全文获取类型
收费全文 | 11619篇 |
免费 | 874篇 |
国内免费 | 396篇 |
专业分类
财政金融 | 391篇 |
工业经济 | 107篇 |
计划管理 | 740篇 |
经济学 | 1363篇 |
综合类 | 1518篇 |
运输经济 | 62篇 |
旅游经济 | 133篇 |
贸易经济 | 676篇 |
农业经济 | 1584篇 |
经济概况 | 1645篇 |
水利工程 | 4670篇 |
出版年
2024年 | 84篇 |
2023年 | 210篇 |
2022年 | 270篇 |
2021年 | 350篇 |
2020年 | 369篇 |
2019年 | 318篇 |
2018年 | 287篇 |
2017年 | 331篇 |
2016年 | 404篇 |
2015年 | 412篇 |
2014年 | 758篇 |
2013年 | 681篇 |
2012年 | 986篇 |
2011年 | 1130篇 |
2010年 | 882篇 |
2009年 | 940篇 |
2008年 | 938篇 |
2007年 | 799篇 |
2006年 | 758篇 |
2005年 | 478篇 |
2004年 | 328篇 |
2003年 | 225篇 |
2002年 | 211篇 |
2001年 | 164篇 |
2000年 | 128篇 |
1999年 | 105篇 |
1998年 | 71篇 |
1997年 | 56篇 |
1996年 | 51篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1993年 | 34篇 |
1992年 | 31篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 15篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
851.
玛纳斯河流域水资源管理信息系统研究 总被引:3,自引:0,他引:3
玛纳斯河流域水资源管理信息系统的开发研究主要针对水资源管理的需要,解决目前管理效率低,水市场机制不完善等问题,建设高效可靠的、实用先进的综合查询信息系统。根据水资源管理信息系统(WRMIS)的开发目标,分析系统的功能需求和结构,提出新的开发方式,强调开发过程中用户参与的重要性,提高工作效率和管理水平。 相似文献
852.
黄河干流水体污染时空变化特征 总被引:2,自引:1,他引:2
黄河水体污染加剧黄河水资源的短缺情势。本文根据1992年~1999年监测资料对黄河干流水质级别以及溶解氧、氨氮、高锰酸盐指数和BOD。等4种典型污染物的时空变化进行评价,分析产生这些变化的原因,揭示了黄河干流多年来水体污染的时空变化规律。最后以1998年2月和8月为例,对干流各站点的水质水量进行联合评价。 相似文献
853.
汉江上游流域水文特性分析 总被引:15,自引:1,他引:15
李文浩 《水资源与水工程学报》2004,15(2):54-58
通过安康长系列水文资料分析,论述了汉江上游流域内降水、径流、泥沙的变化规律,同时提出了暴雨洪水特性、水力资源有效利用两个主要问题。 相似文献
854.
塔里木河流域水文动态数据库管理信息系统设计 总被引:2,自引:0,他引:2
依据现代管理学理念,从系统控制的角度出发,借助于计算机技术,建议建立塔里木河流域水文动态数据库管理信息系统。在建立水文数据库的基础上,开发相应的管理信息系统,以期实现对塔里木河水文数据的动态管理,进而建立对塔里木河水资源利用的决策支持。 相似文献
855.
Hydroelectric dams may affect anadromous fish survival and recruitment by limiting access to upstream habitats and adversely affecting quality of downstream habitats. In the Manistee River, a tributary to Lake Michigan, two hydroelectric dams potentially limit recruitment of anadromous rainbow trout (steelhead) by increasing tailrace water temperatures to levels that significantly reduce survival of young‐of‐year (YOY) fish. The objectives of this study were to determine whether proposed restoration scenarios (dam removals or a bottom withdrawal retrofit) would alter the Manistee River thermal regime and, consequently, improve wild steelhead survival and recruitment. Physical process models were used to predict Manistee River thermal regimes following each dam alteration scenario. Empirical relationships were derived from historical field surveys to quantify the effect of temperature on YOY production and potential recruitment of Manistee River steelhead. Both dam alteration scenarios lowered summer temperatures and increased steelhead recruitment by between 59% and 129%, but total recruitments were still low compared to other Great Lakes tributaries. Considering only temperature effects, bottom withdrawal provides the greatest promise for increasing natural steelhead recruitment by decreasing the likelihood of year‐class failures in the warmest summers. Results of this study may allow managers to evaluate mitigation alternatives for Manistee River dams during future relicensing negotiations, and illustrate the utility of physical process temperature models in groundwater‐fed rivers. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
856.
