全文获取类型
收费全文 | 2140篇 |
免费 | 316篇 |
国内免费 | 131篇 |
专业分类
测绘学 | 36篇 |
大气科学 | 53篇 |
地球物理 | 542篇 |
地质学 | 1658篇 |
海洋学 | 23篇 |
天文学 | 4篇 |
综合类 | 58篇 |
自然地理 | 213篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 33篇 |
2021年 | 42篇 |
2020年 | 51篇 |
2019年 | 58篇 |
2018年 | 37篇 |
2017年 | 56篇 |
2016年 | 78篇 |
2015年 | 80篇 |
2014年 | 104篇 |
2013年 | 115篇 |
2012年 | 74篇 |
2011年 | 86篇 |
2010年 | 87篇 |
2009年 | 171篇 |
2008年 | 221篇 |
2007年 | 197篇 |
2006年 | 209篇 |
2005年 | 138篇 |
2004年 | 135篇 |
2003年 | 81篇 |
2002年 | 79篇 |
2001年 | 63篇 |
2000年 | 52篇 |
1999年 | 45篇 |
1998年 | 45篇 |
1997年 | 47篇 |
1996年 | 38篇 |
1995年 | 43篇 |
1994年 | 32篇 |
1993年 | 26篇 |
1992年 | 17篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2587条查询结果,搜索用时 62 毫秒
951.
Effects of Activated Irrigation Water on Soil Physicochemical Properties and Crop Growth and Analysis of the Probable Pathway 总被引:2,自引:0,他引:2
Quanjiu Wang Yan Sun Songrui Ning Jihong Zhang Beibei Zhou Lijun Su Yuyang Shan 《地球科学进展》2019,34(6):660-670
With the problem of shortage of water resources becoming increasingly prominent, the improvement of production efficiency of agricultural water resources in China has become an important research content of modern irrigated agriculture. The technology of activated irrigation water provides a new way to excavate the physiological production potential of irrigation water and improve the comprehensive efficacy of irrigation water in agro-ecosystems. In this study, the research progress of the variable characteristics of physicochemical properties of activated irrigation water, the transport and transformation of soil material by activated irrigation water, and the promotion of crop growth by activated irrigation water were comprehensively analyzed. On this basis, according to the basic theories of soil physics, crop physiology, and material transport dynamics, the effects of activated irrigation water on soil material transport, soil material transformation, water and nutrition uptake by root, and crop yield formation and the probable pathway were analyzed. The key problems of basic science and applied technology in the future research are put forward to provide reference for the scientific and reasonable utilization of activated irrigation water technology. 相似文献
952.
953.
针对邓州市地下水环境质量研究相对薄弱,水质监测数据缺乏系统分析等问题,开展了地表水、地下水质量评价,以及地下水污染评价。地表水质量评价选用单指标评价法,评价结果为小洪渠、刁北干渠、湍北干渠水质为为Ⅳ类水,湍河上游、下游及刁河上游水质为V类水。地下水质量评价选用内梅罗综合指数法,分别对浅层及中深层地下水水质分析评价,其中浅层地下水16组样品中,3组为优良,4组为良好,8组为较好,1组为较差;中深层地下水19组评价样品中,16组评价结果为良好,3组较差。基本查明了地下水环境质量,为地下水资源保护及合理开发利用提供科学依据。 相似文献
954.
