全文获取类型
收费全文 | 436篇 |
免费 | 45篇 |
国内免费 | 35篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 22篇 |
地球物理 | 113篇 |
地质学 | 281篇 |
海洋学 | 20篇 |
天文学 | 18篇 |
综合类 | 29篇 |
自然地理 | 23篇 |
出版年
2023年 | 8篇 |
2022年 | 21篇 |
2021年 | 46篇 |
2020年 | 33篇 |
2019年 | 25篇 |
2018年 | 78篇 |
2017年 | 43篇 |
2016年 | 62篇 |
2015年 | 36篇 |
2014年 | 29篇 |
2013年 | 38篇 |
2012年 | 15篇 |
2011年 | 21篇 |
2010年 | 8篇 |
2009年 | 14篇 |
2008年 | 7篇 |
2007年 | 2篇 |
2006年 | 4篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1989年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有516条查询结果,搜索用时 15 毫秒
491.
492.
Muhammad Mohsin Gunter Sp?ck Jürgen Pilz 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(7):925-945
A new bivariate pseudo Pareto distribution is proposed, and its distributional characteristics are investigated. The parameters of this distribution are estimated by the moment-, the maximum likelihood- and the Bayesian method. Point estimators of the parameters are presented for different sample sizes. Asymptotic confidence intervals are constructed and the parameter modeling the dependency between two variables is checked. The performance of the different estimation methods is investigated by using the bootstrap method. A Markov Chain Monte Carlo simulation is conducted to estimate the Bayesian posterior distribution for different sample sizes. For illustrative purposes, a real set of drought data is investigated. 相似文献
493.
494.
Christoph Mahrenholtz Pao‐Chun Lin An‐Chien Wu Keh‐Chyuan Tsai Shyh‐Jiann Hwang Ruei‐Yan Lin Muhammad Y. Bhayusukma 《地震工程与结构动力学》2015,44(1):59-78
Damage to buildings observed in recent earthquakes suggests that many old reinforced concrete structures may be vulnerable to the effects of severe earthquakes. One suitable seismic retrofit solution is the installation of steel braces to increase the strength and ductility of a building. Steel bracings have some compelling advantages such as their comparatively low weight, their suitability for prefabrication, and the possibility of openings for utilities, access, and light. The braces are typically connected to steel frames that are fixed to the concrete structure using post‐installed concrete anchors along the perimeter. However, these framed steel braces are not without some disadvantages such as heavier steel usage and greater difficulties during the installation. Therefore, braces without steel frames appear to be an attractive alternative. In this study, braces were connected to gussets furnished with anchor brackets, which were fixed by means of a few post‐installed concrete anchors. The clear structural system and the increased utilization of the anchors allowed the anchorage to be designed precisely and economically. The use of buckling‐restrained braces (BRBs) provides additional benefits in comparison with conventional braces. BRBs improve the energy dissipation efficiency and allow the limitation of the brace force to be taken up by the highly stressed anchorage. Cyclic loading tests were conducted to investigate the seismic performance of BRBs connected with post‐installed anchors used to retrofit reinforced concrete frames. The tests showed that the proposed design method is feasible and increases strength as well as ductility to an adequate seismic performance level. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
495.
496.
Delineation of three-dimensional well capture zones for complex multi-aquifer systems 总被引:10,自引:0,他引:10
The delineation of well capture zones is a basic component of ground water protection. The conventional methodology for capture zone delineation is backward advective particle tracking, often applied under the assumption of a two-dimensional aquifer. The suitability of the conventional approach for complex heterogeneous multi-aquifer systems was investigated, using the Waterloo Moraine aquifer system as an example. It was found that the conventional approach produces irregular particle tracks that require judgment to interpret in a meaningful way, and it can raise questions that may affect the credibility of the capture zone delineation. As an alternative, the potentially powerful but little-used backward-in-time advective-dispersive transport approach was investigated. A key advantage of this approach is its capability to represent local heterogeneities through the dispersion term. The dispersion process has a natural smoothing effect that results in unambiguous capture zones without the need for interpretation, thus enhancing credibility. The question of capture zone validation is also addressed. The meaning of a three-dimensional capture zone is considered, and it is shown that a fully three-dimensional representation of the system is crucial for valid results. The distinction between the maximum extent capture zone and the surface capture zone is also explained. In the case of complex heterogeneous systems, advective particle tracking can be used as an initial screening tool, whereas the more realistic backward-transport modeling approach can be used for final capture-zone delineation. 相似文献
497.
