全文获取类型
收费全文 | 259063篇 |
免费 | 4380篇 |
国内免费 | 3386篇 |
专业分类
测绘学 | 6898篇 |
大气科学 | 19100篇 |
地球物理 | 54206篇 |
地质学 | 89777篇 |
海洋学 | 21537篇 |
天文学 | 56274篇 |
综合类 | 1024篇 |
自然地理 | 18013篇 |
出版年
2021年 | 2233篇 |
2020年 | 2585篇 |
2019年 | 2844篇 |
2018年 | 3562篇 |
2017年 | 3299篇 |
2016年 | 5710篇 |
2015年 | 4201篇 |
2014年 | 6895篇 |
2013年 | 14178篇 |
2012年 | 6494篇 |
2011年 | 7916篇 |
2010年 | 6972篇 |
2009年 | 9573篇 |
2008年 | 8404篇 |
2007年 | 7949篇 |
2006年 | 9676篇 |
2005年 | 7760篇 |
2004年 | 7633篇 |
2003年 | 7152篇 |
2002年 | 6726篇 |
2001年 | 6003篇 |
2000年 | 5950篇 |
1999年 | 5201篇 |
1998年 | 5235篇 |
1997年 | 5035篇 |
1996年 | 4670篇 |
1995年 | 4434篇 |
1994年 | 4105篇 |
1993年 | 3842篇 |
1992年 | 3632篇 |
1991年 | 3599篇 |
1990年 | 3763篇 |
1989年 | 3508篇 |
1988年 | 3303篇 |
1987年 | 3847篇 |
1986年 | 3409篇 |
1985年 | 4219篇 |
1984年 | 4736篇 |
1983年 | 4410篇 |
1982年 | 4310篇 |
1981年 | 3917篇 |
1980年 | 3638篇 |
1979年 | 3512篇 |
1978年 | 3485篇 |
1977年 | 3280篇 |
1976年 | 3047篇 |
1975年 | 2964篇 |
1974年 | 2920篇 |
1973年 | 3079篇 |
1972年 | 2028篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
The changing nature of, and approaches to, UK coastal management at the start of the twenty-first century 总被引:2,自引:0,他引:2
Peter W French 《The Geographical journal》2004,170(2):116-125
As we enter the twenty-first century, effective coastal management will become more of a central issue for coastal users and governors alike. The new century sees the review of many of the UK's existing management plans, and the subsequent publication of revised versions. Some of these new editions will have to show changes from their predecessors because of natural processes of erosion and accretion, yet other changes will be because of human interference. In this, we mean the continued ignoring of previous management plan recommendations regarding new development and coastal usage. Coastal management needs to adapt and develop, yet along with this, increased education and awareness is also necessary to allow users to understand and appreciate what is being recommended in management plans. 相似文献
994.
Rainfall thresholds for landsliding in the Himalayas of Nepal 总被引:5,自引:0,他引:5
Emmanuel J. Gabet Douglas W. Burbank Jaakko K. Putkonen Beth A. Pratt-Sitaula Tank Ojha 《Geomorphology》2004,63(3-4):131-143
Landsliding of the hillslope regolith is an important source of sediment to the fluvial network in the unglaciated portions of the Himalayas of Nepal. These landslides can produce abrupt increases of up to three orders of magnitude in the fluvial sediment load in less than a day. An analysis of 3 years of daily sediment load and daily rainfall data defines a relationship between monsoonal rainfall and the triggering of landslides in the Annapurna region of Nepal. Two distinct rainfall thresholds, a seasonal accumulation and a daily total, must be overcome before landslides are initiated. To explore the geomorphological controls on these thresholds, we develop a slope stability model, driven by daily rainfall data, which accounts for changes in regolith moisture. The pattern of rainfall thresholds predicted by the model is similar to the field data, including the decrease in the daily rainfall threshold as the seasonal rainfall accumulation increases. Results from the model suggest that, for a given hillslope, regolith thickness determines the seasonal rainfall necessary for failure, whereas slope angle controls the daily rainfall required for failure. 相似文献
995.
We present an evaluation of the procedure by which model prediction bias is examined in palaeolimnological transfer function inference models. We argue that most of the prediction biases commonly reported in the literature are, in fact, fallacious, and are the artificial consequence of the inappropriate manner in which residuals are traditionally examined. We show that the extent of the specious model bias is entirely predictable from first principles and is essentially determined by the strength of the predictive model. We suggest that the analysis of residuals should always be examined as a function of the model's predictions and we discuss the implications of the old and new approaches. 相似文献
996.
997.
This article examines the recent progress of geography education as an academic subfield of geography and as an area of activity in K–12 education. Challenges to both endeavors are described. A restructuring of geography education's research program that focuses on spatial thinking and reasoning and merges applied and theoretical research is proposed. 相似文献
998.
CLARISSA T. KIMBER 《Geographical review》2004,94(3):263-283
ABSTRACT. Investigations of dooryard gardens, kitchen gardens, home gardens, and houselot gardens fall unequally into one of three groupings. The first are those that treat the plants in the gardens as biological entities and define a space considered a culturally controlled biological community or habitat. The second are those that consider plants cultural traits and the space defined by their positions a setting for household activities. The third conceives of plants as design elements within a garden or a landscape that frames a house or provides a setting for formal human performances. Recent decades have witnessed a broadening focus in the study of gardens, from spatial characteristics and biological content to social and cultural concerns such as reciprocity networks, contested spaces, and the concept of “dwelling.” 相似文献
999.
1000.