全文获取类型
收费全文 | 760篇 |
免费 | 29篇 |
国内免费 | 35篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 42篇 |
地球物理 | 193篇 |
地质学 | 313篇 |
海洋学 | 65篇 |
天文学 | 65篇 |
综合类 | 3篇 |
自然地理 | 124篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 12篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 19篇 |
2017年 | 19篇 |
2016年 | 21篇 |
2015年 | 12篇 |
2014年 | 45篇 |
2013年 | 51篇 |
2012年 | 19篇 |
2011年 | 49篇 |
2010年 | 30篇 |
2009年 | 39篇 |
2008年 | 45篇 |
2007年 | 29篇 |
2006年 | 24篇 |
2005年 | 32篇 |
2004年 | 24篇 |
2003年 | 30篇 |
2002年 | 21篇 |
2001年 | 18篇 |
2000年 | 13篇 |
1999年 | 21篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 19篇 |
1995年 | 11篇 |
1994年 | 20篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1973年 | 3篇 |
1969年 | 2篇 |
排序方式: 共有824条查询结果,搜索用时 109 毫秒
191.
Susan M. Waugh Dominique P. Filippi David S. Kirby Edward Abraham Nathan Walker 《Marine Policy》2012,36(4):933-946
The risk of seabird–fishery interactions in the Western and Central Pacific Ocean (WCPO) was examined by analysing the overlap of seabird distributions with tuna and swordfish pelagic longline fisheries managed by the Western and Central Pacific Fisheries Commission (WCPFC) and its constituent members. The study used spatially-explicit Productivity–Susceptibility Analysis (PSA). Key data inputs were species productivity, fishing effort, likelihood of capture and species density by region. The outputs tailored results to the needs of fisheries- and wildlife-managers, indicating areas of greatest risk of species interactions, species of greatest concern for population impacts, and the flags or fisheries most likely to contribute to the risk. Large albatross species were found to be most likely to suffer population effects when exposed to longline fishing activity, followed by the larger petrels from the genuses Procellaria, Macronectes and Pterodroma. A mixture of coastal states with nesting seabird populations in their Exclusive Economic Zones (New Zealand, Australia and United States of America), distant water fishing nations (Japan, Taiwan) and flags of convenience (Vanuatu) contributed 90% of the risk to seabird populations. Recommendations include enhancing the level of fisheries observer monitoring in areas indicated as high to medium risk for seabird interactions, and consideration of spatial management tools, such as more intensive or more stringent seabird bycatch mitigation requirements in high- to medium-risk areas. The methods used, and similar studies conducted in the Atlantic Ocean could lead to improved targeting of monitoring resources, and greater specificity in the needs for seabird-mitigation measures. This will assist in reducing seabird mortality in longline fishing operations and with more effective use of resources for fishery managers in both domestic fisheries and RFMOs. 相似文献
192.
Estimates of greenhouse gas evasion from rivers have been refined over the past decades to constrain their role in global carbon cycle processes. However, despite 55% of the human population living in urban areas, urban rivers have had limited attention. We monitored carbon dynamics in an urbanized river (River Kelvin, 331 km2, UK) to explore the drivers of dissolved carbon lateral and vertical export. Over a 2-year sampling period, riverine methane (CH4) and carbon dioxide (CO2) concentrations were consistently oversaturated with respect to atmospheric equilibria, leading to continual degassing to the atmosphere. Carbon stable isotopic compositions (δ13C) indicated that terrestrially derived carbon comprised most of the riverine CH4 and dissolved CO2 (CO2*) load while dissolved inorganic carbon (DIC) from groundwater was the main form of riverine DIC. The dynamics of CH4, CO2*, and DIC in the river were primarily hydrology-controlled, that is, [CH4] and [CO2*] both increased with elevated discharge, total [DIC] decreased with elevated discharge while the proportion of biologically derived DIC increased with increasing discharge. The concentration of dissolved organic carbon (DOC) showed a weak relationship with river hydrology in summer and autumn and was likely influenced by the combined sewer overflows. Carbon emission to the atmosphere is estimated to be 3.10 ± 0.61 kg C·m−2·yr−1 normalized to water surface area, with more than 99% emitted as CO2. Annual carbon loss to the coastal estuary is approximately 4.69 ± 0.70 Gg C yr−1, with annual DIC export approximately double that of DOC. Per unit area, the River Kelvin was a smaller carbon source to the atmosphere than natural rivers/streams but shows elevated fluxes of DIC and DOC under comparable conditions. This research illustrates the role urban systems may have on riverine carbon dynamics and demonstrates the potential tight link between urbanization and riverine carbon export. 相似文献
193.
