全文获取类型
收费全文 | 6695篇 |
免费 | 1219篇 |
国内免费 | 1788篇 |
专业分类
测绘学 | 678篇 |
大气科学 | 1342篇 |
地球物理 | 1757篇 |
地质学 | 2812篇 |
海洋学 | 803篇 |
天文学 | 293篇 |
综合类 | 477篇 |
自然地理 | 1540篇 |
出版年
2024年 | 32篇 |
2023年 | 96篇 |
2022年 | 267篇 |
2021年 | 277篇 |
2020年 | 346篇 |
2019年 | 343篇 |
2018年 | 297篇 |
2017年 | 341篇 |
2016年 | 333篇 |
2015年 | 382篇 |
2014年 | 417篇 |
2013年 | 442篇 |
2012年 | 478篇 |
2011年 | 479篇 |
2010年 | 363篇 |
2009年 | 439篇 |
2008年 | 424篇 |
2007年 | 465篇 |
2006年 | 458篇 |
2005年 | 381篇 |
2004年 | 362篇 |
2003年 | 304篇 |
2002年 | 270篇 |
2001年 | 227篇 |
2000年 | 245篇 |
1999年 | 182篇 |
1998年 | 193篇 |
1997年 | 151篇 |
1996年 | 128篇 |
1995年 | 104篇 |
1994年 | 102篇 |
1993年 | 100篇 |
1992年 | 64篇 |
1991年 | 61篇 |
1990年 | 29篇 |
1989年 | 35篇 |
1988年 | 26篇 |
1987年 | 21篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有9702条查询结果,搜索用时 15 毫秒
121.
山岳型旅游区人文建筑环境后效与调控模型 总被引:4,自引:1,他引:4
许多山岳型旅游区内或其流域上游,都建有人文建筑,而且在急剧增多,导致自然环境日趋恶化,其中乱建疗养院和旅馆的影响最为严重。通过地监测并全面分析张家界环境演变趋势,发现住宿施对环境的影响,比其他游乐设施更为明显。张家界国家森林公园生态环境的脆弱因子是金鞭溪水质。金鞭溪水质恶化主要表现为蓝藻,绿藻迅速繁殖,感官质量下降。主要原因是磷污染较重,总磷年均值100%超标。本文提出了基于环境脆弱因子的动态阈值调控模型,通过计算得出:在不超出张家界景区最为脆弱的环境因子-金鞭溪水质标准:总磷≤0.02前提下,金鞭溪上游接待区住宿设施生态阈值的动态系列:春季临界床位数为1186,夏季为3057,冬季为545,秋季为333。目前的建筑规模已超过了金鞭溪上游接待区住宿设施生态阈值。 相似文献
122.
123.
Spatial patterns and replacement in ten cacti were studied on an island of the coastal desert of Sinaloa, México. Four platyopuntias had 74–92% of their individuals beneath shrub canopies, whereas three globose cacti, one columnar cactus and two cylindropuntias had similar or higher percentages of individuals in open spaces. This study advances the idea that open-space colonization is enhanced by less harsh physical and biotic conditions in coastal deserts, and by certain morphological and physiological adaptations of cacti. The absence of nurse-shrub replacement is understood as a result of induced co-existence by physical damage from cyclones in the coastal zone. 相似文献
124.
David Delaney 《The Professional geographer》2002,54(1):6-14
This essay is a revision of a paper prepared for an NSF workshop on race and geography. Participants in the workshop were asked to offer their views on the topic and our suggestions for further research. This contribution explores some aspects of the relationship and relevance of geography to the question of race in North America. It touches on three “places” that constitute the discipline: the place of research, the place of teaching, and the workplace. With respect to research, it suggests some promising lines of inquiry. Among these are studies of the relationship of scale to the politics of identity and studies of “passing” in connection with studies of geographies of experience and geographies of power. 相似文献
125.
Geographically or sociologically defined resource management units, such as buffer zones or community resource management territories, seek to harmonize local land–use practices with protected–area management objectives. The geographically restricted nature of these models often results in simplistic representations of society–nature relations over time and space. Conservation areas are misrepresented as ecologically and socially homogeneous, as well as politically neutral. This study examines the limits of a spatially defined conservation and development project designed around the physical geographical unit of the watershed at Lake Nakuru National Park, Kenya. It argues that politically motivated violence that has plagued the area since the early 1990s has severely undermined the suitability of such narrowly defined conservation territories. Specifically, the case study points to the permeability of the Lake Nakuru watershed to national and regional political forces that ultimately constrain participation in conservation activities. The spaces of conservation and development must be enlarged to include these extralocal arenas and processes if environmental problems are to be effectively addressed. 相似文献
126.
127.
128.
高山增水效应及其水资源意义 总被引:9,自引:1,他引:9
根据高山上云、雾、雨、雪、径流等水资源丰富现象,分析了高山冰川、植被、地形等与汽-水作用关系,提出高山增水效应概念和高山区水资源开发与保护的新思路。高大山体及其造成的垂向对流、高山冰川和高山植被共同作用形成了高山增水效应,并形成良性增水系统。山体愈高大,增水效应愈明显。对内陆干旱地区开发利用更多的高山水资源具有意义。 相似文献
129.
130.