全文获取类型
收费全文 | 3588篇 |
免费 | 473篇 |
国内免费 | 671篇 |
专业分类
测绘学 | 392篇 |
大气科学 | 682篇 |
地球物理 | 626篇 |
地质学 | 1045篇 |
海洋学 | 483篇 |
天文学 | 68篇 |
综合类 | 263篇 |
自然地理 | 1173篇 |
出版年
2024年 | 11篇 |
2023年 | 42篇 |
2022年 | 123篇 |
2021年 | 145篇 |
2020年 | 167篇 |
2019年 | 164篇 |
2018年 | 122篇 |
2017年 | 137篇 |
2016年 | 166篇 |
2015年 | 170篇 |
2014年 | 199篇 |
2013年 | 283篇 |
2012年 | 218篇 |
2011年 | 207篇 |
2010年 | 176篇 |
2009年 | 183篇 |
2008年 | 212篇 |
2007年 | 241篇 |
2006年 | 231篇 |
2005年 | 180篇 |
2004年 | 184篇 |
2003年 | 161篇 |
2002年 | 147篇 |
2001年 | 120篇 |
2000年 | 99篇 |
1999年 | 113篇 |
1998年 | 89篇 |
1997年 | 91篇 |
1996年 | 63篇 |
1995年 | 63篇 |
1994年 | 46篇 |
1993年 | 40篇 |
1992年 | 33篇 |
1991年 | 18篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1978年 | 3篇 |
排序方式: 共有4732条查询结果,搜索用时 109 毫秒
991.
The morphological evolution, hydrodynamics and sediment dynamics of the lower Ebro are studied from historical and current
data in order to determine the main changes that have governed the evolution of the Ebro channel near the river mouth during
the last few centuries. The evolution of the mouth of this river during the last 2000-years, from an estuary to a delta, is
interpreted as a process that has been accelerated by human land management. However, an inverse trend has been observed during
recent decades: (1) the river mouth has been affected by erosion due to a drastic decrease in the river sediment discharge,
and (2) the lower Ebro tends to evolve towards a quasi-permanent salt-wedge estuary as a consequence of the decrease in the
river water discharge. Freshwater and sediment discharge decreases are mainly related to intense river water management during
this century. The salt wedge favours erosion in the river banks, widening the river channel and causing an aggradational trend
in the lower Ebro. Accretion-erosion rates and the sediment budget in the river mouth are estimated for different conditions.
Received: 13 November 1995 · Accepted: 17 June 1996 相似文献
992.
Ute C. Herzfeld Craig S. Lingle Cecily Freeman Chris A. Higginson Michael P. Lambert Li-Her Lee Vera A. Voronina 《Mathematical Geology》1997,29(6):859-890
The Antarctic Ice Sheet plays a major role in the global system, and the large ice streams discharging into the circumpolar
sea represent its gateways to the world’s oceans. Satellite radar altimeter data provide an opportunity for mapping surface
elevation at kilometerresolution with meteraccuracy. Geostaristical methods have been developed for the analysis of these
data. Applications to Seasat data and data from the Geosat Exact Repeat Mission indicate that the grounding line of Lambert
Glacier/Amery Ice Shelf, the largest ice stream in East Antarctica, has advanced 10–12 km between 1978 and 1987–89. The objectives
of this paper are to explore possibilities and limitations of satellite-altimetry-based mapping to capture changes for shorter
time windows and for smaller areas, and to investigate some methodological aspects of the data analysis. We establish that
one season of radar altimeter data is sufficient for constructing a map. This allows study of interannual variation and is
the key for a limeseries analysis approach to study changes in ice streams. Maps of the lower Lambert Glacier and the entire
Amery Ice Shelf are presented for austral winters 1978, 1987, 1988, and 1989. As a first step toward understanding the dynamics
of the ice-stream/iceshelf system, elevation changes are calculated for grounded ice, the grounding zone, and floating ice.
In the absence of (sufficient) surface gravity control for the Lambert Glacier/Amery Ice Shelf area, altimetry-based maps
may facilitate improvement of geoid models as they provide constraints on the terrain correction in the inverse gravimetric
problem. 相似文献
993.
