全文获取类型
收费全文 | 117096篇 |
免费 | 10809篇 |
国内免费 | 5869篇 |
专业分类
电工技术 | 7608篇 |
技术理论 | 5篇 |
综合类 | 8349篇 |
化学工业 | 18677篇 |
金属工艺 | 6960篇 |
机械仪表 | 7967篇 |
建筑科学 | 9560篇 |
矿业工程 | 3669篇 |
能源动力 | 3285篇 |
轻工业 | 7942篇 |
水利工程 | 2410篇 |
石油天然气 | 6939篇 |
武器工业 | 1140篇 |
无线电 | 13667篇 |
一般工业技术 | 13399篇 |
冶金工业 | 5242篇 |
原子能技术 | 1288篇 |
自动化技术 | 15667篇 |
出版年
2024年 | 550篇 |
2023年 | 2123篇 |
2022年 | 3893篇 |
2021年 | 5261篇 |
2020年 | 4070篇 |
2019年 | 3254篇 |
2018年 | 3483篇 |
2017年 | 4051篇 |
2016年 | 3540篇 |
2015年 | 5051篇 |
2014年 | 6346篇 |
2013年 | 7329篇 |
2012年 | 7870篇 |
2011年 | 8806篇 |
2010年 | 7687篇 |
2009年 | 7342篇 |
2008年 | 7217篇 |
2007年 | 6510篇 |
2006年 | 6309篇 |
2005年 | 5172篇 |
2004年 | 3510篇 |
2003年 | 2949篇 |
2002年 | 2854篇 |
2001年 | 2518篇 |
2000年 | 2254篇 |
1999年 | 2474篇 |
1998年 | 2059篇 |
1997年 | 1764篇 |
1996年 | 1602篇 |
1995年 | 1368篇 |
1994年 | 1102篇 |
1993年 | 824篇 |
1992年 | 654篇 |
1991年 | 478篇 |
1990年 | 356篇 |
1989年 | 282篇 |
1988年 | 217篇 |
1987年 | 139篇 |
1986年 | 119篇 |
1985年 | 77篇 |
1984年 | 58篇 |
1983年 | 59篇 |
1982年 | 51篇 |
1981年 | 35篇 |
1980年 | 38篇 |
1979年 | 18篇 |
1976年 | 4篇 |
1959年 | 4篇 |
1951年 | 7篇 |
1940年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Online Raman spectra, obtained at different points along the spin line during pilot‐scale nonisothermal melt spinning of high density polyethylene (HDPE) fibers, are presented for the first time. The fraction of the crystalline phase corresponding to each spectrum was determined from the normalized integrated intensity of the 1418 cm?1 Raman band. It is well established that this band represents the orthorhombic crystalline phase in polyethylene. The estimates of percent crystallinity obtained from decomposition of the Raman spectrum were compared with the percent crystallinity from differential scanning calorimetry (DSC) measurements. It is concluded that online Raman spectroscopy can be successfully used to monitor the development of crystallinity in HDPE fibers as a function of distance from the spinneret. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 545–549, 2003 相似文献
22.
Data mining extracts implicit, previously unknown, and potentially useful information from databases. Many approaches have been proposed to extract information, and one of the most important ones is finding association rules. Although a large amount of research has been devoted to this subject, none of it finds association rules from directed acyclic graph (DAG) data. Without such a mining method, the hidden knowledge, if any, cannot be discovered from the databases storing DAG data such as family genealogy profiles, product structures, XML documents, task precedence relations, and course structures. In this article, we define a new kind of association rule in DAG databases called the predecessor–successor rule, where a node x is a predecessor of another node y if we can find a path in DAG where x appears before y. The predecessor–successor rules enable us to observe how the characteristics of the predecessors influence the successors. An approach containing four stages is proposed to discover the predecessor–successor rules. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 621–637, 2006. 相似文献
23.
24.
大型往复式压缩机功率大、占地面积大,管道振动问题也更为突出。笔者结合实践经验,对大型往复式压缩机的配管设计进行探讨,说明了平面布置与管道防振设计的密切关系,并介绍了管道防振设计的方法和步骤,以及相对简单的复杂管系气柱固有频率的转移矩阵计算方法。 相似文献
25.
