全文获取类型
收费全文 | 27978篇 |
免费 | 1523篇 |
国内免费 | 807篇 |
专业分类
电工技术 | 772篇 |
技术理论 | 10篇 |
综合类 | 7538篇 |
化学工业 | 3178篇 |
金属工艺 | 684篇 |
机械仪表 | 933篇 |
建筑科学 | 4518篇 |
矿业工程 | 845篇 |
能源动力 | 727篇 |
轻工业 | 1025篇 |
水利工程 | 1111篇 |
石油天然气 | 453篇 |
武器工业 | 83篇 |
无线电 | 1188篇 |
一般工业技术 | 1540篇 |
冶金工业 | 1788篇 |
原子能技术 | 141篇 |
自动化技术 | 3774篇 |
出版年
2024年 | 95篇 |
2023年 | 345篇 |
2022年 | 596篇 |
2021年 | 855篇 |
2020年 | 718篇 |
2019年 | 566篇 |
2018年 | 466篇 |
2017年 | 477篇 |
2016年 | 612篇 |
2015年 | 741篇 |
2014年 | 1899篇 |
2013年 | 1684篇 |
2012年 | 1895篇 |
2011年 | 2099篇 |
2010年 | 1973篇 |
2009年 | 1931篇 |
2008年 | 1685篇 |
2007年 | 1839篇 |
2006年 | 1746篇 |
2005年 | 1450篇 |
2004年 | 1284篇 |
2003年 | 1231篇 |
2002年 | 1064篇 |
2001年 | 668篇 |
2000年 | 612篇 |
1999年 | 416篇 |
1998年 | 223篇 |
1997年 | 178篇 |
1996年 | 119篇 |
1995年 | 115篇 |
1994年 | 91篇 |
1993年 | 54篇 |
1992年 | 63篇 |
1991年 | 46篇 |
1990年 | 46篇 |
1989年 | 39篇 |
1988年 | 49篇 |
1987年 | 34篇 |
1986年 | 24篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1982年 | 37篇 |
1981年 | 10篇 |
1979年 | 11篇 |
1964年 | 12篇 |
1958年 | 11篇 |
1957年 | 21篇 |
1955年 | 19篇 |
1954年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
112.
Capital cost correlations are given for oil-water separators, equalization basins, primary clarifiers, clarifiers and clarifier mechanisms, reverse osmosis unit, ultrafiltration units, gravity filters and miroscreens. Data are included for raw sewage, intermediate and recirculation pumping stations and for preliminary treatment (or bar screens, grit removal, overflow and bypass chamber and Parshall flume), for grit removal, comminution and gas stripping. The correlations are accurate to ± 30%, expressed in Canadian dollars and adjusted to a Marshall and Swift value of 1000. Details as to what components are included in the cost are given. Data are given for the labour and material costs to create a working process module. For inflation indices, a critique of the Engineering News Record, EPA small city, Marshall and Swift, Chemical Engineering and Southam inflation indices suggested that the Marshall and Swift index is most appropriate for the construction and process equipment studied here. Concerning the currency exchange, for the equipment and processes in this study, equipment costs the same whether expressed directly in US or Canadian dollars. To put the current data into perspective, several hundred sources of cost data were analyzed. The major correlations are compared, on a consistent basis, with current data. 相似文献
113.
Environmental Effects of Hydro-Electric Power Generation in Africa and the Potential for Artificial Floods 总被引:1,自引:0,他引:1
Electricity is a fundamental requirement for economic growth, and hydro-electric power is often thought to be environmentally benign. However, the construction and operation of many hydro-power dams in Africa have had significant negative impacts on the environment and rural economies. Reduced downstream flooding has destroyed fisheries and starved the floodplain soils of moisture and nutrients. Often the worst-affected areas have no electrification and therefore do not benefit from power generation. New dams which are planned in Kenya and Tanzania have been specifically designed to make flood releases. This will allow electricity to be generated whilst maintaining a dynamic flooding pattern for the short-term economic importance of fisheries and agriculture and the longer-term importance of soil fertility and biodiversity. Involvement of local community representatives in deciding when flood waters should be released on the Phongolo River in South Africa has resulted in substantial benefits to floodplain users. 相似文献
114.
J. Schanda 《Color research and application》2007,32(3):233-235
This is a comment to the editorial by J. Hutchings on “Talking about Color… and Ethics.” © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 233–235, 2007 相似文献
115.
赖永凯 《数字社区&智能家居》2006,(14)
对目前常见网络考试分析系统的功能和特点进行了对比分析,然后提出改进方案,建立相应的系统模型,并明确作为检验网络教学效果的重要手段之一,设计一套完善的测试结果分析工具是非常必要的。 相似文献
116.
117.
三峡蓄水初期水库近坝区水环境特性分析 总被引:3,自引:0,他引:3
通过现场观测和数值模拟的方法,对三峡水库近坝区在蓄水初期的水流和水环境特性进行了
分析。对蓄水初期的溶解氧、BOD、COD和NH3-N、Cu等水质参数进行了观测,将蓄水初期水质资料与蓄水之前的结果进行了对比,分析了近坝区水环境变化趋势。采用大涡模拟紊流模型,考虑水体表面的热交换,对三峡近坝区的流动和水温分布特性进行了模拟。研究结果表明,三峡水库蓄水初期近坝区水流特性明显改变,主要表现为水深增加、流速变缓,部分地段有回流区出现。水质指标变化不明显,坝前断面溶解氧浓度、悬浮物浓度有所降低,和悬浮物密切相关的污染物总磷、重金属也随之降低;蓄水初期139m水位时坝前水域尚没有出现温度分层现象。 相似文献
118.
119.
Thomachan.A. Kattakayam Sumanta Khan Kandadai Srinivasan 《Solar Energy Materials & Solar Cells》1996,44(1):25
This article describes the development of an instrumentation system for characterizing photovoltaic panels. It uses an add on card (which contains DAC, ADC and digital input/output ports) in conjunction with a PC-AT. The panels in a field are selected in succession through a set of relays actuated by the digital output port. The selected panel is loaded in discreet steps by a transistor loading circuit which is activated by the digital to analog convertor to trace the most significant portion of the I-V curve. The data shows that the power output is invariably lower than that specified by the manufacturer. The reasons for drop in output have been analyzed. It is shown that these effects can be represented by the curvature of I-V characteristic at the maximum power point (OP). The loss of power due to accumulation of dust and the increase in temperature of the panels can be significant. 相似文献
120.
The European Commission has been requested by member states to study the incorporation of air transport into their existing emissions trading scheme (ETS). Only CO2 is to be included, at least initially. 相似文献