首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4714篇
  免费   386篇
  国内免费   292篇
测绘学   91篇
大气科学   122篇
地球物理   2288篇
地质学   1196篇
海洋学   307篇
天文学   19篇
综合类   155篇
自然地理   1214篇
  2024年   36篇
  2023年   93篇
  2022年   163篇
  2021年   170篇
  2020年   172篇
  2019年   185篇
  2018年   163篇
  2017年   165篇
  2016年   183篇
  2015年   180篇
  2014年   239篇
  2013年   267篇
  2012年   229篇
  2011年   230篇
  2010年   184篇
  2009年   239篇
  2008年   238篇
  2007年   273篇
  2006年   250篇
  2005年   189篇
  2004年   195篇
  2003年   165篇
  2002年   142篇
  2001年   101篇
  2000年   108篇
  1999年   111篇
  1998年   158篇
  1997年   106篇
  1996年   97篇
  1995年   75篇
  1994年   78篇
  1993年   67篇
  1992年   61篇
  1991年   22篇
  1990年   23篇
  1989年   11篇
  1988年   9篇
  1987年   4篇
  1986年   5篇
  1985年   2篇
  1984年   4篇
排序方式: 共有5392条查询结果,搜索用时 15 毫秒
891.
Abstract

The Coupled Routing and Excess STorage model (CREST, jointly developed by the University of Oklahoma and NASA SERVIR) is a distributed hydrological model developed to simulate the spatial and temporal variation of land surface, and subsurface water fluxes and storages by cell-to-cell simulation. CREST's distinguishing characteristics include: (1) distributed rainfall–runoff generation and cell-to-cell routing; (2) coupled runoff generation and routing via three feedback mechanisms; and (3) representation of sub-grid cell variability of soil moisture storage capacity and sub-grid cell routing (via linear reservoirs). The coupling between the runoff generation and routing mechanisms allows detailed and realistic treatment of hydrological variables such as soil moisture. Furthermore, the representation of soil moisture variability and routing processes at the sub-grid scale enables the CREST model to be readily scalable to multi-scale modelling research. This paper presents the model development and demonstrates its applicability for a case study in the Nzoia basin located in Lake Victoria, Africa.

Citation Wang, J., Yang, H., Li, L., Gourley, J. J., Sadiq, I. K., Yilmaz, K. K., Adler, R. F., Policelli, F. S., Habib, S., Irwn, D., Limaye, A. S., Korme, T. &; Okello, L. (2011) The coupled routing and excess storage (CREST) distributed hydrological model. Hydrol. Sci. J. 56(1), 84–98.  相似文献   
892.
ABSTRACT

With global climate change and impacts of human activity, the water cycle, which has a close relationship with local water resources, has changed rapidly. Based on different greenhouse gas emission scenarios, five relatively independent global climate models are selected from 47 CMIP5 models to simulate future climatic conditions. Data are downscaled to the local projection, with bias neutralized before applying them to the hydrological models, by which availability of future water resources are calculated for the Dongting Lake basin. The results show that the water resources of the Dongting Lake basin are likely to increase in the future, but be distributed more unevenly. All scenarios indicate that water availability will increase during the flood season and decrease during the dry season, with a prominent increase in annual discharge. The scenarios also predict that the greater the greenhouse gas emissions, the more uneven the water distribution becomes. Overall, the water resources of the Dongting Lake catchment show the same increasing and unevenly distributed trend in the future, which could be further accelerated by human activities.
Editor Z.W. Kundzewicz; Associate editor Q. Zhang  相似文献   
893.
《水文科学杂志》2013,58(1):98-99
Abstract

Lake Poopó, within the large Altiplano basin of Bolivia, is connected upstream to Lake Titicaca and downstream to the salares, the big salt fields. Small changes in precipitation and river inflows strongly affect the extent of the lake surface area. For times when there are no satellite images, it is difficult to determine the extent of the lake from observations. Water balance computations were performed to create a water-level series for Lake Poopó extending back in time. The dominant water inflow to Lake Poopó is from the River Desaguadero, which constitutes the outflow of Lake Titicaca. The water-balance computations confirm the crude peasant knowledge about historical lake status. It is found that if the lake level is less than 1 m during the wet season, there is a risk that this shallow lake dries out in the dry season.  相似文献   
894.
《水文科学杂志》2013,58(2):363-374
Abstract

