全文获取类型
收费全文 | 76546篇 |
免费 | 8970篇 |
国内免费 | 4542篇 |
专业分类
电工技术 | 3381篇 |
技术理论 | 1篇 |
综合类 | 5925篇 |
化学工业 | 13915篇 |
金属工艺 | 8614篇 |
机械仪表 | 3778篇 |
建筑科学 | 4131篇 |
矿业工程 | 4936篇 |
能源动力 | 2945篇 |
轻工业 | 4666篇 |
水利工程 | 1666篇 |
石油天然气 | 5650篇 |
武器工业 | 804篇 |
无线电 | 6370篇 |
一般工业技术 | 9403篇 |
冶金工业 | 7981篇 |
原子能技术 | 1577篇 |
自动化技术 | 4315篇 |
出版年
2024年 | 301篇 |
2023年 | 1458篇 |
2022年 | 2141篇 |
2021年 | 2747篇 |
2020年 | 2954篇 |
2019年 | 2689篇 |
2018年 | 2352篇 |
2017年 | 2942篇 |
2016年 | 3122篇 |
2015年 | 3069篇 |
2014年 | 4614篇 |
2013年 | 5157篇 |
2012年 | 5694篇 |
2011年 | 5648篇 |
2010年 | 4137篇 |
2009年 | 4101篇 |
2008年 | 3662篇 |
2007年 | 4674篇 |
2006年 | 4186篇 |
2005年 | 3733篇 |
2004年 | 3118篇 |
2003年 | 2951篇 |
2002年 | 2454篇 |
2001年 | 2073篇 |
2000年 | 1877篇 |
1999年 | 1499篇 |
1998年 | 1248篇 |
1997年 | 998篇 |
1996年 | 928篇 |
1995年 | 751篇 |
1994年 | 570篇 |
1993年 | 458篇 |
1992年 | 386篇 |
1991年 | 311篇 |
1990年 | 252篇 |
1989年 | 199篇 |
1988年 | 121篇 |
1987年 | 85篇 |
1986年 | 67篇 |
1985年 | 70篇 |
1984年 | 64篇 |
1983年 | 44篇 |
1982年 | 35篇 |
1981年 | 19篇 |
1980年 | 21篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1975年 | 13篇 |
1959年 | 10篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
稠油微生物开采技术现状及进展 总被引:2,自引:0,他引:2
综述了用微生物方法开采稠油的技术现状与进展,论题如下。①概述。②基本方法:异源微生物采油,包括微生物吞吐和微生物驱;本源微生物采油压大港孔店油田的实例。③主要机理,包括产表面活性剂,降解稠油中重质组分及其他。④技术研究,包括机理性、可行性及经济效益研究,列举了国内外6个实例。⑤现场应用,包括国外1个、国内6个实例。⑥该技术的优势及问题。参22。 相似文献
73.
X.W. Lou C. Yuan E. Rhoades Q. Zhang L.A. Archer 《Advanced functional materials》2006,16(13):1679-1684
We report a general template strategy for rational fabrication of a new class of nanostructured materials consisting of multicore shell particles. Our approach is demonstrated by encapsulating Au or Pt nanoparticles in silica shells. Other superstructures of these hollow shells, like dimers, trimers, and tetramers can also be formed by nanoparticle‐mediated self‐assembly. We have also used the as‐prepared multicore Au–silica hollow particles to perform the first studies of Ostwald ripening in confined microspace, in which chloride was found to be an efficient mediating ligand. After treatment with aqua regia, Au–Cl complex is formed inside the shell, and is found to be very active under in situ transmission electron microscopy observations while confined in a microcell. This aspect of the work is expected to motivate further in situ studies of confined crystal growth. 相似文献
74.
75.
Yang Aiying Wang Ziyu Zhang Zhaoyi Chen Zhangyuan Wu Deming 《电子科学学刊(英文版)》2003,20(6):461-466
A 10Gbit/s recirculating system is configured with Chirped Fiber Bragg Grating (CFBG) for the dispersion compensation. For the first time, the transmission distance in the loop reaches 1000km with bit error rate of 10-9. The effect of the group delay ripple of the fiber grating is also investigated in the recirculating systems, and it is shown that the transmission distance is limited to 4 cycles (4×167.1km ) in the loop with the power penalty fluctuation below 1.0dB. Thus the group delay ripple should be reduced to allow for the wavelength drift of±5GHz. At the end of this letter, the principles are given for designing long haul recirculating systems with dispersion compensation CFBG. 相似文献
76.
