全文获取类型
收费全文 | 4753篇 |
免费 | 127篇 |
国内免费 | 54篇 |
专业分类
测绘学 | 110篇 |
大气科学 | 417篇 |
地球物理 | 990篇 |
地质学 | 1574篇 |
海洋学 | 426篇 |
天文学 | 882篇 |
综合类 | 11篇 |
自然地理 | 524篇 |
出版年
2021年 | 50篇 |
2020年 | 55篇 |
2019年 | 73篇 |
2018年 | 78篇 |
2017年 | 80篇 |
2016年 | 103篇 |
2015年 | 115篇 |
2014年 | 109篇 |
2013年 | 253篇 |
2012年 | 150篇 |
2011年 | 228篇 |
2010年 | 190篇 |
2009年 | 272篇 |
2008年 | 194篇 |
2007年 | 181篇 |
2006年 | 170篇 |
2005年 | 156篇 |
2004年 | 168篇 |
2003年 | 166篇 |
2002年 | 160篇 |
2001年 | 102篇 |
2000年 | 104篇 |
1999年 | 98篇 |
1998年 | 94篇 |
1997年 | 59篇 |
1996年 | 73篇 |
1995年 | 64篇 |
1994年 | 59篇 |
1993年 | 58篇 |
1992年 | 52篇 |
1991年 | 67篇 |
1990年 | 52篇 |
1989年 | 50篇 |
1988年 | 43篇 |
1987年 | 67篇 |
1986年 | 47篇 |
1985年 | 61篇 |
1984年 | 79篇 |
1983年 | 60篇 |
1982年 | 55篇 |
1981年 | 70篇 |
1980年 | 60篇 |
1979年 | 51篇 |
1978年 | 67篇 |
1977年 | 48篇 |
1976年 | 54篇 |
1975年 | 36篇 |
1974年 | 39篇 |
1973年 | 36篇 |
1971年 | 35篇 |
排序方式: 共有4934条查询结果,搜索用时 15 毫秒
31.
Portable autonomous vertical profiler for estuarine applications 总被引:1,自引:0,他引:1
Janelle V. Reynolds-Fleming Jason G. Fleming Richard A. Luettich 《Estuaries and Coasts》2002,25(1):142-147
The design and implementation of a portable autonomous vertical profiler are documented and example data sets from a mesotidal estuary and a microtidal, wind-driven estuary are presented. The profiler sampling range dynamically adjusts to changes in water column depth, and a typical vertical sampling resolution of 4 cm is attained. Example data show the onset and vertical and temporal extent of stratification in the water column. The profiler is ideal for water quality monitoring programs in shallow estuaries that require frequent profiles of hydrographic, chemical, and biological parameters that can be measured in situ. 相似文献
32.
Benjamin A.S Van Mooy Richard G KeilAllan H Devol 《Geochimica et cosmochimica acta》2002,66(3):457-465
Fluxes of particulate organic carbon (POC) through the oxygen deficient waters in the eastern tropical North Pacific were found to be relatively less attenuated with depth than elsewhere in the eastern North Pacific. The attenuation coefficient (b) for the flux was found to be 0.40 versus the composite value of 0.86 determined by Martin et al. (1987). To examine this further, sinking POC was collected using sediment traps and allowed to degrade in oxic and suboxic experiments. Using a kinetic model, it was found that degradation proceeded at similar rates (roughly 0.8 day−1) under oxic and suboxic conditions, but a greater fraction of bulk POC was resistant to degradation in the suboxic experiments (61% vs. 23%). Amino acids accounted for 37% of POC collected at 75m, but following degradation the value dropped to 17% and 16% in the oxic and suboxic experiments respectively. POC collected from 500m was 10% amino acids. The non-AA component of POC collected at 75m was not degraded under suboxic conditions, while under oxic conditions it was. These results suggest that microbes degrading OC under suboxic conditions via denitrification preferentially utilize nitrogen-rich amino acids. This preferential degradation of amino acids suggests that 9% more nitrogen may be lost via water column denitrification than is accounted for when a more “Redfieldian” stoichiometry for POC is assumed. 相似文献
33.
34.
35.
36.
37.
Application of discovery process models in estimating petroleum resources at the play level in China
Discovery process modeling has gained wide acceptance in the Chinese exploration community. In recent years, a variety of
discovery process models have been applied to the prediction of undiscovered petroleum resources at the play level in sedimentary
basins in China. However, challenging problems have been encountered, particularly when one method alone has been applied
to small plays in nonmarine sedimentary basins or in plays with an unusual order of discovery wells. This paper presents results
gotten by using the lognormal discovery process model of the Geological Survey of Canada and the geoanchored method for three
petroleum plays in basins with different geologic settings. Although the predicted shapes of the parentsize distributions
which use these two models, were not always similar, the expected values of the total resources and the number of fields (pools)
to be discovered are comparable. The combined use of two discovery process models in the same play compensates for the weaknesses
in one method compared with the other and vice versa. Thus, more reliable estimates are the result. 相似文献
38.
39.
In our study, 48 U.S. departments that grant geography PhDs are compared along four measures of academic productivity. Using 1980–1994 as the base period, research productivity of faculty was assessed by counting book titles, as well as authorships in 77 journals. Teaching productivity was determined by placement of PhDs in graduate programs of geography in North America, and by a weighted index of teaching outcomes. Data were summed for departments, but are reported primarily as productivity per person (per FTE count). The results point to a wide variety of departmental profiles, from those departments that appear to emphasize teaching outcomes to those that are more productive in book publishing and journal authorship, with several exhibiting a balance between teaching and research. 相似文献
40.
Sources of Water Supplying Pumpage from Regional Aquifer Systems of the United States 总被引:1,自引:0,他引:1
Richard H. Johnston 《Hydrogeology Journal》1997,5(2):54-63