全文获取类型
收费全文 | 168141篇 |
免费 | 7036篇 |
国内免费 | 3319篇 |
专业分类
电工技术 | 5115篇 |
技术理论 | 9篇 |
综合类 | 6796篇 |
化学工业 | 26602篇 |
金属工艺 | 9100篇 |
机械仪表 | 8151篇 |
建筑科学 | 9151篇 |
矿业工程 | 2538篇 |
能源动力 | 3551篇 |
轻工业 | 8414篇 |
水利工程 | 2688篇 |
石油天然气 | 4861篇 |
武器工业 | 488篇 |
无线电 | 19397篇 |
一般工业技术 | 27148篇 |
冶金工业 | 7258篇 |
原子能技术 | 1072篇 |
自动化技术 | 36157篇 |
出版年
2024年 | 324篇 |
2023年 | 1314篇 |
2022年 | 2280篇 |
2021年 | 3118篇 |
2020年 | 2339篇 |
2019年 | 2037篇 |
2018年 | 16320篇 |
2017年 | 15527篇 |
2016年 | 12053篇 |
2015年 | 3524篇 |
2014年 | 4231篇 |
2013年 | 5248篇 |
2012年 | 8285篇 |
2011年 | 14706篇 |
2010年 | 12961篇 |
2009年 | 10099篇 |
2008年 | 11066篇 |
2007年 | 12016篇 |
2006年 | 4753篇 |
2005年 | 5320篇 |
2004年 | 3873篇 |
2003年 | 3643篇 |
2002年 | 2714篇 |
2001年 | 2110篇 |
2000年 | 2455篇 |
1999年 | 2614篇 |
1998年 | 2434篇 |
1997年 | 1911篇 |
1996年 | 1786篇 |
1995年 | 1454篇 |
1994年 | 1227篇 |
1993年 | 888篇 |
1992年 | 666篇 |
1991年 | 565篇 |
1990年 | 409篇 |
1989年 | 367篇 |
1988年 | 327篇 |
1987年 | 175篇 |
1986年 | 165篇 |
1985年 | 112篇 |
1984年 | 98篇 |
1983年 | 63篇 |
1982年 | 60篇 |
1981年 | 54篇 |
1980年 | 38篇 |
1968年 | 45篇 |
1966年 | 43篇 |
1965年 | 45篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Enhancement of islanding-detection of distributed generation systems via wavelet transform-based approaches 总被引:1,自引:1,他引:0
Cheng-Tao Hsieh Jeu-Min Lin Shyh-Jier Huang 《International Journal of Electrical Power & Energy Systems》2008,30(10):575-580
In this paper, a wavelet transform-based approach is proposed to detect the occurrence of islanding events in distributed generation systems. Thanks to time–frequency localization capabilities exhibited by wavelet transform, the approach embedded with this transform technique has grasped the appearance of the islanding event in a highly effective manner. Moreover, for those regions which are in need of a better visualization, the proposed approach would serve as an efficient aid such that the mains power disconnection can be better distinguished. To validate the feasibility of this approach, the method has been validated through several scenarios. Test results supported the effectiveness of the method for the application considered. 相似文献
42.
43.
44.
45.
46.
Sianchang Huang Likarn Wang 《Lightwave Technology, Journal of》1996,14(5):661-664
The power penalty induced by imperfect phase recovery in PSK homodyne communication systems with balanced phase-locked loop receivers are exactly evaluated. Optimum phase deviations between the mark-state and the space-state bits are used in this study. This study for the first time shows the imperfect-phase-recovery-induced power penalty as a function of laser linewidth with optimum phase deviations considered. It can be estimated from the theoretical result that an optimal balanced PLL receiver requires the laser linewidth as Δν⩽1.15×10-6× (bit rate) in contrast to the previous reported one Δν⩽5.88×10-6× (bit rate). We also point out here that the previously reported laser linewidth requirement was wrongly estimated 相似文献
47.
Jifu Huang Ke Wu 《Microwave Theory and Techniques》1996,44(8):1508-1511
A generalized transmission line matrix (TLM) algorithm is developed in the frequency domain to tackle arbitrary both reciprocal and nonreciprocal anisotropic waveguiding problems. In particular, the modeling issue for arbitrary planar structures is stressed in this work. A new three-dimensional (3-D) condensed node is used to consider the effect of both electric and magnetic constitutive tensors. Various results indicate how the modal dispersive behavior can be manipulated by changing not only the anisotropic characteristics of the substrate, but also the strip/slot geometry as well as the magnitude and orientation of the applied static magnetic field. The present algorithm is useful for CAD and simulation of a large class of gyrotropic waveguide-based microwave and millimeter-wave circuits 相似文献
48.
49.
Transdermal Iontophoretic Delivery of Thyrotropin-Releasing Hormone Across Excised Rabbit Pinna Skin
Enhanced transport of a model peptide drug thyrotropin-releasing hormone (TRH), a tripeptide of molar mass 362 g and a pKa 6.2, through excised rabbit pinna skin was achieved by means of iontophoresis with continuous current or monophase periodically pulsed current. The resulting flux in the steady state was proportional to the applied current density. In the transdermal iontophoretic delivery of TRH, the pulsed iontophoretic flux exceeded that obtained with a continuous current. At a low ionic strength, an increased degree of protonation in TRH increased the rate of permeation. The flux of TRH in a buffer at pH 4 is greater than that at pH 8 when the ionic strength is 0.1 M. At a greater ionic strength, the trend is reversed. The enhanced flux of unprotonated TRH during transdermal iontophoresis is attributed largely to electro-osmotic volume flow. An increased rate of permeation of TRH crossing the skin is achieved at low ionic strength, moderate pH, and a large duly cycle of current; the frequency of pulsed current had no significant influence on the rate of transdermal iontophoretic delivery of TRH. 相似文献
50.