全文获取类型
收费全文 | 33545篇 |
免费 | 3201篇 |
国内免费 | 1861篇 |
专业分类
电工技术 | 2958篇 |
技术理论 | 3篇 |
综合类 | 2926篇 |
化学工业 | 3828篇 |
金属工艺 | 1070篇 |
机械仪表 | 2147篇 |
建筑科学 | 3212篇 |
矿业工程 | 2028篇 |
能源动力 | 3960篇 |
轻工业 | 1268篇 |
水利工程 | 821篇 |
石油天然气 | 1941篇 |
武器工业 | 367篇 |
无线电 | 4390篇 |
一般工业技术 | 2709篇 |
冶金工业 | 1435篇 |
原子能技术 | 561篇 |
自动化技术 | 2983篇 |
出版年
2024年 | 111篇 |
2023年 | 514篇 |
2022年 | 901篇 |
2021年 | 1183篇 |
2020年 | 1271篇 |
2019年 | 1006篇 |
2018年 | 956篇 |
2017年 | 1154篇 |
2016年 | 1376篇 |
2015年 | 1447篇 |
2014年 | 2286篇 |
2013年 | 2216篇 |
2012年 | 2561篇 |
2011年 | 2662篇 |
2010年 | 2066篇 |
2009年 | 2071篇 |
2008年 | 1938篇 |
2007年 | 2072篇 |
2006年 | 1894篇 |
2005年 | 1501篇 |
2004年 | 1236篇 |
2003年 | 1096篇 |
2002年 | 918篇 |
2001年 | 778篇 |
2000年 | 656篇 |
1999年 | 539篇 |
1998年 | 378篇 |
1997年 | 340篇 |
1996年 | 315篇 |
1995年 | 242篇 |
1994年 | 205篇 |
1993年 | 133篇 |
1992年 | 102篇 |
1991年 | 106篇 |
1990年 | 70篇 |
1989年 | 66篇 |
1988年 | 42篇 |
1987年 | 38篇 |
1986年 | 31篇 |
1985年 | 22篇 |
1984年 | 22篇 |
1983年 | 14篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1979年 | 4篇 |
1959年 | 4篇 |
1957年 | 4篇 |
1956年 | 3篇 |
1955年 | 4篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
81.
杜永泰 《电气电子教学学报》2002,24(6):37-39,52
本文讨论了调幅系数为任意值的调幅波,给出了它的表达式,频谱与调幅系数,调制效率和信噪比增益的计算公式。 相似文献
82.
针对烧结机新老蒸汽系统各自独立,使用效率低,不能充分发挥效能的状态,提出了蒸汽系统新老余热管网并网改造,经过一年多的运行,取得了显著的效果。 相似文献
83.
房间空调器高效节能技术分析 总被引:2,自引:0,他引:2
周彬 《制冷与空调(北京)》2003,3(4):44-46
本文主要介绍了高效节能型空调器的优化设计,包括选用高效压缩机、增大换热面积,增大风量、管路的合理设计,旨在提高制冷量,降低功耗,提高能效比。 相似文献
84.
Global competition, commitment to the Kyoto Protocol and a deregulated, integrated European electricity market will in all probability increase the demand for energy efficiency on the part of companies in Sweden. Investment decisions are an important part of meeting the new demands, because they decide the future efficiency of industrial energy systems. The objective of this study is to investigate, from a managerial perspective, the need to improve decision support in some industries, which can help to facilitate and improve investment decisions concerning energy efficiency. This work has been conducted through in-depth interviews with representatives for a number of energy-intensive companies and non-energy-intensive companies from different sectors. One need that was identified was the improvement of working methods in order to support the decision-making process. Here, external players seem to be playing an increasingly important role. Access to correct information, better follow-up activities, and transparent, understandable calculations are also considered to be important. The study will form the foundation for subsequent work on decision support and energy efficiency in industry. 相似文献
85.
86.
S. Shivakumara U. Manohar Y. Arthoba Naik T. V. Venkatesha 《Bulletin of Materials Science》2007,30(5):455-462
The influence of a condensation product (CP) of veratraldehyde (VRTD) and p-amino benzoic acid (PABA) on Zn-Ni alloy electrodeposited onto mild steel was studied in acidic sulphate solutions. Ethylenediaminetetraaceticacid
(EDTA) and cetyltrimethylammoniumbromide (CTAB) were used as complexing and wetting agents, respectively. The effect of bath
constituents, pH, current density and temperature on nature of deposit were studied through Hull cell experiments. The bath
constituents and operating parameters were optimized. Deposit properties and corrosion resistance were discussed. Throwing
power, current efficiency and polarization studies were carried out. SEM photomicrographs of the deposit obtained from optimum
bath revealed fine-grained deposit of the alloy in the presence of condensation product and hence modified the morphology
of zinc-nickel alloy deposit. IR spectrum of the scrapped deposit showed inclusion of addition agent. 相似文献
87.
晶体硅薄膜电池制备技术及研究现状 总被引:2,自引:0,他引:2
晶体硅薄膜太阳电池近些年来得到广泛的研究和初步的商业化探索。根据所采用的晶体硅薄膜沉积工艺中温度范围的不同,晶体硅薄膜电池研究可分为高温路线和低温路线两个不同发展方向。本文分别从这两个方向综述了目前国外晶体硅薄膜电池制备技术的最新进展,最新实验室研究结果。报导了晶体硅薄膜电池商业化进展状况,指出了晶体硅薄膜电池实现产业化必须解决的问题。 相似文献
88.
