全文获取类型
收费全文 | 136914篇 |
免费 | 13773篇 |
国内免费 | 7532篇 |
专业分类
电工技术 | 9932篇 |
技术理论 | 8篇 |
综合类 | 11235篇 |
化学工业 | 21450篇 |
金属工艺 | 7639篇 |
机械仪表 | 8850篇 |
建筑科学 | 11097篇 |
矿业工程 | 3947篇 |
能源动力 | 3634篇 |
轻工业 | 13123篇 |
水利工程 | 3142篇 |
石油天然气 | 5977篇 |
武器工业 | 1442篇 |
无线电 | 15526篇 |
一般工业技术 | 14634篇 |
冶金工业 | 5332篇 |
原子能技术 | 1900篇 |
自动化技术 | 19351篇 |
出版年
2024年 | 650篇 |
2023年 | 2351篇 |
2022年 | 4742篇 |
2021年 | 6297篇 |
2020年 | 4763篇 |
2019年 | 3700篇 |
2018年 | 4195篇 |
2017年 | 4636篇 |
2016年 | 4047篇 |
2015年 | 5911篇 |
2014年 | 7690篇 |
2013年 | 8913篇 |
2012年 | 10262篇 |
2011年 | 10720篇 |
2010年 | 9745篇 |
2009年 | 9244篇 |
2008年 | 9123篇 |
2007年 | 8487篇 |
2006年 | 7813篇 |
2005年 | 6438篇 |
2004年 | 4484篇 |
2003年 | 3524篇 |
2002年 | 3318篇 |
2001年 | 2762篇 |
2000年 | 2629篇 |
1999年 | 2423篇 |
1998年 | 1720篇 |
1997年 | 1484篇 |
1996年 | 1307篇 |
1995年 | 1136篇 |
1994年 | 825篇 |
1993年 | 634篇 |
1992年 | 540篇 |
1991年 | 384篇 |
1990年 | 287篇 |
1989年 | 270篇 |
1988年 | 204篇 |
1987年 | 106篇 |
1986年 | 98篇 |
1985年 | 61篇 |
1984年 | 52篇 |
1983年 | 31篇 |
1982年 | 39篇 |
1981年 | 33篇 |
1980年 | 45篇 |
1979年 | 22篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1959年 | 8篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
111.
Lei Zhou Yu-Dong Yao Heffes H. Ruifeng Zhang 《Wireless Communications, IEEE Transactions on》2006,5(4):779-788
A reduced-rate retransmission (RRR) scheme is proposed for improving the throughput performance of spread-spectrum packet radio networks. The scheme takes advantages of the available multi-rate scalable source coding techniques. It assumes that several versions of a data packet with different sizes (number of information bits) are available. The transmission of a packet starts from its full-size version. If the full-size version is not correctly received, its half-size version is used in the retransmission. If further retransmissions are needed, the quarter-size version and so on are used. The shrunk packets are transmitted either in a minislot if the processing gain is kept the same, or occupying a slot duration by increasing the processing gain proportionally. In both cases, the effective signal to interference ratio for a packet is increased. As a result, the system throughput is improved. Theoretical and numerical results are provided in this paper which illustrate the throughput improvement. Another advantage of the proposed RRR scheme is that the packet-size reduction provides finer granules for link adaptation. Therefore, it is especially suitable for multimedia applications for which codes of variable rate for the source data are available and which can tolerate gracefully degraded quality of service. The performance of the proposed scheme in fading channels is also addressed. 相似文献
112.
添加剂对工业齿轮油性能影响的研究 总被引:3,自引:0,他引:3
研究了硫化烯烃、磷酸酯胺盐、硫磷酸酯极压抗磨剂,含氮杂环衍生物多功能添加剂和防锈剂等,对工业齿轮油抗乳化性能、极压抗磨性能、防锈性能的影响;以及硫化烯烃、磷酸酯盐极压抗磨剂与含氮杂环衍生物多功能添加剂之间的协和效应。试验结果表明:1.2%~1.6%复合添加剂调制的CKD220工业齿轮油中,磷酸脂盐的正确选用可以提高齿轮油的抗乳化性能、防锈性能和减少防锈剂用量。硫化烯烃与磷酸脂盐、含氮杂环衍生物多功能添加剂的合理组合,可以提高齿轮油的极压抗磨性能和防锈性能,减少添加剂总加剂量。 相似文献
113.
