全文获取类型
收费全文 | 1043篇 |
免费 | 177篇 |
国内免费 | 219篇 |
专业分类
测绘学 | 45篇 |
大气科学 | 224篇 |
地球物理 | 353篇 |
地质学 | 431篇 |
海洋学 | 100篇 |
天文学 | 5篇 |
综合类 | 52篇 |
自然地理 | 229篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 19篇 |
2021年 | 47篇 |
2020年 | 44篇 |
2019年 | 43篇 |
2018年 | 51篇 |
2017年 | 44篇 |
2016年 | 50篇 |
2015年 | 46篇 |
2014年 | 71篇 |
2013年 | 92篇 |
2012年 | 53篇 |
2011年 | 50篇 |
2010年 | 49篇 |
2009年 | 61篇 |
2008年 | 76篇 |
2007年 | 73篇 |
2006年 | 56篇 |
2005年 | 54篇 |
2004年 | 50篇 |
2003年 | 29篇 |
2002年 | 34篇 |
2001年 | 42篇 |
2000年 | 47篇 |
1999年 | 34篇 |
1998年 | 35篇 |
1997年 | 31篇 |
1996年 | 24篇 |
1995年 | 23篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 13篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1976年 | 2篇 |
排序方式: 共有1439条查询结果,搜索用时 62 毫秒
951.
Nguyen Cao Don Nguyen Thi Minh Hang Hiroyuki Araki Hiroyuki Yamanishi Kenichi Koga 《Environmental Geology》2006,49(4):601-609
A sinking of the land surface due to the pumping of groundwater has long been recognized as an environmental issue in the
Shiroishi plain of Saga, Japan. Land subsidence can have several negative economic and social implications such as changes
in groundwater and surface water flow patterns, restrictions on pumping in land subsidence prone areas, localized flooding,
failure of well casings as well as shearing of structures. To minimize such an environmental effect, groundwater management
should be considered in this area. In this study, a new integrated numerical model that integrates a three-dimensional numerical
groundwater flow model coupled with a one-dimensional soil consolidation model and a groundwater optimization model was developed
to simulate groundwater movement, to predict ground settlement and to search for optimal safe yield of groundwater without
violating physical, environmental and socio-economic constraints. It is found that groundwater levels in the aquifers greatly
vary from season to season in response to the varying climatic and pumping conditions. Consequently, land subsidence has occurred
rapidly throughout the area with the Shiroishi plain being the most prone. The predicted optimal safe yield of the pumping
amount is about 5 million m3. The study also suggests that pumping with this optimal amount will minimize the rate of land subsidence over the entire
area.
An erratum to this article can be found at 相似文献
952.
北京市生态农业地质及其前景 总被引:2,自引:0,他引:2
论述了北京市土壤元素含量和农作物优质高产与土壤环境中化学元素有密切的关系。提出了生态农业地质研究的目的、内容、方法、管理及其前景。 相似文献
953.
The Tibetan Plateau is characterized by lower atmospheric pressure, lower air temperature and high daily and seasonal variation due to high elevation. The photosynthesis of plants is significantly influenced by these alpine environmental factors. Apparent quantum yield (αA) is one of the basic parameters of photosynthesis and mass production. Its accuracy determination is of significance to model photosynthesis of C3 plants and global change on the plateau. In the Lhasa Plateau Ecological Station with 65.4 kPa of atmospheric pressure at an elevation of 3688 m, Li-Cor 6400 portable photosynthesis system was used to measure light response curves of winter wheat in different temperatures and intercellular CO2 concentration (Ci).The slope of light response curve in weak light area of PFD from 0 to 150 μmol m-2 S-1 was used to evaluate the value of αA. The dependence of αA on temperature and intercellular concentration was analyzed. In 30℃, the average value of αAWaS 0.0476 ± 0.0038. It is not quite different from the values in low elevation areas. αA is influenced both by temperature and by the ratio of CO2and O2 partial pressure ([CO2]/[O2]). The measured values in the previous study were much lower.This might be due to systematic errors from instrument and data processing methods. The values of αA decreased linearly with temperature. It decreased 0.0007 in every 1℃ increase of temperature. The decrease slope is similar to those of C3 plants in the previous researches. While [O2] is constant, αA increases with Ciwith a hyperbolic relationship. In comparison with low elevation areas, the αA on the Tibetan Plateau is more sensitive to increase of CO2. 相似文献
954.
