全文获取类型
收费全文 | 470篇 |
免费 | 17篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 44篇 |
地球物理 | 94篇 |
地质学 | 186篇 |
海洋学 | 23篇 |
天文学 | 100篇 |
自然地理 | 39篇 |
出版年
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 7篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 36篇 |
2012年 | 14篇 |
2011年 | 21篇 |
2010年 | 11篇 |
2009年 | 20篇 |
2008年 | 22篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1971年 | 6篇 |
1965年 | 2篇 |
排序方式: 共有494条查询结果,搜索用时 0 毫秒
491.
Flooded underground mines are attractive for groundwater heat pump systems, as the voids created during mining operations enhance the subsurface permeability and storage capacity, which allows the extraction of significant volumes of groundwater without requiring extensive drilling. Heat exchange at a flooded mine is, however, difficult to predict because of the complex geometry of the underground network of tunnels. A case study is presented here to demonstrate that numerical simulations of groundwater flow and heat transfer can help assess production temperatures required to optimize the design of a heat pump system that uses mine water. A 3D numerical model was developed for the Gaspé Mines located in Murdochville, Canada, where a district heating and cooling system is being studied. The underground mining tunnels and shafts are represented in the model with 1D elements whose flow and heat transfer contributions are superimposed to those of the 3D porous medium. The numerical model is calibrated to simultaneously reproduce the groundwater rebound that occurred when the mine closed and the drawdown measured during a pumping test conducted in a former mining shaft. Predictive simulations over a period of 50 years are subsequently performed to minimize pumping rate and determine maximum heat extraction rate. 相似文献
492.
Raymond A. Duraiswami Purva Gadpallu Babaji Maskare Aishwarya Purwant Pooja Meena P. Krishnamurthy B. Mahabaleshwar 《Journal of the Geological Society of India》2017,90(6):742-747
Flow mapping and physical volcanology of 15 basaltic lavas exposed in three critical road pass sections (ghats) in the Koyna-Warna region of the western Deccan Traps is presented in this paper. Transitional lavas like rubbly pahoehoe are most common morpho-type exposed in these ghat sections. Sinking of rubbly breccia into flow interiors and formation of breccia-cored rosette are common in some lava flows. Few rubbly lavas exhibit slabby tendencies. The amount and nature of the associated rubble is variable and result from the mechanical fracturing and auto-brecciation of the upper vesicular crust in response to distinctive stages in the cooling, crystallization and emplacement history of individual lava flows. Occurrence of aa and pahoehoe morpho-types in the lava flow sequence is subordinate. Three prominent pahoehoe flows separated by red bole horizons are seen in the upper parts of the Kumbharli ghat. These are thick, P-type sheet pahoehoe. The pahoehoe lavas represent compound flow fields that grew by budding, endogenous lava transfer and inflation. Presence of pahoehoe lavas in the Koyna-Warna region hints at possible hitherto unrecorded southern extension of Bushe-like flow fields. This study reconfirms the existence of pahoehoe-slabby-rubbly-aa flow fields and transitions even in the upper echelons of the Deccan Trap stratigraphy. The study of morphology and internal structure of lava flows exposed at the ghat sections in the Koyna-Warna region could guide subsurface core-logging that is critical in deciphering the physical volcanology and emplacement dynamics of basaltic lava flows penetrated by drill holes sunk under the scientific deep drilling programme. 相似文献
493.
Raymond C. H. Koo Julian S. H. Kwan Carlos Lam Charles W. W. Ng Jack Yiu Clarence E. Choi Axel K. L. Ng Ken K. S. Ho W. K. Pun 《Landslides》2017,14(3):905-916
Flexible steel barriers are commonly constructed on steep hillsides to mitigate rockfall. The evaluation of the dynamic response of proprietary flexible barriers is conventionally performed using full-scale field tests by dropping a weight onto the barriers in accordance with the European test standard ETAG 27. The weight typically has a spherical or polyhedral shape and cannot reproduce more complex rockfall scenarios encountered in the field. A rigid slab may load a barrier over a larger area and its effect has not been investigated. In this study, a calibrated three-dimensional finite-element model was developed to study the performance of vertically and horizontally orientated rockfall barriers under concentrated areal impact loads. A new bilinear force-displacement model was incorporated into the model to simulate the behavior of the energy-dissipating devices on the barriers. The effect of different weight geometries was studied by considering impacts by a rigid single spherical boulder and a rigid slab. Results reveal that areal loading induced by a rigid slab increases the loading on the barrier foundation by up to 40 % in both horizontally and vertically positioned barriers when compared to a concentrated load scenario with a single boulder. This indicates that barriers tested under the current test standard does not give the worst-case scenario in terms of foundation loads, and barrier designers should take into account the possible effect of increased foundation loads by reinforcing the barrier posts and/or increasing their spacing. 相似文献
494.
Temporospatial dynamics and public health significance of bacterial flora identified on a major leatherback turtle (Dermochelys coriacea) nesting beach in the Southern Caribbean
下载免费PDF全文
![点击此处可从《Marine Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ayanna Carla N. Phillips Johanna Coutou Stacy Rajh Neville Stewart Antonio Watson Adam Jehu Hamish Asmath Francis Dziva Chandrashekhar Unakal Ridley Holder Raymond Raoul Carthy 《Marine Ecology》2017,38(2)
Grande Riviere beach, on the island of Trinidad, supports the largest nesting population of leatherback turtles in the Caribbean region. Throughout the nesting season, nests are naturally disturbed by newly nesting females, resulting in egg breakage and loss of some nest viability. This environment is ideal for the growth and proliferation of microorganisms. The range of bacterial flora present in beach sand and egg shells was examined, with emphasis on bacteria that may pose a threat to public and animal health. The extent to which the bacterial load and genera on the beach changed throughout the season was also assessed. Twenty‐five genera were identified, with Pseudomonas spp. found to be the most predominant environmental bacteria. Four genera identified possess zoonotic potential, while five additional genera are known to be of public and animal health significance. Distinct shifts in the density and distribution of bacteria were observed along the beach from early to peak nesting season. Shifts were seen across heavily traversed zones, thus highlighting the potential exposure threats posed to beach visitors and animals alike. Further studies aimed at speciating this population of bacteria, as well as isolating potential fungal pathogens may mitigate this threat. Identification of bacterial agents that are specifically pathogenic to leatherback turtles, turtle eggs, hatchlings and those who may interact with these animals will serve to enhance and guide efforts to better conserve this species and protect the health of all who visit this ecologically significant site. 相似文献