全文获取类型
收费全文 | 292篇 |
免费 | 12篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 27篇 |
地球物理 | 59篇 |
地质学 | 120篇 |
海洋学 | 38篇 |
天文学 | 34篇 |
自然地理 | 29篇 |
出版年
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 11篇 |
2017年 | 5篇 |
2016年 | 11篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 27篇 |
2012年 | 9篇 |
2011年 | 12篇 |
2010年 | 11篇 |
2009年 | 19篇 |
2008年 | 12篇 |
2007年 | 5篇 |
2006年 | 9篇 |
2005年 | 15篇 |
2004年 | 6篇 |
2003年 | 13篇 |
2002年 | 7篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 4篇 |
1967年 | 1篇 |
排序方式: 共有311条查询结果,搜索用时 125 毫秒
1.
Gang Yang Aaron Zimmerman Nicole C. Hurtig Svetoslav V. Georgiev Vineet Goswami Judith L. Hannah Holly J. Stein 《Geostandards and Geoanalytical Research》2020,44(2):231-242
Rhenium–osmium geochronometry for samples with low Re and complex matrices requires improved Re extraction methods. Here, we investigate plausible controls on efficiency and efficacy of Re extraction during our anion resin bead purification. Four different protocols are compared, each isolating a single variable to test. Rhenium concentrations for solutions at each step of each protocol document differences in chemical recovery/yield. The negative‐thermal ionisation mass spectrometry (N‐TIMS) signal intensity serves as a proxy for Re yield and purity. These data document correlations between the N‐TIMS signal intensity and (a) the duration of anion resin bead conditioning prior to loading with Re‐bearing solution, and (b) both duration and strength of nitric acid used during rinsing of the Re‐loaded anion resin bead. The optimal protocol improved Re signal intensity around fourteen times compared with our current Re extraction protocol, an aggregate of 2.4 times improvement in chemical recovery (yield) and 5.8 times improvement in emission efficiency (purity). Repeated N‐TIMS isotopic measurements on our in‐house Re standard solution (1407) verify that our optimal protocol‐3 does not fractionate Re isotopes. The improved anion resin bead method considerably lowers the Re detection limit and allows Re‐Os isotopic analysis of picogram‐level Re hosted in geological samples with complex matrices. 相似文献
2.
Murray Close Phil Abraham Judith Webber Eliza Cowey Bronwyn Humphries Graham Fenwick Simon Howard Kimberly Huynh Travis Grace Pierre-Yves Dupont Louise Weaver 《Ground water》2020,58(6):901-912
The vast majority of microorganisms in aquifers live as biofilms on sediment surfaces, which presents significant challenges for sampling as only the suspended microbes will be sampled through normal pumping. The use of a down-well low frequency sonicator has been suggested as a method of detaching microbes from the biofilm and allowing rapid sampling of this community. We developed a portable, easy to use, low-frequency electric sonicator and evaluated its performance for a range of well depths (tested up to 42 m below ground level) and casing types. Three sonicators were characterized in laboratory experiments using a 1 m long tank filled with pea gravel. These included a commercially available pneumatic sonicator, a rotating flexible shaft sonicator, and the prototype electric sonicator. The electric sonicator detached between 56 and 74% of microbes grown on gravel-containing biobags at distances ranging between 2 and 50 cm from the sonicator. The field testing comprises of a total of 55 sampling events from 48 wells located in 4 regions throughout New Zealand. Pre- and post-sonication samples showed an average 33 times increase in bacterial counts. Microbial sequence data showed that the same classes are present in pre- and post-sonicated samples and only slight differences were seen in the proportions present. The sampling process was rapid and the significant increases in bacterial counts mean that microbial samples can be quickly obtained from wells, which permits more detailed analysis than previously possible. 相似文献
3.
4.
5.
Judith Curry 《Climatic change》2011,108(4):723-732
This paper argues that the IPCC has oversimplified the issue of uncertainty in its Assessment Reports, which can lead to misleading
overconfidence. A concerted effort by the IPCC is needed to identify better ways of framing the climate change problem, explore
and characterize uncertainty, reason about uncertainty in the context of evidence-based logical hierarchies, and eliminate
bias from the consensus building process itself. 相似文献
6.