Daniel J. Meininger William S. Kinman Susan K. Hanson 《Geostandards and Geoanalytical Research》2023,47(2):457-465
The isotopic composition of cadmium in nuclear debris was measured by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). Mass-independent perturbations due to fission product decay on the isotopes of Cd were observed. Relative fission yields for masses 111, 112, 114 and 116 were determined in each sample of nuclear debris and compared with reported values found in irradiated plutonium and uranium fuels. Mass spectrometry measurements of the valley fission product endpoints are extremely challenging due to the low cumulative fission yields and small amounts of each isotope that are produced. To overcome these challenges, a new purification method for Cd was developed and validated by examination of a number of geological reference materials. 相似文献
194.
Application of GIS and remote sensing techniques in frost risk mapping for mitigating agricultural losses in the Aberdare ecosystem,Kenya 总被引:1,自引:0,他引:1
Frost is a perennial agricultural hazard that normally causes crop damage leading to huge agricultural losses within the Kenyan highlands; aggravated by inadequate information on frost. This research mapped frost hotspots within the Aberdare and Mount Kenya regions and identified the extent of arable land under frost risk while establishing the trend of minimum temperature occurrences between the years 2000 and 2013. Minimum temperature values were extracted from daily Moderate Resolution Imaging Spectroradiometer land surface temperature data-sets, and frost risk categorized into very severe frost (<250 K), severe frost (250–260 K), moderate frost (260–270 K), minor frost (270–280 K) and areas of no frost. Concentration of frost (<273 K) was mapped within regions above 1500 m asl and occasional occurrences within valleys lower than this altitude with recurrent occurrences in the months of April, May, July, August and November. Elevation, land surface convexity and humidity were found to influence frost occurrence. Improved agricultural practice to mitigate against losses is recommended. 相似文献
195.
Susan L. Cutter Lindsey Barnes Melissa Berry Christopher Burton Elijah Evans Eric Tate Jennifer Webb 《Global Environmental Change》2008,18(4):598
There is considerable research interest on the meaning and measurement of resilience from a variety of research perspectives including those from the hazards/disasters and global change communities. The identification of standards and metrics for measuring disaster resilience is one of the challenges faced by local, state, and federal agencies, especially in the United States. This paper provides a new framework, the disaster resilience of place (DROP) model, designed to improve comparative assessments of disaster resilience at the local or community level. A candidate set of variables for implementing the model are also presented as a first step towards its implementation. 相似文献
196.
Joseph J. Fontaine Karie L. Decker Susan K. Skagen Charles van Riper III 《Climatic change》2009,97(1-2):305-311
Recent changes in global climate have dramatically altered worldwide temperatures and the corresponding timing of seasonal climate conditions. Recognizing the degree to which species respond to changing climates is therefore an area of increasing conservation concern as species that are unable to respond face increased risk of extinction. Here we examine spatial and temporal heterogeneity in the rate of climate change across western North America and discuss the potential for conditions to arise that may limit the ability of western migratory birds to adapt to changing climates. Based on 52 years of climate data, we show that changes in temperature and precipitation differ significantly between spring migration habitats in the desert southwest and breeding habitats throughout western North America. Such differences may ultimately increase costs to individual birds and thereby threaten the long-term population viability of many species. 相似文献
197.
