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   3983篇
  免费   224篇
  国内免费   71篇
电工技术   170篇
综合类   54篇
化学工业   832篇
金属工艺   110篇
机械仪表   152篇
建筑科学   94篇
矿业工程   19篇
能源动力   141篇
轻工业   204篇
水利工程   31篇
石油天然气   31篇
武器工业   8篇
无线电   813篇
一般工业技术   674篇
冶金工业   374篇
原子能技术   29篇
自动化技术   542篇
  2024年   11篇
  2023年   36篇
  2022年   103篇
  2021年   129篇
  2020年   78篇
  2019年   66篇
  2018年   87篇
  2017年   92篇
  2016年   95篇
  2015年   114篇
  2014年   178篇
  2013年   323篇
  2012年   262篇
  2011年   265篇
  2010年   214篇
  2009年   202篇
  2008年   204篇
  2007年   195篇
  2006年   185篇
  2005年   107篇
  2004年   106篇
  2003年   105篇
  2002年   81篇
  2001年   62篇
  2000年   65篇
  1999年   68篇
  1998年   152篇
  1997年   108篇
  1996年   83篇
  1995年   53篇
  1994年   68篇
  1993年   55篇
  1992年   49篇
  1991年   32篇
  1990年   36篇
  1989年   35篇
  1988年   21篇
  1987年   19篇
  1986年   13篇
  1985年   18篇
  1984年   17篇
  1983年   7篇
  1982年   8篇
  1981年   9篇
  1980年   6篇
  1978年   8篇
  1977年   7篇
  1976年   9篇
  1975年   7篇
  1973年   5篇
排序方式: 共有4278条查询结果,搜索用时 17 毫秒
61.
In the past few years, motion compensation has been widely used in the coding of image sequences. Most of motion estimation and compensation schemes belong to block-based framework. The framework simplifies the complexity of motion estimation, but gives over constraints to the motion field, which results in worse accuracy on the boundary of moving objects. This paper presents a novel technique for raising motion field accuracy. It uses several pre-defined pattern types to segment the motion fields of the previous frame of a sequence. The segmentation is based on the MAP framework that uses iterative method to obtain the solution. In addition, we develop a predictive scheme to predict the location of motion field discontinuities in the current frame, which further reduces the side information for the representation of segmentation.  相似文献   
62.
Culture performance for the production of penicillin acylase (PAC) in a bioreactor was investigated using HB101 or ATCC11105 as the host and pCLL2902, pCLL3201 or pTrcKnPAC2902 as the expression plasmid. We observed that the production of PAC by HB101 harboring pCLL3201 was, similar to ATCC11105, induced by phenyl acetic acid (PAA) and catabolicaily repressed by glucose, whereas the production of PAC by HB101 harboring pCLL2902 did not require PAA for induction and was not repressed by glucose. PAC activity of HB101 harboring pCLL2902 was significantly higher than that of HB101 harboring pCLL3201. There was no significant effect of host or carbon source on the production of PAC using pCLL2902. The production of PAC by HB101 harboring pTrcKnPAC2902, in which the pac gene expression was controlled by the trc promoter system, was about the same as that by HB101 harboring pCLL2902, when the culture was appropriately induced with isopropyl beta-d-thiogalactopyranoside (IPTG). Therefore, the use of both pCLL2902 and pTrcKnPAC2902 could be expected to be feasible for industrial applications. However, optimization of IPTG induction for HB101 harboring pTrcKnPAC2902 might be required, since formation of inclusion bodies tends to limit the production of PAC in some cases.  相似文献   
63.
Technology for simultaneous demultiplexing of subrate tributaries is described and applied to 320-Gb/s return-to-zero input. The parametric architecture is scalable with respect to processed input rate and relies on cascaded all-optical multicasting and subrate sampling. Processing of 320-Gb/s input was achieved by creating eight channel copies, followed by a 20-THz-wide parametric gate. Multicasting was based on a self-seeded two-pump broadband fiber-optic parametric amplifier. The architecture was used to demonstrate error-free parallel demultiplexing of eight 320-Gb/s tributary channels at 40 Gb/s.  相似文献   
64.
