全文获取类型
收费全文 | 190118篇 |
免费 | 17819篇 |
国内免费 | 10006篇 |
专业分类
电工技术 | 13562篇 |
技术理论 | 9篇 |
综合类 | 14300篇 |
化学工业 | 29742篇 |
金属工艺 | 10868篇 |
机械仪表 | 12547篇 |
建筑科学 | 16186篇 |
矿业工程 | 5684篇 |
能源动力 | 5681篇 |
轻工业 | 13887篇 |
水利工程 | 4055篇 |
石油天然气 | 10387篇 |
武器工业 | 1796篇 |
无线电 | 21818篇 |
一般工业技术 | 20757篇 |
冶金工业 | 8213篇 |
原子能技术 | 2222篇 |
自动化技术 | 26229篇 |
出版年
2024年 | 898篇 |
2023年 | 3067篇 |
2022年 | 5708篇 |
2021年 | 7691篇 |
2020年 | 5954篇 |
2019年 | 4803篇 |
2018年 | 5345篇 |
2017年 | 6127篇 |
2016年 | 5291篇 |
2015年 | 7613篇 |
2014年 | 9614篇 |
2013年 | 11086篇 |
2012年 | 12643篇 |
2011年 | 13392篇 |
2010年 | 12112篇 |
2009年 | 11702篇 |
2008年 | 11586篇 |
2007年 | 10800篇 |
2006年 | 10932篇 |
2005年 | 9212篇 |
2004年 | 6762篇 |
2003年 | 6140篇 |
2002年 | 6653篇 |
2001年 | 5786篇 |
2000年 | 4704篇 |
1999年 | 4303篇 |
1998年 | 3283篇 |
1997年 | 2779篇 |
1996年 | 2523篇 |
1995年 | 2179篇 |
1994年 | 1760篇 |
1993年 | 1240篇 |
1992年 | 1006篇 |
1991年 | 799篇 |
1990年 | 578篇 |
1989年 | 512篇 |
1988年 | 396篇 |
1987年 | 285篇 |
1986年 | 197篇 |
1985年 | 105篇 |
1984年 | 76篇 |
1983年 | 53篇 |
1982年 | 76篇 |
1981年 | 56篇 |
1980年 | 46篇 |
1979年 | 23篇 |
1978年 | 5篇 |
1965年 | 3篇 |
1959年 | 21篇 |
1951年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
结合工程实例,介绍了我国第一座可拆装高架火炬的基本原理及组成,并对可拆装高架火炬与普通高架火炬在安全、技术、安装、维修、占地面积、投资等方面进行了比较,还分析了高架火炬未来的发展趋势. 相似文献
42.
Environmental factors such as oxygen, temperature, and microbial species may have significant effects on decomposition of biodegradable polymers. A representative biodegradable, thermoplastic polymer, poly(3‐hydroxybutyrate‐co‐hydroxyvalerate) (PHBV), was decomposed in an aqueous medium under controlled laboratory conditions by soil microbes for the intrinsic degradation kinetics and the effects of the environmental factors on polymer biodegradation. The amount of proteins, including the PHBV depolymerases, that attached to the polymer surfaces was quite constant during the period of significant mass loss of the polymer specimens. The microbial polymer degradation followed a zero‐order rate model, so the residual mass fraction of PHBV films declined linearly with time. The mixed aerobic microbial organisms from fertile soil showed a higher activity of polymer degradation than an aerobic PHBV‐producing bacterium and the mixed anaerobes in the same soil. The mixed anaerobic microorganisms from barren soil decomposed the polymer at a slower rate than the anaerobes from fertile soil, and this was attributed to fewer microbial cells in the barren soil instead of the difference in the microbial species. The temperature effect on PHBV degradation can be described with an Arrhenius equation, and the activation energy is around 16 kcal/mol. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 205–213, 2003 相似文献
43.
随着我国经济的高速发展,业主要求提交资料的时间越来越短。为了提高工作效率,保质保量地完成工作,本文介绍了一些AutoCAD 2000及其以上版本的比较实用的技巧。灵活掌握了以下技巧后,绘图速度大约能提高50%。 相似文献
44.
