全文获取类型
收费全文 | 576篇 |
免费 | 29篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 40篇 |
地球物理 | 184篇 |
地质学 | 178篇 |
海洋学 | 47篇 |
天文学 | 56篇 |
综合类 | 2篇 |
自然地理 | 106篇 |
出版年
2022年 | 4篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 12篇 |
2015年 | 18篇 |
2014年 | 11篇 |
2013年 | 37篇 |
2012年 | 23篇 |
2011年 | 20篇 |
2010年 | 32篇 |
2009年 | 26篇 |
2008年 | 40篇 |
2007年 | 25篇 |
2006年 | 23篇 |
2005年 | 26篇 |
2004年 | 18篇 |
2003年 | 22篇 |
2002年 | 17篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 14篇 |
1993年 | 8篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1970年 | 3篇 |
排序方式: 共有616条查询结果,搜索用时 125 毫秒
221.
L. Robin M. Cocks Leonid E. Popov 《Proceedings of the Geologists' Association. Geologists' Association》2019,130(6):677-690
The Early Ordovician brachiopods of south-west Wales (Pembrokeshire and Carmarthenshire) are identified, in most cases for the first time. That period is termed the local Arenig Stage in Britain, but it is now correlated with the Floian, Dapingian, and earlier half of the Darriwilian, which are more recently established international stages in the system of stratigraphical nomenclature. The rocks in south-west Wales were laid down as turbidites in a backarc basin which formed part of the margin of the relatively small independent microcontinent of Avalonia at that time. However, since the Rheic Ocean between Avalonia and the immense Gondwana continent was relatively narrow in the Arenig, the brachiopods reviewed here can be established to be part of the Mediterranean Province, which was also extensive in the higher-latitude sectors in and around Gondwana in the Early Ordovician. The 17 brachiopod species identified within the Arenig brachiopod faunas of south-west Wales are described, including the new species Aporthophyla prisca, Tritoechia bolohaulensis, Skenidoides pontyfennensis and Paurorthis? llangynogensis. 相似文献
222.
This study verifies how the adoption of agroecology and conventional farming techniques varies among different socio-economic characteristics. Data acquisition involved the administering of 200 questionnaires and the organization of two focus group discussions (FGDs). The data collected were analysed using: frequencies, means, probabilities, odds and odd ratios. The FGDs were analysed using context analysis. The analyses were performed in SPSS version 20 and Wordstat 7. The results reveal that older respondents tend to adopt conventional farming techniques more than other categories due mainly to inertia or the inability to adapt to changes and their limited propensity to adopt agroecology techniques. Farmers with fewer years of farming experience are more open to agroecology related techniques due to higher inertia while those with more years of farming experience converge with older farmers who tend to prefer conventional farming. The higher the level of income, the more frequent the use of agroecology techniques. Families with more members who live and work on the farm are more open to agroecology; however, there is a limit beyond which the more the number of family members who live and work on the farm, the less the probability of adopting agroecology techniques. The higher the level of education, the greater the propensity to adopt and experiment with agroecology. 相似文献
223.
Anozie Ebigbo Rainer Helmig Alfred B. Cunningham Holger Class Robin Gerlach 《Advances in water resources》2010
The concentration of greenhouse gases – particularly carbon dioxide (CO2) – in the atmosphere has been on the rise in the past decades. One of the methods which have been proposed to help reduce anthropogenic CO2 emissions is the capture of CO2from large, stationary point sources and storage in deep geological formations. The caprock is an impermeable geological layer which prevents the leakage of stored CO2, and its integrity is of utmost importance for storage security. Due to the high pressure build-up during injection, the caprock in the vicinity of the well is particularly at risk of fracturing. Biofilms could be used as biobarriers which help prevent the leakage of CO2 through the caprock in injection well vicinity by blocking leakage pathways. The biofilm could also protect well cement from corrosion by CO2-rich brine. 相似文献
224.