77.
渤海湾盆地石油地质储量和产量增长趋势的预测 总被引:3,自引:1,他引:2
渤海湾盆地的石油地质储量发现过程具有明显的渐进性、阶段性和长期性,石油产量的增长也具有一定的起伏性,用一个周期的单旋回哈伯特模型难以预测其发展趋势。通过分析渤海湾盆地的勘探开发历程,结合新一轮常规油气资源评价的结果,分别采用4个和3个哈伯特旋回拟合石油地质储量发现和产量增长曲线。预测结果显示,2005-2015年渤海湾盆地处于石油地质储量发现高峰期,2015年左右其石油产量达到高峰,之后处于下降趋势。实践证明,利用多旋回哈伯特模型对具有“多峰”特征的石油地质储量和产量的未来趋势进行预测是一种有效的方法。 相似文献
78.
Yu Zhao Zhigang Xu Zongshi Li Weihong Qiao Lubai Cheng 《Petroleum Science and Technology》2006,24(7):821-827
Heavy alkyl benzene sulfonates (HABS) were synthesized, and their interfacial tensions were measured and compared with those of petroleum sulfonates ORS-41. Effects of their coupling with lignosulfonate were also studied. The results showed that HABS exhibited good interfacial activities and the system of HABS blending with LS displayed better interfacial activities than ORS-41 and therefore reduced the prime cost. Their best proportions of synergism were from 3:1 to 4:1. HABS might be a more promising alkali-surfactant-polymer (ASP) flooding agent. 相似文献
79.
新型壳聚糖/纳米二氧化硅杂化材料的制备与性能 总被引:10,自引:5,他引:5
在纳米S iO2颗粒表面引入羟丙基氯活性基团,得到功能化S iO2颗粒,再将羟丙基氯化的S iO2颗粒交联固定在壳聚糖上,制备了一种新型的壳聚糖/纳米S iO2杂化材料(简称杂化材料);通过傅里叶变换红外光谱、透射电镜、扫描电镜方法对杂化材料进行表征,采用热重(TG)分析研究杂化材料的热性能;考察了杂化材料的沉降速率和对金属离子Ca2+和M g2+的吸附能力。电镜分析结果表明,杂化材料微粒为纳米尺度的无机S iO2加强化的微粒,S iO2颗粒分散在材料中,形成均匀的表面;TG分析结果表明,杂化材料的热性能有所提高;沉降实验测得壳聚糖和杂化材料作为吸附剂的沉降时间分别为130.3,68.5s,表明杂化材料的沉降速率比壳聚糖的沉降速率快了近一倍;杂化材料对金属离子Ca2+和M g2+的吸附量分别可达到0.289 3,1.445 6mm ol/g。 相似文献
80.
Ben-Jye Chang 《Telecommunication Systems》2006,33(4):333-352
3G Wideband CDMA systems adopt the Orthogonal Variable Spreading Factor code tree as the channelization codes management for
achieving high data rate transmission in personal multimedia communications. It assigns a single channelization code for each
accepted connection. Nevertheless, it wastes the system capacity when the required rate is not powers of two of the basic
rate. One good solution is to assign multiple codes for each accepted connection but it causes two inevitable drawbacks: long
handoff delay and new call setup delay due to high complexity of processing with multiple channelization codes, and high cost
of using more number of rake combiners. Especially, long handoff delay may result in more call dropping probability and higher
Grade of Service, which will degrade significantly the utilization and revenue of the 3G cellular systems. Therefore, we propose
herein an adaptive efficient codes determination algorithm based on the Markov Decision Process analysis approach to reduce
the waste rate and reassignments significantly while providing fast handoff. Numerical results demonstrate that the proposed
approach yields several advantages, including the lowest GOS, the least waste rate, and the least number of reassignments.
Meanwhile, the optimal number of rake combiners is also analyzed in this paper.
This research was supported in part by the National Science Council of Taiwan, ROC, under contract NSC-93-2213-E-324-018. 相似文献