In‐stream chinook salmon (Oncorhynchus tschawytscha) spawning habitat in California's Central Valley has been degraded by minimal gravel recruitment due to river impoundment and historic gravel extraction. In a recent project marking a new direction for spawning habitat rehabilitation, 2450 m3 of gravel and several boulders were used to craft bars and chutes. To improve the design of future projects, a test was carried out in which a commercial modelling package was used to design and evaluate alternative gravel configurations in relation to the actual pre‐ and post‐project configurations. Tested scenarios included alternate bars, central braid, a combination of alternate bars and a braid, and a flat riffle with uniformly spaced boulders. All runs were compared for their spawning habitat value and for susceptibility to erosion. The flat riffle scenario produced the most total, high, and medium quality habitat, but would yield little habitat under flows deviating from the design discharge. Bar and braid scenarios were highly gravel efficient, with nearly 1 m2 of habitat per 1 m3 of gravel added, and yielded large contiguous high quality habitat patches that were superior to the actual design. At near bankfull flow, negligible sediment entrainment was predicted for any scenario. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
857.
Nitrogen dynamics were studied in the interstitial environment (i.e. hyporheic zone) of a sandy‐bottom stream in a rural landscape. A third‐order stream in Brittany (France) was studied at 11 stations (riffles) to evaluate spatial patterns of water exchange between surface and interstitial habitats. More intensive sampling was conducted in three riffles selected according to their hydrological characteristics. Chemical characteristics (especially nitrogen) and microbial denitrification were studied at 12.5 and 25 cm depth upstream, and 25 cm depth downstream of each riffle. This study confirms that the interstitial habitat of a N‐rich stream acts as a sink for the nitrate‐nitrogen. Experimental manipulation of sediment cores indicates that denitrification is limited by carbon in surface (i.e. benthic) and by nitrate in hyporheic sediments. River regulation increases inputs of fine sediments, modifies river channel location, and generates changes in the spatial patterns of biogeochemical processes, water origins, and hydrologic exchanges. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
858.
Christine Bratrich Bernhard Truffer Klaus Jorde Jochen Markard Werner Meier Armin Peter Matthias Schneider Bernhard Wehrli 《河流研究与利用》2004,20(7):865-882
Hydropower is the most important renewable electricity source worldwide. It shows clear advantages for the global CO2 balance but creates serious ecological impacts on a local scale. As a consequence, concern for the conservation of natural river ecosystems is growing within society and more people are willing to pay extra for so‐called ‘green electricity’. The definition of ‘green’, however, is not straightforward and customers cannot directly examine the quality of electricity products. Therefore, credible certification of high ecological standards is essential for successful green electricity marketing. In this paper we introduce a new assessment procedure for evaluating environmentally compatible hydropower production. This so‐called ‘Green Hydro’ concept was developed in the context of a multidisciplinary case study on a 400 MW hydropower scheme in the Southern Alps of Switzerland. The concept guarantees both general standards for different schemes operating in different types of watersheds and flexibility for local particularities. We developed an environmental management matrix that considers basic criteria and eco‐investments and covers five environmental areas of concern (i.e. hydrological character, connectivity, morphology, landscape, and biological communities). The ecological perspective is complemented by five management domains (i.e. instream flow regimes, hydropeaking, reservoir and bedload management, and power plant structures). Applying assessment and modelling tools for the Green Hydro procedure showed that dynamic habitat models allowed quantification of the effects of different instream flow regulations at morphologically distinct sites. In this case, morphological restoration could be more beneficial than increasing the minimum flow. The first experience with the Green Hydro certification is encouraging. So far, 13 facilities have successfully passed the certification procedure. They produce a total of 186 GWh green electricity per year, which is sufficient for the supply of almost 40 000 households in Switzerland. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
859.
860.
结合山区河流基本特征,从生态功能和人类服务功能两方面建立了山区河流可持续发展能力评价指标体系。基于信息熵和逼近于理想解的排序方法,提出了山区河流可持续发展能力的评价模型。以怒江中游为例,通过比较分析水电开发和旅游开发两种开发方式的可持续发展能力,验证了本文模型的科学性和可行性。分析结果表明:水电开发对怒江中游可持续发展的影响要大于旅游开发,主要体现在水电开发对当地社会经济的发展贡献较大,对生态环境的保护力度较大,但对自然的改变也较大。最后提出了多目标协同开发的山区河流可持续发展的对策。 相似文献