全文获取类型
收费全文 | 13859篇 |
免费 | 2203篇 |
国内免费 | 1379篇 |
专业分类
电工技术 | 1095篇 |
技术理论 | 5篇 |
综合类 | 1213篇 |
化学工业 | 1445篇 |
金属工艺 | 1094篇 |
机械仪表 | 475篇 |
建筑科学 | 929篇 |
矿业工程 | 437篇 |
能源动力 | 2169篇 |
轻工业 | 244篇 |
水利工程 | 723篇 |
石油天然气 | 1477篇 |
武器工业 | 86篇 |
无线电 | 1254篇 |
一般工业技术 | 1912篇 |
冶金工业 | 419篇 |
原子能技术 | 92篇 |
自动化技术 | 2372篇 |
出版年
2024年 | 58篇 |
2023年 | 717篇 |
2022年 | 964篇 |
2021年 | 983篇 |
2020年 | 1011篇 |
2019年 | 901篇 |
2018年 | 751篇 |
2017年 | 764篇 |
2016年 | 655篇 |
2015年 | 663篇 |
2014年 | 762篇 |
2013年 | 820篇 |
2012年 | 948篇 |
2011年 | 1056篇 |
2010年 | 753篇 |
2009年 | 715篇 |
2008年 | 671篇 |
2007年 | 693篇 |
2006年 | 611篇 |
2005年 | 503篇 |
2004年 | 410篇 |
2003年 | 339篇 |
2002年 | 292篇 |
2001年 | 221篇 |
2000年 | 232篇 |
1999年 | 178篇 |
1998年 | 132篇 |
1997年 | 113篇 |
1996年 | 112篇 |
1995年 | 69篇 |
1994年 | 87篇 |
1993年 | 40篇 |
1992年 | 33篇 |
1991年 | 29篇 |
1990年 | 23篇 |
1989年 | 27篇 |
1988年 | 26篇 |
1987年 | 15篇 |
1986年 | 25篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1970年 | 2篇 |
1959年 | 2篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
电力系统谐波检测的现状与发展 总被引:7,自引:0,他引:7
准确、实时地对电力系统谐波进行检测有着重要的意义。本文根据电力系统谐波测量的基本方法,对近年来电力系统谐波检测的新方法进行了分析和评述。最后对电力系统的谐波测量进行了总结并提出了看法。 相似文献
52.
通过分析黄河口河道在纵剖面、横断面、河型等方面的演变过程,总结归纳出黄河口河道的演变规律。指出:黄河口泥沙在潮汐涨落等因素影响下,河口河道纵剖面逐渐形成台阶状,与此同时,河口滩地横比降逐渐发展为倒比降;河口河道中段由顺直型河道逐渐转为弯曲型河道,而下段仍为相对顺直、游荡型河道。当河口河道中段比降减小到一定程度后,此河段开始漫滩、卡冰、出汊。河口台阶的形成揭示了黄河口流路由单股河道逐渐转为出汊的过程,即黄河口流路由“青壮期”逐渐转为“衰亡期”的过程。延长黄河口流路使用年限的途径是:①尽量减少黄河下游输向黄河口的泥沙量;②采取河口挖沙或人工改汊措施,地点宜选在河口河道的中下段。 相似文献
53.
中扬子及邻区层序地层与原型盆地演化 总被引:11,自引:0,他引:11
戴少武 《石油与天然气地质》2002,23(3):229-235
中扬子及邻区原型盆地可划分为 9个大层序,其中,1~6大层序由中、古生代海相地层组成;第 7大层序为早、中侏罗纪的陆相沉积;第 8大层序为晚侏罗世的前渊沉积;第 9层序为晚白垩世至第三纪的伸展盆地。震旦纪,中部地区为台地相环境,向南为浅海陆棚环境,向北以陆表海为主;寒武纪至早奥陶世为典型的大陆边缘盆地;中、晚奥陶世至志留纪为裂谷盆地发展阶段;泥盆纪至石炭纪该区发生广泛海侵,与华南海域和太平洋海域多处相连;二叠纪至早、中三叠世为原型盆地的重要转型时期,随着分隔秦岭微板块与扬子板块的勉略古洋盆向东打开,扬子北缘由前期的区域性隆起转变为向北加深的大陆边缘盆地;晚三叠世经历了两次幕式旋回,巴东组沉积时期盆地沉降缓慢,九里岗组沉积时期则较快;早、中侏罗世原型盆地早幕 (早侏罗世)沉积缓慢,晚幕 (中侏罗世)快速沉降,以水下沉积作用为主;晚侏罗世可划分为两大构造演化阶段,早期构造活动相对平静,晚期强烈;晚白垩世至老第三纪,盆地范围缩小,以湖泊、河流体系为主。由此,中扬子及邻区在地质历史时期经历了 4种不同性质的原型盆地,具有幕式充填特征。 相似文献
54.
