全文获取类型
收费全文 | 1858篇 |
免费 | 155篇 |
国内免费 | 170篇 |
专业分类
测绘学 | 845篇 |
大气科学 | 150篇 |
地球物理 | 258篇 |
地质学 | 461篇 |
海洋学 | 127篇 |
天文学 | 26篇 |
综合类 | 111篇 |
自然地理 | 205篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 28篇 |
2021年 | 19篇 |
2020年 | 53篇 |
2019年 | 59篇 |
2018年 | 33篇 |
2017年 | 55篇 |
2016年 | 51篇 |
2015年 | 70篇 |
2014年 | 79篇 |
2013年 | 118篇 |
2012年 | 72篇 |
2011年 | 128篇 |
2010年 | 85篇 |
2009年 | 124篇 |
2008年 | 127篇 |
2007年 | 125篇 |
2006年 | 102篇 |
2005年 | 110篇 |
2004年 | 84篇 |
2003年 | 104篇 |
2002年 | 73篇 |
2001年 | 58篇 |
2000年 | 52篇 |
1999年 | 61篇 |
1998年 | 70篇 |
1997年 | 48篇 |
1996年 | 31篇 |
1995年 | 30篇 |
1994年 | 21篇 |
1993年 | 27篇 |
1992年 | 23篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有2183条查询结果,搜索用时 15 毫秒
91.
在管道检测、探测、铺设、修复和更新等工程中,非开挖技术正在发挥着巨大的作用。通过笔者参加的2010年11月国际非开挖技术协会(ISTT)在新加坡召开的第28届年会和之前在新加坡南洋理工大学召开的第12届国际非开挖技术研讨会,从国际会议的论文中和研讨会上各国教授的介绍中提炼了非开挖工程方面的发展近况,从管道探测、检测、修复和新材料四个方面入手,简单扼要地阐述了非开挖工程的最新进展.希望对国内非开挖工程领域的研究有所帮助。 相似文献
92.
The Ras Al-Subiyah area is considered one of the most promising areas in Kuwait for future development. This development will
include a new town called Subiyah and its associated infrastructure. This area is also being considered as the location for
connection between Boubyan Island, which is now undergoing major development and the Kuwait mainland. The present study investigates
the geomorphology of the Ras Al-Sabiyah area in the northern sector of Kuwait. The study area is generally flat, and it is
located west of the Jal Az-Zor escarpment. It is bordered on the east by the Khor Al-Sabiyah tidal channel and on the south
by Kuwait Bay. The area receives sediments from several sources; currently the most important are aeolian sediments and the
deposition of mud delivered through the Khor Al-Sabiyah from the Iraqi marshes. The study area has been subjected to severe
environmental changes due to the Gulf wars and the drainage of Iraqi marshes and the associated artificial changes in fluvial
system. Twenty-two surface sediments were collected from the Ras Al-Subiyah area. Samples were collected to include the main
geomorphologic characteristic features of the study area. Field observations and remote sensing images from 1990 and 2001
were used to produce an updated geomorphologic map for the Ras Al-Subiyah and a map showing geomorphic changes between 1990
and 2001. Grain size of the surface sediment ranges from gravel to medium sand. In general, grain size statistical analysis
indicates that most of the areas are composed of two or more classes of sands transported and deposited from different sources
including aeolian, sabkhas, river and the bays. The variability in the grain size statistical parameters may be attributed
to the complexity of surface morphology as well as the diversity in the type of depositional environment in the Ras Al-Subiyah
area. The total area subjected to change during the 12-year period (1990–2001) is about 32 km2 as calculated using GIS techniques. 相似文献
93.
文章以MATLAB技术为平台,以西藏自治区雄村铜矿床为实例,详细讨论了如何开发以克立格理论为基础的固体资源储量估算系统,其中包括模块:数据预处理、变异函数分析、克立格估值、储量估算、地质可靠度评价等.论文使用该系统对西藏自治区雄村铜矿床进行储量预测,得出结果数据表格;并对原生矿体、次生矿体、氧化矿体、总矿体、矿体的自然形态以及在工业品位规范下的矿体形态进行拟合.通过与专业储量估算软件Minesjght的估算结果对比,证明了本系统的可靠性和实用性. 相似文献
94.
Soil erosion prediction using the Revised Universal Soil Loss Equation (RUSLE) in a GIS framework,Chania, Northwestern Crete,Greece 总被引:7,自引:0,他引:7
Soil erosion is a growing problem in southern Greece and particularly in the island of Crete, the biggest Greek island with
great agricultural activity. Soil erosion not only decreases agricultural productivity, but also reduces the water availability.
