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   2655篇
  免费   416篇
  国内免费   543篇
测绘学   154篇
大气科学   83篇
地球物理   481篇
地质学   2088篇
海洋学   49篇
天文学   3篇
综合类   177篇
自然地理   579篇
  2024年   7篇
  2023年   23篇
  2022年   93篇
  2021年   120篇
  2020年   108篇
  2019年   107篇
  2018年   96篇
  2017年   117篇
  2016年   109篇
  2015年   113篇
  2014年   164篇
  2013年   173篇
  2012年   161篇
  2011年   191篇
  2010年   163篇
  2009年   166篇
  2008年   188篇
  2007年   230篇
  2006年   194篇
  2005年   191篇
  2004年   146篇
  2003年   124篇
  2002年   99篇
  2001年   98篇
  2000年   95篇
  1999年   58篇
  1998年   44篇
  1997年   37篇
  1996年   44篇
  1995年   34篇
  1994年   23篇
  1993年   22篇
  1992年   18篇
  1991年   20篇
  1990年   8篇
  1989年   10篇
  1988年   9篇
  1987年   3篇
  1986年   3篇
  1984年   2篇
  1983年   2篇
  1979年   1篇
排序方式: 共有3614条查询结果,搜索用时 20 毫秒
111.
滑坡变形立体监测网建设   总被引:1,自引:0,他引:1  
论文简要介绍了滑坡监测工作内容和监测方法,对现有技术方法在实际工作中的优缺点进行了简要评述。认为在滑坡稳定性监测工作中应该建立全方位、多种手段的立体监测网,仅仅运用某一种或者某一单方面的监测方法是不行的,是片面的,无法准确了解滑坡的动态。所说的立体监测网既有水平位移监测又有垂直位移监测,既有滑坡地表表层变形监测又有滑体深部变形监测,既有专业监测又有群测群防体系。同时监测有可能准确地掌握使滑坡失稳的各种因素(自然因素和人为因素)。因此建议在滑坡监测中建立全方位、多种手段的立体监测网,并提出了立体监测网建设的主要内容。  相似文献   
112.
厦门市海沧区北市花岗岩矿滑坡发生于2004年10月30日14时。滑坡位于呆场的西端帮顶部的第四系填土和淤泥质土层中,滑体将该区域原设的抗滑桩剪断、拔出、推移,土石迅速越过矿区运输公路,塌落到采场工作面,将正在作业的2名工人和生产设备掩埋。滑坡宽度约60m,最大垂直厚度约14m,总体积约13000m^3。由于滑坡对原有防护体系的破坏,根据滑体调查和极限平衡计算结果,滑坡处于不稳定状态,直接威胁着整个采场设备和未来生产的安全。必须对北市花岗岩矿滑坡进行专项治理。滑坡宜采用治水、削坡减载和支挡相结合的综合治理措施。  相似文献   
113.
On Shikoku Island, which is one of the four main islands of Japan, a large number of large-scale crystalline schist landslides have been revealed and are being monitored by an observation system. Seasonal heavy rainfall is the most active meteorological factor that can threaten the stability of this kind of site-specific landslide. In this paper, on the basis of the study of the rainfall-related behavior of a typical crystalline schist landslide, the Zentoku landslide, by analyzing the precisely and continuously observed piezometric and movement data, a method was developed to quantitatively assess the effect of heavy rainfall on a large-scale landslide. The results indicated that heavy rainfall-induced landslide displacement shows good correlation with the variation of groundwater levels. Variations of groundwater level have been simulated with the use of a tank model. The simulation using this model permits the change in water levels for future rainfall events to be predicted. By combining the predicted results with the empirical relation between displacements and water levels, rainfall-induced landslide movement during extreme rainfall events can be estimated in advance. The effect of heavy rainfall on sliding behavior can be quantified in terms of the change in displacement. Thus warning information or advisories for the local residents can be provided.  相似文献   
114.
采用3类InSAR产品和DEM数据开展金沙江流域乌东德水电站段的潜在滑坡探测,成功识别出多处已知和未知的滑坡点,并探测出滑坡体的形态及稳定性,提供了一种高效的大范围滑坡探测技术。同时采用小基线集InSAR技术对金坪子滑坡进行监测,不仅获得该滑坡的空间分区特征,也获取重点滑坡区的时间序列结果,并且与地面监测结果比较,精度达1.8 cm。展示了不同InSAR技术在不同尺度滑坡调查与监测中的应用特点。  相似文献   
115.
