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   257122篇
  免费   2886篇
  国内免费   875篇
电工技术   4927篇
综合类   201篇
化学工业   37129篇
金属工艺   9594篇
机械仪表   7631篇
建筑科学   6346篇
矿业工程   900篇
能源动力   7328篇
轻工业   21531篇
水利工程   2259篇
石油天然气   3238篇
武器工业   15篇
无线电   34574篇
一般工业技术   50514篇
冶金工业   49319篇
原子能技术   5143篇
自动化技术   20234篇
  2021年   2234篇
  2020年   1600篇
  2019年   1967篇
  2018年   3312篇
  2017年   3359篇
  2016年   3462篇
  2015年   2286篇
  2014年   4050篇
  2013年   11660篇
  2012年   6362篇
  2011年   8767篇
  2010年   7033篇
  2009年   8013篇
  2008年   8559篇
  2007年   8435篇
  2006年   7499篇
  2005年   6604篇
  2004年   6384篇
  2003年   6645篇
  2002年   6128篇
  2001年   6576篇
  2000年   6033篇
  1999年   6459篇
  1998年   16603篇
  1997年   11517篇
  1996年   8870篇
  1995年   6687篇
  1994年   5969篇
  1993年   5901篇
  1992年   4180篇
  1991年   4069篇
  1990年   3915篇
  1989年   3703篇
  1988年   3609篇
  1987年   3075篇
  1986年   2991篇
  1985年   3270篇
  1984年   2983篇
  1983年   2887篇
  1982年   2687篇
  1981年   2585篇
  1980年   2497篇
  1979年   2350篇
  1978年   2167篇
  1977年   2661篇
  1976年   3627篇
  1975年   1819篇
  1974年   1779篇
  1973年   1722篇
  1972年   1507篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Bone marrow examination revealed a lipid-laden histiocytosis in seven patients undergoing long-term total parenteral nutrition necessitated by extensive short-bowel surgical resection. Clinical abnormalities occurred during this treatment which required bone marrow examination. These included hepatosplenomegaly and peripheral blood cytopenia; the median time to the detection of these abnormalities was 64 months. The most striking change within the bone marrow was the presence of many pigment-laden histiocytes which had the typical morphology of sea-blue histiocytes seen in the so-called idiopathic sea-blue histiocyte syndrome. The occurrence of sea-blue histiocytosis in the bone marrow in association with long-term parenteral nutrition for short-bowel syndrome has not, to our knowledge, been reported previously and should now be considered in the differential diagnosis of bone marrow sea-blue histiocytosis.  相似文献   
32.
One month following the Great Hanshin Earthquake of January 17, 1995, we conducted a survey of 173 hospitals in Aichi Prefecture to pinpoint problems related to their actual disaster-readiness and the medical backup systems in place to deal with such disasters. This study revealed that staff at 50% of the surveyed hospitals could reach the hospital within an hour, but that communication is almost entirely dependent on phone lines, suggesting that cordless/portable/mobile phones, radio systems, Internet, communications satellites and the like should be studied in the days to come for possible use as effective communication alternatives in times of disaster. Whereas 92% of the surveyed hospitals had manuals dealing with fire outbreaks, other areas were less well represented. For example, only 36.9% of surveyed hospitals had manuals for earthquakes, 31.7% had manuals for power outages and 14.2% had manuals to deal with flooding and water disasters. New manuals must be developed incorporating the key points garnered from experience (especially Hanshin) and be ready for use immediately. It is the time for each hospital to seriously rethink the measures it should take to deal with disasters.  相似文献   
33.
The biotransformation of oxazepam by Bifidobacterium bifidum was studied. The major metabolite was purified by chromatographic methods and found to be desmethyldiazepam using NMR, IR and other physicochemical data.  相似文献   
34.
35.
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   
36.
37.
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   
38.
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   
39.
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   
40.
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   
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