红树林海岸带研究的一个新方向—生物地貌研究 总被引:3,自引:0,他引:3
介绍了红树林海岸生物地貌研究产生的背景,讨论了研究的目标和研究的主要内容,以及几点建议性的研究方法。 相似文献
994.
Rosi LIEM Research Engineers Institute of Hydraulic Engineering Water Resources Management Aachen Univer-s of Technology Germany Volker SPORK Research Engineers Institute of Hydraulic Engineering Water Resources Management Aachen Univer- 《国际泥沙研究》1997,(3)
I.INTRODUCTIONToconstructanidealmeasuringdeviceforin-situstUdiesincomparisontolaboratorydeVicesastrongeremphasishastobesetonthehandlingoftheSystemandtheresistanceunderwater,whichaughtbethereasonwhynotmanyapproachesonrealin-situinvestigationwerecaaccedoutlately.Sincetheedupandtheconstructionseemtodemandahigheramountofcostsandeffort,quasiin-siamstudieswerecAnedoutrefetringtoanundisturbedsedimentsampledrawnfromthesedimentbedoutofthewaterintothesamplingchamberofameasuringdevice.Evenifthisisa… 相似文献
995.
The equivalent operator equation is derived from the full primitive nonlinear equations of the atmospheric motion and the properties and physical senses of the operators are studied.In the infinite dimensional Hilbert space,the global asymptotic behavior of the atmosphere system with the non-stationary external forcing is studied under the assumption of the bounded external forcing.The existence theorems of the global absorbing set and the global attractor are obtained.Thus,the conclusions deduced from the large-scale atmosphere(Li and Chou 1996a;1996b) are extended to the general atmosphere. 相似文献
996.
3S——应用领域十分广泛的高新技术 总被引:2,自引:0,他引:2
遥感(RS)、地理信息系统(GIS)和全球定位系统(GPS)统简3S,是近年来发展迅猛、应用广泛的高新技术。本文介绍了应用遥感技术对黄土高原信息系统的研究工作。阐述了支持区域规划与辅助决策的智能地理信息系统的数据模型和物理数据结构的设计与实现。说明了将GPS与RS和GIS组成的信息系统相结合,提高系统性能的方法 相似文献
997.
西宁盆地大墩岭黄土剖面L1、L2、L15中存在3层古风成砂。沉积年代及各种环境的分析表明,这3层风成砂分别代表了1.2MaB.P.以来西宁盆地中更新世初,中更新世末和晚更新世晚期发生的3次较大规模的流沙活动。进一分析得出西宁盆地的沙漠化正逆过程受地第四纪全球气候波动变化以及青藏高原隆升的影响。第四经青藏高原冰川的冰缘作用为其边缘的沙漠、黄土沉积提供了丰富的物质来源。 相似文献
998.
SEASONAL CHANGES OF SOIL MOISTURE INDUCED BY INCREASED CO2 AS SIMULATED BY THE ATMOSPHERIC GENERAL CIRCULATION AND MIXED LAYER OCEAN MODEL
下载免费PDF全文
![点击此处可从《Acta Meteorologica Sinica》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The atmospheric general circulation model coupled to the mixed layer ocean model has been used to simulate thechanges of the global soil moisture.Comparing the simulated results with observations,it is shown that the model is ca-pable of doing sensitive experiments about the carbon dioxide change.The 2×CO_2/1×CO_2 comparison shows that there are the obvious changes of the soil moisture in the global forfour seasons.There are the wet soil moisture in the lower latitudes of both hemispheres and dry soil moisture in the mid-dle latitudes of both hemispheres for four seasons.The dry soil moisture in summer and wet in other seasons are foundin the northern higher latitudes.The analyses of the physical feedbacks responsible for the CO_2-induced changes of soil moisture show that the bud-gets of the surface water and heat are the important factors. 相似文献
999.
Genetic algorithms in seismic waveform inversion 总被引:24,自引:0,他引:24
1000.