Use of X-ray computed microtomography to understand why gels reduce relative permeability to water more than that to oil 总被引:1,自引:0,他引:1
R. S. Seright J. Liang W. Brent Lindquist John H. Dunsmuir 《Journal of Petroleum Science and Engineering》2003,39(3-4):217
X-ray computed microtomography (XMT) was used to investigate why gels reduce relative permeability to water more than that to oil in strongly water-wet Berea sandstone. XMT allows saturation differences to be monitored for individual pores during various stages of oil, water, and gelant flooding. The method also characterizes distributions of pore size, aspect ratio, and coordination number for the porous media. We studied a Cr(III) acetate–HPAM gel that reduced permeability to water (at Sor) by a factor 80–90 times more than that to oil (at Swr). In Berea, the gel caused disproportionate permeability reduction by trapping substantial volumes of oil that remained immobile during water flooding (i.e., 43.5% Sor before gel placement versus 78.7% Sor after gel placement). With this high trapped oil saturation, water was forced to flow through narrow films, through the smallest pores, and through the gel itself. In contrast, during oil flooding, oil pathways remained relatively free from constriction by the gel. 相似文献
26.
Edward Mutafungwa Liang Yong 《Journal of Infrared, Millimeter and Terahertz Waves》2004,25(2):365-381
Indoor infrared communication systems is one of the possible ways of offering data rates in excess of 100 Mbit/s without the need for wiring. Multiple users can share an infrared channel by code division-multiple access (CDMA) techniques. However, the CDMA system performance is limited by both background noise and co-channel interference. In this paper we study the use of angle diversity for mitigating the effects of the noise and interference. The system considered uses on-off shift keying modulation with multibeam transmitters and imaging receivers. The overall system performance for different diversity combining techniques is evaluated and compared to a system without diversity. Numerical results for a 2-user CDMA system indicate that signal to noise and interference ratio (SNIR) improvement (over systems with no diversity) of 5 dB is obtained for at least 50% of an ensemble of 10000 sample evaluations. The generalized selection combining (GSC)--a new diversity technique yet to be implemented for infrared systems--offers the best performance even with its reduced complexity. 相似文献
27.
Yang C.W. Fang Y.K. Lin C.S. Tsair Y.S. Chen S.M. Wang W.D. Wang M.F. Cheng J.Y. Chen C.H. Yao L.G. Chen S.C. Liang M.S. 《Electronics letters》2003,39(21):1499-1501
A novel technique to form high-K dielectric of HfSiON by doping base oxide with Hf and nitridation with NH/sub 3/, sequentially, is proposed. The HfSiON gate dielectric demonstrates excellent device performances such as only 10% degradation of saturation drain current and almost 45 times of magnitude reduction in gate leakage compared with conventional SiO/sub 2/ gate at the approximately same equivalent oxide thickness. Additionally, negligible flatband voltage shift is achieved with this technique. Time-dependent dielectric breakdown tests indicate that the lifetime of HfSiON is longer than 10 years at V/sub dd/=2 V. 相似文献
28.
29.
甲烷无氧芳构化研究进展及其工业应用前景 总被引:5,自引:0,他引:5
综述了最近20多年来甲烷无氧芳构化催化剂的制备、积炭失活和再生方面的研究进展,特别分析了催化剂再生过程的工程化问题及反应器型式;还根据甲烷芳构化技术产业化的需要,分析了甲烷芳构化技术的发展趋势。 相似文献
30.
Finite element piezothermoelasticity analysis and the active control of FGM plates with integrated piezoelectric sensors and actuators 总被引:3,自引:0,他引:3
An efficient finite element model is presented for the static and dynamic piezothermoelastic analysis and control of FGM
plates under temperature gradient environments using integrated piezoelectric sensor/actuator layers. The properties of an FGM plate are functionally graded in the thickness
direction according to a volume fraction power law distribution. A constant displacement-cum-velocity feedback control algorithm that couples the direct and inverse piezoelectric effects is applied to provide active feedback
control of the integrated FGM plate in a closed loop system. Numerical results for the static and dynamic control are presented
for the FGM plate, which consists of zirconia and aluminum. The effects of the constituent volume fractions and the influence
of feedback control gain on the static and dynamic responses of the FGM plates are examined.
Received: 13 March 2002 / Accepted: 5 March 2003
The work described in this paper was supported by a grant awarded by the Research Grants Council of the Hong Kong Special
Administrative Region, China (Project No. CityU 1024/01E). 相似文献