全文获取类型
收费全文 | 32465篇 |
免费 | 2477篇 |
国内免费 | 1280篇 |
专业分类
电工技术 | 1730篇 |
技术理论 | 1篇 |
综合类 | 1955篇 |
化学工业 | 5587篇 |
金属工艺 | 1609篇 |
机械仪表 | 2121篇 |
建筑科学 | 2593篇 |
矿业工程 | 1011篇 |
能源动力 | 833篇 |
轻工业 | 1994篇 |
水利工程 | 550篇 |
石油天然气 | 2072篇 |
武器工业 | 214篇 |
无线电 | 3841篇 |
一般工业技术 | 3952篇 |
冶金工业 | 1608篇 |
原子能技术 | 380篇 |
自动化技术 | 4171篇 |
出版年
2024年 | 175篇 |
2023年 | 584篇 |
2022年 | 886篇 |
2021年 | 1264篇 |
2020年 | 933篇 |
2019年 | 842篇 |
2018年 | 927篇 |
2017年 | 991篇 |
2016年 | 868篇 |
2015年 | 1161篇 |
2014年 | 1542篇 |
2013年 | 1822篇 |
2012年 | 1950篇 |
2011年 | 2044篇 |
2010年 | 1795篇 |
2009年 | 1764篇 |
2008年 | 1617篇 |
2007年 | 1639篇 |
2006年 | 1791篇 |
2005年 | 1608篇 |
2004年 | 1032篇 |
2003年 | 953篇 |
2002年 | 913篇 |
2001年 | 788篇 |
2000年 | 906篇 |
1999年 | 959篇 |
1998年 | 791篇 |
1997年 | 694篇 |
1996年 | 671篇 |
1995年 | 531篇 |
1994年 | 437篇 |
1993年 | 327篇 |
1992年 | 259篇 |
1991年 | 202篇 |
1990年 | 151篇 |
1989年 | 117篇 |
1988年 | 95篇 |
1987年 | 53篇 |
1986年 | 36篇 |
1985年 | 28篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 22篇 |
1981年 | 13篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
热物理性质测试技术研究现状和发展趋势 总被引:3,自引:0,他引:3
本文在对热物理性质研究在热能工程、材料科学、信息科学、航天工程、环境工程、生物科学、微电子技术和计量学等众多科技领域中的重要性进行探讨的基础上,评述了热物理性质测试技术的研究现状和发展趋势。鉴于薄膜材料在微电子器件、集成电路和微电子机械系统等领域中日益广泛的应用,本文还综述了亚微米-纳米尺度薄膜材料热导率和热扩散率的测试新技术。 相似文献
32.
Mushroom-like ZnO microcrystals have been prepared via a solution calcination route, using Zn(NO3)2 as Zn source in the absence of any surfactants, templates or catalysts. This is the first example to prepare mushroom-like crystals as semiconductors, which are expected to show particular physical properties. The ZnO products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL) spectrum measurements. A suitable concentration of Zn(NO3)2 solution was important for the growth of the mushroom-like products. The reported synthetic procedure is straightforward and inexpensive, and thus can be readily adopted to produce large quantities of mushroom-like ZnO microcrystals. 相似文献
33.
34.
A Novel Segmentation and Feedback Model for Resolving Contention in Optical Burst Switching 总被引:2,自引:0,他引:2
A novel segmentation and feedback model (SFM) applied to resolve contention is proposed. Simulation and performance analyses show that the SFM effectively avoids contentions in optical burst switching (OBS). The long delay time of deflection routing and the immature technology of wavelength converters and optical buffers are not deployed in the SFM. The SFM does not only realize fast switching but also allows preemption by higher priority bursts. 相似文献
35.
Many recent studies have convincingly demonstrated that network traffic exhibits a noticeable self-similar nature, which has a considerable impact on network performance, and most studies of optical burst switching (OBS) networks are under a fundamental assumption that full wavelength conversion is available throughout the network. In practice, however, economic and technical considerations are likely to dictate a more limited and sparse deployment of wavelength converters in the optical network. Therefore, we present a novel scheme for OBS networks, called logical cascaded private subnet (LCPN) with start wavelength assignment policy. We define the concept of canoe relative to cluster in self-similar traffic, and introduce a new device named payload segregator at the edge node as a gateway to the core node in OBS Networks. According to the changes in the edge node framework, we put forward the concept of cluster private subnet and canoe private subnet in the core node correspondingly. A new start wavelength assignment policy is proposed for the absence of (full) wavelength conversion capabilities in the core node of OBS Networks. The performance study indicates that, our new scheme is robust under self-similar traffic and wavelength continuity constraint. 相似文献
36.
本文提出一种基于本地缓存的弹性分组环保护倒换机制(WrapProtectionBasedOnLocalBuffers,简称WP-LB)。其主要思想是当环路上任何位于源节点和故障区域之间的中间节点接收到含有故障信息的控制信令后,就不再向下游转发数据分组,而是在本地缓存这些数据。等到保护通路建立好之后,再把缓存的数据分组经过保护通路发送给目的节点。分析计算表明,与原有的保护倒换(WrapProtection,简称WP)机制相比,WP-LB机制不仅提高带宽利用率,减少平均时延,并且还能避免数据包的丢失和失序。 相似文献
37.
38.
Chongjin Xie Xiang Liu 《Photonics Technology Letters, IEEE》2003,15(8):1070-1072
We propose a novel polarization-mode dispersion (PMD) compensation scheme for wavelength-division-multiplexing (WDM) systems, in which many WDM channels share one or a few PMD compensators at receiver site. It is shown, both analytically and numerically, that this scheme can achieve virtually the same performance as that using per-channel-based PMD compensation. 相似文献
39.
40.
Flowers G.T. Fei Xie Bozack M.J. Malucci R.D. 《Components and Packaging Technologies, IEEE Transactions on》2004,27(1):65-71
Single frequency vibration tests were used to induce fretting corrosion in tin alloy plated contacts. The samples used in this study were connectors consisting of 25 pairs of mated pin and socket contacts. Experimental results for a variety of vibration levels, frequencies, and wiring tie-off lengths are presented. The experiments consisted of running a series of vibration tests at each frequency where the excitation level was stepped through a range of g-levels. During each test run contact resistance was monitored as a performance characteristic. The results exhibit threshold behavior at each frequency for the onset of fretting degradation. Typically a plateau region was observed where similar g-levels produced similar fretting rates. It was also found that outside the plateau region the g-levels varied according to the dynamic behavior of the mechanical system. In addition, a transfer matrix model was used to analyze these results. An empirical fit of the data correlated well with the model when damping was used. This analysis revealed the importance of the bending moment induced at the contact interface as a result of excitation levels and tie-off configurations. Consequently, it is concluded that dynamic response of the mechanical system under various g-levels and tie off configurations can greatly impact the performance of a connector system subjected to vibration stresses. 相似文献