全文获取类型
收费全文 | 192篇 |
免费 | 8篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 2篇 |
综合类 | 4篇 |
化学工业 | 2篇 |
机械仪表 | 1篇 |
建筑科学 | 31篇 |
矿业工程 | 7篇 |
能源动力 | 4篇 |
水利工程 | 72篇 |
一般工业技术 | 3篇 |
冶金工业 | 24篇 |
原子能技术 | 1篇 |
自动化技术 | 51篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 9篇 |
2014年 | 9篇 |
2013年 | 14篇 |
2012年 | 2篇 |
2011年 | 21篇 |
2010年 | 11篇 |
2009年 | 9篇 |
2008年 | 13篇 |
2007年 | 16篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 8篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 1篇 |
排序方式: 共有202条查询结果,搜索用时 7 毫秒
61.
设计洪水是确定河流治理方案和开发水利水电工程规模的重要基础数据,其成果的可靠与否直接关系到工程的规模和工程的安全性。阳河干流大菜园水文站的实测资料系列在进行一致性处理后刚好满足《水利水电工程设计洪水计算规范》(SL 44-2006)关于资料系列不少于30年的要求,但因其上游上已建成3座水库(总调洪库容5 900万m3)削峰作用较大,故对该站洪水系列进行了插补延长,对历史洪水重现期作了考证,对不同系列的设计洪水成果作了分析比较,并提出了较合理的设计洪水成果。通过这些工作,说明了资料“三性(可靠性、一致性、代表性)”分析的重要性,尤其说明了即使测站具有30年资料系列,其代表性仍可能有不足这一现象,建议在工程设计中应尽可能地延长资料系列以提高系列的代表性,不能仅局限于满足30年资料系列即可。 相似文献
62.
The goal of this paper is to handle the large variation issues in fuzzy data by constructing a variable spread multivariate adaptive regression splines (MARS) fuzzy regression model with crisp parameters estimation and fuzzy error terms. It deals with imprecise measurement of response variable and crisp measurement of explanatory variables. The proposed method is a two-phase procedure which applies the MARS technique at phase one and an optimization problem at phase two to estimate the center and fuzziness of the response variable. The proposed method, therefore, handles two problems simultaneously: the problem of large variation issue and the problem of variation spreads in fuzzy observations. A realistic application of the proposed method is also presented, by which the suspended load is modeled using discharge in a hydrology engineering problem. Empirical results demonstrate that the proposed approach is more efficient and more realistic than some well-known least-squares fuzzy regression models. 相似文献
63.
64.
65.
Policy implications of a pan-tropic assessment of the simultaneous hydrological and biodiversity impacts of deforestation 总被引:2,自引:0,他引:2
Ellen M. Douglas Stanley Wood Kate Sebastian Charles J. Vörösmarty Kenneth M. Chomitz Thomas P. Tomich 《Water Resources Management》2007,21(1):211-232
Tropical deforestation has many consequences, amongst which alteration of the hydrological cycle and loss of habitat and biodiversity
are the focus of much public interest and scientific research. Here we examine the potential biodiversity and hydrological
impacts of an extreme deforestation scenario – the loss of all tropical forest areas currently identified by the World Wildlife
Fund as being threatened. Existing tropical forest areas are first classified according to two categories of biological distinctiveness
– high and low – using indicators developed by the WWF. We apply the tropical deforestation scenario to a macro-scale hydrologic
model, keeping track of the share of change in basin runoff that originates from the deforestation of areas of high versus
low biological distinctiveness and where that change could impact human populations. Of particular interest are those basins
where loss of the most threatened tropical forest areas would give rise to significant biodiversity loss and to potentially large hydrological impacts. In such cases it is conceivable that biodiversity conservation could “free-ride”
on the concerns of resident populations to maintain the forests for the purpose of minimizing hydrological change. Where such
an outcome seems likely, biodiversity conservation efforts might be better targeted elsewhere, perhaps to basins where the
loss of forest areas with high biological distinctiveness would have less population impacts, hence requiring an alliance
between biological and hydrological interests to gain sufficient social and financial support for conservation. 相似文献
66.
New Paradigm for Sizing Riparian Buffers to Reduce Risks of Polluted Storm Water: Practical Synthesis 总被引:2,自引:0,他引:2
M. Todd Walter Josephine A. Archibald Brian Buchanan Helen Dahlke Zachary M. Easton Rebecca D. Marjerison Asha N. Sharma Stephen B. Shaw 《Canadian Metallurgical Quarterly》2009,135(2):200-209
Riparian buffers are commonly promoted to protect stream water quality. A common conceptual assumption is that buffers “intercept” and treat upland runoff. As a shift in paradigm, it is proposed instead that riparian buffers should be recognized as the parts of the landscape that most frequently generate storm runoff. Thus, water quality can be protected from contaminated storm runoff by disassociating riparian buffers from potentially polluting activities. This paper reviews and synthesizes some simple engineering approaches that can be used to delineate riparian buffers for rural watersheds based on risk of generating runoff. Although reference is made to specific future research that may improve the proposed methods for delineating riparian buffers, the approaches described here provide planners and engineers with a set of currently available scientifically defensible tools. It is recommended that planners and engineers use available rainfall and stream discharge data to parameterize the buffer-sizing equations and use variable-width buffers, based on a topographic index, to achieve a realistic representation of runoff generating areas. 相似文献
67.