Parallel-coupled microstrip filters are designed to suppress spurious response at twice the passband frequency (2f/sub o/) with a uniform dielectric overlay. The overlay dielectric is used to equalize the modal phase velocities of each coupled stage. Based on the method, we have a large degree of freedom in choosing thickness and permittivity of the overlay dielectric. The image impedances of all the coupled stages in such a filter need adjusting to complete the filter synthesis. Two filters are fabricated and measured results show a good agreement with the simulation. A suppression of at least 40 dB to the spurious responses at 2f/sub o/ is achieved.  相似文献   
65.
In a MOS structure, the generation of hot carrier interface states is a critical feature of the item's reliability. On the nano-scale, there are problems with degradation in transconductance, shift in threshold voltage, and decrease in drain current capability. Quantum mechanics has been used to relate this decrease to degradation, and device failure. Although the lifetime, and degradation of a device are typically used to characterize its reliability, in this paper we model the distribution of hot-electron activation energies, which has appeal because it exhibits a two-point discrete mixture of logistic distributions. The logistic mixture presents computational problems that are addressed in simulation.  相似文献   
66.
在28 nm低功耗工艺平台开发过程中,对1.26 V测试条件下出现的SRAM双比特失效问题进行了电性能失效模式分析及物性平面和物性断面分析.指出失效比特右侧位线接触孔底部空洞为SRAM制程上的缺陷所导致.并通过元素成分分析确定接触孔底部钨(W)的缺失,接触孔底部外围粘结阻挡层的氮化钛(TiN)填充完整.结合SRAM写操作的原理从电阻分压的机理上解释了较高压下双比特失效,1.05 V常压下单比特不稳定失效,0.84 V低电压下失效比特却通过测试的原因.1.26 V电压下容易发生的双比特失效是一种很特殊的SRAM失效,其分析过程及结论在集成电路制造行业尤其是对先进工艺制程研发过程具有较好的参考价值.  相似文献   
67.
Fast mode decision algorithms have been widely used in the video encoder implementation to reduce encoding complexity yet without much sacrifice in the coding performance. Optimal stopping theory, which addresses early termination for a generic class of decision problems, is adopted in this paper to achieve fast mode decision for the H.264/Scalable Video Coding standard. A constrained model is developed with optimal stopping, and the solutions to this model are employed to initialize the candidate mode list and predict the early termination. Comprehensive simulation results are conducted to demonstrate that the proposed method strikes a good balance between low encoding complexity and high coding efficiency.  相似文献   
68.
This paper presents a methodology for analyzing the forward link performance of a pilot-aided coherent DS-CDMA system under correlated Rician fading. In the forward link of a CDMA system, orthogonal modulation is usually used to minimize the self-interference. To maintain the orthogonality and reduce the receiver complexity, a common pilot channel (shared by all users) is employed to provide the reference for coherent demodulation. A tradeoff shows that a higher pilot ratio yields good channel estimates but takes away some capacity from traffic users, while a lower pilot ratio results in poorer channel estimates and leads to higher traffic power per user. This paper derives the analytical error performance, which includes (1) imperfect channel estimation by the pilot channel, (2) a very general channel model where correlations between paths as well as Rician fading are considered, and (3) interference patterns due to multiple paths and the surrounding base stations' transmissions. This paper also considers self-interference due to the loss of orthogonality caused by pulse shaping  相似文献   
69.
The authors present a BiCMOS dynamic multiplier, which is free from race and charge-sharing problems, using Wallace tree reduction architecture and 1.5-V full-swing BiCMOS dynamic logic circuit. Based on a 1-μm BiCMOS technology, a 1.5-V 8×8 multiplier designed, shows a 2.3× improvement in speed as compared to the CMOS static one  相似文献   
70.
AlGalnP-based visible 650-nm GalnP-AlGalnP resonant-cavity light-emitting diodes (RCLEDs) with high-temperature stability were fabricated by wafer-bonding techniques on Si substrates. In this study, the metal-bonding RCLEDs (MBRCLEDs) devices were designed with 84-mum apertures for light output. The MBRCLEDs with a maximum wall-plug efficiency of 13.7% were demonstrated at an injection current of 2.5 mA. In addition, the improved heat sinking of MBRCLEDs led to lower junction temperature, and resulted in a very low power decay of 0.31 dB from room temperature to 100degC at an injection current of 20 mA.  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