
Zeolite beta with a low SiO2/Al2O3 ratio was synthesized by a novel two-step process.The synthesized sample was characterized with XRD,SEM,FTIR,and N2 adsorption-desorption and solid-state MAS NMR.The results showed that aluminium species were inserted into the framework of zeolite beta.The BET surface area,volume,and particle size of the zeolite beta sample decreased with decreasing SiO2/Al2O3 ratio.Our process was proved an efficient route to synthesize zeolite beta with a low SiO2/Al2O3 ratio. 相似文献
150.
Bong-Un Lee Hwa-Suk Oh Ja-Young Kang 《Journal of Mechanical Science and Technology》2007,21(3):436-447
The geometric singularity problem is one of principal difficulty when using single-gimbal control moment gyros as spacecraft
attitude control devices. To overcome singularity, new steering logics are suggested in this paper which results in a reduction
in the difficulty of generating gimbal rates around a singular state. One of the suggested steering laws presented is the
reduced dimensional singular value decomposition steering law, which adopts the singular value decomposition in reduced dimensional
forms. Two other steering laws make use of the least square method in reduced dimensional forms. All of the suggested steering
laws have been generated for the compensation of the torque insufficiency. These logics are verified mathematically and simulations
at a singular condition and non-singular condition are performed to see how well they work. 相似文献