全文获取类型
收费全文 | 74369篇 |
免费 | 7233篇 |
国内免费 | 5430篇 |
专业分类
电工技术 | 2328篇 |
技术理论 | 1篇 |
综合类 | 4816篇 |
化学工业 | 19367篇 |
金属工艺 | 6436篇 |
机械仪表 | 3920篇 |
建筑科学 | 2689篇 |
矿业工程 | 2089篇 |
能源动力 | 1859篇 |
轻工业 | 4998篇 |
水利工程 | 1115篇 |
石油天然气 | 2708篇 |
武器工业 | 601篇 |
无线电 | 9040篇 |
一般工业技术 | 10675篇 |
冶金工业 | 3022篇 |
原子能技术 | 979篇 |
自动化技术 | 10389篇 |
出版年
2024年 | 242篇 |
2023年 | 1353篇 |
2022年 | 2178篇 |
2021年 | 2955篇 |
2020年 | 2404篇 |
2019年 | 2168篇 |
2018年 | 1951篇 |
2017年 | 2409篇 |
2016年 | 2674篇 |
2015年 | 2694篇 |
2014年 | 3932篇 |
2013年 | 4238篇 |
2012年 | 4906篇 |
2011年 | 6266篇 |
2010年 | 4628篇 |
2009年 | 5198篇 |
2008年 | 4575篇 |
2007年 | 5272篇 |
2006年 | 4713篇 |
2005年 | 3963篇 |
2004年 | 3061篇 |
2003年 | 2696篇 |
2002年 | 2149篇 |
2001年 | 1631篇 |
2000年 | 1593篇 |
1999年 | 1288篇 |
1998年 | 1028篇 |
1997年 | 804篇 |
1996年 | 766篇 |
1995年 | 596篇 |
1994年 | 568篇 |
1993年 | 441篇 |
1992年 | 347篇 |
1991年 | 286篇 |
1990年 | 214篇 |
1989年 | 175篇 |
1988年 | 115篇 |
1987年 | 100篇 |
1986年 | 108篇 |
1985年 | 57篇 |
1984年 | 39篇 |
1983年 | 38篇 |
1982年 | 45篇 |
1981年 | 23篇 |
1980年 | 38篇 |
1979年 | 29篇 |
1977年 | 17篇 |
1976年 | 16篇 |
1975年 | 9篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
171.
Application-level performance is a key to the adoption and success of the CDMA 2000. To predict this performance in advance,
a detailed end-to-end simulation model of a CDMA network is built to include application traffic characteristics, network
architecture, network element details using the proposed simulation methodology. We assess the user-perceived application
performance when a RAN and a CN adopt different transport architectures such as ATM and IP. To evaluate the user-perceived
quality of voice service, we compare the end-to-end packet delay for different vocoder schemes such as G.711, G.726 (PCM),
G.726 (ADPCM), and vocoder bypass scheme. By the simulation results, the vocoder bypass scenario shows 30% performance improvement
over the others. We also compare the quality of voice service with and without DPS scheduling scheme. We know that DPS scheme
keep the voice delay bound even if the service traffic is high. For data packet performance, HTTP v.1.1 shows better performance
than that of HTTP v.1.0 due to the pipelining and TCP persistent connection. We may conclude that IP transport technology
is better solution for higher FER environment since the packet overhead of IP is smaller than that of ATM for web browsing
data traffic, while it shows opposite effect to the small size voice packet in RAN architecture. We show that the 3G-1X EV-DO
system gives much better packet delay performance than 3G-1X RTT. The main conclusion is that end-to-end application-level
performance is affected by various elements and layers of the network and thus it must be considered in all phases of the
development process.
Jae-Hyun Kim He received the B.S., M.S., and Ph.D. degrees, all in computer science and engineering, from Hanyang University, Ansan, Korea,
in 1991, 1993, and 1996 respectively. In 1996, he was with the Communication Research Laboratory, Tokyo, Japan, as a Visiting
Scholar. From April 1997 to October 1998, he was a post-doctoral fellow at the department of electrical engineering, University
of California, Los Angeles. From November 1998 to February 2003, he worked as a member of technical staff in Performance Modeling
and QoS management department, Bell laboratories, Lucent Technologies, Holmdel, NJ. He has been with the department of electrical
engineering, Ajou University, Suwon, Korea, as an assistant professor since 2003. His research interests include QoS issues
and cross layer optimization for high-speed wireless communication. Dr. Kim was the recipient of the LGIC Thesis Prize and
Samsung Human-Tech Thesis Prize in 1993 and 1997, respectively. He is a member of the Korean Institute of Communication Sciences
(KICS), Korea Institute of Telematics and Electronis (KITE), Korea Information Science Society (KISS), and IEEE.
Hyun-Jin Lee received the B.S. degree in electrical engineering from Ajou University, Suwon, Korea, in 2004, and is working toward the
M.S. degree and Ph. D. degree in electrical engineering at Ajou University. He has been awarded Samsung Human-Tech Thesis
Prize in 2004. His research interests QoS, especially network optimization and wireless packet scheduling. He is a member
of the KICS.
Sung-Min Oh received the B.S. and M. S. degrees in electrical engineering form Ajou University, Suwon, Korea, in 2004, and is working
toward the Ph. D. degree in electrical engineering at Ajou University. His research interests QoS performance analysis and
4G network. He is a member of the KICS.