服务质量测量技术及其应用 总被引:3,自引:0,他引:3
文章在概述服务质量测量技术的基础上,介绍了服务质量测量技术的服务质量性能评估、网络推测、网络定位等应用,并给出了服务质量测量的一般数学模型。 相似文献
114.
W. Wang J. Dai J. Tang D.-T. Jiang Y. Chen J. Fang J. He W. Zhou L. Spinu 《Journal of Superconductivity》2003,16(1):155-157
Ball-milling method was applied to dissolve Fe into titanium dioxide (TiO2). X-ray diffraction indicated the starting anatase changed to a rutile-type structure with oxygen deficiency after ball milling. Transmission electron microscopy and X-ray absorption experiments were conducted to examine the possible existence of magnetic impurities in the ball-milled powders after they were leached in HCl solutions. Temperature dependence of the resistivity shows semiconducting behavior and the magnetic hysteresis loops at 5 and 300 K exhibit ferromagnetic characteristics. Fe-doped TiO2 films were also prepared by pulsed laser deposition. The magnetic properties of the films are discussed. 相似文献
115.
Field Static Load Test on Kao-Ping-Hsi Cable-Stayed Bridge 总被引:1,自引:0,他引:1
Field load testing is an effective method for understanding the behavior and fundamental characteristics of a cable-stayed bridge. This paper presents the results of field static load tests on the Kao-Ping-Hsi cable-stayed bridge, the longest cable-stayed bridge in Taiwan, before it was open to traffic. A total of 40 loading cases, including the unit and distributed bending and torsion loading effects, were conducted to investigate the bridge behavior. The atmospheric temperature effect on the variations of the main girder deflections was also monitored. The results of static load testing include the main girder deflections, the flexural strains of the prestressed concrete girder, and the variations of the cable forces. A three-dimensional finite-element model was developed. The results show that the bridge under the planned load test conditions has linear superposition characteristics and the analytical model shows a very good agreement with the bridge responses. Further discussion of deflection and cable forces of the design specifications for a cable-stayed bridge is also presented. 相似文献
116.
磷酸酯类离子液体在燃油深度脱硫中的应用 总被引:16,自引:6,他引:10
研究了3种磷酸酯类离子液体,即1,3-二甲基咪唑磷酸二甲酯盐([MM im]DM P)、1-乙基-3-甲基咪唑磷酸二乙酯盐([EM im]DEP)和1-丁基-3-甲基咪唑磷酸二丁酯盐([BM im]DBP)的制备过程,考察了这3种磷酸酯类离子液体对模型油中3-甲基噻吩、苯并噻吩和二苯并噻吩的脱除效果及磷酸酯类离子液体的电化学再生方法。实验结果表明,这3种磷酸酯类离子液体的脱硫能力强弱顺序为:[EM im]DEP>[BM im]DBP[MM im]DM P;且对二苯并噻吩的脱除效果最好,对苯并噻吩的脱除效果次之,对3-甲基噻吩的脱除效果较差。以[EM im]DEP为萃取剂,油剂质量比为1∶1时,经5次萃取后,二苯并噻吩的脱除率可达到99.5%。利用电解法对[EM im]DEP进行了再生,在5~10V电压下电解10h,[EM im]DEP的脱硫率可以达到新鲜[EM im]DEP的90%以上。 相似文献
117.
118.
Removal of gold from basic solutions containing [Au(CN)2]? has been demonstrated using the inherently conducting polymer polypyrrole. Polymers containing sulfonated aromatic dopants have been found to display a significant ability to remove gold from such solutions. Experiments performed in solutions containing both gold and copper cyanide complexes indicate that the recovery process is not highly selective. However, the polypyrroles used display significantly faster rates of gold recovery than activated carbon. © 2003 Society of Chemical Industry 相似文献
119.
120.
Si3N4 ceramic was jointed to itself using a filler alloy of Cu76.5Pd8.5Ti15, and the mechanical properties of the jointwere measured and analyzed. By using a filler alloy of Cu76.5Pd8.5Ti15, the SisN4/SisN4 joints were obtained bybrazing at 1373~1473 K f 相似文献