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   2851篇
  免费   202篇
  国内免费   309篇
测绘学   258篇
大气科学   49篇
地球物理   271篇
地质学   750篇
海洋学   164篇
天文学   10篇
综合类   217篇
自然地理   1643篇
  2024年   9篇
  2023年   28篇
  2022年   78篇
  2021年   122篇
  2020年   97篇
  2019年   106篇
  2018年   94篇
  2017年   132篇
  2016年   120篇
  2015年   108篇
  2014年   121篇
  2013年   195篇
  2012年   154篇
  2011年   171篇
  2010年   126篇
  2009年   167篇
  2008年   152篇
  2007年   163篇
  2006年   191篇
  2005年   185篇
  2004年   147篇
  2003年   138篇
  2002年   132篇
  2001年   87篇
  2000年   69篇
  1999年   63篇
  1998年   46篇
  1997年   38篇
  1996年   23篇
  1995年   25篇
  1994年   15篇
  1993年   12篇
  1992年   8篇
  1991年   3篇
  1990年   5篇
  1989年   1篇
  1988年   5篇
  1987年   7篇
  1986年   7篇
  1985年   3篇
  1984年   3篇
  1983年   3篇
  1982年   2篇
  1976年   1篇
排序方式: 共有3362条查询结果,搜索用时 15 毫秒
71.
呼和浩特市城市边缘区景观格局动态变化研究   总被引:2,自引:0,他引:2  
利用GIS技术对1987,2000年两期航空遥感影像进行空间叠加对比分析,从斑块及景观2个尺度对呼和浩特市城市边缘区景观格局变化进行了研究。结果表明:在斑块尺度上,边缘区两期景观结构均以农田景观为基质,研究期内,农田景观、草地景观等缓慢减少,建筑景观明显增多;在景观尺度上,边缘区景观多样性指数趋于增大,优势度指数趋于降低.景观组分趋于复杂化、破碎化和多元化。分析其影响因素可知:经济发展和城市化的加快、政策导向是变化的根本原因,人口的增加、土地利用方式的改变是变化的直接原因。  相似文献   
72.
The retreat of valley glaciers has a dramatic effect on the stability of glaciated valleys and exerts a prolonged influence on the subsequent fluvial sediment transport regime. We have studied the evolution of an idealized glaciated valley during the period following retreat of ice using a numerical model. The model incorporates a stochastic process to represent deep‐seated landsliding, non‐linear diffusion to represent shallow landsliding and an approximation of the Bagnold relation to represent fluvial sediment transport. It was calibrated using field data from several recent surveys within British Columbia, Canada. We present ensemble model results and compare them with results from a deterministic linear‐diffusion model to show that explicit representation of large landslides is necessary to reproduce the morphology and channel network structure of a typical postglacial valley. Our model predicts a rapid rate of fluvial sediment transport following deglaciation with a subsequent gradual decline, similar to that inferred for Holocene time. We also describe how changes in the model parameters affect the estimated magnitude and duration of the paraglacial sediment pulse. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
73.
大梁金矿是通过森林沼泽景观区开展1:50000和1:25000地球化学测量及综合地质工作而发现的,证明采用的森林沼泽景观中大比例尺化探方法是行之有效的.  相似文献   
74.
以安阳市第五人民医院整体搬迁工程的设计为例,通过设计思路的详细介绍,阐述了传染病医院规划设计中注意到的几点问题。  相似文献   
75.
Twenty‐six sites with remnants of gravelly saprolites (grus) have been located in southeast Sweden. Joint block hills (castle kopjes) and steep rock walls with weathered joints as well as rounded boulders are documented to have an origin in deep weathering and subsequent stripping of saprolites. The saprolite remnants and landforms result from the fragmentation of the re‐exposed sub‐Cambrian peneplain along fracture systems. Only shallow saprolites occur on the elevated intact parts of the sub‐Cambrian peneplain, while saprolites up to 20 m thick are encountered in areas where the sub‐Cambrian peneplain is fractured and dissected. Neogene uplift with reactivation of the weathering system is thought to be the main cause of saprolite formation. Deep weathering is thus judged to have been the major agent of landform formation in the study area, while glacial and glaciofluvial erosion has contributed mainly by stripping saprolites, detaching corestones, and plucking joint blocks along weathered joints.  相似文献   
76.