Tomaso R. R. Bontognali Judith A. McKenzie Rolf J. Warthmann Crisogono Vasconcelos 《地学学报》2014,26(1):72-77
Some species of sulphate‐reducing bacteria (SRB) are known to mediate the formation of dolomite and Mg‐calcite. However, their exact role in the mineralization process remains elusive. Here, we present the result of a laboratory experiment that was designed to test whether formation of carbonate minerals by SRB can occur in the absence of living cells, through passive mineralization of their exopolymeric substances (EPS). SRB capable of mediating dolomite were cultivated in the laboratory, allowing them to secrete EPS. Microbial activity within the cultures was subsequently inhibited with antibiotics. Only after this step, Ca2+ and Mg2+ were added to the solution and carbonate minerals could form. Mg‐calcite and disordered Ca‐dolomite precipitated in association with EPS. The mol.% of Mg2+ in the crystals increased with longer incubation times. This result demonstrates that organic compounds produced by SRB can mediate the formation of Ca‐Mg carbonates in the absence of an active metabolism. 相似文献
7.
8.
The European Water Framework Directive demands to assess and report the chemical and ecological status of water bodies (WB). Linking their status to drivers and pressures and deriving suitable mitigation measures require knowledge of the shape and area of WB catchments. We derived a network of 26 570 WB catchments in Germany using the hydrologically-defined drainage basins of the German federal states. We established a network of 338 149 drainage basins. This network underwent plausibility checks and a validation with the catchment areas of 348 monitoring stations across Germany. To this network, we assigned the longest intersecting or the next downstream WB code. To account for geometric inaccuracies we revised spurious intersections resulting in splittings and cycles in the WB network. As WB may be ecologically but not hydrologically well defined, we split them at confluences and intersections. The network of drainage basins matched the monitoring stations with a Nash-Sutcliffe efficiency of 1.00. The final WB network contained 11 005 out of the 11 586 original WBs longer than 1 m. The corresponding local catchment areas range from <<0.0001 to 446 km2, with a median of 10 km2. The dataset combines the requirements of hydrological and ecological modelling applications at basin or national scales with the needs of the EU reporting which can foster their acceptance by state authorities and river-basin management. 相似文献
9.
Polar coronal holes (PCHs) trace the magnetic variability of the Sun throughout the solar cycle. Their size and evolution have been studied as proxies for the global magnetic field. We present measurements of the PCH areas from 1996 through 2010, derived from an updated perimeter-tracing method and two synoptic-map methods. The perimeter-tracing method detects PCH boundaries along the solar limb, using full-disk images from the SOlar and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope (SOHO/EIT). One synoptic-map method uses the line-of-sight magnetic field from the SOHO/Michelson Doppler Imager (MDI) to determine the unipolarity boundaries near the poles. The other method applies thresholding techniques to synoptic maps created from EUV image data from EIT. The results from all three methods suggest that the solar maxima and minima of the two hemispheres are out of phase. The maximum PCH area, averaged over the methods in each hemisphere, is approximately 6 % during both solar minima spanned by the data (between Solar Cycles 22/23 and 23/24). The northern PCH area began a declining trend in 2010, suggesting a downturn toward the maximum of Solar Cycle 24 in that hemisphere, while the southern hole remained large throughout 2010. 相似文献
10.
Crystele Leauthaud Stéphanie Duvail Olivier Hamerlynck Jean-Luc Paul Hubert Cochet Judith Nyunja Jean Albergel Olivier Grünberger 《Global Environmental Change》2013,23(1):252-263
Wetlands are highly dynamic and productive systems that have been under increased pressure from changes in land use and water management strategies. In Eastern Africa, wetlands provide resources at multiple spatial and temporal levels through farming, fishing, livestock ownership and a host of other ecosystem services that sustain the local economy and individual livelihoods. As part of a broader effort to describe future development scenarios for East African coastal wetlands, this qualitative study focuses on understanding the processes by which river water depletion has affected local food production systems in Kenya's Tana River Delta over the past 50 years, and how this situation has impacted residents’ livelihoods and well-being. Interviews performed in six villages among various ethnic groups, geographical locations and resource profiles indicated that the agro-ecological production systems formerly in place were adapted to the river's dynamic flooding patterns. As these flooding patterns changed, the local population diversified and abandoned or adopted various farming, fishing and livestock-rearing techniques. Despite these efforts, the decrease in water availability affected each subcomponent of the production systems under study, which led to their collapse in the 1990s. Water depletion negatively impacted local human well-being through the loss of food security. The current study provides a detailed account of the dynamics of agro-ecological production systems facing the effects of river water depletion in a wetland-associated environment in Sub-Saharan Africa. 相似文献