全文获取类型
收费全文 | 6357篇 |
免费 | 863篇 |
国内免费 | 423篇 |
专业分类
电工技术 | 295篇 |
技术理论 | 2篇 |
综合类 | 630篇 |
化学工业 | 143篇 |
金属工艺 | 10篇 |
机械仪表 | 35篇 |
建筑科学 | 1149篇 |
矿业工程 | 144篇 |
能源动力 | 292篇 |
轻工业 | 46篇 |
水利工程 | 4268篇 |
石油天然气 | 284篇 |
武器工业 | 9篇 |
无线电 | 38篇 |
一般工业技术 | 72篇 |
冶金工业 | 34篇 |
原子能技术 | 7篇 |
自动化技术 | 185篇 |
出版年
2024年 | 13篇 |
2023年 | 88篇 |
2022年 | 157篇 |
2021年 | 203篇 |
2020年 | 201篇 |
2019年 | 226篇 |
2018年 | 186篇 |
2017年 | 253篇 |
2016年 | 300篇 |
2015年 | 312篇 |
2014年 | 417篇 |
2013年 | 355篇 |
2012年 | 486篇 |
2011年 | 489篇 |
2010年 | 370篇 |
2009年 | 347篇 |
2008年 | 332篇 |
2007年 | 460篇 |
2006年 | 421篇 |
2005年 | 363篇 |
2004年 | 276篇 |
2003年 | 212篇 |
2002年 | 231篇 |
2001年 | 176篇 |
2000年 | 123篇 |
1999年 | 125篇 |
1998年 | 88篇 |
1997年 | 72篇 |
1996年 | 70篇 |
1995年 | 47篇 |
1994年 | 45篇 |
1993年 | 37篇 |
1992年 | 47篇 |
1991年 | 22篇 |
1990年 | 17篇 |
1989年 | 25篇 |
1988年 | 18篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有7643条查询结果,搜索用时 203 毫秒
81.
结合实践,介绍了苏州河水环境治理情况,阐述了苏州河的基本状况,提出了苏州河具体整治措施,总结了苏州河整治所取得的效果,指出苏州河整治的经验对长沙市捞刀河的整治起到了一定的作用。 相似文献
82.
不同生态河道基质材料对氮磷的吸附对比研究 总被引:6,自引:0,他引:6
生态河道构建是一种有效的河流水体修复技术,选择合适的基质材料构建生态河道,能改善其对污染物质的净化效果.对比研究了砾石、砂子和沸石3种不同生态材料在不同氮磷水平下对氮磷的强化吸附性能,并对其吸附机理进行了初步探讨.试验结果表明,Freundlich等温吸附方程能较好地描述3种材料的吸附性能,对于氮、磷的饱和吸附能力依次为沸石>砾石>砂子.开发利用吸附能力较强的砾石或是利用吸附能力更强的沸石作为生态河道基质材料,是构建生态河道的一种有效措施. 相似文献
83.
Models are being used extensively to study the impact on the environment of a wide range of man-made influences. These include land-use change (e.g. afforestation), effluent discharges, flood-relief channels, reservoir developments, atmospheric pollution and the impacts of agrochemicals. In this paper several models are described which are being used by the Institute of Hydrology for environmental impact assessment. These models include MAGIC (Model of Acidification of Groundwater in Catchments), QUASAR (Quality Simulation Along Rivers) and a nitrogen simulation model for investigating the behaviour of nitrate in reservoirs. 相似文献
84.