Soil moisture is essential for vegetation restoration in arid and semi-arid regions. Ascertaining the vertical distribution and transportation of soil moisture under different vegetation types has a profound effect on the ecological construction. In this study, the soil moisture at a depth of 500 cm for four typical vegetation types, including Robinia pseudoacacia, Caragana korshinskii, Stipa bungeana, and corn, were investigated and compared in the Zhifanggou watershed of the Loess plateau. Additionally, hydrogen and oxygen stable isotopes were detected to identify the transport mechanism of soil moisture. The results showed vertical distribution and transportation of soil moisture were different under different vegetation types. Depth-averaged soil moisture under S. bungeana and corn generally increased along the profile, while C. korshinskii and R. pseudoacacia showed weakly increasing and relatively stable after an obvious decreasing trend (0–40 cm). The soil moisture under R. pseudoacacia was lower than that under other vegetation types, especially in deep layer. However, the effect of R. pseudoacacia on soil moisture in the topsoil (< 30 cm) could be positive. For R. pseudoacacia (160–500 cm), C. korshinskii (0–500 cm), and S. bungeana (0–100 cm), the soil moisture declined with increased in vegetation age. Planting arbor species such as R. pseudoacacia intensified the decline of soil moisture on the Loess Plateau. The capacity of evaporation fractionation of soil moisture followed the sequence: corn > S. bungeana > R. pseudoacacia > C. korshinskii. The δ18O values in soil water fluctuated across the profile. The δ18O values changed sharply in upper layer and generally remained stable in deep layer. However, in middle layer, the vertical distribution characteristics of the δ18O values were different under different vegetation types. We estimated that piston flow was the main mode of precipitation infiltration, and the occurrence of preferential flow was related to vegetation types. These results were helpful to improve the understanding of the response of deep soil moisture to vegetation restoration and inform practices for sustainable water management.  相似文献   
116.
正1.HYDROGEOLOGY20142452Chang Chengcao(Institute of Coalfield Geological Survey and Design of Jilin Province,Changchun 130062,China)Hydrogeological Type Division of Coal Mine No.2Mine in Yitong Manchu Autonomous County,Jilin Province(Jilin Geology,ISSN1001-2427,CN22-1099/P,32(4),2013,p.129-131,3refs.)  相似文献   
117.
种群的空间格局是研究植物种群相互作用及种群与环境关系的重要方法。红砂(Reaumuria soongarica)是黄土高原半干旱区的主要物种,通过野外的群落调查,运用空间点格局分析法中的Ripley K函数,分析甘肃皋兰老虎台荒漠植被不同坡向红砂种群的空间分布格局与种内关联。结果显示:红砂种群为增长型种群,其在不同坡向的分布具有显著差异;南坡及西南坡坡向上,红砂种群Ⅰ、Ⅱ级个体在小尺度上呈显著聚集分布,随着龄级及空间尺度的增加,红砂种群聚集强度逐渐减弱,最后趋于随机分布。西坡、西北坡坡向上生长大量的蓍状亚菊(Ajania achilloides)和短花针茅(Stipa breviflora)等对红砂的生长造成抑制并加剧种间竞争,各级红砂种群的分布格局均以随机分布为主。不同坡向上,红砂种群Ⅰ、Ⅱ龄级个体之间在小尺度内表现为负关联,随着尺度增加关联度降低,Ⅲ、Ⅳ龄级与Ⅰ、Ⅱ龄级个体之间呈显著的负关联,而Ⅲ、Ⅳ龄级之间没有明显关联性,表明龄级相近的个体在空间分布上是相互独立的。综上所述,在黄土高原半干旱区,影响红砂种群分布的主要因素除了其自身的生物、生态学特性外,微生境的影响也十分重要。  相似文献   
118.
Global climate change and diverse human activities have resulted in distinct temporal–spatial variability of watershed hydrological regimes, especially in water‐limited areas. This study presented a comprehensive investigation of streamflow and sediment load changes on multi‐temporal scales (annual, flood season, monthly and daily scales) during 1952–2011 in the Yanhe watershed, Loess Plateau. The results indicated that the decreasing trend of precipitation and increasing trend of potential evapotranspiration and aridity index were not significant. Significant decreasing trends (p < 0.01) were detected for both the annual and flood season streamflow, sediment load, sediment concentration and sediment coefficient. The runoff coefficient exhibited a significantly negative trend (p < 0.01) on the flood season scale, whereas the decreasing trend on the annual scale was not significant. The streamflow and sediment load during July–August contributed 46.7% and 86.2% to the annual total, respectively. The maximum daily streamflow and sediment load had the median occurrence date of July 31, and they accounted for 9.7% and 29.2% of the annual total, respectively. All of these monthly and daily hydrological characteristics exhibited remarkable decreasing trends (p < 0.01). However, the contribution of the maximum daily streamflow to the annual total progressively decreased (?0.07% year?1), while that of maximum daily sediment load increased over the last 60 years (0.08% year?1). The transfer of sloping cropland for afforestation and construction of check‐dams represented the dominant causes of streamflow and sediment load reductions, which also made the sediment grain finer. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
119.
重庆市是滑坡灾害高发的城市,滑坡灾害每年都会造成大量的人员伤亡和经济损失。本文结合历年滑坡统计资料,基于GIS平台,分析重庆市滑坡灾害的时空分布特征。自1980年起,重庆发生滑坡的次数明显增加,且集中发生在5~9月,尤其是7月。80%以上的滑坡为降雨引发,其次是自然灾害和人类活动,人类活动诱发滑坡灾害增长速度最快。重庆滑坡密度大的地区为市区以及万州区、忠县等三峡库区核心地带,滑坡高发地区有东北向西南方向变化的趋势。  相似文献   
120.
传统基于GPS和全站仪的地表变形监测手段由于监测点少,难以对滑坡体进行整体监测,本文提出基于点云所成模型间比较的变形信息提取方法,结合试验验证了算法的效果。结果表明,地面三维激光扫描技术应用于变形监测领域是完全可行的,虽然其在测量精度上略低于GPS、全站仪等传统监测手段,但对大范围区域快速、连续、全方位监测的优势是其他监测手段所不具备的。  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