全文获取类型
收费全文 | 3879篇 |
免费 | 141篇 |
国内免费 | 38篇 |
专业分类
电工技术 | 58篇 |
综合类 | 60篇 |
化学工业 | 684篇 |
金属工艺 | 131篇 |
机械仪表 | 107篇 |
建筑科学 | 103篇 |
矿业工程 | 12篇 |
能源动力 | 171篇 |
轻工业 | 219篇 |
水利工程 | 19篇 |
石油天然气 | 17篇 |
武器工业 | 2篇 |
无线电 | 575篇 |
一般工业技术 | 850篇 |
冶金工业 | 487篇 |
原子能技术 | 40篇 |
自动化技术 | 523篇 |
出版年
2023年 | 26篇 |
2022年 | 73篇 |
2021年 | 87篇 |
2020年 | 55篇 |
2019年 | 61篇 |
2018年 | 67篇 |
2017年 | 84篇 |
2016年 | 87篇 |
2015年 | 60篇 |
2014年 | 115篇 |
2013年 | 294篇 |
2012年 | 202篇 |
2011年 | 210篇 |
2010年 | 182篇 |
2009年 | 205篇 |
2008年 | 177篇 |
2007年 | 166篇 |
2006年 | 176篇 |
2005年 | 128篇 |
2004年 | 109篇 |
2003年 | 92篇 |
2002年 | 78篇 |
2001年 | 74篇 |
2000年 | 74篇 |
1999年 | 85篇 |
1998年 | 129篇 |
1997年 | 109篇 |
1996年 | 131篇 |
1995年 | 85篇 |
1994年 | 76篇 |
1993年 | 63篇 |
1992年 | 60篇 |
1991年 | 47篇 |
1990年 | 46篇 |
1989年 | 50篇 |
1988年 | 44篇 |
1987年 | 28篇 |
1986年 | 36篇 |
1985年 | 22篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 23篇 |
1980年 | 13篇 |
1979年 | 15篇 |
1978年 | 5篇 |
1977年 | 16篇 |
1976年 | 19篇 |
1975年 | 6篇 |
1972年 | 6篇 |
排序方式: 共有4058条查询结果,搜索用时 15 毫秒
21.
The stress buffer layer (SBL) is a widely applied improvement in many advanced packages used to release the stress concentration at solder joints. However, it has been generally found that the metal line adjacent to the SBL may suffer larger deformation and its reliability should be addressed. In this study, the panel level package (PLP) technology with solder on polymer (SOP) structure is selected as the testing sample to investigate the effect of SBL. The ball shear strength test is conducted first to investigate the reliability of metal trace in PLP. In addition, finite element (FE) analysis is applied to understand the actual thermo-mechanical behavior of PLP after its assembly. The package-level and board-level reliability assessments are compared, and the suggested layout of the redistribution layer on the SBL is provided herein. 相似文献
22.
Tahui Wang Chimoon Huang Chou P.C. Chung S.S.-S. Tse-En Chang 《Electron Devices, IEEE Transactions on》1994,41(9):1618-1622
A two-dimensional numerical simulation including a new interface state generation model has been developed to study the performance variation of a LDD MOSFET after a dc voltage stress. The spatial distribution of hot carrier induced interface states is calculated with a breaking silicon-hydrogen bond model. Mobility degradation and reduction of conduction charge due to interface traps are considered. A 0.6 μm LDD MOSFET was fabricated. The drain current degradation and the substrate current variation after a stress were characterized to compare the simulation. A reduction of the substrate current at Vg ≃0.5 Vd in a stressed device was observed from both the measurement and the simulation. Our study reveals that the reduction is attributed to a distance between a maximum channel electric field and generated interface states 相似文献
23.
We have utilized a variable energy positron beam and infrared transmission spectroscopy to study defects in GaAs epilayers
grown at low temperatures (LT-GaAs) by molecular beam epitaxy. We have measured the Doppler broadening of the positron-electron
annihilation gamma ray spectra as a function of positron implantation energy. From these measurements, we have obtained results
for the depth profiles of Ga monovacancies in unannealed LT-GaAs and Ga monovacancies and arsenic cluster related defects
in annealed LT-GaAs. We have also studied the effects of the Si impurities in annealed LT-GaAs. The infrared transmission
measurements on unannealed LT-GaAs furnish a broad defect band, related to As antisites, centered at 0.370 eV below the conduction
band. 相似文献
24.
基于媒体用户访问行为偏好模型的代理缓存算法 总被引:2,自引:0,他引:2
目前,代理缓存技术广泛应用于改善流媒体传输的服务质量.文章从实际用户日志文件的分析出发,利用发现的用户浏览流媒体对象时的行为分布模型,提出了一种新的视频流媒体缓存算法.仿真结果证明,该算法可以通过记录很少的用户访问信息获取较高的性能表现. 相似文献
25.
A wireless/mobile network supporting multilevel quality of service (QoS) is considered. In such a network, users or applications can tolerate a certain degree of QoS degradation. Bandwidth allocation to users can, therefore, be adjusted dynamically according to the underlying network condition so as to increase bandwidth utilization and service provider's revenue. However, arbitrary QoS degradation may be unsatisfactory or unacceptable to the users, hence resulting in their subsequent defection. Instead of only focusing on bandwidth utilization or blocking/dropping probability, two new user-perceived QoS metrics, degradation ratio and upgrade/degrade frequency, are proposed. A Markov model is then provided to derive these QoS metrics. Using this model, we evaluate the effects of adaptive bandwidth allocation on user-perceived QoS and show the existence of trade offs between system performance and user-perceived QoS. We also show how to exploit adaptive bandwidth allocation to increase system utilization (for the system administrator) with controlled QoS degradation (for the users). By considering various mobility patterns, the simulation results are shown to match our analytical results, demonstrating the applicability of our analytical model to more general cases. 相似文献
26.
Shang-Ching Chou 《Journal of Automated Reasoning》1988,4(3):237-267
Wu's algebraic method for mechanically proving geometry theorems is presented at a level as elementary as possible with sufficient examples for further understanding the complete method.The work reported here was supported by NSF Grant DCR-8503498. 相似文献
27.
28.
Electrochemical impedance measurements have been used to characterize zinc selenide films prepared by electrochemical co-deposition at a platinum rotating disk electrode. Estimations of capacitance and polarization resistance of variously prepared electrodeposits have been carried out to determine charge carrier density and corrosion rates. 相似文献
29.
Risks always exist in construction projects and often cause schedule delay or cost overrun. Risk management is a key issue in project management. The first step of risk management is risk identification. It includes the recognition of potential risk event conditions in the project and the clarification of risk responsibilities. We conducted multiple-case studies using a systematic analytical procedure to identify risks in highway projects in Taiwan, to recognize risk allocation by contract clauses, and to analyze the influence of risk allocation on the contractor’s risk handling strategies. The results show that the owner allocates risks by stipulating specific contract clauses into five kinds of risk allocation conditions. If a risk is more controllable by the contractor, the owner has a greater tendency to allocate the risk to the contractor. Risk allocation determines which kinds of risks the contractor would take and influences the contractor’s risk handling decisions. The analysis furthermore indicates that, if the probability of a certain risk event condition is uncontrollable, then with the increasing possibility of taking the risk, the contractor’s tendency of risk handling changes from actively transferring the risk to passively retaining the risk. In contrast, if a risk is controllable and certainly allocated to the contractor, the contractor tends to take the initiative to reduce the impact caused by the risk event rather than retain the risk. 相似文献
30.