全文获取类型
收费全文 | 89047篇 |
免费 | 1115篇 |
国内免费 | 1440篇 |
专业分类
测绘学 | 2910篇 |
大气科学 | 6617篇 |
地球物理 | 17346篇 |
地质学 | 34118篇 |
海洋学 | 6957篇 |
天文学 | 16189篇 |
综合类 | 2267篇 |
自然地理 | 5198篇 |
出版年
2021年 | 631篇 |
2020年 | 656篇 |
2019年 | 727篇 |
2018年 | 6022篇 |
2017年 | 5251篇 |
2016年 | 4244篇 |
2015年 | 1234篇 |
2014年 | 1742篇 |
2013年 | 3436篇 |
2012年 | 2808篇 |
2011年 | 5120篇 |
2010年 | 4251篇 |
2009年 | 5199篇 |
2008年 | 4373篇 |
2007年 | 4854篇 |
2006年 | 2557篇 |
2005年 | 2149篇 |
2004年 | 2323篇 |
2003年 | 2236篇 |
2002年 | 2045篇 |
2001年 | 1692篇 |
2000年 | 1614篇 |
1999年 | 1279篇 |
1998年 | 1287篇 |
1997年 | 1329篇 |
1996年 | 1059篇 |
1995年 | 1079篇 |
1994年 | 1001篇 |
1993年 | 896篇 |
1992年 | 861篇 |
1991年 | 798篇 |
1990年 | 838篇 |
1989年 | 792篇 |
1988年 | 775篇 |
1987年 | 875篇 |
1986年 | 756篇 |
1985年 | 962篇 |
1984年 | 1008篇 |
1983年 | 983篇 |
1982年 | 883篇 |
1981年 | 916篇 |
1980年 | 848篇 |
1979年 | 756篇 |
1978年 | 715篇 |
1977年 | 691篇 |
1976年 | 624篇 |
1975年 | 603篇 |
1974年 | 609篇 |
1973年 | 611篇 |
1971年 | 374篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Carlsberg Ridge, northern Indian Ocean: gravity and isostasy 总被引:1,自引:0,他引:1
992.
993.
D. C. OVADIA 《International journal of geographical information science》2013,27(2):190-191
994.
Jonathan D. Phillips 《自然地理学》2013,34(4):321-332
Landscapes, environments, and ecosystems (i.e., places) are historically and spatially contingent and therefore unique. Generalizations and laws are based on “all other things being equal.” Owing to historical and spatial contingency, all other things are never completely equal and often do not approach that ideal closely enough to allow for reliable prediction. The problem is illustrated by examining effects of grazing and fire suppression on transitions between grass and woody vegetation communities. In three different environments in the southern United States (central Texas, southwestern Virginia, and eastern North Carolina), three different relationships exist between grazing and fire regime, and vegetation. Other examples are common in the geographic and environmental literature. This suggests that the search for a single applicable generalization or predictive model of a given human-induced environmental change that can be applied without accounting for the particular characteristics of places may be futile. Several general ways to address this issue are suggested. First is the recognition that place matters. Conditions specific to a location or region will influence what, how, or even if generalizations apply. Second is the adoption of a “demographic” approach. This is based on the idea that for places, like people, it is possible to make aggregate or probabilistic generalizations or predictions, but these cannot be applied to deterministic prediction of individuals. Third is a synoptic approach based on forecasting not via simple cause-effect relationships, but based on a typology of situations that recognizes and incorporates the unique characteristics of site and situation. Several converging threads of inquiry in geography and geosciences explicitly or implicitly address the issue of historical and spatial contingency. [Key words: landscape, environment, place, prediction.] 相似文献
995.
A. Geddes D.A. Elston M.E.A. Hodgson R. V. Birnie 《International journal of geographical information science》2013,27(4):785-803
Handling of uncertainty in the estimation of values from source areas to target areas poses a challenge in areal interpolation research. Stochastic model-based methods offer a basis for incorporating such uncertainty, but to date they have not been widely adopted by the GIS community. In this article, we propose one use of such methods based in the problem of interpolating count data from a source set of zones (parishes) to a more widely used target zone geography (postcode sectors). The model developed also uses ancillary statistical count data for a third set of areas nested within both source and target zones. The interpolation procedure was implemented within a Bayesian statistical framework using Markov chain Monte Carlo methods, enabling us to take account of all sources of uncertainty included in the model. Distributions of estimated values at the target zone level are presented using both summary statistics and as individual realisations selected to illustrate the degree of uncertainty in the interpolation results. We aim to describe the use of such stochastic approaches in an accessible way and to highlight the need for quantifying estimation uncertainty arising in areal interpolation, especially given the implications arising when interpolated values are used in subsequent analyses of relationships. 相似文献
996.
