全文获取类型
收费全文 | 2238篇 |
免费 | 130篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 30篇 |
综合类 | 1篇 |
化学工业 | 495篇 |
金属工艺 | 42篇 |
机械仪表 | 78篇 |
建筑科学 | 112篇 |
能源动力 | 193篇 |
轻工业 | 381篇 |
水利工程 | 14篇 |
石油天然气 | 9篇 |
无线电 | 128篇 |
一般工业技术 | 442篇 |
冶金工业 | 76篇 |
原子能技术 | 14篇 |
自动化技术 | 358篇 |
出版年
2024年 | 8篇 |
2023年 | 26篇 |
2022年 | 55篇 |
2021年 | 98篇 |
2020年 | 90篇 |
2019年 | 93篇 |
2018年 | 108篇 |
2017年 | 92篇 |
2016年 | 124篇 |
2015年 | 72篇 |
2014年 | 109篇 |
2013年 | 202篇 |
2012年 | 140篇 |
2011年 | 181篇 |
2010年 | 120篇 |
2009年 | 161篇 |
2008年 | 134篇 |
2007年 | 114篇 |
2006年 | 76篇 |
2005年 | 64篇 |
2004年 | 59篇 |
2003年 | 42篇 |
2002年 | 44篇 |
2001年 | 14篇 |
2000年 | 14篇 |
1999年 | 24篇 |
1998年 | 26篇 |
1997年 | 11篇 |
1996年 | 19篇 |
1995年 | 8篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有2373条查询结果,搜索用时 12 毫秒
21.
Muhammad Yaseen Kashif Saleem Mehmet A. Orgun Abdelouahid Derhab Haider Abbas Jalal Al-Muhtadi Waseem Iqbal Imran Rashid 《Telematics and Informatics》2018,35(4):702-726
Recent advances in hardware technology have led to the development of low cost, power efficient and more feature rich devices that are amongst the most critical parts of communication networks. These devices or sensors can now sense data with more accuracy, process it by themselves and send it to the neighboring node or the sink node. However, robust and reliable security mechanisms are not yet properly implemented on these sensors due to their limited energy and computation power. Sensors also play a very important role in eHealthcare systems where ubiquitous patient monitoring is performed. As data is generated from the sensor nodes, reliable, secure and attack-resistant data acquisition and transmission is important for an efficient eHealthcare systems. This survey focuses on security issues of sensors data acquisition and transmission protocols, describing their main security features and comparing them in the context of a secure eHealthcare system. A taxonomy of open issues and future challenges is also discussed with respect to specific security metrics described in the paper. 相似文献
22.
Mehmet Ali Erturk Luca Vollero Muhammed Ali Aydin 《International Journal of Communication Systems》2018,31(2)
Wireless hotspots, ie, infrastructures composed of several IEEE 802.11 access points (APs), are today the most common solution in providing Internet access to a wide and rapidly changing population of users. According to common device implementation, stations establish associations with APs based on the measured strongest Received Signal Strength Indicator level. This usually leads to an uneven distribution of users to APs, increasing the chances of local network congestion. Load balancing (LB) solutions aim at mitigating this problem controlling the distribution of users. The LB algorithms enforce stations to associate with APs that manage a low number of users and/or that have a low traffic load. Usually, LB solutions do not consider traffic priorities or they assume some a priori quality of service (QoS) configuration for users. In this study, we propose a QoS‐LB solution based on the cell breathing technique with the goal of balancing the load in IEEE 802.11e Enhanced Distributed Channel Access (EDCA) Hotspots. The proposed algorithm explores the space of possible power/EDCA configurations by using a branch and bound approach that reduces the number of analyzed configurations and, hence, the time required to find the global optimal solution. The algorithm has been analytically defined and its performance evaluated through simulations and tests in a real test bed. The results prove that the proposed solution is effective in solving the optimal QoS‐LB configuration problem in WiFi hotspots of average size. 相似文献
23.
IEEE 802.11 wireless network standard has become one of the most used wireless networking technologies for smart devices as it offers mobility support and low cost deployment. However, these devices deeply rely on the energy provided by their batteries, which results in limited running time. IEEE 802.11 network standard provides stations with carrier sense multiple access with collision avoidance for the medium access. Yet it results in stations to consume an important amount of power. Therefore, minimizing WiFi‐based energy consumption in smart devices has been received substantial attention in both academia and industry. Accordingly, this paper * proposes a novel beacon‐based energy‐efficient collision‐free medium access control protocol for any type of IEEE 802.11 stations, regardless of being stationary or mobile, or having different amount of traffic flow, transmission rates, or traffic types. The proposed scheme is valid for all types of low or wide bandwidth, single or multiuser multiple‐input multiple‐output WLAN channels, such as IEEE 802.11a\b\g\n\ac. In the proposed scheme, energy saving is achieved, enabling stations to transmit on the right time and maintaining stations in the doze state during a predetermined sleep_time interval after each successful frame transmission, by making use of modified control and management frames of the standard IEEE 802.11 protocol. The proposed scheme reduces the probability of collisions and may allow stations to enter the collision‐free state, regardless of the number of stations on the channel and their traffic types. Widespread simulations have been executed to validate the efficiency of the proposed method. The results demonstrate that the proposed method significantly increases overall throughput and reduces power consumption of stations over IEEE 802.11 WLANs. 相似文献
24.
