全文获取类型
收费全文 | 14659篇 |
免费 | 1144篇 |
国内免费 | 713篇 |
专业分类
电工技术 | 721篇 |
综合类 | 1098篇 |
化学工业 | 1206篇 |
金属工艺 | 446篇 |
机械仪表 | 2025篇 |
建筑科学 | 1585篇 |
矿业工程 | 922篇 |
能源动力 | 486篇 |
轻工业 | 797篇 |
水利工程 | 363篇 |
石油天然气 | 782篇 |
武器工业 | 127篇 |
无线电 | 881篇 |
一般工业技术 | 807篇 |
冶金工业 | 534篇 |
原子能技术 | 158篇 |
自动化技术 | 3578篇 |
出版年
2024年 | 26篇 |
2023年 | 97篇 |
2022年 | 197篇 |
2021年 | 297篇 |
2020年 | 286篇 |
2019年 | 198篇 |
2018年 | 254篇 |
2017年 | 267篇 |
2016年 | 421篇 |
2015年 | 523篇 |
2014年 | 895篇 |
2013年 | 970篇 |
2012年 | 1089篇 |
2011年 | 1228篇 |
2010年 | 848篇 |
2009年 | 874篇 |
2008年 | 704篇 |
2007年 | 902篇 |
2006年 | 800篇 |
2005年 | 767篇 |
2004年 | 673篇 |
2003年 | 644篇 |
2002年 | 545篇 |
2001年 | 419篇 |
2000年 | 378篇 |
1999年 | 376篇 |
1998年 | 316篇 |
1997年 | 256篇 |
1996年 | 244篇 |
1995年 | 233篇 |
1994年 | 155篇 |
1993年 | 105篇 |
1992年 | 84篇 |
1991年 | 72篇 |
1990年 | 50篇 |
1989年 | 46篇 |
1988年 | 49篇 |
1987年 | 25篇 |
1986年 | 19篇 |
1985年 | 28篇 |
1984年 | 30篇 |
1983年 | 16篇 |
1982年 | 24篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1976年 | 11篇 |
1964年 | 4篇 |
1956年 | 4篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
摘要:回转窑是一种高温处理物料的热工设备,充分了解回转窑内发生的物理与化学变化对生产具有指导意义,而人眼观察或利用仪器等方式难以探查窑内情况。为掌握回转窑内处理物料的情况并提高生产效率,国内外利用建模与仿真的方法模拟回转窑结构、窑内热场、物料运动。现有模拟已经涉及到了回转窑整体、窑壁、耐火材料、烟气、燃料、火焰、物料等,并利用建模与仿真结果研究了回转窑结构参数及生产参数对部分现象的影响。根据窑内不同区域,综述了回转窑建模与仿真的进展,汇总了建模与仿真的方法与过程及部分参数对回转窑生产的影响。回顾与分析现有的回转窑建模与仿真成果,有助于优化回转窑设备结构的设计及回转窑生产。 相似文献
122.
123.
根据热型连铸技术原理,建立了热型连铸凝固过程一维稳态温度场的物理、数学模型。通过数值计算,得出了铸型出口温度、冷却距离、拉铸速度和喷水冷却强度等工艺参数对铸坯固液界面位置的影响。计算结果与试验结果吻合。 相似文献
124.
气相色谱——质谱法对土壤中多种农药残留的测定方法 总被引:2,自引:0,他引:2
用GC -MS法测定土壤中的农药残留物 ,快速准确 ,回收率 83 %~ 112 %,平均变异系数在 4.8%~ 15 .2 %之间。为科学监测、合理利用土壤资源提供了依据 相似文献
125.
126.
在采矿方案优选的研究中,其决策的正确与否,取决于参与计算的采矿法的定量、定性指标个数以及这些指标的权数。本文通过实例分析了指标权数的波动对采矿方案优劣排序的影响,以减小决策的风险。 相似文献
127.
Factors Influencing Movements of Two Migratory Fishes within the Tailrace of a Large Neotropical Dam and their Implications for Hydropower Impacts 下载免费PDF全文
《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
128.
Responses ofRhagoletis pomonella (Walsh) (Diptera: Tephritidae) flies to host fruit visual stimuli (apples or models of apples) and chemical stimuli (synthetic apple volatile blend) were studied in semidwarf field-caged apple trees. Three different fruit or model densities (1, 4, or 16 fruit or models/ tree) and two odor release rates [ca. 0.7g/hr (close to the natural release rate of a ripe apple) and ca. 500g/hr (amount of odor released by commercially sold apple maggot traps)] were tested. Individually released flies were followed as they moved within a tree for a maximum of 20 min. We recorded three-dimensional search paths followed by foraging flies and computed such variables as total relative distance traveled before alighting on a fruit or model, track length between individual alightment sites, and directness of flight to fruits or models. Effect of odor on propensity to alight on fruit or models and host-searching behavior prior to alighting on fruit or on models varied according to fruit or model color and density. If the fruit visual stimulus was strong (e.g., red color), odor did not increase the probability of finding fruit or fruit models. As the visual stimulus became progressively weaker (red to green to clear), odor (irrespective of concentration) appeared to aid flies during the fruit-finding process. As density of fruit or models increased, the probability of flies finding a fruit or model also increased (e.g., 50% of flies found a red fruit model at 1 model/tree while 90% found a red model at 16 models/tree; 4% of flies found a clear model with odor at 1 model/tree while 35% found a clear model with odor at 16 models/tree). Findings reported elsewhere indicate thatR. pomonella flies are able to discover a point source of odor (an odor-bearing tree in a patch of trees) by flying upwind (in the tree patch) in response to intermittent exposure to odor. Findings here indicate that after arrival on a host tree (point source), flies discover individual apparent and abundant host fruit on the basis of vision. If fruit are less apparent or scarce, odor appears to interact with vision during the fruit-finding process. 相似文献
129.
The corrective reaction time (tcr) is an essential motor property when modelling hand control movements. Many studies designed experiments to estimate tcr, but reported only group means with inconsistent definitions. This study proposes an alternative methodology using Drury's (1994) intermittent illumination model. A total of 24 participants performed circular tracking movements under five levels of visual information delay using a modified monitor in a darkened room. Measured movement speeds and the manipulated delays were used with the model to estimate tcr of individuals and test effects of gender and path width. The results showed excellent model fits and demonstrated individual differences of tcr, which was 273 ms on average and ranged from 87 to 441 ms. The wide range of tcr values was due to significant effects of gender and path width. Male participants required shorter tcr compared to female participants, especially for narrow path widths. 相似文献
130.