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   767篇
  免费   81篇
  国内免费   74篇
测绘学   40篇
大气科学   67篇
地球物理   170篇
地质学   215篇
海洋学   76篇
天文学   1篇
综合类   41篇
自然地理   312篇
  2024年   9篇
  2023年   16篇
  2022年   40篇
  2021年   58篇
  2020年   47篇
  2019年   33篇
  2018年   33篇
  2017年   45篇
  2016年   36篇
  2015年   40篇
  2014年   38篇
  2013年   66篇
  2012年   29篇
  2011年   40篇
  2010年   36篇
  2009年   35篇
  2008年   42篇
  2007年   39篇
  2006年   43篇
  2005年   36篇
  2004年   28篇
  2003年   27篇
  2002年   17篇
  2001年   19篇
  2000年   11篇
  1999年   23篇
  1998年   9篇
  1997年   3篇
  1996年   4篇
  1995年   4篇
  1994年   2篇
  1993年   2篇
  1990年   1篇
  1989年   2篇
  1988年   1篇
  1987年   3篇
  1986年   2篇
  1985年   1篇
  1983年   2篇
排序方式: 共有922条查询结果,搜索用时 31 毫秒
71.
随着我国城市建设的不断推进,城市径流污染越来越受到关注。地表颗粒物(RDS)是重金属的重要载体,雨水径流对地表颗粒物的冲刷引起的径流重金属污染问题凸显。本研究选取北京市城乡接合部作为研究区域,研究区域内地表颗粒物中重金属(As、Cd、Cr、Cu、Mn、Pb、Zn)污染负荷并进行健康风险评估。结果表明,地表颗粒物含有的重金属中,除Mn外,As、Cd、Cr、Cu、Pb、Zn的平均浓度均超过背景值。其中,Cd的平均浓度是其背景值的3倍,Cr的平均浓度是其背景值的4倍之多。在径流冲刷条件下,Cr的污染负荷在各研究区域均最高,为其他重金属的3~4倍。暴露模型计算表明,重金属非致癌日平均暴露量为手口摄入量>皮肤吸收量>吸入空气量,经手口接触是人体地表灰尘暴露风险的主要途径。对于非致癌风险,在芦求路主路以及黄鹅路十字路口区域存在对于儿童的非致癌风险,整体区域内成人所受非致癌风险较低。各研究区域内重金属呼吸暴露途径的总致癌风险均低于环境阈值,致癌风险较低。  相似文献   
72.
目的:观察按摩疗法加健康教育结合乳果糖口服液治疗便秘的临床疗效。方法:将60 例便秘患者随机分为治疗组和对照组,每组各30 例。对照组给予乳果糖口服液治疗,治疗组在对照组基础上采用按摩疗法并结合健康教育。2组均以14 d为1个疗程,共治疗2个疗程。治疗结束后随访1个月,观察2组综合疗效、生活质量(PAC-QOL)评分及症状积分。结果:总有效率治疗组为93.33%(28/30),高于对照组的76.67%(23/30),差异有统计学意义(P<0.05)。2组治疗后PAC-QOL评分比较,差异有统计学意义(P<0.05)。治疗2周后,治疗组排便时间积分、症状总积分低于对照组(均P<0.05);治疗4周后,治疗组排便困难、排便时间、排便感(下坠、不尽、胀感)、排便频度积分及症状总积分低于对照组(均P<0.05);治疗结束后1个月,治疗组粪便性状、排便困难、排便时间、排便感(下坠、不尽、胀感)、排便频度积分及症状总积分低于对照组(均P<0.05)。结论:按摩疗法加健康教育结合乳果糖口服液治疗便秘效果优于单纯乳果糖口服液治疗,值得临床推广应用。  相似文献   
73.
Tracking the financial well-being of vessels that depend on a marine fishery resource is an important function of regulators. This research demonstrates how simple indices can be constructed and utilized to track the economic well-being of vessels operating in the Northeast (USA) Multispecies (Groundfish) Fishery. The indices, which use both public and private data, can separately track trends in inputs, outputs, and prices. For the Northeast Multispecies Fishery, the indices reveal that the economic well-being of the groundfish fleet has improved under catch share management through gains in productivity.  相似文献   
74.
健康是影响不同国家和地区发展的关键因素,全面了解“一带一路”成员国的居民健康状况,是探讨“一带一路”成员国之间健康医疗合作的重要基础。本文选择了4个代表性的健康状况指标(出生期望寿命、总生育率、过早非传染性疾病死亡率和结核病发病率),利用Moran's I指数、Getis-Ord G指数对“一带一路”135个成员国的健康状况进行时空统计,分析了健康状况的空间相关性和空间分布模式,研究了健康状况的时空格局。研究发现:① 2000—2016年“一带一路”大部分成员国的各项健康状况指标均朝着改善和优化方向发展;健康状况指标均呈现显著的正空间自相关性;② 总体而言,在“一带一路”成员国中,欧洲国家的居民健康状况最好;南北美洲和大洋洲国家的居民健康状况良好;亚洲国家的居民健康状况总体良好,但东南亚部分国家的结核病发病率较高;非洲国家的居民健康状况虽有明显改善,但仍处于较低状态。因此,“一带一路”成员国应进一步加强健康医疗合作,共同推动健康丝绸之路的发展。  相似文献   
75.
