首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2886篇
  免费   158篇
  国内免费   14篇
电工技术   45篇
综合类   13篇
化学工业   902篇
金属工艺   51篇
机械仪表   89篇
建筑科学   72篇
能源动力   241篇
轻工业   326篇
水利工程   33篇
石油天然气   28篇
无线电   264篇
一般工业技术   441篇
冶金工业   141篇
原子能技术   6篇
自动化技术   406篇
  2024年   14篇
  2023年   61篇
  2022年   146篇
  2021年   193篇
  2020年   128篇
  2019年   135篇
  2018年   180篇
  2017年   150篇
  2016年   181篇
  2015年   120篇
  2014年   186篇
  2013年   284篇
  2012年   218篇
  2011年   223篇
  2010年   119篇
  2009年   107篇
  2008年   76篇
  2007年   53篇
  2006年   48篇
  2005年   53篇
  2004年   38篇
  2003年   27篇
  2002年   22篇
  2001年   30篇
  2000年   16篇
  1999年   12篇
  1998年   25篇
  1997年   9篇
  1996年   19篇
  1995年   19篇
  1994年   20篇
  1993年   20篇
  1992年   12篇
  1991年   14篇
  1990年   14篇
  1989年   11篇
  1988年   10篇
  1986年   6篇
  1985年   4篇
  1984年   9篇
  1983年   4篇
  1982年   7篇
  1980年   4篇
  1978年   2篇
  1977年   2篇
  1976年   5篇
  1975年   2篇
  1974年   4篇
  1973年   3篇
  1971年   4篇
排序方式: 共有3058条查询结果,搜索用时 15 毫秒
21.
Pain management during dental procedures is a cornerstone for successful daily practice. In current practice, the traditional needle and syringe injection is used to administer local anesthesia. However, the appearance of long needles and the pain associated with it often leads to dental anxiety deterring timely interventions. Microneedles (MNs) have emerged as a minimally invasive alternative to hypodermic needles and shown to be effective in transdermal drug delivery applications. In this article, the potential use of MNs for local anesthesia delivery in dentistry is explored. The development of a novel conductive MN array that can be used in combination with iontophoresis technique to achieve drug penetration through the oral mucosa and the underlying bone tissue is presented. The conductive MN array plays a dual-role, creating micro-conduits and lowering the resistance of the oral mucosa. The reduced tissue resistance further enhances the application of a low-voltage current that is able to direct and accelerate the drug molecules to target the sensory nerves supplying teeth. The successful delivery of lidocaine using this new strategy in a clinically relevant rabbit incisor model is shown to be as effective as the current gold standard.  相似文献   
22.
In this paper, we examine the impact of antenna correlation on transmit antenna selection with receive maximal ratio combining (TAS/MRC) in multiple‐input multiple‐output multiuser underlay cognitive radio network (MIMO‐MCN) over a Nakagami‐m fading environment. The secondary network under consideration consists of a single source and M destinations equipped with multiple correlated antennas at each node. The primary network composed of L primary users, each of which is equipped with multiple correlated antennas. For the considered underlay spectrum sharing paradigm, the transmission power of the proposed secondary system is limited by the peak interference limit on the primary network and the maximum transmission power at the secondary network. In particular, we derive exact closed‐form expressions for the outage probability and average symbol error rate of the proposed secondary system. To gain further insights, simple asymptotic closed‐form expressions for the outage probability and symbol error rate are provided to obtain the achievable diversity order and coding gain of the system. In addition, the impact of antenna correlation on the secondary user ergodic capacity has been investigated by deriving closed‐form expressions for the secondary user capacity. The derived analytical formulas herein are supported by numerical and simulation results to clarify the main contributions. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
23.
24.
Wireless Personal Communications - This paper proposes a novel design of a software-defined matched filter (MF) for digital receivers of synthetic aperture radar (SAR). The block diagram of the...  相似文献   
25.
Multidimensional Systems and Signal Processing - Digital images are commonly used in steganography due to the popularity of digital image transfer and exchange through the Internet. However, the...  相似文献   
26.
Group key management is one of the key security issues in multicast networks. The main challenge is to provide a secure group key management method which avoids high key update cost in terms of the number of transmitted keys. In order to achieve low key update cost for group key management, most of the existing methods increase their encryption/decryption cycles which requires a strong cryptographic function. In this paper, a cost-effective key management method is proposed to address the problem of high key update cost without increasing the encryption/decryption cycles. We evaluated our proposed method with existing tree-based methods by using Markov chain and Poisson Arrival Process. Results indicate the efficiency of our proposed method in reducing the key update cost significantly compared to the existing tree-based key management methods.  相似文献   
27.
As a network-based localized mobility management protocol, Proxy Mobile IPv6 (PMIPv6) enables a Mobile Host (MH) to roam within a localized domain without MH intervention in the mobility-related signalling. However, the PMIPv6 maintains MH mobility support in a restriction domain. Therefore, whenever the MH roams away from the PMIPv6 domain, its reachability status will be broken-down causing high handover latency and inevitable traffic loss for its communication session. This article proposes a proactive mechanism to mange the MH handover and maintain its data session continually across inter-PMIPv6-domains. The proposed mechanism introduces an intermediate global mobility anchor entity, called, which is responsible to coordinate MH handover as well as redirect its traffic across inter-PMIPv6-domains. Through various simulation evaluations, via ns-2, several experiments were conducted, revealing numerous results that verify the proposed mechanism superior performance over the conventional inter-PMIPv6-domain handover schemes in terms of handover latency, achieved throughput, protocol signalling cost and end-to-end traffic delivery latency.  相似文献   
28.
The main service differentiation mechanism introduced by the IEEE 802.11e standard is described in terms of prioritized contention access. Analyzing the performance and service differentiation ability of each of the priority features of the 802.11e standard is an important task, and considerable research effort has recently been dedicated to this subject. In this article, we present a generalized and comprehensive analysis of the prioritized access scheme of the 802.11e standard. Our model corrects and extends the existing models and considers all priority features of the 802.11e Medium Access Control (MAC) protocol. We consider an arbitrary number of priority levels, and provide a detailed parametric analysis of the MAC behavior for the main priority parameters of inter frame spacing, contention window size, and transmission opportunity. We validate the accuracy of our analysis with simulation experiments.
Hussein AlnuweiriEmail:
  相似文献   
29.
Wireless Personal Communications - A prediction-based method is presented to track mobile object and its location in a sensor network area. In recent years, energy consumption and high accuracy...  相似文献   
30.
In a wide area campus, a university provides Wireless Local Area Network (WLAN) for users to connect to the Internet. Most users take advantage of this WLAN benefit by using their laptops. However, the number of smart phone users is growing fast. Since a smart phone is able to get an Internet connection using WLAN, users can use their smart phones without having to pay for a cellular operator. Users tend to use their smart phones more, due to their higher mobility compared to a laptop. This capability enables new services in the market, such as Fixed-Mobile Convergence (FMC), which integrates a fixed network (traditional telephony, WLAN) and a mobile network (cellular) to provide seamless voice communications anytime, anywhere. These new applications require a WLAN connection availability nearly everywhere. However, due to limited budgets, a university can only install APs in places with a high connection demand. We propose a novel WLAN AP placement technique that takes user mobility into consideration. This new approach is more complete than previous approaches, which mainly focus on coverage area and throughput data. Our technique has been implemented in our university. The results show the suitability of the WLAN access point locations in our university campus based on user mobility and activities.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号