全文获取类型
收费全文 | 4907篇 |
免费 | 274篇 |
国内免费 | 89篇 |
专业分类
电工技术 | 569篇 |
综合类 | 175篇 |
化学工业 | 398篇 |
金属工艺 | 123篇 |
机械仪表 | 319篇 |
建筑科学 | 680篇 |
矿业工程 | 65篇 |
能源动力 | 1359篇 |
轻工业 | 48篇 |
水利工程 | 486篇 |
石油天然气 | 58篇 |
武器工业 | 17篇 |
无线电 | 182篇 |
一般工业技术 | 201篇 |
冶金工业 | 187篇 |
原子能技术 | 47篇 |
自动化技术 | 356篇 |
出版年
2024年 | 14篇 |
2023年 | 57篇 |
2022年 | 97篇 |
2021年 | 119篇 |
2020年 | 148篇 |
2019年 | 120篇 |
2018年 | 98篇 |
2017年 | 160篇 |
2016年 | 272篇 |
2015年 | 249篇 |
2014年 | 326篇 |
2013年 | 271篇 |
2012年 | 293篇 |
2011年 | 506篇 |
2010年 | 379篇 |
2009年 | 307篇 |
2008年 | 250篇 |
2007年 | 266篇 |
2006年 | 213篇 |
2005年 | 189篇 |
2004年 | 181篇 |
2003年 | 159篇 |
2002年 | 102篇 |
2001年 | 74篇 |
2000年 | 81篇 |
1999年 | 65篇 |
1998年 | 54篇 |
1997年 | 30篇 |
1996年 | 34篇 |
1995年 | 22篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1989年 | 18篇 |
1988年 | 12篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1977年 | 1篇 |
1959年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有5270条查询结果,搜索用时 109 毫秒
31.
风力发电 总被引:1,自引:0,他引:1
《建设机械技术与管理》2006,19(12):I0008-I0012
过去的十年里,风力发电在能源的供应中扮演着越来越重要的角色,看来这一角色还将继续扮演下去。据William North报道,这对安装建筑商和起重机制造商都提出了独特的挑战。[编者按] 相似文献
32.
在我国经济快速发展的大背景下,能源(水、电、油)的消耗在企业中所占的比重越来越高,也受到愈来愈大的重视。同时也由于房地产的快速发展需求,中央空调的市场需求呈现强劲的增长。在市场容量不断增大的吸引下,越来越多的厂家加入到商用中央空调的领域。变频技术应用于中央空调系统,对提升中央空调自动化水平、降低能耗.减少对电网的冲击,延长机械及管网的使用寿命,都具有重要的意义。 相似文献
33.
Bradley T. Ewing Jamie Brown Kruse Douglas A. Smith 《Journal of Wind Engineering & Industrial Aerodynamics》2007,95(3):209-219
This research examines the interdependence in time series wind speed data measured in the same location at four different heights. A multiple-equation system known as a vector autoregression is proposed for characterizing the time series dynamics of wind. Additionally, the recently developed method of generalized impulse response analysis provides insight into the cross-effects of the wind series and their responses to shocks. Findings are based on analysis of contemporaneous wind speed time histories taken at 13, 33, 70 and 160 ft above ground level with a sampling rate of 10 Hz. The results indicate that wind speeds measured at 70 ft was the most variable. Further, the turbulence persisted longer at the 70-ft measurement than at the other heights. The greatest interdependence is observed at 13 ft. Gusts at 160 ft led to the greatest persistence to an “own” shock and led to greatest persistence in the responses of the other wind series. 相似文献
34.
Rajesh R. Shrestha Barrie R. Bonsal Ashish Kayastha Yonas B. Dibike Christopher Spence 《Journal of Great Lakes research》2021,47(3):677-689
This study assesses snow response in the Assiniboine-Red River basin, located in the Lake Winnipeg watershed, due to anthropogenic climate change. We use a process-based distributed snow model driven by an ensemble of eight statistically downscaled global climate models (GCMs) to project future changes under policy-relevant global mean temperature (GMT) increases of 1.0 °C to 3.0 °C above the pre-industrial period. Results indicate that basin scale seasonal warmings generally exceed the GMT increases, with greater warming in winter months. The majority of GCMs project wetter winters and springs, and drier summers, while autumn could become either drier or wetter. An analysis of snow water equivalent (SWE) responses under GMT changes reveal higher correlations of snow cover duration (SCD), snowmelt rate, maximum SWE (SWEmax) and timing of SWEmax with winter and spring temperatures compared to precipitation, implying that these variables are predominantly temperature controlled. Consequently, under the GMT increases from 1.0 °C to 3.0 °C, the basin will experience successively shorter SCD, slower snowmelt, smaller monthly SWE and SWEmax, earlier SWEmax, and a transition from snow-dominated to rain-snow hybrid regime. Further, while the winter precipitation increases for some GCMs compensate the temperature-driven changes in SWE, the increases for most GCMs occur as rainfall, thus limiting the positive contribution to snow storage. Overall, this study provides a detailed diagnosis of the snow regime changes under the policy-relevant GMT changes, and a basis for further investigations on water quantity and quality changes. 相似文献
35.