Abu Muhammad Shajaat Ali 《Natural Hazards》2007,40(1):89-111
This paper examines the nature and causes of September 2004 hazardous flood that affected the dry and drought prone southwestern
region of Bangladesh. It also examines human perception of this new hazard and their methods of adjustments to its negative
impacts. Field research for this study includes personal interviews of 453 victim families living in four thanas (lowest administrative
units) in Jessore and Satkhira districts of southwestern Bangladesh. Findings of the study suggest that all victim respondents
viewed this flood event as a natural hazard, which has caused severe damage to standing crops, fish ponds, permanent trees
and homesteads, and deteriorated human health and sanitation conditions. Its long-term impacts on fish farming, soil quality
degradation, as well as changing land use/land coverage are also noteworthy but yet to be adequately explored. Both perceived
and scientific causes of this flood event include high rainfall for a week before the flood, unusual movement of low pressure
system into the affected area, cloudy weather and low evaporation, siltation of the regional riverbeds, and rolling back of
the Ganges River water through the Ichamati and Bhagirati rivers. These factors also caused hazardous flooding at the same
time in the Ichamati and Bhagirati Rivers and their floodplains in the West Bengal province of India. To release the overflow
of flood water inside India, the Indian border patrol breached the Ichamati river embankment in several places along Satkhira
and Jessore international border which had aggravated the flood situation in the study area. 相似文献
498.
Kalam Shams Khan Rizwan Ahmed Khan Shahnawaz Faizan Muhammad Amin Muhammad Ajaib Rameez Abu-Khamsin Sidqi A. 《Natural Resources Research》2021,30(2):1697-1717
Natural Resources Research - Low-salinity waterflooding (LSWF) has, in the past decade, attained a lot of attention to enhance oil recovery. In LSWF, diluted water is injected into an oil reservoir... 相似文献
499.
Recharge to a saline, unconfined shallow-water-table aquifer is normally considered as an irrecoverable loss of water, but
such thinking could be reviewed empirically. The use of an appropriate groundwater harvesting system does not only provide
an opportunity to recover this lost water, but can also help in catchment salinity management and improvement. Agricultural-based
land-drainage systems such as those that use serial biological concentration (SBC) of salts, provide examples of such harvesting
methods. The impact of groundwater harvesting has been assessed on the hydro-salinity of a saline catchment in southeastern
Australia through modeling. For both the below average rainfall and very wet years, the “do nothing” scenario resulted in
increasing salinization in the catchment. However, after introducing a SBC system, groundwater salinity showed a decreasing
trend while hydraulic heads tended to stabilize around the depth of subsurface collector wells. However, for a successful
groundwater harvesting system, proper understanding of the groundwater flows and salt mobilization associated with a catchment
is necessary. The outcomes of this modelling study have the potential to address similar issues (salinization) and/or needs
(water harvesting) existing elsewhere in the world, particularly in semi-arid regions.
相似文献
Muhammad Nadeem AsgharEmail: |
500.
Glacier mass balance is a key component of glacier monitoring programs. Information on the mass balance of Sawir Mountains is poor due to a dearth of in-situ measurements. This paper introduces the applicability of an ultra-long-range terrestrial laser scanner(TLS) to monitor the mass balance of Muz Taw Glacier, Sawir Mountains, China. The Riegl VZ?-6000 TLS is exceptionally well-suited for measuring snowy and icy terrain. Here, we use TLS to create repeated high spatiotemporal resolution DEMs, focusing on the annual mass balance(June 2, 2015 to July 25, 2016). According to TLS-derived high spatial resolution point clouds, the front variation(glacier retreat) of Muz Taw Glacier was 9.3 m. The mean geodetic elevation change was 4.55 m at the ablation area. By comparing with glaciological measurements, the glaciological elevation change of individual stakes and the TLS-derived geodetic elevation change of corresponding points matched closely, and the calculated balance was-3.864±0.378 m w.e.. This data indicates that TLS provides accurate results and is therefore suitable to monitor mass balance evolution of Muz Taw Glacier. 相似文献