全文获取类型
收费全文 | 295篇 |
免费 | 15篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 32篇 |
大气科学 | 16篇 |
地球物理 | 114篇 |
地质学 | 82篇 |
海洋学 | 25篇 |
天文学 | 38篇 |
综合类 | 3篇 |
自然地理 | 6篇 |
出版年
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 7篇 |
2018年 | 12篇 |
2017年 | 17篇 |
2016年 | 17篇 |
2015年 | 15篇 |
2014年 | 14篇 |
2013年 | 18篇 |
2012年 | 17篇 |
2011年 | 15篇 |
2010年 | 11篇 |
2009年 | 13篇 |
2008年 | 17篇 |
2007年 | 14篇 |
2006年 | 11篇 |
2005年 | 10篇 |
2004年 | 5篇 |
2003年 | 9篇 |
2002年 | 7篇 |
2001年 | 8篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有316条查询结果,搜索用时 988 毫秒
181.
182.
Anil Kumar Haritash Ramanathan Baskar Nirmal Sharma Sumit Paliwal 《Environmental Geology》2007,51(8):1439-1445
Slate quarrying in Mahendragarh district of Haryana state has resulted in changes in soil properties. Most of the mining area
is devoid of vegetation. The soil in and around the mining area (0–1 km) is alkaline (pH 11.2–11.7) but non-saline (electrical
conductivity < 4). The alkaline nature of the soil was attributed to the high concentrations of hydroxyl (OH−), carbonate (CO32−) and bicarbonate (HCO3
−) present in minerals of mined materials. Biotite, limonite, kaolinite, gibbsite, muscovite, geothite, dolomite and so on
were the chief minerals added to soil through mining. The physical properties of soil, i.e. porosity, water-holding capacity
(WHC), bulk density and particle density represented poor soil health in mining area (34.4, 29.8%, 1.636, 2.496 g/cc, respectively)
and they improved with distance away from it (46.4, 38.3%, 1.070, 2.180 g/cc, respectively, at a distance of 1 km). Porosity
and WHC were found to be a function of increased organic matter away from the mining area. CO32−, HCO3−, phosphate (PO43−), lead (Pb) and iron (Fe) were more in mining area and decreased with distance. On the other hand, sodium (Na+), potassium (K+), chloride (Cl−), sulphate (SO42−), organic carbon, total Kjeldahl’s nitrogen, cation exchange capacity, chromium (Cr) and cadmium (Cd) increased with distance
from mining area. High concentration of heavy metals in mining area was a cause of concern (0.93 μg/g Cd, 22.35 μg/g Cr, 26.25 μg/g
Pb, 1,383.75 μg/g Fe). The change in physico-chemical properties could be because of the addition of chemical constituents
that are a part of major minerals present in mined material. The soil away from mining area represented comparatively better
properties. 相似文献
183.
184.
Classifying urban land cover from high-resolution satellite imagery is challenging, and those challenges are compounded when the imagery databases are very large. Accurate land cover data is a crucial component of the population distribution modeling efforts of the Oak Ridge National Laboratory’s (ORNL) LandScan Program. Currently, LandScan Program imagery analysts manually interpret high-resolution (1–5 m) imagery to augment existing satellite-derived medium (30 m) and coarse (1 km) resolution land cover datasets. For LandScan, the high-resolution image archives that require interpretation are on the order of terabytes. The goal of this research is to automate human settlement mapping by utilizing ORNL’s high performance computing capabilities. Our algorithm employs gray-level and local edge-pattern co-occurrence matrices to generate texture and edge patterns. Areas of urban land cover correlate with statistical features derived from these texture and edge patterns. We have parallelized our algorithms for implementation on a 64-node system using a single instruction multiple data programming model (SIMD) with Message Passing Interface (MPI) as the communication mode. Our parallel-configured classifier performs 30–40 times faster than stand-alone alternatives. We have tested our system on IKONOS imagery. The early results are promising, pointing towards future large-scale classification of human settlements at high-resolution. 相似文献
185.
186.
A three‐dimensional model for approximate inelastic analysis of buildings is presented herein. The model is based on a single macro‐element per building storey. The inelastic properties of the model are characterized by the so‐called ultimate storey shear and torque (USST) surfaces. Different algorithms for the construction of these surfaces, as well as their applications in building modelling, are presented and discussed. Two alternative procedures are developed to integrate the force‐deformation constitutive relationship of the macro‐elements. The first one follows the exact trajectory of the load path of the structure on the USST, and the second uses linear programming without ever forming the USST surface. The accuracy of the model and integration procedure is evaluated by means of the earthquake response of single‐storey systems. The model and integration procedure developed is finally used to compute the inelastic response of a seven‐storey R/C building. The results of this investigation show that the model proposed, although approximate, can be effective in estimating the inelastic deformation demand of a building. It also enables the engineer to capture and interpret important features of the three‐dimensional inelastic response of a structure even before performing any inelastic dynamic analysis. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
187.
188.
Kumar Anil Elumalai Suresh Pandian Yang Hsi-Hsien 《Stochastic Environmental Research and Risk Assessment (SERRA)》2020,34(1):183-199
Stochastic Environmental Research and Risk Assessment - The resurfacing of urban road networks is a prevalent practice for extending their life and therefore shares an important contribution to the... 相似文献
189.
Seismic retrofit of MRF buildings using decentralized semi‐active control for multi‐target performances 下载免费PDF全文
Numerous structures have been designed and built without taking earthquake ground motions or outdated seismic design codes into account. In order to improve the seismic performance of existing structures, many retrofit approaches based on performance‐based design have been developed. However, some of these approaches are inapplicable due to structural limitations or because they were developed with the assumption of single‐degree‐of‐freedom, which does not take higher modes into account. To overcome the limitations of these traditional methods, a multi‐performance‐based control design (MPBCD) methodology has been proposed by integrating a decentralized semi‐active control algorithm, magnetorheological dampers, and an advanced multi‐objective optimization method to provide various sets of retrofit control designs to satisfy multiple target performances under multiple seismic intensities without changing structural cross‐section sizes or material properties. This MPBCD method provides engineers with numerous sets of control designs (i.e., control device layouts with control design parameters) to help them select proper control designs to retrofit existing building structures and improve seismic performance. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
190.
Current approaches for sustainable mountain development have several persisting warning signals. Economic globalization, profitoriented market development, and infrastructure development have significantly altered traditional nature-society interactions, increased environmental pressures, and challenged agricultural sustainability in the mountains. Some of the effects of globalization could also be beneficial. Social differentiation and disintegration of mountain communities' have weakened their collective stakes on natural resources resulting in decline in initiatives such as community forestry, collective water management, domestication of rapidly disappearing herbal species, and balancing of economic and ecological concerns. Population growth, food insecurity, unemployment, and increasing economic gaps between rich and poor have led to out-migration of youth. Sustained action promoting ownership of new initiatives for rehabilitating degraded mountain landscapes through macro-level global/national initiatives, mountain specific planning and development efforts is severely lacking in many areas on the Hindu Kush Himalayan region. Therefore, there is an urgent need for widening the scope of efforts directed to help mountain areas and communities, and a future thinking approach to enhance the sustainability of mountain areas as they are a valuable natural resource for humankind. This paper discusses the issues, opportunities, and provides suggestions for the future of mountain development. 相似文献