全文获取类型
收费全文 | 1323篇 |
免费 | 21篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 38篇 |
综合类 | 9篇 |
化学工业 | 91篇 |
金属工艺 | 24篇 |
机械仪表 | 19篇 |
建筑科学 | 20篇 |
矿业工程 | 9篇 |
能源动力 | 70篇 |
轻工业 | 29篇 |
水利工程 | 4篇 |
石油天然气 | 3篇 |
武器工业 | 2篇 |
无线电 | 303篇 |
一般工业技术 | 119篇 |
冶金工业 | 17篇 |
原子能技术 | 12篇 |
自动化技术 | 581篇 |
出版年
2023年 | 44篇 |
2022年 | 17篇 |
2021年 | 34篇 |
2020年 | 35篇 |
2019年 | 27篇 |
2018年 | 26篇 |
2017年 | 111篇 |
2016年 | 107篇 |
2015年 | 67篇 |
2014年 | 132篇 |
2013年 | 104篇 |
2012年 | 48篇 |
2011年 | 59篇 |
2010年 | 49篇 |
2009年 | 51篇 |
2008年 | 41篇 |
2007年 | 47篇 |
2006年 | 40篇 |
2005年 | 30篇 |
2004年 | 18篇 |
2003年 | 10篇 |
2002年 | 26篇 |
2001年 | 38篇 |
2000年 | 19篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 12篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1987年 | 19篇 |
1986年 | 17篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1350条查询结果,搜索用时 0 毫秒
81.
通过自适应调整最小竞争窗口最大化IEEE 802.11 DCF的饱和吞吐量 总被引:7,自引:0,他引:7
最大化802.11 DCF的饱和吞吐量对充分利用无线局域网宝贵的带宽资源具有重要意义。该文在分析802.11 DCF的饱和吞吐量与最小竞争窗口、最大回退等级、网络中竞争信道的节点数的关系的基础上,推导了根据网络中竞争信道的节点数,计算最小竞争窗口的最佳值的简单公式。给出了估计竞争信道的节点数并据此动态调整最小竞争窗口的最佳值的自适应算法。同时,该文对估计竞争节点数的算法的准确性和计算最小竞争窗口最佳值的公式的准确性进行了仿真分析,并比较了改进后的802.11 DCF的饱和吞吐量与原802.11 DCF的饱和吞吐量的大小。仿真结果证明了上述公式、算法是准确和有效的。 相似文献
82.
L. Boon-Brett J. Bousek P. Castello O. Salyk F. Harskamp L. Aldea F. Tinaut 《International Journal of Hydrogen Energy》2008
A facility for testing the performance of hydrogen safety sensors under a wide range of ambient conditions is described. A specific test protocol was developed to test sensors under conditions which could reasonably be expected during the sensors' service life. The tests were based on those described in IEC 61779 and were adapted following consultation with car manufacturers and after careful consideration of the sensors expected service environmental conditions. The protocol was evaluated by using it to test a large number of commercially available sensors. Observations made and experience gained during the testing campaign allowed the test protocol to be fine-tuned bearing in mind the sensor performance and behaviour during tests. The result of this work is an experimentally evaluated methodology which may be used as a guideline for testing the suitability of hydrogen sensors for automotive applications. 相似文献
83.
CIGS薄膜(InGa)2Se3-富Cu-富In(Ga)的演变 总被引:1,自引:0,他引:1
采用三步共蒸发工艺顺序沉积铜铟镓硒(CuInGaSe2,CIGS)薄膜.薄膜的厚度、组份、晶相结构分别由台阶仪、X射线荧光光谱仪(XRF)和X射线衍射仪(XRD)来表征.在(In,Ga)2Se3预制层-富Cu相的演变过程中,依次发生以下相变:Cu(In,Ga)5Se8、Cu(In,Ga)3Se5、Cu2(In,Ga)4Se7(或Cu(In,Ga)2Se3.5)、Cu(In,Ga)Se2(液相CuxSe).在富Cu相-富In(Ga)相的演变过程中,依次发生以下相变:Cu(In,Ga)Se2(液相CuxSe)、Cu2(In,Ga)4Se7(或Cu(In,Ga)2Se3.5)、Cu(In,Ga)3Se5、Cu(In,Ga)5Se8.对这两个演变过程中薄膜的生长机理和结构特性进行了讨论. 相似文献
84.
