全文获取类型
收费全文 | 58144篇 |
免费 | 6114篇 |
国内免费 | 5231篇 |
专业分类
电工技术 | 1787篇 |
技术理论 | 1篇 |
综合类 | 3088篇 |
化学工业 | 6509篇 |
金属工艺 | 26308篇 |
机械仪表 | 3154篇 |
建筑科学 | 1013篇 |
矿业工程 | 1275篇 |
能源动力 | 1281篇 |
轻工业 | 706篇 |
水利工程 | 107篇 |
石油天然气 | 744篇 |
武器工业 | 757篇 |
无线电 | 2179篇 |
一般工业技术 | 10459篇 |
冶金工业 | 6086篇 |
原子能技术 | 402篇 |
自动化技术 | 3633篇 |
出版年
2024年 | 257篇 |
2023年 | 930篇 |
2022年 | 1574篇 |
2021年 | 1894篇 |
2020年 | 2070篇 |
2019年 | 1815篇 |
2018年 | 1806篇 |
2017年 | 2273篇 |
2016年 | 2122篇 |
2015年 | 2262篇 |
2014年 | 3088篇 |
2013年 | 3134篇 |
2012年 | 3523篇 |
2011年 | 4280篇 |
2010年 | 3183篇 |
2009年 | 3373篇 |
2008年 | 2813篇 |
2007年 | 3983篇 |
2006年 | 3986篇 |
2005年 | 3266篇 |
2004年 | 2837篇 |
2003年 | 2450篇 |
2002年 | 2119篇 |
2001年 | 1988篇 |
2000年 | 1582篇 |
1999年 | 1342篇 |
1998年 | 978篇 |
1997年 | 890篇 |
1996年 | 828篇 |
1995年 | 602篇 |
1994年 | 535篇 |
1993年 | 377篇 |
1992年 | 354篇 |
1991年 | 246篇 |
1990年 | 230篇 |
1989年 | 184篇 |
1988年 | 107篇 |
1987年 | 44篇 |
1986年 | 24篇 |
1985年 | 14篇 |
1984年 | 23篇 |
1983年 | 14篇 |
1982年 | 28篇 |
1981年 | 19篇 |
1980年 | 6篇 |
1978年 | 9篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1959年 | 4篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
52.
With the proliferation of mobile computing technologies, location based services have been identified as one of the most promising
target application. We classify mobile information service domains based on feature characteristics of the information sources
and different patterns of mobile information access. By carefully examining the service requirements, we identify the dynamic
data management problem that must be addressed for effective location based services in mobile environments. We then devise
a general architecture and cost model for servicing both location independent and location dependent data. Based on the architecture
and cost model, we propose a set of dynamic data management strategies that employs judicious caching, proactive server pushing
and neighborhood replication to reduce service cost and improve response time under changing user mobility and access patterns.
Detail behavior analysis helps us in precisely capturing when and how to apply these strategies. Simulation results suggest
that different strategies are effective for different types of data in response to different patterns of movement and information
access.
Shiow-yang Wu is an associate professor of the Department of Computer Science and Information Engineering at National Dong Hwa University,
Hualien, Taiwan, R.O.C. He received the BS and MS degrees in computer engineering from National Chiao Tung University, Hsinchu,
Taiwan, ROC, and the PhD degree in computer science from the University of Texas at Austin in 1984, 1986, and 1995, respectively.
His research interests include data/knowledge bases, mobile computing, distributed processing, intelligence information systems,
and electronic commerce.
Kun-Ta Wu was born in Taipei, Taiwan, R.O.C., in 1976. He received the B.S. degree in computer science from Soochow University, Taipei,
Taiwan, R.O.C., in 1999 and the M.S. degree in computer science and information engineering from National Dong Hwa University,
Hualien, Taiwan, R.O.C., in 2001.
Currently, he is an Assistant Researcher in the Domestic Division at Science and Technology Information Center, National Science
Council, R.O.C., as a member of Information Gathering and Analysis Group of National Information and Communication Security
Taskforce. His research interests include mobile computing, wireless network and information security. 相似文献
53.