Anja Bretzler Lucien Stolze Julien Nikiema Franck Lalanne Elaheh Ghadiri Matthias S.Brennwald Massimo Rolle Mario Schirmer 《地学前缘(英文版)》2019,10(5):1685-1699
The semi-arid Sahel regions of West Africa rely heavily on groundwater from shallow to moderately deep(100 m b.g.l.)crystalline bedrock aquifers for drinking water production.Groundwater quality may be affected by high geogenic arsenic(As)concentrations(10μg/L)stemming from the oxidation of sulphide minerals(pyrite,arsenopyrite)in mineralised zones.These aquifers are still little investigated,especially concerning groundwater residence times and the influence of the annual monsoon season on groundwater chemistry.To gain insights on the temporal aspects of As contamination,we have used isotope tracers(noble gases,~3H,stable water isotopes(~2 H,~(18)O))and performed hydrochemical analyses on groundwater abstracted from tube wells and dug wells in a small study area in southwestern Burkina Faso.Results revealed a great variability in groundwater properties(e.g.redox conditions,As concentrations,water level,residence time)over spatial scales of only a few hundred metres,characteristic of the highly heterogeneous fractured underground.Elevated As levels are found in oxic groundwater of circum-neutral pH and show little relation with any of the measured parameters.Arsenic concentrations are relatively stable over the course of the year,with little effect seen by the monsoon.Groundwater residence time does not seem to have an influence on As concentrations,as elevated As can be found both in groundwater with short(50 a)and long(10~3 a)residence times as indicated by ~3He/~4He ratios spanning three orders of magnitude.These results support the hypothesis that the proximity to mineralised zones is the most crucial factor controlling As concentrations in the observed redox/pH conditions.The existence of very old water portions with residence times10~3 years already at depths of50 m b.g.l.is a new finding for the shallow fractured bedrock aquifers of Burkina Faso,suggesting that overexploitation of these relatively low-yielding aquifers may be an issue in the future. 相似文献
955.
Contrasting sorption behaviours affecting groundwater arsenic concentration in Kandal Province,Cambodia 总被引:1,自引:1,他引:0
Laura A.Richards Maria J.Casanueva-Marenco Daniel Magnone Chansopheaktra Sovann Bart E.van Dongen David A.Polya 《地学前缘(英文版)》2019,10(5):1701-1713
Natural arsenic(As)contamination of groundwater which provides drinking water and/or irrigation supplies remains a major public health issue,particularly in South and Southeast Asia.A number of studies have evaluated various aspects of the biogeochemical controls on As mobilization in aquifers typical to this region,however many are predicated on the assumption that key biogeochemical processes may be deduced by sampled water chemistry.The validity of this assumption has not been clearly established even though the role of sorption/desorption of As and other heavy metals onto Fe/Mn(hydr)oxides is an important control in As mobilization.Here,selective chemical extractions of sand-rich and clay-rich sediments from an As-affected aquifer in Kandal Province,Cambodia,were undertaken to explore the potential role of partial re-equilibrium through sorption/desorption reactions of As and related solutes(Fe,Mn and P)between groundwater and the associated solid aquifer matrix.In general,groundwater As is strongly affected by both pH and Eh throughout the study area.However,contrasting sorption behaviour is observed in two distinct sand-dominated(T-Sand)and clay dominated(T-Clay)transects,and plausibly attributed to differing dominant lithologies,biogeochemical and/or hydrogeological conditions.Sorption/desorption processes appear to be re-setting groundwater As concentrations in both transects,but to varying extents and in different ways.In T-Sand,which is typically highly reducing,correlations suggest that dissolved As may be sequestered by sorption/re-adsorption to Fe-bearing mineral phases and/or sedimentary organic matter;in T-Clay Eh is a major control on As mobilization although binding/occlusion of Fe-bearing minerals to sedimentary organic matter may also occur.Multiple linear regression analysis was conducted with groups categorised by transect and by Eh,and the output correlations support the contrasting sorption behaviours encountered in this study area.Irrespective of transect,however,the key biogeochemical processes which initially control As mobilization in such aquifers,may be "masked" by the re-setting of As concentrations through in-aquifer sorption/desorption processes. 相似文献
956.
Under the organization of China Geological Survey,relevant departments have made industry specifications and technical requirements based on hydrogeological survey data collection at the scale of 1:50 000.Among them,groundwater resource map is a must.According to nationally unified technical requirements of mapping groundwater resources put forward in 2018,this paper mainly interprets relevant principles,content,methods,diagrams as well as legend,and further to point out future directions:Higher precision will equal to higher demand of application,so that is there any more effective way to further interpret application aspect rather than only rules? 相似文献
957.