Lake ?uvintas, located in southern Lithuania in the Dovin? River basin, is one of the largest lakes and oldest nature reserves in the country. However, changes in the hydrology of the Dovin? River basin, caused by large-scale land reclamation and water management works carried out in the 20th century, have resulted in a significant decrease in the biodiversity of the lake and surrounding wetlands. In order to halt the ongoing deterioration of the lake and wetlands, solutions have to be found at the basin level. Using the SIMGRO model, various measures were therefore analysed to evaluate their impact on the water management in the Dovin? River basin. The results show that it is impossible to fully restore the water dynamics and flow pattern in the Dovin? River to their original state. However, a good measure for improving the hydrological conditions is to block drainage ditches and remove bushes and trees from the wetlands.  相似文献   
895.
In August 2009, a marine geophysical survey was conducted in Lake Tequesquitengo (located in the state of Morelos, Mexico) to delineate the extent of the remains of a small town that has been submerged since the mid 19th century. The survey consists of the acquisition and mapping of magnetic, single beam bathymetric and side-scan sonar data. A dual receiver marine GPS navigation system was used to position the boat during the survey. Except for the larger structural remains that are visible on the side scan sonar images, the magnetic anomaly map proved to be most useful in delineating the extent of the town. These anomalies exhibit short wavelength components in the area surrounding a submerged church, with the shortest wavelength components being confined to the area immediately east of the church. These short wavelength components are only observed near the church; therefore, we propose that they delineate the buried remnants of the submerged town.  相似文献   
896.
In this paper, the vertical variations of heavy metal elements (including Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn) in the sediments of Songhua Lake are analyzed using sediment cores. A 70‐year evolutionary history of these heavy metal elements in Songhua Lake is described and the sources of the heavy metals in the sediments are investigated by evaluating the pollution characteristics of the metals in terms of their enrichment coefficients and geoaccumulation indexes. The results indicate that Cr, Cu, Mn, Ni, Pb, and Zn in the sediments originated mainly from basin erosion and were transported to the lake by rivers. Cd and Hg in the sediments also originated from basin erosion that occurred prior to the mid‐1990s, and these sediments have since been overlaid by artificial pollution. The distribution of heavy metals in the sediments of Songhua Lake is influenced by many factors, including sediment composition, the relative importance of fluvial input, and artificial pollution.  相似文献   
897.
Human‐induced and natural interruptions with continuous streams of observational data necessitate the development of gap‐filling and prediction strategies towards better understanding, monitoring and management of aquatic systems. This study quantified the efficacy of multiple non‐linear regression (MNLR) versus artificial neural network (ANN) models as well as the temporal partitioning of diurnal versus nocturnal data for the predictions of chlorophyll‐a (chl‐a) and dissolved oxygen (DO) dynamics. The temporal partitioning increased the predictive performances of the best MNLR models of diurnal DO by 45% and nocturnal DO by 4%, relative to the best diel MNLR model of diel DO ($r_{{\rm adj}}^{2} = 68.8\%$ ). The ANN‐based predictions had a higher predictive power than the MNLR‐based predictions for both chl‐a and DO except for diurnal DO dynamics. The best ANNs based on independent validations were multilayer perceptron (MLP) for diel chl‐a, generalized feedforward (GFF) for diurnal and nocturnal chl‐a, MLP for diel DO, GFF for diurnal DO, and MLP for nocturnal DO.  相似文献   
898.
899.
通过对罗布泊古湖盆区域("大耳朵")湖相沉积物含水量与含盐量、介电性质、地表微地貌等理化参量的分析,本文提出了罗布泊古湖盆区域的散射过程与次地表散射结构;利用全极化测量技术(PolSAR, Polarimetric Synthetic Aperture Radar),本文对不同纹理区域进行了物理散射机制的定量化剖析,同极化相关分析与极化度推算结果表明整个"大耳朵"区域后向散射强烈,亮条带比暗条带的散射机制更为复杂,地表微地貌状态是造成"大耳朵"特征的表观原因.在此基础上,本文利用极化分解技术进一步分离不同散射机制分量,通过定量比较各部分贡献对于"大耳朵"特征的表征能力,提出次地表介质性质(如含盐量)是"大耳朵"特征的根本性成因,相关性可达0.784,同时分析了次地表高含水含盐湖相沉积物在SAR响应中的重要性及其与地表形态之间的动力学形成机制.最后,本文论证了合成孔径雷达(SAR, Synthetic Aperture Radar)在罗布泊地区的穿透能力,预示着SAR遥感技术在干旱区环境研究中的应用潜力.  相似文献   
900.
Here we present datasets from a hydroacoustic survey in July 2011 at Lake Torneträsk, northern Sweden. Our hydroacoustic data exhibit lake floor morphologies formed by glacial erosion and accumulation processes, insights into lacustrine sediment accumulation since the beginning of deglaciation, and information on seismic activity along the Pärvie Fault. Features of glacial scouring with a high‐energy relief, steep slopes, and relative reliefs of more than 50 m are observed in the large W‐basin. The remainder of the lacustrine subsurface appears to host a broad variety of well preserved formations from glacial accumulation related to the last retreat of the Fennoscandian ice sheet. Deposition of glaciolacustrine and lacustrine sediments is focused in areas situated in proximity to major inlets. Sediment accumulation in distal areas of the lake seldom exceeds 2 m or is not observable. We assume that lack of sediment deposition in the lake is a result of different factors, including low rates of erosion in the catchment, a previously high lake level leading to deposition of sediments in higher elevated paleodeltas, tributaries carrying low suspension loads as a result of sedimentation in upstream lakes, and an overall low productivity in the lake. A clear off‐shore trace of the Pärvie Fault could not be detected from our hydroacoustic data. However, an absence of sediment disturbance in close proximity to the presumed fault trace implies minimal seismic activity since deposition of the glaciolacustrine and lacustrine sediments.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号