Layered Wyner-Ziv video coding. 总被引:2,自引:0,他引:2
Following recent theoretical works on successive Wyner-Ziv coding (WZC), we propose a practical layered Wyner-Ziv video coder using the DCT, nested scalar quantization, and irregular LDPC code based Slepian-Wolf coding (or lossless source coding with side information at the decoder). Our main novelty is to use the base layer of a standard scalable video coder (e.g., MPEG-4/H.26L FGS or H.263+) as the decoder side information and perform layered WZC for quality enhancement. Similar to FGS coding, there is no performance difference between layered and monolithic WZC when the enhancement bitstream is generated in our proposed coder. Using an H.26L coded version as the base layer, experiments indicate that WZC gives slightly worse performance than FGS coding when the channel (for both the base and enhancement layers) is noiseless. However, when the channel is noisy, extensive simulations of video transmission over wireless networks conforming to the CDMA2000 1X standard show that H.26L base layer coding plus Wyner-Ziv enhancement layer coding are more robust against channel errors than H.26L FGS coding. These results demonstrate that layered Wyner-Ziv video coding is a promising new technique for video streaming over wireless networks. 相似文献
45.
Stewart C. Kai Shen Dwarkadas S. Scott M.L. Jian Yin 《Distributed Systems Online, IEEE》2004,5(10):1-1
The growth of the Internet and of various intranets has spawned a wealth of online services, most of which are implemented on local-area clusters using remote invocation (for example, remote procedure call/remote method invocation) among manually placed application components. Component placement can be a significant challenge for large-scale services, particularly when application resource needs are workload dependent. Automatic component placement has the potential to maximize overall system throughput. The key idea is to construct (offline) a mapping between input workload and individual-component resource consumption. Such mappings, called component profiles, then support high-performance placement. Preliminary results on an online auction benchmark based on J2EE (Java 2 Platform, Enterprise Edition) suggest that profile-driven tools can identify placements that achieve near-optimal overall throughput. 相似文献
46.
Hogari K. Tetsutani S. Jian Zhou Yamamoto F. Sato K. 《Lightwave Technology, Journal of》2003,21(2):540-545
Many cables containing 1.3-/spl mu/m zero-dispersion single-mode (SM) optical fibers are installed in trunk and access networks. Recently, there have been a number of studies on wavelength-division-multiplexing (WDM) systems designed to increase transmission capacity and flexibility. If we can construct WDM systems using SM optical-fiber cable networks designed to transmit using wavelengths in the 1.3-/spl mu/m window (O-band), this will prove very effective in reducing construction costs. It is therefore important to examine the wavelength dependence of the transmission characteristics of SM optical-fiber cables and networks that have already been installed and in which several optical fibers are joined. In this paper, we describe the measured optical characteristics of SM optical-fiber cables and installed optical-fiber cable networks at various wavelengths. The optical characteristics were stable in the 1.46 to 1.625-/spl mu/m wavelength range and we confirmed that the installed SM optical-fiber cable networks could be used for WDM system applications. 相似文献
47.
48.
49.
近两年.IP电话又叫网络电话的发展受到全球的关注。随着宽带接入的发展,基于宽带接入提供的网络电话具有了更大的生命力。从宽带电话的经营模式出发,探究这类业务的出现时现有话音业务市场的影响,进而分析这类业务的发展前景。 相似文献
50.
Object segmentation and labeling by learning from examples 总被引:1,自引:0,他引:1
We propose a system that employs low-level image segmentation followed by color and two-dimensional (2-D) shape matching to automatically group those low-level segments into objects based on their similarity to a set of example object templates presented by the user. A hierarchical content tree data structure is used for each database image to store matching combinations of low-level regions as objects. The system automatically initializes the content tree with only "elementary nodes" representing homogeneous low-level regions. The "learning" phase refers to labeling of combinations of low-level regions that have resulted in successful color and/or 2-D shape matches with the example template(s). These combinations are labeled as "object nodes" in the hierarchical content tree. Once learning is performed, the speed of second-time retrieval of learned objects in the database increases significantly. The learning step can be performed off-line provided that example objects are given in the form of user interest profiles. Experimental results are presented to demonstrate the effectiveness of the proposed system with hierarchical content tree representation and learning by color and 2-D shape matching on collections of car and face images. 相似文献