Mehmet Ali Tan 《Analog Integrated Circuits and Signal Processing》1991,1(4):339-351
Hardware implementation of artificial neural networks has been attracting great attention recently. In this work, the analog VLSI implementation of artificial neural networks by using only transconductors is presented. The signal flow graph approach is used in synthesis. The neural flow graph is defined. Synthesis of various neural network configurations by means of neural flow graph is described. The approach presented in this work is technology independent. This approach can be applied to new neural network topologies to be proposed or used with transconductors designed in future technologies. 相似文献
25.
Mehmet Cem Ece 《国际能源研究杂志》2001,25(14):1221-1232
Steady free convection laminar boundary‐layer flow about a heated vertical cone immersed in a quiescent power‐law fluid is investigated. Surface temperature is assumed to have a power‐law variation with the distance. Similarity solutions are obtained numerically for the boundary‐layer velocity and temperature profiles. Magnitudes of the velocity and temperature profiles are found to decrease with increasing values of the flow behaviour index and the surface temperature exponent. The effects of flow behaviour index and the generalized Prandtl number on the surface shear stress and heat flux are determined. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
26.
This paper proposed a method, namely resistively loaded lines (RLL), to compensate the effects of the DC bias lines after investigating its effects on several types of antennas for terahertz photomixers. The RLL is formed by placing lumped resistances periodically on the DC bias line in order to cease the leakage current virtually, which cause a significant amount of distortion on the antenna performance. The simulation results of the dipole, folded dipole, log-periodic, and spiral antennas show that RLL almost removes the effects of the bias lines and improves the antenna radiation resistance and radiation pattern notably compared with that of the commonly used bias line types, such as coplanar stripline and photonic bandgap type bias lines. 相似文献
27.
Ümit Ayglü Mehmet E. elebi 《AEUE-International Journal of Electronics and Communications》2004,58(4):268-273
In this paper, 4-state and 8-state space-time trellis codes with full rate, full diversity and high coding gain are proposed for MSK modulation, based on a technique similar to the super-orthogonal space-time trellis code (SOSTTC) design. Since the phase continuity requirement of MSK is the main constraint in space-time MSK code design not all the signal matrices corresponding to the trellis branches are orthogonal. The paper shows that the SOSTTC design technique can be extended to nonorthogonal coding structures. The new space-time MSK codes have frame error performances very close to those of their space-time QPSK counterparts given in [1] 相似文献
28.
Süleyman Karda Serkan elik Muhammed Ali Bingl Mehmet Sabir Kiraz Hüseyin Demirci Albert Levi 《Wireless Communications and Mobile Computing》2015,15(18):2150-2166
This paper examines Vaudenay's privacy model, which is one of the first and most complete privacy models that featured the notion of different privacy classes. We enhance this model by introducing two new generic adversary classes, k‐strong and k‐forward adversaries where the adversary is allowed to corrupt a tag at most k times. Moreover, we introduce an extended privacy definition that also covers all privacy classes of Vaudenay's model. In order to achieve highest privacy level, we study low cost primitives such as physically unclonable functions (PUFs). The common assumption of PUFs is that their physical structure is destroyed once tampered. This is an ideal assumption because the tamper resistance depends on the ability of the attacker and the quality of the PUF circuits. In this paper, we have weakened this assumption by introducing a new definition k‐resistant PUFs. k‐PUFs are tamper resistant against at most k attacks; that is, their physical structure remains still functional and correct until at most kth physical attack. Furthermore, we prove that strong privacy can be achieved without public‐key cryptography using k PUF‐based authentication. We finally prove that our extended proposal achieves both reader authentication and k‐strong privacy. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
29.
A novel application on the recently emerging wireless Personal Communications Systems (PCS) is the multimedia communication. In this paper, we evaluate multimedia communications capability and quality of service characteristics of one of the PCS standards, Personal Access Communications System's (PACS) packet channel (PPC) using simulation modeling. The performance of PPC's slot aggregation and data-sense multiple access techniques are studied by considering the downlink and uplink in a single cell and combined uplink/downlink in two cells and changing various parameters such as the number of users and certain protocol parameters. Interconnection of PPC with the Internet is discussed next. Frame rates of MPEG-1 coded images transmitted in a PACS cell as IP datagrams are determined. Handover characteristics of PPC downlink are studied by changing different parameters such as the cell size, the speed of the mobile host and time between handovers. The results clearly establish that multimedia communication on PPC is only feasible at lower bandwidths and frame rates and only a few users per cell can be supported. Careful tuning of PPC protocol parameters is required. There is one parameter whose variation gives opposite results on the downlink and uplink. 相似文献
30.
Mehmet Karapinar 《International journal of food microbiology》1990,10(3-4):193-199
The antifungal and antiaflatoxigenic activity of anethole and eugenol which are active components of commonly used spices was studied against two strains of Aspergillus parasiticus. Anethole, up to concentration of 400 μg/ml where complete inhibition was observed, delayed growth and reduced mycelial weight but it showed a stimulative effect on the toxin production of both strains. At a concentration of 300 μg/ml, eugenol inhibited the growth of both strains; levels of eugenol below 200 μg/ml enhanced production of aflatoxin particularly by A. parasiticus NRRL 299. 相似文献