A fully integrated and effective response to an oil or chemical spill at sea must include a well planned and executed post-incident assessment of environmental contamination and damage. While salvage, rescue and clean-up operations are generally well considered, including reviews and exercises, the expertise, resources, networks and logistical planning required to achieve prompt and effective post-spill impact assessment and monitoring are not generally well established.The arrangement and co-ordination of post-incident monitoring and impact assessment need to consider sampling design, biological effects, chemical analysis and collection/interpretation of expert local knowledge. This paper discusses the risks, impacts and mitigation options associated with accidental spills and considers the importance of pre-considered impact assessment and monitoring programmes in the wider response cycle. The PREMIAM (Pollution Response in Emergencies: Marine Impact Assessment and Monitoring; www.premiam.org) project is considered as an example of an improved approach to the planning, co-ordination and conduct of post-incident monitoring. 相似文献
225.
Claude Robin Pablo Samaniego Jean-Luc Le Pennec Michel Fornari Patricia Mothes Johannes van der Plicht 《Bulletin of Volcanology》2010,72(9):1109-1129
Fieldwork, radiometric (40Ar/39Ar and 14C) ages and whole-rock geochemistry allow a reconstruction of eruptive stages at the active, mainly dacitic, Pichincha Volcanic
Complex (PVC), whose eruptions have repeatedly threatened Quito, most recently from 1999 to 2001. After the emplacement of
basal lavas dated at ∼1100 to 900 ka, the eruptive activity of the old Rucu Pichincha volcano lasted from ∼850 ka to ∼150 ka
before present (BP) and resulted in a 15 × 20 km-wide edifice, which comprises three main building stages: (1) A lower stratocone
(Lower Rucu, ∼160 km3 in volume) developed from ∼850 to 600 ka; (2) This edifice was capped by a steeper-sided and less voluminous cone (the Upper
Rucu, 40–50 km3), the history of which started 450–430 ka ago and ended around 250 ka with a sector collapse; (3) A smaller (8–10 km3) but more explosive edifice grew in the avalanche amphitheatre and ended Rucu Pichincha's history about 150 ka ago. The Guagua
Pichincha volcano (GGP) was developed from 60 ka on the western flank of Rucu with four growth stages separated by major catastrophic
events. (1) From ∼60 to 47 ka, a basal effusive stratocone developed, terminating with a large ash-and-pumice flow event.
(2) This basal volcano was followed by a long-lasting dome building stage and related explosive episodes, the latter occurring
between 28–30 and 22–23 ka. These first two stages formed the main GGP (∼30 km3), a large part of which was removed by a major collapse 11 ka BP. (3) Sustained explosive activity and viscous lava extrusions
gave rise to a new edifice, Toaza (4–5 km3 in volume), which in turn collapsed around 4 ka BP. (4) The ensuing amphitheatre was partly filled by the ∼1-km3 Cristal dome, which is the historically active centre of the Pichincha complex. The average output rate for the whole PVC
is 0.29 km3/ka. Nevertheless, the chronostratigraphic resolution we obtained for Lower Rucu Pichincha and for the two main edifices of
Guagua Pichincha (main GGP and Toaza), leads to eruptive rates of 0.60–0.65 km3/ka during these construction stages. These output rates are compared to those of other mainly dacitic volcanoes from continental
arcs. Our study also supports an overall SiO2 and large-ion lithophile elements enrichment as the PVC develops. In particular, distinctive geochemical signatures indicate
the involvement of a new magma batch at the transition between Rucu and Guagua. At the GGP, the same phenomenon occurs at
each major collapse event marking the onset of the ensuing magmatic stage. Since the 11-ka-BP collapse event, this magmatic
behaviour has led to increasingly explosive activity. Four explosive cycles of between 100 and 200 years long have taken place
at the Cristal dome in the past 3.7 ka, and repose intervals between these cycles have tended to decrease with time. As a
consequence, we suggest that the 1999–2001 eruptive period may have initiated a new eruptive cycle that might pose a future
hazard to Quito (∼2 million inhabitants). 相似文献
226.
