首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   301638篇
  免费   27695篇
  国内免费   16231篇
电工技术   20115篇
技术理论   14篇
综合类   21959篇
化学工业   47158篇
金属工艺   17391篇
机械仪表   19364篇
建筑科学   24484篇
矿业工程   8700篇
能源动力   8456篇
轻工业   23264篇
水利工程   6507篇
石油天然气   13881篇
武器工业   2759篇
无线电   36146篇
一般工业技术   34796篇
冶金工业   14260篇
原子能技术   3945篇
自动化技术   42365篇
  2024年   1270篇
  2023年   4514篇
  2022年   9510篇
  2021年   12697篇
  2020年   9148篇
  2019年   7325篇
  2018年   7925篇
  2017年   8979篇
  2016年   8165篇
  2015年   11518篇
  2014年   14859篇
  2013年   18870篇
  2012年   20540篇
  2011年   22071篇
  2010年   19682篇
  2009年   19291篇
  2008年   19138篇
  2007年   18789篇
  2006年   17994篇
  2005年   15588篇
  2004年   10790篇
  2003年   8441篇
  2002年   7750篇
  2001年   6948篇
  2000年   6616篇
  1999年   6262篇
  1998年   5432篇
  1997年   4474篇
  1996年   4029篇
  1995年   3378篇
  1994年   2821篇
  1993年   2238篇
  1992年   1760篇
  1991年   1308篇
  1990年   1069篇
  1989年   933篇
  1988年   702篇
  1987年   533篇
  1986年   402篇
  1985年   334篇
  1984年   213篇
  1983年   202篇
  1982年   158篇
  1981年   159篇
  1980年   153篇
  1979年   113篇
  1978年   63篇
  1977年   63篇
  1976年   77篇
  1975年   38篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Due to the salient characteristics such as the time-varying and error-prone wireless links, the dynamic and limited bandwidth, the time-varying traffic pattern and user locations, and the energy constraints, it is a challenging task to efficiently support heterogeneous traffic with different quality of service (CoS) requirements in multihop mobile ad hoc networks. In the last few years, many channel-dependent mechanisms are proposed to address this issue based on the cross-layer design philosophy. However, a lot of problems remain before more efficient solutions are found. One of the problems is how to alleviate the conflict between throughput and fairness for different prioritized traffic, especially how to avoid the bandwidth starvation problem for low-priority traffic when the high-priority traffic load is very high. In this paper, we propose a novel scheme named Courtesy Piggybacking to address this problem. With the recognition of interlayer coupling, our Courtesy Piggybacking scheme exploits the channel dynamics and stochastic traffic features to alleviate the conflict. The basic idea is to let the high-priority traffic help the low-priority traffic by sharing unused residual bandwidth with courtesy. Another noteworthy feature of the proposed scheme is its implementation simplicity: The scheme is easy to implement and is applicable in networks using either reservation-based or contention-based MAC protocols.  相似文献   
982.
生物膜法处理2,3-二甲基苯胺废水试验研究   总被引:2,自引:0,他引:2  
采用缺氧折流板生物膜和循环移动载体生物膜反应器处理2,3-二甲基苯胺废水,结果表明,缺氧折流板反应器具有厌氧滤池和厌氧折流板反应器的优点,当水力停留时间为10.5h(缺氧5.5h,好氧5h)时,系统去除率可达89.7%。  相似文献   
983.
We demonstrate the first programmable group-delay module based on polarization switching. With a unique binary tuning mechanism, the device can generate any differential group delay value from -45 to +45 ps with a resolution of 1.40 ps, or any true-time-delay value from 0 to 45 ps with a resolution of 0.7 ps. The delay varying speeds for both applications are under 1 ms and can be as fast as 0.1 ms. We evaluate both the dynamic and static performances of the device while paying special attention to its dynamic figures of merit for polarization-mode dispersion emulation and compensation applications. Our experiment shows that the device exhibits a negligible transient-effect induced power penalty (<0.2 dB) in a 10-Gb/s nonreturn-to-zero system.  相似文献   
984.
STUDY ON PHASE PERCEPTION IN SPEECH   总被引:4,自引:0,他引:4  
The perceptual effect of the phase information in speech has been studied by auditory subjective tests. On the condition that the phase spectrum in speech is changed while amplitude spectrum is unchanged, the tests show that: (1) If the envelop of the reconstructed speech signal is unchanged, there is indistinctive auditory perception between the original speech and the reconstructed speech; (2) The auditory perception effect of the reconstructed speech mainly lies on the amplitude of the derivative of the additive phase; (3) td is the maximum relative time shift between different frequency components of the reconstructed speech signal. The speech quality is excellent while td <10ms; good while 10ms< td <20ms; common while 20ms< td <35ms, and poor while td >35ms.  相似文献   
985.
In this paper, we report on a novel family of monodisperse thermo‐sensitive core–shell hydrogel microspheres that is featured with high monodispersity and positively thermo‐responsive volume phase transition characteristics with tunable swelling kinetics, i.e., the particle swelling is induced by an increase rather than a decrease in temperature. The microspheres were fabricated in a three‐step process. In the first step, monodisperse poly(acrylamide‐co‐styrene) seeds were prepared by emulsifier‐free emulsion polymerization. In the second step, poly(acrylamide) or poly[acrylamide‐co‐(butyl methacrylate)] shells were fabricated on the microsphere seeds by free radical polymerization. In the third step, the core–shell microspheres with poly‐ (acrylamide)/poly(acrylic acid) based interpenetrating polymer network (IPN) shells were finished by a method of sequential IPN synthesis. The proposed monodisperse core–shell microspheres provide a new mode of the phase transition behavior for thermo‐sensitive “smart” or “intelligent” monodisperse micro‐actuators that is highly attractive for targeting drug delivery systems, chemical separations, sensors, and so on.  相似文献   
986.
一种快速CRC 算法①的硬件实现方法   总被引:12,自引:0,他引:12       下载免费PDF全文
介绍了CRC校验算法的硬件电路实现方法。CRC校验广泛应用于通信、存储系统,在串行CRC实现的基础上,对电路结构提出了改进的方案,并实现了CRC的并行计算,由此进一步可以适用于任意位数据宽度的数据输入情况。  相似文献   
987.
1 IntroductionHandoverbetweencellsisplayinganimportantroleincellularcommunicationsystems[1~ 1 2 ] .Thehandoverprocedureanditseffectivenessareseriouslylimitedbythecellulararchitectureasaresultofmar ketplanning .Basedonthehexagonalcellulararchi tecture,manyhandoverprocedureshavebeendis cussedandevaluated ,andmostoftheimprovementproposedonthemleadstotheintroductionofsector ingcellularorlayeredcellularmodel.Otherwise ,abetterhandoverprocedureisessentialinmaintainingacallinprogressbutitreflectshi…  相似文献   
988.
989.
通过模型试验 ,对位于西安市东郊因采沙使河道破坏严重的灞河河段进行了复现试验和研究 ,并以此为依据 ,通过优化比较为设计部门提供了合理的橡胶坝坝址和坝座高程。在此基础上 ,又对建坝后橡胶坝对上下游冲淤变化的影响进行了试验研究和分析 ,解决了工程设计中的一些关键技术问题  相似文献   
990.
介绍一种基于 16位单片机的电磁平板硫化机控制系统,该系统能有效地提高现场控制的实时性和程序运行的稳定性  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号