The oxidation behavior of Hastelloy-XR alloy was investigated to obtain the optimum surface condition for corrosion-resistant glass-coatings. The surface morphology of oxide scales changed significantly with variation of temperatureand oxygen partial pressure (po2 ). The oxidation kinetics was mainly parabolic independent of oxidation conditions.The oxide scales were consisted of inner Cr2O3 and outer spinel layers. The phase component of spinel layers wereMn1.5Cr1.5O4 and (Mn,Ni)(Cr,Fe)2O4 for the oxygen partial pressures po2<10 kPa and po2>10 kPa, respectively.The optimum oxidation condition to obtain an oxide scale for well-adhered glass-coating to the substrate was 1248 Kand po2 =0.01 kPa for the oxidation time of 43 ks. 相似文献
54.
应用静态吸附、动态吸附、程序升温脱附和程序升温还原等实验方法,考察了噻吩在Ni基非晶态合金上的吸附和脱附行为。常温下,噻吩分子首先吸附在清洁的Ni表面,并立刻被活化,发生氢解反应,C-S键断裂,释放出烃类部分,S留在Ni原子上。噻吩可以在Ni基非晶态合金表面发生强度不同的化学吸附。弱化学吸附的噻吩可以脱附;强化学吸附的噻吩不会脱附,而在高温下发生氢解反应。 相似文献
55.
介绍采用聚合氯化铁(PFC)为絮凝剂,对海水进行混凝除浊预处理方法。考察了原海水pH、搅拌速度、反应时间及PFC用量对海水预处理效果的影响。结果表明,在原海水pH凋至9.0,搅拌速度控制在200min^-1,反应时间选择8—10min,PFC用量0.10μg/g的最佳条件下,能使处理后的海水浊度降至0.05mol/L,而联产的酸性废水中和剂浆料中Mg(OH)2含量在25%~45%,大肠菌群的去除率大于89.3%。 相似文献
56.
57.
We have improved the electronic properties of narrow-bandgap (Tauc gap below 1.5 eV) amorphous-silicon germanium alloys (a-SiGe:H) grown by hot-wire chemical vapor deposition (HWCVD) by lowering the substrate temperature and deposition rate. Prior to this work, we were unable to grow a-SiGe:H alloys with bandgaps below 1.5 eV that had photo-to-dark conductivity ratios comparable with our plasma-enhanced CVD (PECVD) grown materials [B.P. Nelson et al., Mater. Res. Soc. Symp. 507 (1998) 447]. Decreasing the filament diameter from our standard configuration of 0.5 mm to 0.38 or 0.25 mm provides first big improvements in the photoresponse of these alloys. Lowering the substrate temperature from our previous optimal temperatures (Tsub starting at 435 °C) to at 250 °C provides additional photo-to-dark conductivity ratio increasing by two orders of magnitude for growth conditions containing 20–30% GeH4 in the gas phase (relative to the total GeH4+SiH4 flow). 相似文献
58.
This article presents a method that can be applied to molten AA-6101 alloy to improve electrical properties of the aluminium part of the optical ground wire (OPGW) used in overhead transmission lines to protect phase conductors from lightning strike and to transmit signals and data. AA-6101 alloy in casting of the log as 6 m length and 178 mm diameter for extrusion has been inoculated by AlB2 to decrease detrimental effects of Cr, Ti, V, and Zr on the conductivity of the material. After inoculation, improved billets were extruded as 9.5 mm diameter feedstock. Required wires drawn from the feedstock according to the construction types of OPGW to be tested were exposed to aging at 175°C, 6 h (T-8). Upon completion of the back-twist and performing-type stranding process, resistance, and short-circuit current capacity and breaking load of the OPGW 88/44 constructions with other metal combinations have been examined and tested to show improvement. Results are summarized in tables and graphically. 相似文献
59.
A.Molin K.GhanbariAhari B.Josiek J.Molint 《中国耐火材料》2003,12(4):7-10
Physical properties and microstructural evolution on firing of 3 types of bauxite based refractory bricks were carried out using techniques such as porosimetry,XRD and SEM.The groups differed from each other by progressive refining of the matrix or bond phase.It is revealed that such a refinement of the matrix can improve the high temperature properties of the bricks made from poor grade materials. 相似文献
60.
Al-10Mg型固溶合金自然时效稳定性研究 总被引:3,自引:0,他引:3
测定了ZL30 5合金自然时效 33年的力学性能变化 ,观察了晶界的析出相 ,研究了组织和性能的关系 ,从而确定了ZL30 5合金具有长期自然时效稳定性。 相似文献