Evaluation of ground motion selection and modification procedures using synthetic ground motions
下载免费PDF全文
![点击此处可从《地震工程与结构动力学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This study presents a novel approach for evaluating ground motion selection and modification (GMSM) procedures in the context of probabilistic seismic demand analysis. In essence, synthetic ground motions are employed to derive the benchmark seismic demand hazard curve (SDHC), for any structure and response quantity of interest, and to establish the causal relationship between a GMSM procedure and the bias in its resulting estimate of the SDHC. An example is presented to illustrate how GMSM procedures may be evaluated using synthetic motions. To demonstrate the robustness of the proposed approach, two significantly different stochastic models for simulating ground motions are considered. By quantifying the bias in any estimate of the SDHC, the proposed approach enables the analyst to rank GMSM procedures in their ability to accurately estimate the SDHC, examine the sufficiency of intensity measures employed in ground motion selection, and assess the significance of the conditioning intensity measure in probabilistic seismic demand analysis. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
227.
Authors' reply to the discussion by Brendon A. Bradley of ‘A framework for the evaluation of ground motion selection and modification procedures’
下载免费PDF全文
![点击此处可从《地震工程与结构动力学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this short communication, we respond to the comments made by Dr Brendon A. Bradley and provide additional context to our paper under discussion.Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
228.
Despite increased sexuality education in New Zealand, concern remains about high rates of sexually transmitted infection and unplanned pregnancy among young people. To understand this 'gap', we consider what high school students learn about sexual health, and where they learn it. Narrative evidence reveals the negative, risk-oriented nature of sexual health messages at school and at home. In these power-laden places, little information is imparted about several key issues, including emotions. Students are aware of such absences, and articulate a desire for more open discussions of sexual health and sexuality, as is possible in informal settings occupied by friends. 相似文献
229.
An icy satellite whose interior is composed of a homogeneous ice/rock mixture must avoid melting during its entire history, including during its formation when it was heated by deposition of accretional energy and short-lived radioisotopes. Estimates of the temperature rise associated with radiogenic and accretional heating, coupled with limits on satellite melting can be used to constrain the timing of formation of a partially differentiated satellite relative to the origin of the calcium-aluminum-rich inclusions (CAI's) as a function of its accretion timescale and the protosatellite disk temperature (Td). Geological characterization and spacecraft radio tracking data suggest that Callisto, the outermost regular satellite of Jupiter, and Saturn's mid-sized satellite Rhea, are partially differentiated if their interiors are in hydrostatic equilibrium. Because the specific conditions during the satellites' formation are uncertain, we determine accretional temperature profiles for a range of values for Td and accretion time scales with the limiting assumption that impactors deposit all their energy close to the surface, leading to maximally effective radiative cooling. We find that Callisto can remain unmelted during formation if it accreted on a time scale longer than 0.6 Myr. Considering both radiogenic and accretional heating, Callisto must have finished accreting no earlier than ∼4 Myr after formation of CAI's for Td=100 K. Warmer disks or larger impactors that deposit their energy at depth in the satellite would require longer and/or later formation times. If Rhea accreted slowly (in 105 to 106 years), its growth must have finished no earlier than ∼2 Myr after CAI's for 70 K?Td?250 K to avoid early melting. If Rhea formed quickly (?103 yr), its formation must have been delayed until at least 2 to 7 Myr after CAI's and in a disk with Td<190 K in the small impactor limit. If the satellites form in slow-inflow-supplied disks as proposed by Canup and Ward [Canup, R.M., Ward, W.R., 2002. Astron. J. 124, 3404-3423], the implied satellite ages suggest that gas inflow to the giant planets ceased no earlier than ∼4 Myr after CAI's, comparable to average nebular lifetimes inferred from observations of circumstellar disks. 相似文献
230.
The environmental threat from oil spills remains significant across the globe and particularly in regions of high oil production and transport such as the Gulf. The ultimate damage caused can be limited by mitigation actions that responders deploy. The responsible and appropriate use of oil spill treatment products (e.g. dispersants, sorbents etc.) can offer response options that can result in substantial net environmental benefit. However, the approval and choice of what products to use needs careful consideration. The United Kingdom has had in place a statutory approval scheme for oil spill treatment products for 30 years. It is based on measures of efficiency and environmental acceptability. Two toxicity tests form an integral part of the assessment, the Sea test and the Rocky Shore test, and work on the premise that approved products will not make the situation significantly worse when added to spilled oil. This paper outlines the UK approach and how its rationale might be applied to the approval of products specific for the Gulf region. Issues such as species choice, higher temperatures and salinity and regional environmental conditions are considered. 相似文献