The Haji-Gak iron deposit of eastern Bamyan Province, eastern Afghanistan, was studied extensively and resource calculations
were made in the 1960s by Afghan and Russian geologists. Recalculation of the resource estimates verifies the original estimates
for categories A (in-place resources known in detail), B (in-place resources known in moderate detail), and C1 (in-place resources estimated on sparse data), totaling 110.8 Mt, or about 6% of the resources as being supportable for the
methods used in the 1960s. C2 (based on a loose exploration grid with little data) resources are based on one ore grade from one drill hole, and P2 (prognosis) resources are based on field observations, field measurements, and an ore grade derived from averaging grades
from three better sampled ore bodies. C2 and P2 resources are 1,659.1 Mt or about 94% of the total resources in the deposit. The vast P2 resources have not been drilled or sampled to confirm their extent or quality. The purpose of this article is to independently
evaluate the resources of the Haji-Gak iron deposit by using the available geologic and mineral resource information including
geologic maps and cross sections, sampling data, and the analog-estimating techniques of the 1960s to determine the size and
tenor of the deposit. 相似文献
997.
998.
Susceptibility assessment of earthquake-triggered landslides in El Salvador using logistic regression 总被引:13,自引:0,他引:13
This work has evaluated the probability of earthquake-triggered landslide occurrence in the whole of El Salvador, with a Geographic Information System (GIS) and a logistic regression model. Slope gradient, elevation, aspect, mean annual precipitation, lithology, land use, and terrain roughness are the predictor variables used to determine the dependent variable of occurrence or non-occurrence of landslides within an individual grid cell. The results illustrate the importance of terrain roughness and soil type as key factors within the model — using only these two variables the analysis returned a significance level of 89.4%. The results obtained from the model within the GIS were then used to produce a map of relative landslide susceptibility. 相似文献
999.
G. Wilson D. Damaske H.-D. Möller K. Tinto T. Jordan 《Geophysical Journal International》2007,170(1):93-100
Magnetic anomaly data are presented from a new helicopter-borne high-resolution aeromagnetic survey in southern McMurdo Sound. Anomaly data have been acquired at a common 305 m elevation above the McMurdo and southern McMurdo ice shelves and draped over the volcanic islands that pin them. The resulting anomaly patterns provide a significant advance in the understanding of the rift related geology beneath the floating ice shelves. More extensive Erebus Volcanic Province (McMurdo Volcanic Group) rocks are indicated along with a significant blanket of glaci-volcaniclastic sediment on the seafloor between the volcanic islands in southern McMurdo Sound. These glaci-volcaniclastic sediments are inferred to originate from former grounding of the southern McMurdo Ice Shelf as a marine ice sheet. A strong N–S fabric is also observed in the anomaly data suggesting that the rift structure observed in the Victoria Land basin persists to the south beneath the McMurdo and southern McMurdo ice shelves. W–N–W transfer faults identified within the Transantarctic Mountain rift flank to the west are not obvious in the aeromagnetic data set, implying that the 'Discovery Accommodation Zone' may be restricted to the region between a southward extension of the range bounding fault that marks the limit of the Victoria Land Basin and the right lateral offset in the Transantarctic Mountain front in southern Victoria Land. 相似文献
1000.
This study of fossils (pollen, plant macrofossils, stomata and fish) and sediments (lithostratigraphy and geochemistry) from
the Wendel site in North Dakota, USA, emphasizes the importance of considering ground-water hydrology when deciphering paleoclimate
signals from lakes in postglacial landscapes. The Wendel site was a paleolake from about 11,500 14C yr BP to 11,100 14C yr BP. Afterwards, the lake-level lowered until it became a prairie marsh by 9,300 14C yr BP and finally, at 8,500 14C yr BP, an ephemeral wetland as it is today. Meanwhile, the vegetation changed from a white spruce parkland (11,500 to 10,500
14C yr BP) to deciduous parkland, followed by grassland at 9,300 14C yr BP. The pattern and timing of these aquatic and terrestrial changes are similar to coeval kettle lake records from adjacent
uplands, providing a regional aridity signal. However, two local sources of ground water were identified from the fossil and
geochemical data, which mediated atmospheric inputs to the Wendel basin. First, the paleolake received water from the melting
of stagnant ice buried under local till for about 900 years after glacier recession. Later, Holocene droughts probably caused
the lower-elevation Wendel site to capture the ground water of up-gradient lakes. 相似文献