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   623篇
  免费   87篇
  国内免费   18篇
电工技术   34篇
综合类   30篇
化学工业   6篇
金属工艺   1篇
机械仪表   28篇
建筑科学   12篇
矿业工程   11篇
能源动力   8篇
轻工业   4篇
水利工程   100篇
石油天然气   130篇
武器工业   63篇
无线电   140篇
一般工业技术   24篇
冶金工业   2篇
原子能技术   1篇
自动化技术   134篇
  2024年   5篇
  2023年   9篇
  2022年   17篇
  2021年   18篇
  2020年   24篇
  2019年   19篇
  2018年   16篇
  2017年   24篇
  2016年   32篇
  2015年   31篇
  2014年   50篇
  2013年   39篇
  2012年   54篇
  2011年   52篇
  2010年   36篇
  2009年   22篇
  2008年   27篇
  2007年   27篇
  2006年   36篇
  2005年   21篇
  2004年   39篇
  2003年   25篇
  2002年   23篇
  2001年   12篇
  2000年   10篇
  1999年   7篇
  1998年   12篇
  1997年   15篇
  1996年   8篇
  1995年   5篇
  1994年   1篇
  1993年   2篇
  1992年   1篇
  1991年   3篇
  1990年   3篇
  1989年   1篇
  1985年   1篇
  1978年   1篇
排序方式: 共有728条查询结果,搜索用时 15 毫秒
1.
张立英  屈万里  王国平  于国华 《测井技术》2002,26(5):435-436,440
简要介绍了多功能井下超声成像测井仪的总体构思,然后较详细地阐述了其中的一个关键部分-传输短节的设计与开发过程。在短节中应用了单片机系统和FPGA技术,实现了一种包括大数据量井下超声成像测井仪在组合测井新方法,为今后井下超声成像测井仪的发展拓宽了道路。  相似文献   
2.
提出了利用遥测的过载、俯仰角信息和光测的坐标联合计算弹道关机段速度的方法,从遥测结果的系统误差、随机误差和数值积分的截断误差三万面对剩余误差的影响进行了精度分析,并给出了速度精度的算法。  相似文献   
3.
刘章平  熊宗富 《物探装备》2003,13(2):92-93,96
通过分析SN388地震仪所得的地震记录,发现炮点的能量越强,炮点附近的地震道感应越大。通过实验得出结论,炮点附近的感应是由道间串音引起的,采取适当措施就可解决这种问题。  相似文献   
4.
王晖 《物探装备》2007,17(3):197-198
NZ-24地震仪在野外施工时软件经常出现故障,要恢复软件既烦琐,又耗时。利用Ghost软件可快速备份和恢复仪器整个硬盘数据,一旦软件再出故障,只需做简单的硬盘数据恢复即可。本文介绍了使用Ghost软件快速备份、恢复数据的具体方法。  相似文献   
5.
研究如何挖掘遥测数据系统的效能以适应数据处理任务需求的变化,提出了数据矩阵概念,定义各种分割方式,应用多目标规划理论,对不同需求目标进行任务分配,并求解对应的最优解。  相似文献   
6.
Infrequent captures of invasive, non-native grass carp (Ctenopharyngodon idella) have occurred in Lake Erie over the last 30+ years, with recent evidence suggesting wild reproduction in the lake’s western basin (WB) is occurring. Information on grass carp movements in the Laurentian Great Lakes is lacking, but an improved understanding of large-scale movements and potential areas of aggregation will help inform control strategies and risk assessment if grass carp spread to other parts of Lake Erie and other Great Lakes. Twenty-three grass carp captured in Lake Erie’s WB were implanted with acoustic transmitters and released. Movements were monitored with acoustic receivers deployed throughout Lake Erie and elsewhere in the Great Lakes. Grass carp dispersed up to 236 km, with approximately 25% of fish dispersing greater than 100 km from their release location. Mean daily movements ranged from <0.01 to 2.49 km/day, with the highest daily averages occurring in the spring and summer. The Sandusky, Detroit, and Maumee Rivers, and Plum Creek were the most heavily used WB tributaries. Seventeen percent of grass carp moved into Lake Erie’s central or eastern basins, although all fish eventually returned to the WB. One fish emigrated from Lake Erie through the Huron-Erie Corridor and into Lake Huron. Based on our results, past assessments may have underestimated the potential for grass carp to spread in the Great Lakes. We recommend focusing grass carp control efforts on Sandusky River and Plum Creek given their high use by tagged fish, and secondarily on Maumee and Detroit Rivers.  相似文献   
7.