MENG Yong-hui WANG Ji-ning YU De-Jie ZHANG Li-xia FENG Zai-min YAN Tang ZHOU Yong 《地下水科学与工程》2019,(3):245-252
Based on the geological and hydrogeological conditions along with dynamic changes of groundwater level,this paper analyzes the hydrodynamic characteristics of saltwater intrusion in the study area.According to monitoring data of groundwater quality,the distribution characteristics of macro component are analyzed,and then fuzzy comprehensive evaluation method is adopted to evaluate the impact of saltwater intrusion on groundwater environment.Concerning the influence degree of groundwater environment,the study area is divided into brine area,seriously influenced area,moderately influenced zone,slightly influenced zone and uninfluenced zone.The results can offer references for prevention and control of saltwater intrusion as well as the protection of water resources. 相似文献
958.
GIS支持下的河西走廊黑河中游盆地地下水资源评价与潜力分析 总被引:4,自引:0,他引:4
以先进的地理信息系统(Arc/info8.1)作平台,运用Microsoft Visual Basic 6.0编程语言,以ArcObjects ODE VB或ArcCatalog VBA和ArcTools VBA为应用技术开发模式,建立河西走廊水文地质空间信息系统。该系统主要包括数据库管理子系统、查询检索子系统、空间分析子系统、系统管理子系统、数据转换子系统等,具有对水文地质环境地质信息的数据管理、查询检索、空间专题分析与结果输出等功能。本文以空间分析子系统的地下水资源量计算与分析专题应用模型为例,阐述GIS支持下河西走廊黑河中游张掖盆地九灌区地下水资源评价与潜力分析的具体实现步骤与评价结果,并与该区传统方法的已有成果作对比,具有可靠性强,计算效率高、可视化效果好等特点,从而为西北干旱内陆盆地的区域地下水资源评价与管理提供一种新途径。 相似文献
959.
塔克拉玛干沙漠不同矿化度水灌溉造林试验研究 总被引:12,自引:1,他引:11
为了开发利用塔里木沙漠公路沿线的地下咸水进行防护林建设,在塔克拉玛干沙漠北缘开展了不同矿化度水灌溉造林试验。在流动风沙十和荒漠林土两种类型的土壤上,各设计6个灌溉水矿化度梯度:2g/L、5g/L、10g/L、15g/L、20g/L、28g/L,选择了4种耐盐植物:梭梭柴、头状沙拐枣、盐穗木、沙枣,研究不同类型土壤上灌溉水矿化度对植物生长的影响。结果表明:(1)随着灌溉水矿化度的增加,植物成活率下降,除2g/L水灌溉的植物生长量略低于5~10g/L外。生长量也基本随灌溉水矿化度的增加而减小:(2)土壤类型对植物的生长也有较大影响,流动风沙土中植物的成活率和生长量总体上高于荒漠林土中植物的成活率和生长量;(3)从四种植物之间的对比来看,梭梭柴适应能力最好,盐穗木和头状沙拐枣次之,沙枣适应能力最差。 相似文献
960.
Mohsen Jalali 《Environmental Geology》2009,56(7):1479-1488
This study was conducted to evaluate factors regulating groundwater quality in an area with agriculture as main use. Thirty
groundwater samples have been collected from Razan area (Hamadan, Iran) for hydrochemical investigations to understand the
sources of dissolved ions and assess the chemical quality of the groundwater. The chemical compositions of the groundwater
are dominated by Na+, Ca2+, HCO3
−, Cl− and SO4
2−, which have been derived largely from natural chemical weathering of carbonate, gypsum and anthropogenic activities of fertilizer’s
source. The production of SO4
2− has multiple origins, mainly from dissolution of sulphate minerals, oxidation of sulphide minerals and anthropogenic sources.
The major anthropogenic components in the groundwater include Na+, Cl−, SO4
2− and NO3
−, with Cl− and NO3
− being the main contributors to groundwater pollution in Razan area. 相似文献