全文获取类型
收费全文 | 50724篇 |
免费 | 6190篇 |
国内免费 | 3735篇 |
专业分类
电工技术 | 5054篇 |
技术理论 | 3篇 |
综合类 | 4916篇 |
化学工业 | 9060篇 |
金属工艺 | 2127篇 |
机械仪表 | 4189篇 |
建筑科学 | 2652篇 |
矿业工程 | 1560篇 |
能源动力 | 5110篇 |
轻工业 | 1114篇 |
水利工程 | 5185篇 |
石油天然气 | 3884篇 |
武器工业 | 595篇 |
无线电 | 1669篇 |
一般工业技术 | 4217篇 |
冶金工业 | 2746篇 |
原子能技术 | 1362篇 |
自动化技术 | 5206篇 |
出版年
2024年 | 212篇 |
2023年 | 751篇 |
2022年 | 1413篇 |
2021年 | 1674篇 |
2020年 | 1757篇 |
2019年 | 1521篇 |
2018年 | 1407篇 |
2017年 | 1788篇 |
2016年 | 2003篇 |
2015年 | 2062篇 |
2014年 | 2846篇 |
2013年 | 3431篇 |
2012年 | 3380篇 |
2011年 | 3970篇 |
2010年 | 2722篇 |
2009年 | 2985篇 |
2008年 | 2785篇 |
2007年 | 3286篇 |
2006年 | 3094篇 |
2005年 | 2782篇 |
2004年 | 2309篇 |
2003年 | 2072篇 |
2002年 | 1664篇 |
2001年 | 1407篇 |
2000年 | 1211篇 |
1999年 | 1023篇 |
1998年 | 852篇 |
1997年 | 717篇 |
1996年 | 672篇 |
1995年 | 600篇 |
1994年 | 502篇 |
1993年 | 388篇 |
1992年 | 328篇 |
1991年 | 208篇 |
1990年 | 213篇 |
1989年 | 155篇 |
1988年 | 113篇 |
1987年 | 80篇 |
1986年 | 57篇 |
1985年 | 28篇 |
1984年 | 43篇 |
1983年 | 32篇 |
1982年 | 18篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 15篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1959年 | 21篇 |
1951年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Differential pressure fluctuation time series were obtained at different locations in a two-dimensional spout-fluid bed with a cross section of 300 × 30 mm and height 2000 mm. Shannon entropy analysis of differential pressure fluctuations was developed to characterize the dynamic behavior. Effects of two important operating parameters (spouting gas velocity and fluidizing gas flow rate) on the Shannon entropy were examined. It was demonstrated that a spout-fluid bed at a high spouting gas velocity or fluidizing gas flow rate was a deterministic chaos system since the Shannon entropies at all bed locations increased sharply and asymmetric unstable flows occurred. Shannon entropies were found to be significantly different at various bed locations. Shannon entropies of different flow regimes were distinct, so they were used to identify the flow regimes. The results show that the Shannon entropy helps to grasp the complex characteristics of dynamic behavior in spout-fluid beds. 相似文献
102.
介绍了天铁炼钢厂中间包水模实验原理和过程,分析了斜、直、圆三种型式挡渣墙模拟结果,提出了合理的挡渣控流方案,在生产实践中使用效果良好。 相似文献
103.
李得天 《真空科学与技术学报》2003,23(4):289-294
在真空技术应用中 ,高精度气体微流量计用于连续膨胀法校准系统压力的产生、漏孔漏率的测量以及真空泵抽速的测定。PTB先后研制了三代气体微流量计 ,第一代为手动型 ,第二代为半自动型 ,第三代为全自动型。本文详细介绍了PTB研制的气体微流量计的性能和特点 ,并介绍了气体微流量计在真空漏孔的漏率测量方面的应用。另外 ,还介绍了PTB最近研制的大气压力下漏孔漏率测量系统的性能和特点 相似文献
104.
Sushil K. Singh 《Canadian Metallurgical Quarterly》2007,133(2):155-161
A semianalytical model is developed for computing drawdowns in and around a partially penetrating large diameter well. The new model can take into account an unsteady pumping discharge and thus drawdowns during recovery can be computed. This model can also yield the unsteady contributions from well and aquifer storages to the pumped discharge. While developing the model, the flow from the bottom of the well is also accounted. 相似文献
105.
River ice jams are a common occurrence on northern rivers, and their formation can present a severe flood risk to nearby communities. As more and more river regulation projects are developed to provide an alternative to fossil fuels for electrical power-generating capacity, our need to understand the mechanisms associated with ice jam formation under variable flow conditions becomes more vital. This is because, at present, hydropeaking operations are often severely curtailed during the ice-affected seasons due to concerns that sudden flow fluctuations might instigate ice jams and associated flooding. Here, an experimental investigation explores the effects of rapid increases in discharge on ice jam formation and evolution. It is found that the thickness of ice jams formed under highly dynamic flow conditions tend to be slightly thinner than those formed during steady carrier flows for comparable discharges. Also, despite the highly dynamic nature of these consolidation events, the resulting ice thicknesses appear reasonably well approximated by steady flow theory. 相似文献
106.
107.
官泓 《有色冶金设计与研究》2003,24(3):49-51
阐述水厂设计中对水厂规模、水源地、净水厂位置及净水工艺的确定过程,根据原水的特点,通过分析对无阀滤池进行改良。 相似文献
108.
在研究发现旋风分离器减阻杆的基础上,研究了减阻杆对流场的影响,发现了减阻杆使切向速度分布趋于平缓、轴向速度上升峰值内移、径向上压力梯度减小、轴向上中心区从逆压梯度变为顺压梯度等重要规律,从而为分析旋风分离器减阻杆的减阻机理提供了依据。同时本文还首次发现旋风分离器入口附近有近24%的短路流量,提出设法减小这部分短路流量是提高分离效率的一个研究方向。 相似文献
109.
Kang Hai-gui 《水动力学研究与进展(B辑)》1994,(2)
HYDRODYNAMIC FORCE ON SMOOTH HORIZONTAL CYLINDER IN UNIFORM OSCILLATORY FLOWHYDRODYNAMICFORCEONSMOOTHHORIZONTALCYLINDERINUNIF... 相似文献
110.
J.M Mäkynen J.K Jokiniemi P.P Ahonen E.I Kauppinen R Zilliacus 《Nuclear Engineering and Design》1997,178(1):74
Hygroscopic NaOH, CsI, CsOH and inert Ag aerosol behaviour at different temperatures and relative humidities (RH) has been studied in a well instrumented and controlled vessel of 1.81 m3 total free volume. Homogeneous thermal-hydraulic conditions for aerosol measurement in the vessel were achieved. The aerosol number and mass concentration were measured continuously during the experiments using a Condensation Nucleus Counter and a Tapered Element Oscillating Microbalance. The particle size distribution and chemical composition in the test conditions were measured by Berner low pressure impactors. In the case of NaOH the half life of the aerosol mass concentration was more than four times longer at low RH (22%) as compared to high RH (96%). The half lives of the CsOH and CsI aerosols were only twice as long at low RH as compared to high RH. Thus at high RH (96–97%) the half lives of CsOH and CsI were twice as long as the half life for the NaOH aerosol. The faster decay of the NaOH aerosol is due to the smaller density decrease of NaOH during water condensation. CsOH particles grew rapidly to their equilibrium size at all humidities. The measured equilibrium size for CsOH aerosol agree well with the calculated particle size at different RHs. Experimental results were also compared with calculations obtained by severe accident computer codes. These calculated results will be presented in a later paper. 相似文献