全文获取类型
收费全文 | 3731篇 |
免费 | 329篇 |
国内免费 | 152篇 |
专业分类
电工技术 | 50篇 |
综合类 | 369篇 |
化学工业 | 535篇 |
金属工艺 | 53篇 |
机械仪表 | 58篇 |
建筑科学 | 1584篇 |
矿业工程 | 53篇 |
能源动力 | 42篇 |
轻工业 | 80篇 |
水利工程 | 159篇 |
石油天然气 | 37篇 |
武器工业 | 45篇 |
无线电 | 233篇 |
一般工业技术 | 308篇 |
冶金工业 | 50篇 |
原子能技术 | 20篇 |
自动化技术 | 536篇 |
出版年
2024年 | 17篇 |
2023年 | 44篇 |
2022年 | 100篇 |
2021年 | 109篇 |
2020年 | 88篇 |
2019年 | 65篇 |
2018年 | 66篇 |
2017年 | 103篇 |
2016年 | 106篇 |
2015年 | 156篇 |
2014年 | 251篇 |
2013年 | 194篇 |
2012年 | 280篇 |
2011年 | 311篇 |
2010年 | 229篇 |
2009年 | 257篇 |
2008年 | 259篇 |
2007年 | 305篇 |
2006年 | 272篇 |
2005年 | 239篇 |
2004年 | 134篇 |
2003年 | 173篇 |
2002年 | 140篇 |
2001年 | 78篇 |
2000年 | 53篇 |
1999年 | 39篇 |
1998年 | 27篇 |
1997年 | 19篇 |
1996年 | 16篇 |
1995年 | 4篇 |
1994年 | 14篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1981年 | 1篇 |
1980年 | 11篇 |
1978年 | 1篇 |
排序方式: 共有4212条查询结果,搜索用时 15 毫秒
41.
42.
Alexander Haynack Jithender J. Timothy Thomas Kränkel Christoph Gehlen 《Advanced Engineering Materials》2023,25(19):2300265
Surface deterioration of concrete subjected to freezing and thawing in combination with deicing salts is one of the most important factors determining the durability of concrete infrastructure in cold climates. The freeze–thaw deicing salt (FTDS) resistance of cementitious materials can be determined by the capillary suction of de-icing chemicals and freeze–thaw (CDF) test. Specimens are subjected to repeated freeze–thaw cycles with simultaneous addition of deicing salt and the amount of material scaled off near the surface is determined. For concretes with adequate FTDS resistance, this test method works very well. However, specimens with unknown performance often experience increased edge scaling. This leads to a falsification of results and consequently to an underestimation of the actual freeze–thaw resistance. In materials research, however, concretes with high levels of surface deterioration are studied in order to investigate various factors of influence on the freeze–thaw resistance of concretes in a targeted manner. This article presents a novel methodology that delivers new information regarding surface deterioration of CDF samples using high-resolution 3D scan data. Change of volume is used to support deterioration results of the standard CDF methodology. Increase of surface area is used to estimate change in roughness of samples. 相似文献
43.
探讨了特细砂砂浆流动度和含砂率对特细砂砂浆自流密实能力的影响,提出用强度比表示特细砂砂浆的自流密实能力,目的在于充分发挥特细砂砂浆的自流密实能力,节约水泥. 相似文献
44.
45.
46.
论述了一种基于公共密钥基础设施PKI体系结构的数字签名实现方式。数字签名不容易伪造,且由CA颁发的数字证书可以确定用户身份的合法性,因此,可以利用PKI技术,并结合公钥加密原理来实现数字签名,采用权威机构CA发放的证书作为通信双方的身份标识。在内部网上将办公流程与数字签名相结合保证了整个办公过程中信息的确定性与完整性。 相似文献
47.
Dynamic duty cycle and adaptive contention window based QoS-MAC protocol for wireless multimedia sensor networks 总被引:2,自引:0,他引:2
Rapid penetration of small, customized wireless devices and enormous growth of wireless communication technologies has already set the stage for large-scale deployment of wireless sensor networks. While the need to minimize the energy consumption has driven significant researches in wireless sensor networks, offering some precise quality of service (QoS) for multimedia transmission over sensor networks has not received significant attention. However, the emerging new applications like video surveillance, telemedicine and traffic monitoring needs transmission of wireless multimedia over sensor networks. Naturally, offering some better QoS for wireless multimedia over sensor networks raises significant challenges. The network needs to cope up with battery-constraints, while providing improved QoS (end-to-end delay and bandwidth requirement). This calls for a suitable sensory MAC protocol capable of achieving application-specific QoS. In this paper, we have proposed a new QoS-based sensory MAC protocol, which not only adapts to application-oriented QoS, but also attempts to conserve energy without violating QoS-constraints. Performance modeling, analysis and simulation results demonstrate that the proposed protocol is capable of providing lower delay and better throughput, at the cost of reasonable energy consumption, in comparison to other existing sensory MAC protocols. 相似文献
48.
网上电子支付系统分析 总被引:12,自引:2,他引:10
介绍了电子支付系统的基本概念,重点讨论了基于SET协议下电子支付系统的结构、支付流程,以及支付系统中所涉及的各项费用。 相似文献
49.
证书状态查询是PKI系统中的一个关键问题,OCSP是解决这个问题的一种重要机制。本文分析并改进了OCSP协议,并在此基础上设计了一种高效的证书状态查询系统。文中对该系统的重要组成部分以及关键技术进行了详细的论述。 相似文献
50.
Nguyen Quoc Dinh Author VitaeDong-Sung KimAuthor Vitae 《Computer Standards & Interfaces》2012,34(1):117-123
The International Society of Automation recently released ISA100.11a as an open standard for reliable wireless networks for industrial automation. ISA100.11a uses the TDMA scheme in the medium access layer to provide deterministic services. However, ISA100.11a adopts the CSMA-CA mechanism with priorities for retransmission from failure on dedicated links, sporadic data, and network configuration.This paper evaluates ISA100.11a CSMA-CA by simulation, considering the effects of backoff procedures and priority settings to probability of collision and successful use of slots. It's demonstrated that a high number of priority classes enable better network utilization resulting in less number of packets exceeding their lifetime. 相似文献