Blanket peat erosion and sediment yield in an upland reservoir catchment in the southern Pennines,UK
This paper investigates temporal variations in fluxes of peat and other sediment in the catchment of March Haigh Reservoir, West Yorkshire. Long‐term estimates of sediment yield were derived from a study of reservoir sediments. Magnetic properties were used to correlate ten cores to a master profile dated using 210Pb and 137Cs. A 14C date suggests that most of the organic component of the sediment is allochthonous and derived from peat eroded from the catchment. Organic sediment yields suggest low catchment erosion rates between 1838 and 1963. Blanket peat erosion increased significantly after 1963, and peaked between 1976 and 1984. Estimates of total sediment yield range between 2 and 28 t km?2 a?1. These yields are significantly lower than those from some previous studies examining reservoir sedimentation in other blanket peat‐covered catchments. The low yield estimates may be due to relatively low rates of erosion in the basin, but may also be partly explained by maintenance of silt traps during the early life of the reservoir and removal of sediment by scouring. Sedimentation within the reservoir is spatially variable, and bathymetry and sediment source appear to be the dominant controls on sedimentation patterns within the reservoir. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
955.
956.
A sharp decrease in total suspended solids (TSS) concentration has occurred in the Mekong River after the closure of the Manwan Dam in China in 1993, the first of a planned cascade of eight dams. This paper describes the upstream developments on the Mekong River, concentrating on the effects of hydropower dams and reservoirs. The reservoir-related changes in total suspended solids, suspended sediment concentration (SSC), and hydrology have been analyzed, and the impacts of such possible changes on the Lower Mekong Basin discussed. The theoretical trapping efficiency of the proposed dams has been computed and the amount of sediment to be trapped in the reservoirs estimated. The reservoir trapping of sediments and the changing of natural flow patterns will impact the countries downstream in this international river basin. Both positive and negative possible effects of such impacts have been reviewed, based on the available data from the Mekong and studies on other basins. 相似文献
957.
文章分析了孔隙充水矿井的充水水源和通道,利用非线性的BP人工神经网络建立了徐州韩桥煤矿涌水量短期预测模型,选取每天的降水量作为影响因子,用已有的涌水量资料训练得到权值和阈值来表示充水通道,并对-200m水平、-270m水平、-330m水平和全矿井涌水量进行了预测。结果显示,涌水量的预测值与实测值吻合得较好,说明该模型具有一定实用性。 相似文献
958.
959.
Reliable estimates for how much water can be safely withdrawn from aquifers without harming the environment is crucial for
identifying new water supply sources and fostering sustainable growth. Methodologies to estimate groundwater availability
that are rooted in science and yet accomplishable with minimal data are particularly useful for effectual aquifer management.
Also, as groundwater management is increasingly becoming a participatory process, these methodologies must be transparent
and easily understood by a wide range of audiences. In addition, proposed approaches must also reconcile imprecision and uncertainties
arising from lack of data, differences in stakeholders’ perceptions and limitations associated with incomplete aquifer characterization.
In this study, the fundamental concept of water balance is coupled with fuzzy regression to develop a scheme for assessing
regional-scale groundwater availability. Using the mass-balance approach, anthropogenic water demands (municipal, industrial
and agricultural) and ecological demands (baseflows to rivers) can be incorporated into the availability estimation process.
The use of fuzzy regression enables the specification of decision makers’ preferences to the adopted procedure and renders
the parameter estimation to be more robust in the presence of extreme values. The methodology is illustrated by using it to
estimate groundwater availability in the Gulf coast aquifer, underlying Refugio County, TX, USA. 相似文献
960.