ABSTRACT. Alaska was strategically key to the U.S. defense plan during the cold war (1946–1989). As such, it was the scene of an enormous and sustained military investment, the effect of which was amplified by Alaska's undiversified economy, sparse development, small resident population, and marginalized political status at the beginning of the era. The strong military presence affected Alaskan demographics, economic development, and infrastructure and figured prominently in the admission of Alaska to the union in 1959. The high profile and long‐term presence of the U.S. military had such a dramatic affect on the course of Alaska that the result was tantamount to a “militarized landscape.”  相似文献   
77.
Throughout Australia thousands of volunteers are engaged in Landcare projects that should help rehabilitate degraded landscapes. Many of these projects involve tree planting, but their seed is not necessarily of local provenance. Based on a survey of 85 Landcare groups working in the Hawkesbury–Nepean catchment, data were collected about Landcare groups' knowledge of their seed source, understanding of local provenance and the ecosystem in which they were planting trees and the source of funding for their projects. The findings from the study indicate that about one in five (21%) of the groups surveyed that introduced plant material were not aware of local provenance issues. Indirect indications were that a large number of Landcare groups state-wide may be doing more harm than good to the landscape while trying to rehabilitate it. The data also showed that one in seven (13%) of the groups funded by the Australian Government through the Natural Heritage Trust (NHT) had limited awareness of local provenance issues. With millions of dollars being spent on 'works on the ground', it would be prudent to allocate some funds to document and monitor current Landcare activities, so that the environmental outcomes can be quantified and more effective Landcare policies can be developed in the future.  相似文献   
78.
Some considerations concerning seismic geomorphology and paleoseismology   总被引:3,自引:1,他引:3  
F. Dramis  A.M. Blumetti   《Tectonophysics》2005,408(1-4):177
Seismic geomorphology studies landforms which developed in connection with earthquakes. Among them, two different end members may be distinguished: 1) seismo-tectonic landforms, including surface faults and fractures, land uplift and subsidence at different scales, surface bulges, elongate ridges, and any other permanent ground deformations directly related to tectonic stress, and 2) seismo-gravitational landforms, such as landslides, deep-seated gravitational slope deformations, sinkholes, and fissures due to sediment compaction or liquefaction and sand blows, connected with both seismic shaking and gravitational stress.A clear-cut distinction between the two categories of landforms is not always easy to make (and in many instances not really useful), while there are, in many cases, ground effects that might be (and should be) considered as simultaneous combinations of seismo-tectonic and seismo-gravitational processes. This applies especially to surface fracturing and faulting which could be the combined result of tectonic stress, stress produced by seismic shaking, and gravitational stress.The objective of this paper is to review selected case histories mainly from Italy and the Mediterranean region, in order to show the importance of a comprehensive study of earthquake-generated landforms for understanding the seismicity level of the area under investigation. We argue that in earthquake prone areas, seismic landforms often constitute typical patterns (seismic landscapes) whose recognition, mapping and paleoseismological analysis may help in the evaluation of seismic hazards.  相似文献   
79.
The recent evolution of the north German Basin (NGB), which is presently a low-seismic area, was partly affected by glacial loading and unloading of the ice masses. Major stresses acting within the NGB are induced by the North-Atlantic ridge push, the ongoing Alpine collision, and the post-glacial rebound of Fennoscandia. Present-day horizontal stresses within the NGB are directed generally NW–SE, but fan and bend north of 52°N towards NNE. Major basement faults are directed NW–SE, minor faults NE–SW and NNE–SSW, and are clearly detectable in geomorphological and satellite lineaments. Furthermore, the drainage pattern and the distribution of lakes in northern Germany follow exactly block boundaries and, hence, mark zones of present-day subsidence. The understanding of the post-glacial morphology and reactivation of faults requires a view into the very heterogeneous crust and upper mantle below the NGB. The re-adjustment of the individual fault blocks during post-glacial relaxation of the lithosphere leads to differential, crust-dependent uplift and, probably, to the formation of Urstrom valleys. The Urstrom valleys and terminal moraines in northern Germany appear to parallel the major tectonic lineaments and lithospheric “block” boundaries. The lithospheric memory is expressed in the post-glacial landscape evolution of the NGB.  相似文献   
80.
The Zhangye Region of Gansu Province is an important agricultural base in arid northwestern China. During the twentieth century, especially in the last five decades, the region has experienced sandy desertification. To document the status and causes of this deterioration, satellite images, meteorological and socioeconomic data to assess landscape change from 1993 to 2002 were interpreted and analyzed. The results show that during the intervening 9-year period the area of sandy lands has increased by 642.2 km2, which consist of aeolian sand dune (357.1 km2) and potential sandy land (216.3 km2). Although the development and reversion of sandy desertification co-exist, the sandy desertification in this area seems serious and is attributable to the irrational use of water and land.  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