In the current study, an effort to predict potential annual soil loss has been conducted. For the prediction, the Revised
Universal Soil Loss Equation (RUSLE) has been adopted in a Geographical Information System framework. The RUSLE factors were
calculated (in the form of raster layers) for the nine major watersheds which cover the northern part of the Chania Prefecture.
The R-factor was calculated from monthly and annual precipitation data. The K-factor was estimated using soil maps available from the Soil Geographical Data Base of Europe at a scale of 1:1,000,000.
The LS-factor was calculated from a 30-m digital elevation model. The C-factor was calculated using Remote Sensing techniques. The P-factor in absence of data was set to 1. The results show that an extended part of the area is undergoing severe erosion.
The mean annual soil loss is predicted up to ∼200 (t/ha year−1) for some watersheds showing extended erosion and demanding the attention of local administrators. 相似文献
95.
Li Li Yang Hong Jiahu Wang Robert F. Adler Frederick S. Policelli Shahid Habib Daniel Irwn Tesfaye Korme Lawrence Okello 《Natural Hazards》2009,50(1):109-123
Many researchers seek to take advantage of the recently available and virtually uninterrupted supply of satellite-based rainfall
information as an alternative and supplement to the ground-based observations in order to implement a cost-effective flood
prediction in many under-gauged regions around the world. Recently, NASA Applied Science Program has partnered with USAID
and African-RCMRD to implement an operational water-hazard warning system, SERVIR-Africa. The ultimate goal of the project
is to build up disaster management capacity in East Africa by providing local governmental officials and international aid
organizations a practical decision-support tool in order to better assess emerging flood impacts and to quantify spatial extent
of flood risk, as well as to respond to such flood emergencies more expediently. The objective of this article is to evaluate
the applicability of integrating NASA’s standard satellite precipitation product with a flood prediction model for disaster
management in Nzoia, sub-basin of Lake Victoria, Africa. This research first evaluated the TMPA real-time rainfall data against
gauged rainfall data from the year 2002 through 2006. Then, the gridded Xinanjiang Model was calibrated to Nzoia basin for
period of 1985–2006. Benchmark streamflow simulations were produced with the calibrated hydrological model using the rain
gauge and observed streamflow data. Afterward, continuous discharge predictions forced by TMPA 3B42RT real-time data from
2002 through 2006 were simulated, and acceptable results were obtained in comparison with the benchmark performance according
to the designated statistic indices such as bias ratio (20%) and NSCE (0.67). Moreover, it is identified that the flood prediction
results were improved with systematically bias-corrected TMPA rainfall data with less bias (3.6%) and higher NSCE (0.71).
Although the results justify to suggest to us that TMPA real-time data can be acceptably used to drive hydrological models
for flood prediction purpose in Nzoia basin, continuous progress in space-borne rainfall estimation technology toward higher
accuracy and higher spatial resolution is highly appreciated. Finally, it is also highly recommended that to increase flood
forecasting lead time, more reliable and more accurate short- or medium-range quantitative precipitation forecasts is a must. 相似文献
96.
Outgoing long wave radiation variability from IR satellite data prior to major earthquakes 总被引:12,自引:1,他引:12
Dimitar Ouzounov Defu Liu Kang Chunli Guido Cervone Menas Kafatos Patrick Taylor 《Tectonophysics》2007,431(1-4):211
Our analysis of the continuous outgoing long wave earth radiation (OLR) indicates anomalous variations prior to a number of medium to large earthquakes. The most recent analysis of OLR is from the M9.0 Sumatra Andaman Islands mega trust event. We compared the reference fields for December 2001 to 2004 and found OLR anomalous values, > 80 W/m2, (2σ) within the epicentral area on Dec 21, 2004, 5 days before the event. We used the NOAA/IR daily (one degree) and monthly (two and half degree) gridded data to differentiate between the global and seasonal variability and the transient local anomalies. The cause of such anomalies is not fully understood; one possible explanation is the existence of thermal outgoing radiation as a result of near ground air ionization and latent heat change due to change of air humidity and temperature. This phenomenon is hypothesized to be part of a relationship between tectonic stresses, electrochemical and thermodynamic processes in the atmosphere and increasing mid IR flux, all part of a family of electromagnetic (EM) phenomena related to earthquake activity. The time scale of the observed variations is a few weeks before the onset of the seismic event. In comparison with several years of data, the observed time-series preceding the earthquake had unusually high OLR. The OLR anomaly corresponds to a large area of ground coverage and coincides with the main epicentral zone. The significance of these observations is explored using data from most recent East Asian earthquake swarm of December 2004 and three other earthquakes. 相似文献
97.