Understanding relationships between freshwater fishes and habitat is critical for effective fisheries and habitat management. Habitat suitability indices (HSI) are commonly used to describe fish–habitat associations in rivers and other freshwater ecosystems. When applied to large lakes however, standard sampling procedures are inadequate because of larger sampling areas and an increased risk of fish collection bias through one-time observations. Here, we use lake bathymetry, substrate, and multiple fish telemetry detections collected from a systematically deployed receiver grid to develop HSI for four fish species (lake sturgeon, freshwater drum, common carp, and walleye) in Lake Winnipeg. Seasonal variations in habitat use based on water depth and substrate were observed in three of four species. Lake sturgeon remained in shallow locations with predominantly gravel substrate near the mouth of the Winnipeg River regardless of season. Freshwater drum persisted over fine substrate in both summer and winter but had a broader depth range in the summer compared to winter. Common carp shifted from mid-range depths and silt substrate in the summer to shallow depths and gravel substrate in the winter. Walleye showed an unchanging association to fine substrate but expanded from primarily mid-range depths in the summer to include shallower depths in the winter. These findings show how multiple telemetry detections per fish can be combined with hydroacoustic data to provide informative habitat associations for fishes in a large lacustrine ecosystem.  相似文献   
8.
Restoration of a wild-produced lake trout Salvelinus namaycush population in Lake Ontario has not been successful despite the adult population often meeting or exceeding restoration targets. Lack of high-quality spawning habitat in Lake Ontario is suggested as one impediment to recruitment of wild lake trout, although the quantity and location of spawning habitat is poorly understood. If high-quality spawning habitat is limited in Lake Ontario, lake trout may be using uncommon spawning locations such as rivers. Anecdotal angler accounts point to the Niagara River as a lake trout spawning location. To better understand the potential of the Niagara River as a spawning location, egg and juvenile fish collections were conducted 12–14 river kilometers from the mouth of the Niagara River from 2010 to 2012; and mature female lake trout with surgically implanted acoustic tags were monitored from 2015 to 2019. Genetic analyses confirmed 60% of collected eggs and 93% of collected post-hatch juvenile fish in the Niagara River were lake trout. Tagged female lake trout returned to the Niagara River over consecutive years during the spawning season. The short duration of lake trout presence in the river (mean = 56 days/year) suggests female lake trout use the Niagara River primarily for spawning. Diversity in spawning locations may provide lake trout population’s resilience against environmental variability through a portfolio effect. Improved identification of riverine spawning locations, including their overall contribution to wild recruitment, may be a useful tool for managers to restore a wild-produced population of lake trout in Lake Ontario.  相似文献   
9.
针对国内小卫星常用的统一遥测模式,讨论了在遥测速率受限的条件下,分包遥测格式设计应满足的基本条件;定义了分包遥测数据格式设计过程中的包编码损失率,并以此作为包数据格式编码效率的评价函数;分析了分包遥测数据格式设计过程中包长度、包采样周期等参数变化对评价函数的影响,进而给出了分包遥测数据格式设计中的应满足的条件和遵循的原则。  相似文献   
10.
《河流研究与利用》2017,33(4):514-523
Fish attempting to move upstream through hydroelectric dams can be trapped and killed in turbines. Understanding fish movement patterns can provide useful insights for how to manage dam operations to minimize fish kill in turbines. We evaluated the movements of two migratory fish (Curimba—Prochilodus argenteus and Mandi—Pimelodus maculatus ) using acoustic telemetry in the tailrace of Três Marias Dam (São Francisco River, Brazil) from 31 October 2011 to 16 February 2012. The majority of tagged fish left the tailrace in less than one week; however, some individuals returned, performing several visits to the tailrace. Mandi remained longer in the tailrace than Curimba. The number of visits was influenced by diel period, turbine and spillway discharge. Although the diel period was the only important contributor to the visits performed by Curimba, the movements of Mandi were significantly influenced by three factors. We found that whereas Curimba was predominantly diurnal, Mandi showed nocturnal habits. Additionally, visits of Mandi were significantly greater during higher turbine and spillway discharge. We discuss the implications of these results for understanding fish movements in the Três Marias Dam tailrace and their potential implications for adapting hydroelectric operations to minimize fish kills. Copyright © 2016 John Wiley & Sons, Ltd.  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