全文获取类型
收费全文 | 432篇 |
免费 | 24篇 |
国内免费 | 22篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 2篇 |
地球物理 | 200篇 |
地质学 | 123篇 |
海洋学 | 37篇 |
天文学 | 4篇 |
综合类 | 4篇 |
自然地理 | 92篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 2篇 |
2019年 | 10篇 |
2018年 | 6篇 |
2017年 | 11篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 19篇 |
2013年 | 16篇 |
2012年 | 8篇 |
2011年 | 21篇 |
2010年 | 10篇 |
2009年 | 29篇 |
2008年 | 41篇 |
2007年 | 24篇 |
2006年 | 30篇 |
2005年 | 21篇 |
2004年 | 17篇 |
2003年 | 18篇 |
2002年 | 14篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有478条查询结果,搜索用时 15 毫秒
11.
1 INTRODUCTIONFrom 1989 to 1993, as project managers of the UNDP/UNESCO project entitled Regional TrainingProgramme on Erosion and Sedimentation for Asia, the writers had the privilege of meeting manyoutstanding hydraulic engineers of this region and came to learn of some important erosion andsedimentation problems thereof. Some issues as noted by the writers are presented in the followingalong the some comments. These issues are mainly concerned with rivers. It should be stated tha… 相似文献
12.
J. M. Roels 《地球表面变化过程与地形》1985,10(6):587-595
The paper is prompted by apparent deficiencies in the design of plot studies in regional erosion surveys. The principal shortcomings of observational erosion research have been poor sampling design and inadequate analyses of data. The paper identifies various sources of bias which must be taken into account before plot data can be extrapolated to land units in a regional survey. Judging from soil loss data of a case-study in the Ardèche rangelands one may conclude that even accurate plot measurements can still be rather a rough basis for regional erosion assessment. Finally, the paper highlights strategies that might be used to improve erosion sampling. 相似文献
13.
Liancong LUO Boqiang QIN Guang GAO Guangwei ZHU Jinshan ZHANG 《国际泥沙研究》2006,21(4):312-320
1 INTRODUCTION Large amounts of nutrients and contaminants such as trace metals are transported into large lakes frominflow rivers and then absorbed onto or associated with fine-grained sediment particles (Sheng and Lick,1979). The nutrients and contamina… 相似文献
14.
Calvin W. Rose Bofu Yu William L. Hogarth Augustine E. A. Okom Hossein Ghadiri 《Journal of Hydrology》2003,280(1-4):33-51
The spatial and size distribution of sediment deposited from short periods of overland flow due to the effect of a simulated grass buffer strip was measured for low slopes of 1.6, 3.4 and 5.1%. These data were analysed so as to critically evaluate two alternative models of the process of re-entrainment of recently deposited sediment. A model of re-entrainment, previously thought to be appropriate only for a steady-state or equilibrium situation, was found to give better agreement with experiments than did a model previously used in the literature on this subject. 相似文献
15.
F. García-Rodríguez N. Mazzeo P. Sprechmann D. Metzeltin F. Sosa H.C. Treutler M. Renom B. Scharf C. Gaucher 《Journal of Paleolimnology》2002,28(4):457-468
Paleolimnological techniques were used to assess human impacts onLake Blanca, a small (0.6 km2), coastal fresh waterbodyin southern Uruguay, which is the drinking water source for 100,000 localresidents. We retrieved a core that extends to about 1100 14Cyr BP. 210Pb ages, organic mater, CO3, totalcarbon, nutrients, fossil pigments and diatoms allowed us to establishlimnological conditions before and after cultural impacts. Soil removal(1880–1960) and intensive cattle and sheep grazing (1943–1966) ledto gully formation in the catchment. This watershed erosion resulted inincreased sedimentation rates. The aquatic system appeared to be mesotrophicwith dominance of epibenthic diatoms until 1966, at which timeeutrophication intensified with forestry activities. Increases in nutrients, aswell as blooms of planktonic diatoms, were observed. During the last decade,tourist/urban development as well as high drinking water demand caused areduction in lake area. Subsequent marked increases in rainfall led to furtherphytoplankton blooms and macrophyte proliferation. 相似文献
16.