黄柏石  刘晔  潘泽瀚 《热带地理》2021,41(5):906-917
基于2010年第六次全国人口普查微观数据和夜间灯光数据等,运用多层级logistic回归模型估计中国城镇化水平和速度与老年人自评健康的关联,分析城镇化健康效应在不同老年人群体间的差异,并运用倾向得分匹配方法,控制“自选择”机制对分析结果的干扰。结果表明:1)中国县区城镇化水平和速度与老年人自评健康呈显著正相关关系,居住于城镇化水平中等和城镇化速度较快县区的老年人更可能自评为健康;2)城镇化水平和速度与老年人自评健康的关系在不同受教育程度和户口状态的老年人群体间存在显著差异,城镇化水平和速度对受教育程度较低、持有本地户口老年人健康水平的提升效益更大;3)控制了老年人居住“自选择”的干扰后,县区城镇化水平和速度与老年人自评健康的正向关联依然稳健,表明“自选择偏误”对中国县区城镇化水平和速度与老年人自评健康的关系没有显著的影响。  相似文献   
76.
Regional ecological health,the core of comprehensive ecosystem assessments,is an important foundation for regional exploration,environmental conservation,and sustainable development.The mountainous areas in southwest China are backward in economy,but industrialization and urbanization have been rapid in recent years.This study assessed the ecosystem health of the Sichuan and Yunnan provinces in China using a pressure-state-response(PSR)model.Spatiotemporal patterns of regional ecosystem health were analyzed from 2000 to 2016,including overall characteristics as well as local characteristics.Ecosystem health in most regions was improved over time(Y=0.0058 X–11.0132,R2=0.95,P<0.001),and areas with poorer ecosystem health decreased from half to one-third of the total area.Analysis of the primacy ratio and the variation coefficient confirmed that the gap in health scores between regions has gradually expanded since 2007,but there are more high quality regions overall(Z of Moran’s index<1.96,P>0.05).Overall,the regional ecosystems to the east of the Hu line-an imaginary line dividing east and west China into roughly equivalent parts-were healthier than those to the west.The pressure and state scores of ecosystems were determined by physiographic condition,and the response scores by government policies and social concern.The spatiotemporal patterns of ecosystem health were dominated to a greater extent by natural than anthropogenic factors,which explains why the shift in the patterns aligned with the direction of the Hu line.Dividing regions into key management areas based on natural geographical conditions and socioeconomic development could contribute to the formulation of a reasonable ecological and environmental protection policy,guaranteeing ecosystem services in the long run.  相似文献   
77.
We compare changes in low birth weight and child malnutrition in 13 African countries under projected climate change versus socio-economic development scenarios. Climate scenarios are created by linking surface temperature gradients with declines in seasonal rainfall sea along with warming values of 1 °C and 2 °C. Socio-economic scenarios are developed by assigning regionally specific changes in access to household electricity and mother's education. Using these scenarios, in combination with established models of children's health, we investigate and compare the changes in predicted health outcomes. We find that the negative effects of warming and drying on child stunting could be mitigated by positive development trends associated with increasing mothers’ educational status and household access to electricity. We find less potential for these trends to mitigate how warming and drying trends impact birth weights. In short, under warming and drying, the risk of more malnourished children is greater than the risk of more children with low birth weights, but increases in child malnutrition could be averted in regions that increase access to educational resources and basic infrastructure.  相似文献   
78.
Public concern about earthquakes linked to wastewater injection from fracking operations is rising. However, few have examined how “induced seismicity” is acted upon by state officials. For some, an incremental response to smaller quakes can be viewed as an acceptable risk policy orientation because of the sizeable economic benefits that accompany drilling activities while others prefer risk mitigation policies (such as the use of “threshold policies”) as a better way to address quake-related problems. To account for state response to induced seismicity impacts, we examine three factors: the emergence of quakes as focusing events, the economic importance of oil and gas to state jobs and revenue, and selected characteristics of earthquakes as a policy issue, i.e., complexity and categorical precedence. Using information drawn from documentary sources, we consider which factors are most helpful in accounting for agency decisions aimed at reducing seismic risks linked to nearby injection wells.  相似文献   
79.
The purpose of this article is to provide an overview of an emerging theme within the subfield of nutritional geography we call the geography of malnutrition. Work relating to malnutrition is a high-priority research topic, with growing relevance to geographical concepts, but there is no overview of geographical approaches to this theme. Using keyword searches in Google Scholar and Web of Science to obtain relevant publications, we identified the major foci of work within this theme: undernutrition, diseases that cause malnutrition, the nutrition transition, and critical and feminist approaches to malnutrition. We review these foci, provide examples of prominent work, and identify areas of research concerning malnutrition that are highly spatial but have yet to be effectively studied using geographic techniques.  相似文献   
80.
基于倾向值匹配法的城市建成环境对居民生理健康的影响   总被引:5,自引:1,他引:4  
张延吉  秦波  唐杰 《地理学报》2018,73(2):333-345
伴随着城市化和机动化进程,肥胖及其引致的慢性疾病已成为中国严峻的社会问题。本文利用2010年中国社会综合调查、空间兴趣点POI、道路网等数据,探究城市建成环境对居民生理健康状况的影响,并通过倾向值匹配法控制自选择机制的干扰。研究发现:① 高密度的土地利用对居民总体的身体健康状况具有负向影响,而功能混合、支路网通达的城市肌理、以及充足的健康设施在降低身体质量指数BMI、抑制超重和减少慢性病方面发挥着积极作用。② 各类建成环境特征对中高社会阶层的影响集中在主观的健康感知,对中低阶层人群的影响则主要作用于客观的健康指标。③ 小尺度范围内的建成环境与中低阶层群体的身体健康水平存在更为密切的关联,但这一规律在中高社会阶层并不明显。本研究证明了主动式空间干预手段在促进居民生理健康过程中的有效性,进而就建成环境的优化策略提出了初步建议。  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