全文获取类型
收费全文 | 64447篇 |
免费 | 5114篇 |
国内免费 | 2825篇 |
专业分类
电工技术 | 3630篇 |
技术理论 | 7篇 |
综合类 | 4229篇 |
化学工业 | 10997篇 |
金属工艺 | 3571篇 |
机械仪表 | 3941篇 |
建筑科学 | 5455篇 |
矿业工程 | 1855篇 |
能源动力 | 1876篇 |
轻工业 | 4119篇 |
水利工程 | 1158篇 |
石油天然气 | 4509篇 |
武器工业 | 450篇 |
无线电 | 7068篇 |
一般工业技术 | 8013篇 |
冶金工业 | 3104篇 |
原子能技术 | 719篇 |
自动化技术 | 7685篇 |
出版年
2024年 | 226篇 |
2023年 | 1043篇 |
2022年 | 1728篇 |
2021年 | 2451篇 |
2020年 | 1899篇 |
2019年 | 1655篇 |
2018年 | 1868篇 |
2017年 | 2101篇 |
2016年 | 1909篇 |
2015年 | 2378篇 |
2014年 | 3214篇 |
2013年 | 3670篇 |
2012年 | 4086篇 |
2011年 | 4426篇 |
2010年 | 3880篇 |
2009年 | 3686篇 |
2008年 | 3610篇 |
2007年 | 3511篇 |
2006年 | 3567篇 |
2005年 | 3083篇 |
2004年 | 2090篇 |
2003年 | 1879篇 |
2002年 | 1645篇 |
2001年 | 1600篇 |
2000年 | 1653篇 |
1999年 | 1770篇 |
1998年 | 1383篇 |
1997年 | 1169篇 |
1996年 | 1050篇 |
1995年 | 937篇 |
1994年 | 769篇 |
1993年 | 556篇 |
1992年 | 433篇 |
1991年 | 336篇 |
1990年 | 312篇 |
1989年 | 226篇 |
1988年 | 174篇 |
1987年 | 107篇 |
1986年 | 104篇 |
1985年 | 60篇 |
1984年 | 41篇 |
1983年 | 26篇 |
1982年 | 33篇 |
1981年 | 22篇 |
1980年 | 13篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
53.
概述了鞍钢1780mm生产线技术改造工程中供电、传动及自动控制系统的构成、安装及调试技术要点,以及技术经济效果评述,可供同类工程施工参考. 相似文献
54.
55.
A Subcarriers Allocation Scheme for Cognitive Radio Systems Based on Multi-Carrier Modulation 总被引:1,自引:0,他引:1
Tao Luo Tao Jiang Weidong Xiang Hsiao-Hwa Chen 《Wireless Communications, IEEE Transactions on》2008,7(9):3335-3340
Cognitive radio (CR) is a dynamic spectrum access technology as a solution to spectrum under-utilization problem in some licensed bands. Operating over an exceedingly wide spectrum, CR systems usually adopt multi-carrier modulation (MCM) to implement flexible channelization. Consequently, efficient channel allocation scheme becomes extremely important to an MCM based CR (MCM-CR) system. In this paper, a maximum likelihood detection model is developed to detect the presence and locations of licensed users (LUs) signals in the frequency domain. Performance of the detection model, including the optimal detection region, detection probability and false alarm probability, is analyzed. A one-order two-state Markovian chain model is proposed to predict channel status information. In particular, a novel subcarrier allocation scheme for MCM-CR systems is proposed, taking into account the confidence of channel estimation, quality of services (QoS) of rental users (RUs) and throughput. To validate the analytical results, simulations have been conducted to show effectiveness of the proposed scheme. 相似文献
56.
Magnesiumandmagnesiumalloyshavebeenin vestigatedashydrogenstoragematerialsforseveralde cadesbecausefarmorehydrogenbyweightcanbestoredinthemthaninmostoftheothercurrentlyknownhydrogenstoragealloys .Moreover ,thehighnaturalabundanceofMg ,itslightmassandenviron mentalcompatibilitypotentiallymakemagnesiumoneofthemostprospectivecandidatesforfuturehydrogenstoragematerials .Unfortunately ,thepracticalappli cationofMganditsalloyshasbeenlimitedonlytocertainstoragedevicebecauseoftheirpoorhydriding dehydr… 相似文献
57.
本文研究了无线局域网中使信号频谱得到优化的一种简单OFDM子载波加载算法。此算法基于边缘自适应(Margin Adaptive)加载准则及其在室内无线信道上的性能。 相似文献
58.
Xingqun Jiang Mishra N. Turner J.N. Spencer M.G. 《Nanotechnology, IEEE Transactions on》2007,6(3):328-333
A novel method has been developed for fabricating full or partial freestanding anodic alumina. In our method a sacrificial metal layer is introduced between an Al film and a Si3N4 substrate. A freestanding alumina film at wafer scale is successfully achieved by anodizing the double metal layer, during which the alumina is spontaneously stripped off the Si3N4 substrate due to the anodic oxidation of the sacrificial layer. The barrier oxide of the alumina film is effectively removed either by H3PO4 dissolution or by CF4 reactive ion etching. The freestanding alumina film is utilized as a contact mask to transfer its nanoporous pattern to a Si substrate. By patterning the sacrificial metal layer with contact lithography, a partial freestanding alumina film is successfully achieved on the silicon chip, producing a unique micro/nanofluidic channel. Compared with previous techniques, the method reported here is advantageous for its simplicity and flexibility 相似文献
59.
We present a relatively simple and effective method for acquiring gaseous samples into microfluidic channels. Hydrophobic polymers are photopatterned on hydrophilic substrates. Due to surface tension, aqueous liquid is confined by the hydrophobic polymers, but not completely blocked by a physical wall, thus allowing an interface for gas-liquid interaction. Here, the mechanism is demonstrated by using hydrophobic (poly)iso-bornyl acrylate polymer patterns on hydrophilic glass substrates, and through a Nessler's reagent-ammonia reaction that exhibits changes in color and electrical resistance. 相似文献
60.
Study on Adsorption Behavior of Rare Earth Complexes on Nanometer-Size Titanium Dioxide with ICP-AES
Inrecentyears ,rareearthelements (REEs)havebeenwidelyusedinfunctionalmaterials ,cata lystsandotherproductsinindustry ,diagnosisreagentsofmagneticresonanceimaging (MRI)inmedicineandsomefertilizersinagricultureespeciallyinChina .However,asaresultoftheirusage ,moreandmoreREEsaregettingintotheenvironment,andalsointohumanbodyviafoodchain[1,2 ] .Itisnotclearwhetherrareearthelementsareessentialforman ,soitisveryurgenttostudythebiologicaleffectofrareearthelementsinhumanhealthandenvironment .Inthes… 相似文献