McKenna Frank P.; Horswill Mark S.; Alexander Jane L. 《Canadian Metallurgical Quarterly》2006,12(1):1
Skill and risk taking are argued to be independent and to require different remedial programs. However, it is possible to contend that skill-based training could be associated with an increase, a decrease, or no change in risk-taking behavior. In 3 experiments, the authors examined the influence of a skill-based training program (hazard perception) on the risk-taking behavior of car drivers (using video-based driving simulations). Experiment 1 demonstrated a decrease in risk taking for novice drivers. In Experiment 2, the authors examined the possibilities that the skills training might operate through either a nonspecific reduction in risk taking or a specific improvement in hazard perception. Evidence supported the latter. These findings were replicated in a more ecological context in Experiment 3, which compared advanced and nonadvanced police drivers. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
89.
This paper introduces an analytical model to investigate the energy efficiency of the IEEE 802.11 distributed coordinated
function (DCF). This model not only accounts for the number of contending nodes, the contention window, but also the packet
size, and the channel condition. Based on this model, we identify the tradeoff in choosing optimum parameters to optimize
the energy efficiency of DCF in the error-prone environment. The effects of contention window and packet size on the energy
efficiency are examined and compared for both DCF basic scheme and DCF with four-way handshaking. The maximum energy efficiency
can be obtained by combining both the optimal packet size and optimal contention window. To validate our analysis, we have
done extensive simulations in ns-2, and simulation results seem to match well with the presented analytical results.
The Ohio Board of Regents Doctoral Enhancements Funds and the National Science Foundation under Grant CCR 0113361 have supported
this work.
Xiaodong Wang received his B.S. degree in communication engineering from Beijing Information Technical Institute of China in 1995, and
his M.S. degree in electric engineering from Beijing University of Aeronautics and Astronautics of China in 1998. He joined
China Telecom in 1998 where he worked on communication protocols for telecommunication. From June 2000 to July 2002, he worked
on GSM base station software development at Bell-labs China, Beijing, China. Currently he is a Ph.D. student in Computer Engineering
at University of Cincinnati. His research activities include wireless MAC protocols, energy saving for wireless sensor networks.
He is a student member of the IEEE.
Jun Yin received the BS degree in automatic control from Dalian Railway Institute of China in 1997, and the MS degree in flight control
from Beijing University of Aeronautics and Astronautics of China in 2001. Since 2001 she has been a Ph.D. student in the OBR
Research Center for Distributed and Mobile Computing at the University of Cincinnati. Her research interests include performance
evaluation of 802.11 MAC protocol, wireless ad hoc networks and sensor networks. She is a student member of the IEEE.
Dharma P.Agrawal IEEE Fellow, 1987; ACM Fellow, 1998; AAAS Fellow, 2003 Dr. Agrawal is the Ohio Board of Regents Distinguished Professor of
Computer Science and Computer Engineering in the department of Electrical and Computer Engineering and Computer Science, University
of Cincinnati, OH. He has been a faculty member at Wayne State University, (1977–1982) and North Carolina State University
(1982–1998). He has been a consultant to the General Dynamics Land Systems Division, Battelle, Inc., and the U. S. Army. He
has held visiting appointment at AIRMICS, Atlanta, GA, and the AT&T Advanced Communications Laboratory, Whippany, NJ. He has
published a number of papers in the areas of Parallel System Architecture, Multi computer Networks, Routing Techniques, Parallelism
Detection and Scheduling Techniques, Reliability of Real-Time Distributed Systems, Modeling of C-MOS Circuits, and Computer
Arithmetic. His recent research interest includes energy efficient routing, information retrieval, and secured communication
in ad hoc and sensor networks, effective handoff handling and multicasting in integrated wireless networks, interference analysis
in piconets and routing in scatternet, use of smart directional antennas (multibeam) for enhanced QoS, Scheduling of periodic
real-time applications and automatic load balancing in heterogeneous workstation environment. He has four approved patents
and three patent filings in the area of wireless cellular networks. 相似文献
90.
UV法测定聚甲基丙烯酸酯纳米粒中胰岛素的包封率 总被引:3,自引:0,他引:3
建立一种简便易行的测定聚甲基丙烯酸酯胰岛素纳米粒中游离胰岛素含量方法.用Nanosep OD100C33超滤膜分离纳米粒和游离药物,在276 nm处测定药物的吸光度,建立胰岛素含量测定方法,并对线性、回收率、精密度等指标进行考察,最后测定各种胰岛素和载体比例混合的纳米粒的包封率.结果发现,该超滤膜能较好地分离纳米粒和游离的药物,在0.11~1.10 u/mL范围内,药物在276 nm的吸光度和浓度存在良好的线性关系(r=0.999 8),线性方程为A=0.868 8C-0.001 6,高、中、低3种浓度的回收率和精密度良好.该方法操作简单、结果可靠,可用于胰岛素纳米粒中药物包封率的测定. 相似文献