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   473196篇
  免费   4408篇
  国内免费   1098篇
电工技术   8424篇
综合类   276篇
化学工业   71580篇
金属工艺   22989篇
机械仪表   16285篇
建筑科学   9805篇
矿业工程   4290篇
能源动力   10536篇
轻工业   29411篇
水利工程   5900篇
石油天然气   14752篇
武器工业   40篇
无线电   51758篇
一般工业技术   105164篇
冶金工业   77694篇
原子能技术   14624篇
自动化技术   35174篇
  2021年   4654篇
  2019年   4383篇
  2018年   8080篇
  2017年   8341篇
  2016年   8757篇
  2015年   4956篇
  2014年   8697篇
  2013年   20322篇
  2012年   12679篇
  2011年   16455篇
  2010年   13324篇
  2009年   15047篇
  2008年   15566篇
  2007年   15168篇
  2006年   12950篇
  2005年   11381篇
  2004年   11097篇
  2003年   11147篇
  2002年   10552篇
  2001年   10831篇
  2000年   10282篇
  1999年   10140篇
  1998年   23088篇
  1997年   16695篇
  1996年   12810篇
  1995年   9873篇
  1994年   8967篇
  1993年   9062篇
  1992年   6986篇
  1991年   6923篇
  1990年   6892篇
  1989年   6573篇
  1988年   6386篇
  1987年   5872篇
  1986年   5741篇
  1985年   6150篇
  1984年   5807篇
  1983年   5571篇
  1982年   5237篇
  1981年   5214篇
  1980年   5162篇
  1979年   5132篇
  1978年   5157篇
  1977年   5670篇
  1976年   7081篇
  1975年   4612篇
  1974年   4660篇
  1973年   4657篇
  1972年   4089篇
  1971年   3634篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
A method is described for experimentally determining the dose rate created in building bricks by incorporated natural radionuclides. It was established using the thermoluminescence dosimetry method that the measured dose rate depends on the detector thickness, the mass of the ceramic product investigated, and the irradiation geometry. The contributions to the measured dose of weakly penetrating α and β radiation and hard ψ radiation are separated, the ratio between them depending on the experimental conditions. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 62–66, July, 1996.  相似文献   
62.
The paper proposes a structure for quality-of-service (QoS)-centered service level agreements (SLA), and a framework for their real-time management in multiservice packet networks. The SLA is structured to be fair to both parties, the service provider and their customer. The SLA considered here are for QoS assured delivery of aggregate bandwidth from ingress to egress nodes; however, the control and signaling is for the more granular flows or calls. A SLA monitoring scheme is presented in which revenue is generated by the admission of flows into the network, and penalty incurred when flows are lost in periods when the service provider is not SLA compliant. In the SLA management scheme proposed, the results of a prior off-line design are used, in conjunction with measurements taken locally at ingress nodes, to classify the loading status of routes. The routing and resource management are based on virtual partitioning and its supporting mechanism of bandwidth protection. The effectiveness of SLA management is measured by the robustness in performance in the presence of substantial diversity in actual traffic conditions. A simulation testbed called D'ARTAGNAN has been built from which we report numerical results for a case study. The results show that the SLA management scheme is robust, fair and efficient over a broad range of traffic conditions  相似文献   
63.
64.
65.
66.
The effect of high oxide field stress is studied using capacitance-time (C-t) measurements of MOS capacitors. The stress results in parallel shifts of the C-t curve along the time axis. The flatband voltage shift ΔVFB obtained from the initial deep depletion capacitance C(t=0+) follows the same trend as that from the high-frequency C-V characteristics. However, the discrepancy between the two flatband voltages becomes larger as the stress increases due to the effect of interface charges on C-t characteristics. The flatband voltage difference is converted to interface trap density, showing a steady increase of interface trap density with stress, similar to that from low-frequency C-V measurements  相似文献   
67.
This paper presents the design criteria, procedure, and implementation of a soft-switched power-factor-correction (PFC) circuit based on the extended-period quasi-resonant (EPQR) principles. All power electronic devices including switches and diodes in the circuit are fully soft switched. The design method is demonstrated in a prototype circuit. The operating principles are confirmed with computer simulation and experimental results. A comparison of the EP-QR operation and zero-voltage-transition (ZVT) pulse-width modulation (PWM) method  相似文献   
68.
A new lateral MOS-gated thyristor, called the Base-Current-Controlled Thyristor, is described. This device is designed so that most holes at the on-stage reach the P base through the floating P+ region adjacent to the P base and the on-state MOSFET. At the turn-off stage, the interruption of the hole current to the P base due to switching off the above MOSFET occurs simultaneously with the conventional turn-off operation. The concept of this device is verified experimentally by using the fabricated lateral device with the external MOSFET. This device exhibits a better trade-off relation between the on-state voltage and the turn-off time compared uith the conventional MOS-gated thyristor  相似文献   
69.
Single-phase voltage source power converters (VSCs) under consideration are AC-DC current-controlled boost-type power converters with bidirectional power-handling capability. Equivalence between two series-connected two-level power converters and a single three-level power converter is considered here. Further considered is the series operation of three-level power converters. Simulation results and experimental verification for both are provided. Economical configurations of three-level power converters leading to multilevel waveforms are presented thereafter  相似文献   
70.
A novel monitoring method for plasma-charging damage is proposed. This method performs a quick and accurate evaluation using antenna PMOSFET. It was found that not only hot-carrier (HC) lifetime but transistor parameters such as initial gate current and substrate current were changed according to the degree of plasma-charging damage. However, the present work suggests that monitoring the shift of drain current after a few seconds of HC stress is a more accurate method to indicate plasma-charging damage. The monitoring method using the present test structure is demonstrated to be useful for realizing highly reliable devices  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