首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   710篇
  免费   22篇
  国内免费   10篇
测绘学   16篇
大气科学   59篇
地球物理   146篇
地质学   229篇
海洋学   82篇
天文学   120篇
综合类   3篇
自然地理   87篇
  2021年   8篇
  2020年   14篇
  2019年   13篇
  2018年   14篇
  2017年   10篇
  2016年   15篇
  2015年   23篇
  2014年   10篇
  2013年   40篇
  2012年   18篇
  2011年   32篇
  2010年   22篇
  2009年   24篇
  2008年   31篇
  2007年   20篇
  2006年   11篇
  2005年   25篇
  2004年   24篇
  2003年   28篇
  2002年   26篇
  2001年   17篇
  2000年   29篇
  1999年   22篇
  1998年   20篇
  1997年   11篇
  1996年   9篇
  1995年   9篇
  1994年   12篇
  1993年   14篇
  1992年   5篇
  1991年   5篇
  1990年   6篇
  1989年   8篇
  1988年   5篇
  1987年   11篇
  1986年   15篇
  1985年   12篇
  1984年   11篇
  1983年   16篇
  1982年   14篇
  1981年   5篇
  1980年   5篇
  1979年   8篇
  1978年   10篇
  1977年   8篇
  1976年   9篇
  1975年   7篇
  1973年   4篇
  1971年   8篇
  1970年   5篇
排序方式: 共有742条查询结果,搜索用时 31 毫秒
41.
SensePlace3 (SP3) is a geovisual analytics framework and web application that supports overview + detail analysis of social media, focusing on extracting meaningful information from the Twitterverse. SP3 leverages social media related to crisis events. It differs from most existing systems by enabling an analyst to obtain place-relevant information from tweets that have implicit as well as explicit geography. Specifically, SP3 includes not just the ability to utilize the explicit geography of geolocated tweets but also analyze implicit geography by recognizing and geolocating references in both tweet text, which indicates locations tweeted about, and in Twitter profiles, which indicates locations affiliated with users. Key features of SP3 reported here include flexible search and filtering capabilities to support information foraging; an ingest, processing, and indexing pipeline that produces near real-time access for big streaming data; and a novel strategy for implementing a web-based multi-view visual interface with dynamic linking of entities across views. The SP3 system architecture was designed to support crisis management applications, but its design flexibility makes it easily adaptable to other domains. We also report on a user study that provided input to SP3 interface design and suggests next steps for effective spatiotemporal analytics using social media sources.  相似文献   
42.
The Storegga tsunami, dated in Norway to 8150±30 cal. years BP, hit many countries bordering the North Sea. Run-ups of >30 m occurred and 1000s of kilometres of coast were impacted. Whilst recent modelling successfully generated a tsunami wave train, the wave heights and velocities, it under-estimated wave run-ups. Work presented here used luminescence to directly date the Storegga tsunami deposits at the type site of Maryton, Aberdeenshire in Scotland. It also undertook sedimentological characterization to establish provenance, and number and relative power of the tsunami waves. Tsunami model refinement used this to better understand coastal inundation. Luminescence ages successfully date Scottish Storegga tsunami deposits to 8100±250 years. Sedimentology showed that at Montrose, three tsunami waves came from the northeast or east, over-ran pre-existing marine sands and weathered igneous bedrock on the coastal plain. Incorporation of an inundation model predicts well a tsunami impacting on the Montrose Basin in terms of replicate direction and sediment size. However, under-estimation of run-up persisted requiring further consideration of palaeotopography and palaeo-near-shore bathymetry for it to agree with sedimentary evidence. Future model evolution incorporating this will be better able to inform on the hazard risk and potential impacts for future high-magnitude submarine generated tsunami events.  相似文献   
43.
Robinson  Bethany  Herman  Jonathan D. 《Climatic change》2019,152(3-4):431-448
Climatic Change - Recent water resources planning studies have proposed climate adaptation strategies in which infrastructure and policy actions are triggered by observed thresholds or...  相似文献   
44.
Localized (domainal) low-temperature alteration may indicate variations in the chemistry of alteration fluids and/or discrete fluid flow paths during metamorphism. Occurrences of epidote- and pumpellyite-dominated domains are often used as evidence for large fluxes of Ca-rich fluids. However, comparative studies of two domainal alteration styles from basaltic to andesitic lavas and volcaniclastic rocks at Builth Wells, Wales, UK suggest that such interpretations cannot be applied universally. Here, only one set of domains can be attributed to large fluxes of Ca-rich fluids. In contrast, the second set of domains formed where the host rock supplied the necessary Ca, and fluid/rock ratios were relatively low. These domains are hosted by rocks which show a Caledonian regional metamorphic imprint, characterized by the alteration assemblage albite+chlorite+titanite±prehnite±pumpellyite±calcite±muscovite±quartz (considered to have formed at c. 200°C and ≤2.5 kbar). Type 1 domains lie along fluid channelways, such as veins. Pumpellyite is the dominant secondary mineral, but the alteration assemblage is variable with pumpellyite±prehnite±calcite±titanite±chlorite (±quartz). The domains formed at temperatures of 130–230°C during Ordovician hydrothermal activity, before the peak of regional metamorphism. In contrast, Type 2 domains are not associated with obvious fluid channelways. A central prehnite-dominated zone typically has a rim with the assemblage pumpellyite+calcite±prehnite±chlorite±titanite±K-rich phyllosilicate. These domains probably formed from pelitic xenoliths which contained a volcaniclastic component at temperatures of 130–230°C and at relatively low fluid/rock ratios. However, the timing of domain formation is uncertain. Pyrobitumen, in veins and disseminated throughout the rock, may have influenced the formation of both types of domain by stabilizing pumpellyite in preference to epidote and causing metamorphic calcite formation through the release of CO2 to the alteration fluids. © 1996 John Wiley & Sons, Ltd.  相似文献   
45.