Cliff recession on the high rocky coast between Gabicce and Pesaro Adriatic sea causes a wide range of mass movement processes on the whole slope, affecting both the bedrock and the overburden. The outcropping late Miocene rock formations are represented by marls, marly limestones, dark laminated mudstones and bedded sandstones and marls. Mass movements are common because of stratification and discontinuities in the rocks that, together with the presence of groundwater and weathering processes, reduce the overall strength of the slopes. A model for the evolution of this coastal area is proposed, which involves cyclic basal erosion, followed by mass movement that favours debris accumulation at the base of the cliff. The longshore currents have to then remove the material before a new cycle can begin. 相似文献
17.
Norikazu Matsuoka Cline E. Thomachot Chiaki T. Oguchi Tamao Hatta Masahiro Abe Hiroyuki Matsuzaki 《Geomorphology》2006,81(3-4):408-420
Rates and processes of rock weathering, soil formation, and mountain erosion during the Quaternary were evaluated in an inland Antarctic cold desert. The fieldwork involved investigations of weathering features and soil profiles for different stages after deglaciation. Laboratory analyses addressed chemistry of rock coatings and soils, as well as 10Be and 26Al exposure ages of the bedrock. Less resistant gneiss bedrock exposed over 1 Ma shows stone pavements underlain by in situ produced silty soils thinner than 40 cm and rich in sulfates, which reflect the active layer thickness, the absence of cryoturbation, and the predominance of salt weathering. During the same exposure period, more resistant granite bedrock has undergone long-lasting cavernous weathering that produces rootless mushroom-like boulders with a strongly Fe-oxidized coating. The red coating protects the upper surface from weathering while very slow microcracking progresses by the growth of sulfates. Geomorphological evidence and cosmogenic exposure ages combine to provide contrasting average erosion rates. No erosion during the Quaternary is suggested by a striated roche moutonnée exposed more than 2 Ma ago. Differential erosion between granite and gneiss suggests a significant lowering rate of desert pavements in excess of 10 m Ma− 1. The landscape has been (on the whole) stable, but the erosion rate varies spatially according to microclimate, geology, and surface composition. 相似文献
18.
水土腐蚀性评价标准与混凝土结构耐久性设计的防护标准是相互作用,相互影响的。本文通过2个地下水实例,比较了桩基础和地下室底板在不同规范体系下水土腐蚀性评价标准和防护标准的差异。腐蚀环境越严重,混凝土结构耐久性设计差异越大,因此,有必要统一水土腐蚀性评价标准和混凝土结构耐久性设计的防护标准。针对SO42-和CL-腐蚀性评价差异较大的情况,本文给出了干湿交替作用及其强度的定义,提出了一种统一水土腐蚀性评价指标及其分级的建议方案。干湿交替作用是指在固体表面能够形成液相水与气相水交替转换或持续转换的一种现象,干湿交替作用强度定义为固体表面液态水的相对蒸发速率和固体表层饱和度的乘积。 相似文献
19.
区域土壤侵蚀定量研究的国内外进展 总被引:27,自引:0,他引:27
由于水土保持宏观决策的需要、土壤侵蚀学科自身的进步和全球变化研究的促进,过去的10多年来,国内外研究者对区域尺度土壤侵蚀研究给予了高度重视。已经开展的主要研究包括:全球和区域(包括国家尺度)土壤侵蚀调查、区域土壤侵蚀过程和尺度效应、区域土壤侵蚀因子和区域土壤侵蚀模型等。将区域土壤侵蚀作为现代陆地地表过程的一部分,充分考虑全球变化的影响,集成土壤侵蚀研究成果与遥感和GIS技术,开发分布式区域土壤侵蚀模型,成为区域土壤侵蚀定量评价研究的基本趋势。在对国内外区域土壤侵蚀定量评价研究评述的基础上,提出我国近期在区域土壤侵蚀方面研究的重点问题为:区域土壤侵蚀过程及其尺度效应的量化描述、区域土壤侵蚀模型开发、区域土壤侵蚀动态模拟与趋势预测、区域土壤侵蚀与全球变化关系研究和区域土壤侵蚀数据处理与管理方法。 相似文献
20.