全文获取类型
收费全文 | 33729篇 |
免费 | 2667篇 |
国内免费 | 1331篇 |
专业分类
电工技术 | 1729篇 |
技术理论 | 2篇 |
综合类 | 2191篇 |
化学工业 | 5968篇 |
金属工艺 | 1989篇 |
机械仪表 | 1974篇 |
建筑科学 | 2522篇 |
矿业工程 | 1015篇 |
能源动力 | 866篇 |
轻工业 | 1907篇 |
水利工程 | 515篇 |
石油天然气 | 2510篇 |
武器工业 | 229篇 |
无线电 | 3969篇 |
一般工业技术 | 4074篇 |
冶金工业 | 1535篇 |
原子能技术 | 423篇 |
自动化技术 | 4309篇 |
出版年
2024年 | 116篇 |
2023年 | 544篇 |
2022年 | 808篇 |
2021年 | 1336篇 |
2020年 | 1031篇 |
2019年 | 856篇 |
2018年 | 1018篇 |
2017年 | 1124篇 |
2016年 | 939篇 |
2015年 | 1249篇 |
2014年 | 1611篇 |
2013年 | 1998篇 |
2012年 | 2090篇 |
2011年 | 2335篇 |
2010年 | 1968篇 |
2009年 | 1805篇 |
2008年 | 1739篇 |
2007年 | 1628篇 |
2006年 | 1798篇 |
2005年 | 1626篇 |
2004年 | 1104篇 |
2003年 | 942篇 |
2002年 | 863篇 |
2001年 | 748篇 |
2000年 | 863篇 |
1999年 | 1013篇 |
1998年 | 784篇 |
1997年 | 703篇 |
1996年 | 682篇 |
1995年 | 553篇 |
1994年 | 453篇 |
1993年 | 341篇 |
1992年 | 260篇 |
1991年 | 190篇 |
1990年 | 145篇 |
1989年 | 126篇 |
1988年 | 109篇 |
1987年 | 64篇 |
1986年 | 47篇 |
1985年 | 23篇 |
1984年 | 16篇 |
1983年 | 15篇 |
1982年 | 30篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 2篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
991.
介绍了输电线路大跨越工程高塔组立施工技术方案,吊装设备功能需求和安全保障措施;论述了高塔组立施工设备设计方案及原则、荷载计算及组合、有限元分析方法,提出了结构尺寸及重量估算的经验公式、设备基本参数;简要介绍了电视监控、超载保护、吊件位置检测系统、摇臂自动调位装置。 相似文献
992.
第二代碳化硅(SiC)肖特基二极管——thinQ!2G是由一个肖特基结构和一个与它平行的独特的低电阻PN结组成,因此具备更加强大的浪涌电流处理能力,同时又继承了第一代碳化硅肖特基二极管所实现的良好的动态性能。 相似文献
993.
Young-Chai Ko Tao Luo 《Wireless Communications, IEEE Transactions on》2006,5(3):514-518
The performance analysis of dual (two-branch) maximal ratio combining (MRC) under imperfect weight, named imperfect MRC, due to the noise imbalance is derived over independent but non-identical Rayleigh fading channels. Considering the system (or channel) conditions that the noise level of each branch is different, we present the accurate performance analysis of imperfect dual MRC in terms of average combined signal-to-noise ratio (SNR), outage probability and average symbol error rate for a large class of modulations in closed-form and compare them with the performance of the perfect MRC and the perfect selection combining (SC) over non-identical but independent Rayleigh fading channels based on the interesting statistical results on the combined SNR. From the performance results we provide the criterion in choosing the imperfect MRC, perfect MRC, or SC depending on the degree of the difference of the noise level between branches. 相似文献
994.
Xiaoning Qi Gyure A. Yansheng Luo Lo S.C. Shahram M. Singhal K. 《Electron Device Letters, IEEE》2006,27(8):696-698
The on-chip inductive impact on signal integrity has been a problem for designs in deep-submicrometer technologies. The inductive impact increases the clock skew, max timing, and noise of bus signals. In this letter, circuit simulations using silicon-validated macromodels show that there is a significant inductive impact on the signal max timing (/spl sim/ 10% pushout versus RC delay) and noise (/spl sim/2/spl times/RC noise). In nanometer technologies, process variations have become a concern. Results show that device and interconnect process variations add /spl sim/ 3% to the RLC max-timing impact. However, their impact on the RLC signal noise is not appreciable. Finally, inductive impact in 65- and 45-nm technologies is investigated, which indicates that the inductance impact will not diminish as technology scales. 相似文献
995.
Liu H C Luo H Ban D Wchter M Song C Y Wasilewski Z R Buchanan M Aers G C SpringThorpe A J Cao J C Feng S L Williams B S Hu Q 《半导体学报》2006,27(4)
For eventually providing terahertz science with compact and convenient devices,terahertz (1~10THz) quantum-well photodetectors and quantum-cascade lasers are investigated. The design and projected detector performance are presented together with experimental results for several test devices,all working at photon energies below and around optical phonons. Background limited infrared performance (BLIP) operations are observed for all samples (three in total) ,designed for different wavelengths. BLIP temperatures of 17,13, and 12K are achieved for peak detection frequencies of 9.7THz(31μm) ,5.4THz(56μm) ,and 3.2THz(93μm) ,respectively. A set of THz quantum-cascade lasers with identical device parameters except for doping concentration is studied. The δ-doping density for each period varies from 3.2 × 1010 to 4. 8 × 1010cm-2. We observe that the lasing threshold current density increases monotonically with doping concentration. Moreover, the measurements for devices with different cavity lengths provide evidence that the free carrier absorption causes the waveguide loss also to increase monotonically. Interestingly the observed maximum lasing temperature is best at a doping density of 3.6 × 1010cm-2. 相似文献
996.
A novel frequency offset estimation method for OFDM systems with large estimation range 总被引:4,自引:0,他引:4
Chunlin Yan Shaoqian Li Youxi Tang Xiao Luo Jiayi Fang 《Broadcasting, IEEE Transactions on》2006,52(1):58-61
In this paper, we proposed a novel frequency synchronization method which has larger estimation range than conventional method proposed by Tufvesson. A two steps frequency offset estimation method is performed in the new method. In the first step the received signal is correlated with local training sequence to eliminate the influence of training sequence which makes the estimation range of frequency offset is independent of period of the repeated data in the training sequence. The received signal is correlated with its delay in the second step to obtain the fine estimation of frequency offset. Precise estimation can be achieved in the proposed method than Tufvesson's method. The period of the repeated data in the training sequence determines the estimation range of the frequency offset in the conventional method, while in the new method they are irrelevant. Tens of subcarriers spacing can be estimated by the new method. The new method can be used in other cases as long as a known sequence is transmitted, which will introduce valuable flexibility in training sequence design. The validity of the algorithm is verified in AWGN channel and multipath fading channel. 相似文献
997.
998.
研究和讨论了GB 19212.1-2003,5.2和附录B分别规定的单规格变压器的试验规则和"系列变压器的试验"规则,提出了确定变压器型式试验的样品组成和样品数量的一种可操作的方案. 相似文献
999.
1000.
近年来,Web服务器集群技术以其扩展性好、处理能力强等优点受到了国内外研究机构的广泛关注和应用,其中的负载均衡算法更是研究的热点;对Web服务器集群负载均衡进行了研究,为有效地实现任务的均衡分配,提出一种了根据Web服务器系统中各个服务器的负载情况进行动态任务分配的遗传算法,实验表明该方法能有效地实现Web服务器集群的负载均衡服务。 相似文献