Sung-Hyun Cho received his B.S., M.S., and Ph.D. in computer science and engineering from Hanyang University, Korea, in 1995, 1997, and
2001, respectively. From 2001 to 2005, he has been with Samsung Advanced Institute of Technology, where he has been engaged
in the design and standardization of MAC and upper layers of B3G, IEEE 802.16e, and WiBro systems. He is currently a MAC part
leader in the telecommunication R&D center of Samsung Electronics. His research interests include 4G air interface design,
radio resource management, cross layer design, and handoff in wireless systems. 相似文献
172.
均匀设计法分析制备过程对钴钼硫化物催化剂机械强度的影响 总被引:1,自引:1,他引:0
建立了CoMoP/Al2O3加氢精制催化剂机械强度及其可靠性在制备过程中的数学模型,采用均匀设计考察了浸渍、干燥、煅烧、硫化4个制备过程中,浸渍时间、干燥温度、干燥时间、煅烧温度、煅烧时间、硫化温度和硫化升温速率7个实验因子对催化剂强度均值、Weibull模量的影响,同时考察了这些因素对颗粒密度的影响。方差分析表明所有模型都是充足的。实验结果表明,硫化过程是影响催化剂强度均值的主要过程。在实验范围内提高硫化温度、降低硫化时的升温速率有利于提高催化剂的强度。影响催化剂Weibull模量的因素主要为各个制备过程的交互效应。要提高催化剂强度的可靠性就必须全面考虑催化剂制备的各个过程,特别是各个制备过程的交互效应。 相似文献
173.
Chris Harty 《Building Research & Information》2005,33(6):512-522
An alternative approach to understanding innovation is made using two intersecting ideas. The first is that successful innovation requires consideration of the social and organizational contexts in which it is located. The complex context of construction work is characterized by inter-organizational collaboration, a project-based approach and power distributed amongst collaborating organizations. The second is that innovations can be divided into two modes: 'bounded', where the implications of innovation are restricted within a single, coherent sphere of influence, and 'unbounded', where the effects of implementation spill over beyond this. Bounded innovations are adequately explained within the construction literature. However, less discussed are unbounded innovations, where many firms' collaboration is required for successful implementation, even though many innovations can be considered unbounded within construction's inter-organizational context. It is argued that unbounded innovations require an approach to understand and facilitate the interactions both within a range of actors and between the actors and technological artefacts. The insights from a sociology of technology approach can be applied to the multiplicity of negotiations and alignments that constitute the implementation of unbounded innovation. The utility of concepts from the sociology of technology, including 'system building' and 'heterogeneous engineering', is demonstrated by applying them to an empirical study of an unbounded innovation on a major construction project (the new terminal at Heathrow Airport, London, UK). This study suggests that 'system building' contains outcomes that are not only transformations of practices, processes and systems, but also the potential transformation of technologies themselves. 相似文献
174.
对在五坐标数控加工中心上铣制三元流叶轮时出现的叶轮附面尺寸误差问题,进行了详细分析,并提出了问题的解决方法,有效地避免了加工中产生的超差。 相似文献
175.
3-D MCM封装技术及其应用 总被引:1,自引:0,他引:1
介绍了超大规模集成电路(VLSI)用的3-D MCM封装技术的最新发展,重点介绍了3-D MCM封装垂直互连工艺,分析了3-D MCM封装技术的硅效率、复杂程度、热处理、互连密度、系统功率与速度等问题,并对3-D MCM封装的应用作了简要说明。 相似文献
176.
177.
178.
179.
Several types of reinforced Nb3Sn wires have been developed to prevent reduction of superconducting properties by applying a strong electromagnetic force. To fabricate a cryocooled magnet using those reinforced wires, we experimentally measured the minimum quench energy (MQE) under cryocooled conditions of some reinforced Nb3Sn wires. As a result, it became clear that thermal stability expressed as MQE was controlled by the temperature margin between the temperature of the operating condition and the transition temperature from superconductivity to normal. Using the FEM analysis, it was realized that the cause of the decline in thermal stability for the reinforced wires was the low thermal conductivity of the reinforced materials. 相似文献
180.
Ferdinando Auricchio Lorenza Petrini 《International journal for numerical methods in engineering》2004,61(6):807-836
An always increasing knowledge on material properties as well as a progressively more sophisticated production technology make shape memory alloys (SMA) extremely interesting for the industrial world. At the same time, SMA devices are typically characterized by complex multi‐axial stress states as well as non‐homogeneous and non‐isothermal conditions both in space and time. This aspect suggests the finite element method as a useful tool to help and improve application design and realization. With this aim, we focus on a three‐dimensional macroscopic thermo‐mechanical model able to reproduce the most significant SMA features (Int. J. Numer. Methods Eng. 2002; 55 : 1255–1264), proposing a simple modification of such a model. However, the suggested modification allows the development of a time‐discrete solution algorithm, which is more effective and robust than the one previously discussed in the literature. We verify the computational tool ability to simulate realistic mechanical boundary value problems with prescribed temperature dependence, studying three SMA applications: a spring actuator, a self‐expanding stent, a coupling device for vacuum tightness. The effectiveness of the model to solve thermo‐mechanical coupled problems will be discussed in a forthcoming work. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献