During the 1990s, the township of Pōkeno was held up as an example of a declining rural Aotearoa/New Zealand. By‐passed from the national state highway, it lost its status as a service hub and drastic measures were introduced to revitalise the town, including renaming the town “ Jenniferann.com .” Pōkeno has since undergone an unlikely transformation, with foreign investment and its location within an extended Auckland commuter zone meaning that the township has grown exponentially. This article describes the transformation of Pōkeno and uncovers what has been missing from discussions about Pōkeno's reinvention, namely, the place of mana whenua.  相似文献   
46.
Management of the coastal zone often focuses on “islands” of high value ecosystems, in terms of economic value or conservation. However, integrated management requires landscape-level analysis of all ecosystem values. The biodiversity portfolio analysis (BPA) method is derived from the logic used in share (equity) portfolio management in terms of balancing within a portfolio the returns with the risks. Optimising the returns from a share portfolio, or a suite of ecosystems in a landscape, is dependent on the relationship between the units in terms of risk and return. Three case studies are then presented to test the applicability of the BPA method at the international (North West Europe), regional (Durham Heritage Coast, UK) and local (part of South Uist, Outer Hebrides, UK) spatial scale. The Biodiversity Portfolio Analysis for NW Europe showed that risk and return were highly correlated in the studied Member States. The ranking of risk and return, with the highest first, was Ireland > UK > France=Netherlands > Belgium. For these Member States the risks to ecosystem service provision were positively correlated with GNI (r=0.97, P<0.01); suggesting that the higher the economic importance of coastal and marine resources in a Member State the more at risk the resources are. The regional and local case studies were more focussed on providing information on which to base Integrated Coastal Zone Management (ICZM) decision making; both case studies used stakeholder participation to determine risks and returns. The conclusions from these two case studies show how the BPA method can be useful in terms of setting ICZM priorities and in addressing local coastal issues. The BPA involves making a number of assumptions, however, it does provide coastal managers with a potential tool to strategically plan due to increased awareness of the interaction between the ecosystems in the portfolio.There is a need for such techniques, which involve stakeholder participation and which create objective outcomes, to support the implementation of ICZM.  相似文献   
47.
The current study was carried out over a period of one year to characterise the coastal migrant fishery of Kenya. The study looked at gears and vessels used, and ownership, demographic factors including ages of the fishers and family sizes, migrant activity and resource conservation at two main fishing villages in Kenya; Vanga and Mayungu in the south and north coasts, straddling at 4.663°S and 39.215°E and 3.214°S and 40.135°E respectively. Further, the fishers were categorised with regard to fishing, gear and vessel operation and trade, and evolution upon entry into the fishery was also assessed in order to define fisher-stake in the fishery for resource management and conservation planning. Structured questionnaires were used to interview the fishers, and data and information recorded from 1018 fishers during the survey. Migrants accounted for over 63% of the fishers in the two study sites, with majority of the fishers lying in the 15–45 year age bracket. Dependence level averages at 4–6 person families per fisher. Entry to the fishery was mainly at seamen level, progressing to fishermen and finally to fish dealers (tajiris), with the latter holding >62% capital in the fishery. Resource management in the fishery was low and only 10% of the fishers were active participants in marine conservation and community beach management issues. Fisher migrations were mainly monsoon season-linked (>58%) although social factors such as family location determined to a great extent the expanse of the migrations. The revival of fisheries cooperatives and active participation in community resource management and conservation groups is envisaged as the key to the sustainability of both the marine resources and the economies associated with this high mobility, cross-border fishery.  相似文献   
48.
In this study, two designs for a buoy capable of supporting a 10 kW wind turbine and its tower were developed to operate at the University of New Hampshire’s Center of Ocean Renewable Energy testing site located off the Isles of Shoals, New Hampshire. The buoys are to be moored by a catenary chain system. To evaluate wave response, two Froude-scaled models were constructed, tested, and compared at the Ocean Engineering wave tank at the University of New Hampshire. These buoys have been implemented and compared with wave tank measurements of the spar displacement at a reference elevation 2.44 m above the mean water level.  相似文献   
49.
Air–sea gas transfer velocities are estimated for one year using a 1-D upper-ocean model (GOTM) and a modified version of the NOAA–COARE transfer velocity parameterization. Tuning parameters are evaluated with the aim of bringing the physically based NOAA–COARE parameterization in line with current estimates, based on simple wind-speed dependent models derived from bomb-radiocarbon inventories and deliberate tracer release experiments. We suggest that A = 1.3 and B = 1.0, for the sub-layer scaling parameter and the bubble mediated exchange, respectively, are consistent with the global average CO2 transfer velocity k. Using these parameters and a simple 2nd order polynomial approximation, with respect to wind speed, we estimate a global annual average k for CO2 of 16.4 ± 5.6 cm h?1 when using global mean winds of 6.89 m s?1 from the NCEP/NCAR Reanalysis 1 1954–2000. The tuned model can be used to predict the transfer velocity of any gas, with appropriate treatment of the dependence on molecular properties including the strong solubility dependence of bubble-mediated transfer. For example, an initial estimate of the global average transfer velocity of DMS (a relatively soluble gas) is only 11.9 cm h?1 whilst for less soluble methane the estimate is 18.0 cm h?1.  相似文献   
50.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号