全文获取类型
收费全文 | 21552篇 |
免费 | 1548篇 |
国内免费 | 710篇 |
专业分类
电工技术 | 1018篇 |
技术理论 | 3篇 |
综合类 | 1274篇 |
化学工业 | 3857篇 |
金属工艺 | 1072篇 |
机械仪表 | 1285篇 |
建筑科学 | 1675篇 |
矿业工程 | 461篇 |
能源动力 | 584篇 |
轻工业 | 1493篇 |
水利工程 | 356篇 |
石油天然气 | 1105篇 |
武器工业 | 155篇 |
无线电 | 2242篇 |
一般工业技术 | 3147篇 |
冶金工业 | 1198篇 |
原子能技术 | 259篇 |
自动化技术 | 2626篇 |
出版年
2024年 | 79篇 |
2023年 | 288篇 |
2022年 | 465篇 |
2021年 | 619篇 |
2020年 | 524篇 |
2019年 | 462篇 |
2018年 | 482篇 |
2017年 | 621篇 |
2016年 | 548篇 |
2015年 | 722篇 |
2014年 | 873篇 |
2013年 | 1122篇 |
2012年 | 1204篇 |
2011年 | 1297篇 |
2010年 | 1108篇 |
2009年 | 1076篇 |
2008年 | 1150篇 |
2007年 | 1082篇 |
2006年 | 1163篇 |
2005年 | 1133篇 |
2004年 | 722篇 |
2003年 | 676篇 |
2002年 | 624篇 |
2001年 | 545篇 |
2000年 | 697篇 |
1999年 | 749篇 |
1998年 | 646篇 |
1997年 | 572篇 |
1996年 | 515篇 |
1995年 | 468篇 |
1994年 | 345篇 |
1993年 | 257篇 |
1992年 | 216篇 |
1991年 | 176篇 |
1990年 | 137篇 |
1989年 | 122篇 |
1988年 | 94篇 |
1987年 | 50篇 |
1986年 | 49篇 |
1985年 | 43篇 |
1984年 | 19篇 |
1983年 | 5篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1970年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
101.
102.
EV-DO是高通公司在cdma2000基础上提出的基于提高分组数据性能的系统标准。文章从数据业务和传统的语音业务的比较说起,介绍了EV-DO系统中区别于cdma2000的技术特征(包括自适应编码、快速自动重复请求机制(ARQ)、速率控制、时隙导频工作方式等),并以此平台为例阐述了信道估计中的选径意义和策略,最后简单分析不同选径策略的性能,其中选径策略的讨论是基于带导频信道的无线系统平台而提出的,具有一定的普遍性。 相似文献
103.
Lifeng Huang Naresh Eedugurala Anthony Benasco Song Zhang Kevin S. Mayer Daniel J. Adams Benjamin Fowler Molly M. Lockart Mohammad Saghayezhian Hamas Tahir Eric R. King Sarah Morgan Michael K. Bowman Xiaodan Gu Jason D. Azoulay 《Advanced functional materials》2020,30(24)
Conductive polymers largely derive their electronic functionality from chemical doping, processes by which redox and charge‐transfer reactions form mobile carriers. While decades of research have demonstrated fundamentally new technologies that merge the unique functionality of these materials with the chemical versatility of macromolecules, doping and the resultant material properties are not ideal for many applications. Here, it is demonstrated that open‐shell conjugated polymers comprised of alternating cyclopentadithiophene and thiadiazoloquinoxaline units can achieve high electrical conductivities in their native “undoped” form. Spectroscopic, electrochemical, electron paramagnetic resonance, and magnetic susceptibility measurements demonstrate that this donor–acceptor architecture promotes very narrow bandgaps, strong electronic correlations, high‐spin ground states, and long‐range π‐delocalization. A comparative study of structural variants and processing methodologies demonstrates that the conductivity can be tuned up to 8.18 S cm?1. This exceeds other neutral narrow bandgap conjugated polymers, many doped polymers, radical conductors, and is comparable to commercial grades of poly(styrene‐sulfonate)‐doped poly(3,4‐ethylenedioxythiophene). X‐ray and morphological studies trace the high conductivity to rigid backbone conformations emanating from strong π‐interactions and long‐range ordered structures formed through self‐organization that lead to a network of delocalized open‐shell sites in electronic communication. The results offer a new platform for the transport of charge in molecular systems. 相似文献
104.
105.
106.
顾欣 《电信工程技术与标准化》2010,23(5):26-28
本文首先分析了电信运营商在参与大型盛会通信保障任务期间搭建综合指挥体系的必要性,然后结合奥运会和世博会的差异,介绍了移动运营商在两个盛会中综合指挥体系建设模式的区别,从体系架构、事件处理原则和流程、现场团队部署、体系运转方式四个方面进行了详细的对比阐述和总结。 相似文献
107.
The postulate of a linear tensor relation in the measured equation of invariance (MEI) is proposed for three-dimensional (3D) problems. As a result, all three components of the field vector to be solved are coupled in the MEI. Combined with the finite difference method, the present method is applied to the analysis of scattering by 3D conducting objects and results in a significant improvement in the accuracy of numerical results as compared to those obtained with an uncoupled linear relation. 相似文献
108.
Chip-Hong Chang Jiangmin Gu Mingyan Zhang 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2005,13(6):686-695
The general objective of our work is to investigate the area and power-delay performances of low-voltage full adder cells in different CMOS logic styles for the predominating tree structured arithmetic circuits. A new hybrid style full adder circuit is also presented. The sum and carry generation circuits of the proposed full adder are designed with hybrid logic styles. To operate at ultra-low supply voltage, the pass logic circuit that cogenerates the intermediate XOR and XNOR outputs has been improved to overcome the switching delay problem. As full adders are frequently employed in a tree structured configuration for high-performance arithmetic circuits, a cascaded simulation structure is introduced to evaluate the full adders in a realistic application environment. A systematic and elegant procedure to scale the transistor for minimal power-delay product is proposed. The circuits being studied are optimized for energy efficiency at 0.18-/spl mu/m CMOS process technology. With the proposed simulation environment, it is shown that some survival cells in stand alone operation at low voltage may fail when cascaded in a larger circuit, either due to the lack of drivability or unsatisfactory speed of operation. The proposed hybrid full adder exhibits not only the full swing logic and balanced outputs but also strong output drivability. The increase in the transistor count of its complementary CMOS output stage is compensated by its area efficient layout. Therefore, it remains one of the best contenders for designing large tree structured arithmetic circuits with reduced energy consumption while keeping the increase in area to a minimum. 相似文献
109.
110.
Sink scheduling, in the form of scheduling multiple sinks among the available sink sites to relieve the level of traffic burden, is shown to be a promising scheme in wireless sensor networks (WSNs). However, the problem of maximizing the network lifetime via sink scheduling remains quite a challenge since routing issues are tightly coupled. Previous approaches on this topic either suffer from poor performance due to a lack of joint considerations, or are based on relaxed constraints. Therefore, in this paper, we aim to fill in the research blanks. First, we develop a novel notation Placement Pattern (PP) to bound time-varying routes with the placement of sinks. This bounding technique transforms the problem from time domain into pattern domain, and thus, significantly decreases the problem complexity. Then, we formulate this optimization in a pattern-based way and create an efficient Column Generation (CG) based approach to solve it. Simulations not only demonstrate the efficiency of the proposed algorithm but also substantiate the importance of sink mobility for energy-constrained WSNs. 相似文献