55.
准噶尔盆地侏罗系储集层的基本特征及其主控因素分析 总被引:28,自引:8,他引:20
从描述储集层基本特征、分析储集层性质的主控因素、建立储集层成因模式和评价、预测储集层性质这 4个层次 ,研究准噶尔盆地重点勘探目标区的侏罗系储集层。系统总结侏罗系储集层岩石学特征 ,认为成岩压实作用强弱是控制储集层性质的关键因素 ;指出相对优质储集层均为剩余原生粒间孔隙型储集层 ,溶蚀作用对渗透率贡献小 ;非煤系储集层的孔隙保存条件明显比煤系储集层好 ,这是三工河组、头屯河组和吐谷鲁群的物性普遍优于八道湾组和西山窑组的原因。在确定储集层性质的控制因素和控制机理基础上 ,建立了煤系和非煤系两大类储集层的成因 演化模型。在上述研究的基础上 ,分地区、分层位评价了储集层 ,并预测了不同渗透率储集层的深度界线及相对优质储集层的平面分布。图 6参 10 相似文献
56.
57.
指针推进移动性管理策略中指针链长度的概率 总被引:7,自引:1,他引:6
为了降低移动通信网络中位置跟踪操作的代价,指针推进策略被提出.显然,指针链长度的确定对这一策略的有效应用是至为重要的.已有论文假定移动台在位置区的逗留时间服从指数分布的条件下,对指针链的长度进行研究,但指数分布的特殊性,限制了其研究结果的应用.本文推广了上述结果,研究了移动台在位置区的逗留时间服从一般概率分布的指针推进策略,通过构造向量马氏过程,利用密度演化方法,导出了指针链长度的概率公式,这个公式可用于对各种指针推进策略性能的评价. 相似文献
58.
Two different Ti/Pt–Ir materials (commercial and home made) and Ti/PdO + Co3O4 were investigated for their electrocatalytic properties versus Cl2 evolution reaction. The materials were used in a batch electrochemical reactor to treat biologically recalcitrant di-azo compound. An electrochemically driven oxidation, mediated by a Cl2/Cl− couple, proved efficient for destruction of this complex organic molecule, causing cleavage of the conjugated double bonds and destruction of unsatured bonds. Both Ti/Pt–Ir materials performed well; lower kinetics obtained with the Ti/PdO + Co3O4 anode was caused by adsorption of the model compound, evidenced in preliminary voltammetric measurements. The dye oxidation reaction followed the second order kinetics with partial orders in the model compound and (time varying) chlorine concentrations equal to one. Specific energy consumption of 3.12 kWh m−3 proved the process more economic than the homogeneous phase oxidation. 相似文献
59.
Keita Ikeue Shingo Ando Tomohiro Mitsuyama Yusuke Ohta Keishi Arayama Akiko Tsutsumi Masato Machida 《Topics in Catalysis》2008,47(3-4):175-180
Lanthanide-based oxysulfides and sulfide, LnTaO3.5S0.5, Ln10OS14 (Ln = La, Pr, Nd, Sm) and La4In5S13, were successively synthesized by sulfurization in a flowing H2S. The sulfurization decreased the band-gap energies from >4 eV to <3eV, because of the formation of occupied S3p orbitals
on the top of valence band. In accordance with the small band gap, the H2 evolution from a 0.01 M Na2S and 0.01 M Na2SO3 solution system was observed under irradiation of light up to >500 nm. The rate of H2 evolution under light irradiation of >500 nm increased in the order of Ni/LaTaO3.5S0.5 < Ru/La10OS14 < Pt/La4In5S13. 相似文献
60.
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