Scale influences on the remote estimation of evapotranspiration using multiple satellite sensors 总被引:4,自引:0,他引:4
There is considerable interest in using remote sensing to characterize the hydrologic behavior of the land surface on a routine basis. Information on moisture fluxes between the surface and lower atmosphere reveals linkages and land-atmosphere feedback mechanisms, aiding our understanding of energy and water balance cycles. Techniques that combine information on land and atmospheric properties with remotely sensed variables would allow improved prediction for a number of hydrological variables. Over the last few decades, there has been a focus on better determining evapotranspiration and its spatial variability, but for many regions routine prediction is not generally available at a spatial resolution appropriate to the underlying surface heterogeneity. Over agricultural regions, this is particularly critical, since the spatial extent of typical field scales is not regularly resolved within the pixel resolution of satellite sensors. Understanding the role of landscape heterogeneity and its influence on the scaling behavior of surface fluxes as observed by satellite sensors with different spatial resolutions is a critical research need. To attend this task, data from Landsat-ETM (60 m), ASTER (90 m), and MODIS (1020 m) satellite platforms are employed to independently estimate evapotranspiration. The range of the satellite sensor resolutions allows analyses that span scales from (point-scale) in-situ tower measurements to the MODIS kilometer-scale. Evapotranspiration estimates derived at these multiple resolutions were assessed against eddy covariance flux measurements collected during the 2002 Soil Moisture Atmospheric Coupling Experiment (SMACEX) over the Walnut Creek watershed in Iowa. Together, these data allow a comprehensive scale intercomparison of remotely sensed predictions, which include intercomparisons of the evapotranspiration products from the various sensors as well as a statistical analysis for the retrievals at the watershed scale. A high degree of consistency was observed between the retrievals from the higher-resolution satellite platforms (Landsat-ETM and ASTER). The MODIS-based estimates, while unable to discriminate the influence of land surface heterogeneity at the field scale, effectively reproduced the watershed average response, illustrating the utility of this sensor for regional-scale evapotranspiration estimation. 相似文献
68.
《Journal of Great Lakes research》2020,46(6):1661-1673
Tributaries provide spawning habitat for three of four major sub-stocks of Lake Erie walleye (Sander vitreus). Despite anthropogenic degradation and the extirpation of other potamodromous species, the Maumee River, Ohio, USA continues to support one of the largest fish migrations in the Laurentian Great Lakes. To determine if spawning habitat availability and quality could limit production of Maumee River walleye, two habitat suitability models were created for the lower 51 km of the Maumee River and the distribution and numbers of walleye eggs deposited in a 25 km stretch of river were assessed. Walleye eggs were collected using a diaphragm pump at 7 and 10 sites from March/April to May 2014 and 2015. The habitat suitability models showed that <3% of the river yielded ‘good’ walleye spawning habitat and 11–38% yielded ‘moderate’ walleye spawning habitat, depending on the model. However, a large set of rapids at river kilometer 28 and more than five river kilometers of less suitable habitat separated areas of ‘good’ habitat. The rapids may present a migratory barrier for many spawning walleye, as modeled water velocities exceed maximum estimated walleye swim speeds 71–100% of days during pre-spawn migration and spawning during the study period. In both study years, there was a sharp decline in mean egg numbers from spawning sites downstream of the rapids (439.7 eggs/2 min tow ± 990.6 SD) to upstream sites (5.9 eggs/2 min tow ± 19.4 SD). Physical barriers like rapids may reduce spawning habitat connectivity and could limit walleye production in the Maumee River. 相似文献
69.
介绍了“黑河综合遥感联合试验”在水文和生态变量与参数反演、估算和模型应用方面取得的进展。在水文变量遥感方面,利用车载双偏振多普勒雷达在黑河上游和中游分别开展了高精度降水观测,获取了后向散射系数和极化信息与降水强度之间的定量关系。在综合利用多源观测信息,改进和发展蒸散发估算模型方面取得了实质性的进展。发展了利用K和Ka波段机载微波辐射计数据反演山区积雪深度的方法。针对SAR观测数据反演土壤水分中地表粗糙度的显著干扰,发展了消除粗糙度影响的反演方法。在生态过程遥感参量估算方面,提出了一种基于机载激光雷达和高分辨率光学影像的高精度地物信息分类方法。发展了从高光谱航空遥感提取植被自然光照下的荧光,并与NDVI结合的C3/C4植被分类方法。发展和改进了使用多角度、多光谱观测反演叶面积指数的方法,挖掘了激光雷达在植被垂直结构探测上的潜力,探索了叶面积指数遥感中的尺度转换规律。发展了利用高光谱数据中的荧光信息反演光能利用率的新方法;建立了考虑土壤反射率、冠层结构等因素的光合作用有效辐射比率反演模型;改进了利用遥感估计生态系统生产力的模型。发展了利用高光谱遥感数据提取叶绿素含量和叶绿素荧光强度的方法。 相似文献
70.