论地球空间信息科学的形成 总被引:61,自引:3,他引:61
从分析地球空间信息科学与全球变化监测和社会可持续发展的关系出发,回顾了地球空间信息科学产生的背景,提出地球空间信息科学的定义及内涵,概括了学科当前的发展状况,提出了现阶段学科研究的主要内容,最后,展望了地球空间信息科学的发展。 相似文献
98.
In the present investigation, an effort has been made to identify the critical sub-watersheds for the development of best
management plan for a small watershed of Eastern India using a hydrological model, namely, AVSWAT2000. A total of 180 combinations
of various management treatments including crops (rice, maize ground nut and soybean), tillage (zero, conservation, field
cultivator, mould board plough and conventional practices) and fertilizer levels (existing half of recommended and recommended)
have been evaluated. The investigation reveled that rice cannot be replaced by other crops such as groundnut, maize, mungbean,
sorghum and soybean since comparatively these crops resulted in higher sediment yield. The tillage practices with disk plough
have been found to have more impact on sediment yield and nutrient losses than conventional tillage practices for the existing
level of fertilizer. Sediment yield decreased in the case of zero tillage, conservation tillage, field cultivator, moldboard
plough, and conservation tillage as compare to conventional tillage. Lowest NO3–N loss was observed in zero tillage in all the fertilizer treatments, whereas field cultivator, moldboard plough and disk
plough resulted in increase of NO3–N loss. As compared to conventional tillage, the losses of soluble phosphorus were increased in moldboard plough. The losses
of organic nitrogen were also increased as fertilizer dose increased. After zero tillage the conservation tillage preformed
better in all the fertilizer treatments as per loss of organic nitrogen and organic phosphorus is concerned. It can be concluded
that the sediment yield was found to be the highest in the case of disk plough followed by moldboard plough, field cultivator,
conventional tillage, field cultivator and least in zero tillage practices. The nutrient losses were found to be in different
order with tillage practices, resulted highest in disk plough tillage practices. In view of sediment yield and nutrient losses,
the conservation tillage practice was found to be the best as the sediment yield is less than the average soil loss whereas
nutrient loss is within the permissible limit. 相似文献
99.
The Siruyeh landslide occurred at the eastern side of the Siruyeh valley, 22 km west of Semirom city, south of Esfahān on
25th March, 2005 with large dimensions (2,400 m long, 450 m wide with total area of 1 km2). The sliding mass blocked the Siruyeh River making a 35-m-high natural dam and 6-acre lake 570,000 m3 in volume that poses a potential threat for the area. The landslide occurred in soil and intensely weathered marls of the
Tarbur and Kashkan Formations (upper Cretaceous–Paleocene age). The overall comparison and interpretation of the gathered
evidence from satellite images, field trips, and laboratory tests show that the most important factors involved in triggering
the Siruyeh landslide in order of importance are heavy precipitation and snow melt and intense concentration of faults and
fractures as well as weathered and weak lithology. 相似文献
100.
河川径流遥感监测研究进展 总被引:5,自引:0,他引:5
河川径流参数是用于地表水资源评估、全球变化监测和生态环境保护的基础数据.现有的河川径流监测数据基于水文监测站点获取.近年来,受经济和政治原因的影响,全球水文监测站点在逐渐减少.随着全球变化研究对区域乃至全球水文监测数据需求的增加,监测站点有限及监测数据格式多样等问题逐渐凸显.过去15年,卫星遥感技术在河川径流监测领域的研究和应用实践,使上述问题的解决成为了可能.总结了河川径流遥感监测方法和技术研究进展,包括地基高低频雷达、航空航天雷达和多光谱卫星遥感监测3个方面;介绍了全球大型河川径流与湖泊水体动态监测重大应用成果及未来研究计划.指出在未来具有全天时、全天候,高时空分辨率,以及多水文要素探测能力遥感卫星发射之前,应充分利用遥感野外观测实验,完善河川径流监测技术方法,并综合应用已有高时空分辨率的多光谱和微波遥感数据,开展径流监测应用研究. 相似文献