Meta-analysis of 173 rate measurements from 21 publications was used to develop rate laws for chalcopyrite dissolution under environmentally relevant conditions. Multiple linear regression analysis of 28 data for nonoxidative chalcopyrite dissolution in the presence of O2 and Cl− produced the following rate law: 相似文献
198.
Hurricane Katrina storm surge delineation: implications for future storm surge forecasts and warnings 总被引:1,自引:1,他引:0
The storm surge in coastal Mississippi caused by Hurricane Katrina was unprecedented in the region. The height and geographic
extent of the storm surge came as a surprise to many and exceeded pre-impact surge scenarios based on SLOSH models that were
the basis for emergency preparedness and local land use decision-making. This paper explores the spatial accuracy of three
interpolated storm surge surfaces derived from post-event reconnaissance data by comparing the interpolation results to a
specific SLOSH run. The findings are used to suggest improvements in the calibration of existing pre-event storm surge models
such as SLOSH. Finally, the paper provides some suggestions on an optimal surge forecast map that could enhance the communication
of storm surge risks to the public. 相似文献
199.
Jiemin Lu Judson W. Partin Susan D. Hovorka Corinne Wong 《Environmental Earth Sciences》2010,60(2):335-348
In assessing the feasibility of widespread deployment of CO2 geological storage, it is prudent to first assess potential consequences of an error or accident that could lead to CO2 leakage into groundwater resources above a sequestration interval. Information about the sensitivity of the groundwater system
to introduction of CO2 is needed in order to design groundwater monitoring program. A laboratory-batch experiment was conducted to explore the range
of CO2 impact on groundwater quality of a spectrum of representative aquifers, in the Gulf Coast region, USA. Results show that
CO2 elevated concentrations of many cations within hours or days. Two types of cations were recognized according to their concentration
trends. Type I cations—Ca, Mg, Si, K, Sr, Mn, Ba, Co, B, Zn—rapidly increased following initial CO2 flux and reached stable concentrations before the end of the experiment. Type II cations—Fe, Al, Mo, U, V, As, Cr, Cs, Rb,
Ni and Cu—increased at the start of CO2 flux, but declined, in most cases, to levels lower than pre-CO2 concentrations. Dissolution of dolomite and calcite caused the largest increase in concentrations for Ca, Mg, Mn, Ba and
Sr. Cation release rates decreased linearly as pH increased during mineral buffering. Experiment results suggest that carbonate
minerals are the dominant contributor of changes in groundwater quality. Risk assessments of potential degradation of groundwater
and monitoring strategies should focus on these fast-reacting minerals. Mobilization risk of Type II cations, however, may
be self-mitigated because adsorption occurs when pH rebounds. 相似文献
200.
Isaac Luginaah Michael Jerrett Susan Elliott John Eyles Kate Parizeau Stephen Birch Tom Abernathy Gerry Veenstra Brian Hutchinson Chris Giovis 《GeoJournal》2001,53(2):135-147
This paper is part of a larger research program which employs a mixed-methods approach to study the determinants of health at the local level using specific neighborhoods in Hamilton, Ontario, Canada. In this paper, multivariate, spatial statistical techniques and geographic information systems are used to address questions about the characterization of neighbourhoods, based on socioeconomic determinants of health and risk factors such as smoking. While neighbourhood characterization has been a component of public health surveillance for some time, geostatistical techniques can now be used to derive more accurate representation of neighbourhoods for use in subsequent analysis. We utilize principal components analysis to reduce the data and extract the components that represent the underlying local processes. Principal components are also overlayed on comparative mortality figures to visualize where the socio-demographic determinants of health correspond spatially with mortality patterns. Predicted values from the components are then analysed for spatial clustering using local indicators of spatial association. The findings reveal a pattern of distinct neighbourhoods that will be used in subsequent quantitative and qualitative stages in the larger research programme. The results can also be used to inform public health policy and to target public health interventions. 相似文献