全文获取类型
收费全文 | 28939篇 |
免费 | 3908篇 |
国内免费 | 1849篇 |
专业分类
电工技术 | 16033篇 |
综合类 | 2011篇 |
化学工业 | 1516篇 |
金属工艺 | 539篇 |
机械仪表 | 962篇 |
建筑科学 | 803篇 |
矿业工程 | 549篇 |
能源动力 | 1054篇 |
轻工业 | 488篇 |
水利工程 | 300篇 |
石油天然气 | 157篇 |
武器工业 | 64篇 |
无线电 | 4864篇 |
一般工业技术 | 1062篇 |
冶金工业 | 654篇 |
原子能技术 | 288篇 |
自动化技术 | 3352篇 |
出版年
2024年 | 48篇 |
2023年 | 383篇 |
2022年 | 626篇 |
2021年 | 803篇 |
2020年 | 938篇 |
2019年 | 757篇 |
2018年 | 729篇 |
2017年 | 1090篇 |
2016年 | 1182篇 |
2015年 | 1423篇 |
2014年 | 1950篇 |
2013年 | 1701篇 |
2012年 | 2435篇 |
2011年 | 2663篇 |
2010年 | 1837篇 |
2009年 | 2210篇 |
2008年 | 2286篇 |
2007年 | 2229篇 |
2006年 | 2175篇 |
2005年 | 1528篇 |
2004年 | 1091篇 |
2003年 | 958篇 |
2002年 | 751篇 |
2001年 | 682篇 |
2000年 | 514篇 |
1999年 | 376篇 |
1998年 | 237篇 |
1997年 | 199篇 |
1996年 | 181篇 |
1995年 | 149篇 |
1994年 | 129篇 |
1993年 | 112篇 |
1992年 | 78篇 |
1991年 | 48篇 |
1990年 | 42篇 |
1989年 | 31篇 |
1988年 | 27篇 |
1987年 | 20篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1963年 | 3篇 |
1961年 | 3篇 |
1960年 | 2篇 |
1958年 | 2篇 |
1957年 | 3篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
91.
92.
介绍了可控电抗式高压软启动控制系统的原理、静态结构、工作过程,以及在煤矿井下使用实例中的实测波形. 相似文献
93.
94.
Treatment of Acid Leachate from Coal Discard using Calcium Carbonate and Biological Sulphate Removal
J.?P.?MareeEmail author G.?Strobos H.?Greben E.?Netshidaulu E.?Steyn A.?Christie P.?Günther F.?B.?Waanders 《Mine Water and the Environment》2004,23(3):144-151
Abstract.
An integrated approach is proposed for treating acidic coal discard leachate, consisting of CaCO3 handling and dosing, CaCO3-neutralization, and biological sulphate removal. It was found that: powdered CaCO3 can be slurried to a constant density and used to neutralize the acid water, remove Fe (II), Fe (III), and Al, and partially remove the sulphate (to saturation level); biological sulphate removal can be used to lower the sulphate to less than 200 mg/L using ethanol as the carbon and energy source; CO2 produced during calcium carbonate treatment can be used for H2S-stripping and; H2S gas recovered in the sulphate removal stage can be used for iron removal. 相似文献
95.
介绍了 6kV电网单相接地电容电流分布规律和特点 ,以及高压选择性接地保护技术原理及应用现状 ,并对煤矿电网形成比较可靠的选择性接地保护系统进行分析。 相似文献
96.
Biswajit Mukhopadhyay Luciano Bastias Anosua Mukhopadhyay 《Mine Water and the Environment》2007,26(1):29-45
Abstract. Limestone drains are an integral component of some of the most efficacious passive systems for the treatment of acid rock
drainage (ARD). A critical design parameter for a limestone drain is the mass of limestone that will be required for effective
treatment. This in turn depends on the flow rate, limestone dissolution rate, and associated hydraulic detention time necessary
to achieve a certain effluent alkalinity for a given design life. Rates of alkalinity generation and limestone dissolution,
and the quality of the limestone in terms of weight fraction of CaCO3 and percentage CaCO3 available must be known to determine the required mass of limestone. These parameters were experimentally determined for
a natural and synthetic suite of ARD waters. The experimental results show that the empirical change in the alkalinity over
time cannot simply be modeled as a first-order process. During the initial stage, the concentration increase is extremely
fast, giving a linear and steep rise in the alkalinity. Alkalinity concentrations peaked at elapsed times of 90 to 180 minutes
and then declined to a nearly constant value. The decline in alkalinity corresponds with a decline in concentrations of dissolved
iron and aluminum, implying that the consumption of alkalinity by the hydrolysis of these metals is faster than the rate of
alkalinity production by the dissolution of limestone, so that the reaction appears zero order in the early stage and pseudo-first
order later. Because the changes in concentration were complex, considerable uncertainty exists in the rate constants for
estimating alkalinity concentration. This causes problems in design equations based solely on a limestone dissolution rate
that is estimated from alkalinity generation rates. A more applicable design procedure, combining the kinetics of alkalinity
production and consumption with the hydraulics and chemical equilibrium of the system, is illustrated.
Research was conducted while the first and third authors were with Ecology and Environment, Inc, Dallas, TX, USA; 相似文献
97.
在交-交变频调速和调压调速技术分析的基础上,提出将两者相结合的方法,很好地实现了对煤矿提升机起动、匀速和减速运行及爬行等运行方式的控制。 相似文献
98.
D. H. M. Alderton T. Serafimovski B. Mullen K. Fairall S. James 《Mine Water and the Environment》2005,24(3):139-149
Abstract Pollution from current and past mining is a significant problem in several parts of the former Yugoslav Republic of Macedonia.
Water from six different mining areas in Macedonia was analysed to assess the effects of metalliferous mining activities.
Drainage sediments at all locations show evidence of physical and chemical contamination; water compositions, however, were
more variable. Low pH water associated with mining has led to the dissolution of minerals and the mobilization of metals from
the ores and the host rocks. Only Sb was noted to exhibit enhanced mobility in higher pH waters. The Zletevo Pb-Zn mine discharges
low pH water that has high levels of several metals, including Al, Zn, Cd, and Fe; sediment concentrations are grossly elevated
for several km downstream. Toranica and Sasa Pb-Zn mines exhibit similar sediment contamination of Pb, Zn, Cd, and other ore-related
metals. However, concentrations of metals in waters are far lower at both of these mines, due to less pyrite in the ore and
the buffering of the acid waters by carbonate host lithologies. At the Buchim copper mine, waters are both acidic and high
in dissolved solids; Cu concentrations exceed 100 mg/L. Krstov Dol and Alshar are small, disused As-Sb mines that discharge
waters that exceed potable values for some contaminants (e. g. As), but this may be related to the mineralization of the bedrock
rather than the mines. In general, metal concentrations decreased downstream from the source due to dilution from other rivers
and coprecipitation of metals on other mineral phases (e. g. Fe-, Al- and Mn-oxides, and hydroxides). 相似文献
99.
基于空间电压矢量法的风机变频调速系统的设计 总被引:1,自引:0,他引:1
为了消除风机调速中的谐波分量 ,提出了一种新型的风机调速系统。该系统主电路采用三电平PWM变频器 ,以 16位单片机 80 98为核心组成数字控制系统 ,并采用空间电压矢量法的控制方法。该系统用于风机 ,可获得良好的调速特性 相似文献
100.