36.
研究风力发电机系统优化控制问题,对风力发电进行设计,应通过风能带动发电机发电。但风力发电机组模型存在高阶、非线性问题,考虑因素很多。传统方法缺乏总体性能分析。为解决上述问题,建立了包括风力发电机组气动性能、传动系统部分和感应电机部分的一种新的较完善的失速型风力发电机组的动态数学模型。应用在MATLAB软件上,以数学模型为基础搭建了失速型风力发电机组数字仿真模型。并以稳态风速和动态风速为例,对600千瓦失速控制型风力发电机组进行了仿真计算。试验结果表明模型的正确性,为风力发电机组的进一步优化设计和优化控制等均提供了科学依据。 相似文献
37.
研究了含Ag7055铝合金在T6,T73,RRA3种热处理状态下的力学性能、断裂特征及显微组织变化特征。实验结果表明,RRA处理可以在保持T6状态强度的同时,获得较高的电导率,然而试样的延伸率相对较低;断口SEM形貌观察表明,T6状态断裂机制为剪切型穿晶断裂和沿晶断裂同时并存,而T73处理后,主要呈韧窝型穿晶断裂,沿晶断裂部分减少,RRA试样断口则主要为沿晶断裂,并在晶界面上分布有韧窝型断裂特征;由于不同热处理状态下,强化相不同且其阻碍位错滑移能力也不同,同时晶界PFZ宽度也发生变化,这些因素的综合作用导致不同热处理状态下的断裂特征不同。 相似文献
38.
Longitudinal and temporal water temperature patterns in the Yangtze River and its influence on spawning of the Chinese sturgeon (Acipenser sinensis Gray 1835)
下载免费PDF全文
![点击此处可从《河流研究与利用》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this study, water temperature longitudinal and temporal patterns were investigated in four locations of the Yangtze River to identify their influence on spawning of the Chinese sturgeon (Acipenser sinensis Gray 1835). The results showed that, historically (1960–1980), the four locations, Pingshan (PS, 2,687 river kilometres [rkm]), Yichang (YC, 1,640 rkm), Chenglingji (CLJ, 1,265 rkm), and Hukou (HK, 805 rkm), all had similar average annual water temperatures (around 18.0 °C) but very different amplitudes: The upper two locations, PS (11.4–23.2 °C) and YC (9.1–25.9 °C), were relatively stable and had smaller amplitude than the lower two ones, CLJ (6.0–30.0 °C) and HK (5.9–30.8 °C). On the basis of the physiological effects for Chinese sturgeon, we defined three water temperature ranges: stressing (>23 °C), holding (23–20 °C), and spawning (20–16 °C). We found that the upper two locations with successful spawning of the Chinese sturgeon (PS and YC) had short or no stressing period but long holding and spawning periods. Currently (2013–2016), the impoundment of the Three Gorges Reservoir increases the time for water temperature decreasing to 20 °C at the current spawning ground (YC) in autumn, which increases the stressing and holding periods, and has significant negative impact on the spawning of Chinese sturgeon. Nonetheless, considering the very high stressing temperature and the short duration of the holding and spawning periods at CLJ and HK, we propose that YC is still the most suitable spawning location for the Chinese sturgeon. 相似文献
39.
在风光互补发电系统中,蓄电池作为风光互补发电系统的储能设备,在整个发电系统中起着非常重要的作用,而蓄电池充电控制方法的优劣,是影响其使用寿命的一个重要因素。文章对风光互补发电系统中蓄电池的常用充电控制方法进行了分析,提出了一种新的控制策略,即将蓄电池充电电压、充电电流采样值分别与蓄电池事先设定好的恒压过充电压、恒流充电限流值和浮充电流值进行实时比较,来判断采取哪种合理的充电方式,对蓄电池起到尽可能的保护,从而延长了风光互补发电系统中蓄电池使用寿命。 相似文献
40.
Dilute, ‘dense phase 1’, and possibly a third regime-‘dense phase 2’, were observed in a vertical 0.02 m diameter pneumatic conveyor using 210 μm sand particles. The transitions were marked by the alterations in the trend of the measured average solids hold-up while varying the solids mass flowrate at constant air velocity. Hydrodynamic characteristics together with the transition criteria for the various transport modes were established. A novel regime diagram based on average gas velocities and solids mass flowrates was developed to identify the operating conditions for these regimes, as well as the limiting solids carrying capacities of the present conveyor. A probable cause of the dilute to dense phase transition is speculated upon. 相似文献