Yassen Mahmood T. Hussan Mohammed R. Hammas Hussain A. Al-Saedi Hussam Ali Jawad K. 《Wireless Personal Communications》2019,104(2):649-662
Wireless Personal Communications - The design of a fractal based slot antenna, to serve the dual-band communication applications, is proposed in this paper. The structure of the proposed antenna is... 相似文献
85.
针对OFDMA中继网络的两跳特性,提出一种基于两跳匹配的中继网络联合资源分配算法。首先根据中继网络的两跳性建立两跳速率匹配模型,然后利用对偶分解理论将中继网络资源分配的主问题分解为:中继选择、子载波分配和功率分配三个主要的子问题并进行联合优化,同时基于中继网络两跳性在子载波分配的过程中考虑两跳子载波配对,以逼近系统最优解。最后为了保证算法的公平性,考虑子载波分配因子约束以优化子载波分配。仿真结果表明:所提算法将中继选择、两跳子载波配对与功率分配联合优化以进一步提升系统吞吐量,同时引入子载波分配因子约束,保证了算法的公平性。 相似文献
86.
《Optical Fiber Technology》2004,10(1):5-30
We describe the design and performance of cladding-pumped silica fiber lasers with high continuous-wave output powers and broad wavelength tunability in the 1, 1.5, and 2 μm spectral ranges. An ytterbium-doped fiber laser was tuned via wavelength dependent feedback provided by an external cavity containing a diffraction grating from 1027 to 1105 nm at multi-watt power levels. Similarly, high output power and wide wavelength tunability from 1540 to 1600 nm and from 1860 to 2090 nm at multi-watt output power levels has been achieved in Er-Yb co-doped and Tm-doped silica fiber lasers, respectively. A neodymium doped fiber laser was tuned from 1057 to 1118 nm at a lower power level. Limiting factors and the prospects for further improvements in performance are considered. 相似文献
87.
88.
Numerical simulation, using SILVACO-TCAD, is carried out to explain experimentally observed effects of different types of deep levels on the capacitance–voltage characteristics of p-type Si-doped GaAs Schottky diodes grown on high index GaAs substrates. Two diodes were grown on (311)A and (211)A oriented GaAs substrates using Molecular Beam Epitaxy (MBE). Although, deep levels were observed in both structures, the measured capacitance–voltage characteristics show a negative differential capacitance (NDC) for the (311)A diodes, while the (211)A devices display a usual behaviour. The NDC is related to the nature and spatial distribution of the deep levels, which are characterized by the Deep Level Transient Spectroscopy (DLTS) technique. In the (311)A structure only majority deep levels (hole traps) were observed while both majority and minority deep levels were present in the (211)A diodes. The simulation, which calculates the capacitance–voltage characteristics in the absence and presence of different types of deep levels, agrees well with the experimentally observed behaviour. 相似文献
89.
This study conducted an online experiment to examine how persuasion knowledge of online targeted advertising (OTA), coping self-efficacy, and product involvement influenced the perceptions of privacy concerns and ad intrusiveness. These findings indicated that persuasion knowledge increased coping self-efficacy, which, in turn, influenced privacy concerns and perceived ad intrusiveness. Furthermore, the relations between coping self-efficacy and the evaluations of the OTA varied, depending on levels of product involvement. Specifically, when participants had high product involvement, their perceptions of privacy concerns and ad intrusiveness increased as their coping self-efficacy enhanced. However, those relationships did not appear among participants with low levels of product involvement. Theoretical and managerial implications of these findings are discussed later. 相似文献
90.