Turbidity is an important water quality variable, through its relation to light suppression, BOD impact, sediment-associated contaminant transport, and suspended sediment effects on organisms and habitats. Yet few published field investigations of wet-weather turbidity dynamics, through several individual and sequenced rainstorms in extremely urbanised headwater basins, have emerged. This paper aims to address this gap through a turbidity analysis of multiple storm events in spring 2001 in an urban headwater basin (57 km2) of the River Tame, central England, the most urbanised basin for its size in the UK ( approximately 42%). Data were collected at 15-min frequency at automated monitoring stations for rainfall, streamflow and six water quality variables (turbidity, EC, temperature, DO, pH, ammonia). Disturbance experiments also allowed estimates of bed sediment storage to be obtained. Six important and unusual features of the storm event turbidity response were apparent: (1) sluggish early turbidity response, followed by a turbidity 'rush'; (2) quasi-coincident flow and turbidity peaks; (3) anti-clockwise hysteresis in the discharge-turbidity relationship on all but one event, resulting from Falling-LImb Turbidity Extensions (FLITEs); (4) increases in peak turbidity levels through storm sequences; (5) initial micro-pulses (IMP) in turbidity; and (6) secondary turbidity peaks (STP) or 'turbidity shoulders' (TS). These features provided very little evidence of a true 'first-flush' effect: instead, substantial suspended solids transport continued right through the flow recessions, and little storm-event sediment exhaustion was evident. A new, dimensionless, hysteresis index, HI(mid), is developed to quantify the magnitude and direction of hysteresis in a simple, clear, direct and intuitive manner. This allowed the degree of departure from the classic 'first-flush', clockwise hysteresis models to be assessed. Of the 15 turbidity events considered, 10 coincided with ammonia spikes of up to 6.25 mg l(-1) at Water Orton (the downstream station): this suggests that spills from combined sewer overflows (CSO) or waste water treatment works (WwTWs) are significant in the throughput of turbid waters here. Substantial ammonia peaks related most strongly to total storm rainfall receipt, of four rainfall variables considered, and significant ammonia peaks were generated even from low-magnitude storms (rainfall totals <4 mm), indicating that spills are a frequent occurrence. Local bed sediment stores appear to be limited, suggesting that other distal sediment sources, such as road networks and old mineworkings are possibly more important. Biofilms may also play a part in delaying sediment release until late in the hydrograph, and in suppressing late spring turbidity levels. Existing first-flush models appear to be an oversimplification here. Such urban headwater basin responses can provide useful insights into the generation of contaminant waves, and offer vital early-warning systems for pollution events propagating downstream. 相似文献
85.
86.
87.
C. E. Round BSc MSc A. R. Young BSc MSc K. Fox BSc PhD 《Water and Environment Journal》1998,12(6):402-405
Measurements of flow velocity are often required for a broad range of issues surrounding water-resource management, and a velocity-estimation method is therefore desirable where extensive field data are unavailable. This paper presents the development of a model for estimating flow velocity using readily available catchment characteristics, and flow and channel geometry data. The velocity equations were calibrated using UK data, so that their application at any river site in the UK is attainable. The calibrated equation uses the mean flow and the dimensionless magnitude of the flow on the day in question to estimate the mean reach velocity for flows at any river site in the UK. 相似文献
88.
城市河流地区生态环境规划研究--以温瑞塘河为例 总被引:1,自引:0,他引:1
以温瑞塘河沿岸地区生态环境保护规划为例.阐述了城市河流地区的生态环境保护.应将对河流的生态环境的保护和对沿岸地区土地利用的生态化控制和整合紧密结合的思路。 相似文献
89.
浒泊机制砂与河砂混凝土力学性能的对比研究 总被引:4,自引:1,他引:4
针对山西存在的严重缺砂问题,对太谷浒泊人工机制砂与河砂混凝土的力学性能进行了对比研究,研究表明,太谷浒泊人工机制砂在C30及以下的混凝土中应用是可行的。 相似文献
90.
基于城市河流半自然化的生态防洪对策——河滨缓冲带与柔性堤岸设计导引 总被引:6,自引:0,他引:6
旨在将城市河流半自然化与生态防洪对策落实到城市设计层面。根据观测水位、防洪、防潮标准确定缓冲带鼓励淹没范围、堤顶控制点标高,结合亲水性活动、适宜土地利用方式及景观要素,给出8种典型缓冲带断面设计及相应护岸生态工法。设计导引以海河下游为例,采用绩效控制、示例设计方法,主要内容包括目标-策略表、控制要点与编制方法表、示例设计图、应用索引图等。导引有助于消除防洪设施带来的视线遮挡、增强河滨缓冲带土地利用复合性与公共性,缓解防洪与亲水性、城市区生态用地与河滨土地稀缺性等矛盾,以保持河滨持久性活力。 相似文献