全文获取类型
收费全文 | 271篇 |
免费 | 9篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 41篇 |
地球物理 | 43篇 |
地质学 | 83篇 |
海洋学 | 44篇 |
天文学 | 49篇 |
综合类 | 4篇 |
自然地理 | 11篇 |
出版年
2023年 | 1篇 |
2022年 | 9篇 |
2021年 | 8篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 23篇 |
2015年 | 9篇 |
2014年 | 26篇 |
2013年 | 21篇 |
2012年 | 18篇 |
2011年 | 15篇 |
2010年 | 12篇 |
2009年 | 11篇 |
2008年 | 14篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 13篇 |
2004年 | 5篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1984年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有284条查询结果,搜索用时 15 毫秒
81.
Gordon R. Osinski Pascal Lee Kelly Snook Darlene S.S. Lim 《Planetary and Space Science》2010,58(4):646-48
With the prospect of humans returning to Moon by the end of the next decade, considerable attention is being paid to technologies required to transport astronauts to the lunar surface and then to be able to carry out surface science. Recent and ongoing initiatives have focused on scientific questions to be asked. In contrast, few studies have addressed how these scientific priorities will be achieved. In this contribution, we provide some of the lessons learned from the exploration of the Haughton impact structure, an ideal lunar analogue site in the Canadian Arctic. Essentially, by studying how geologists carry out field science, we can provide guidelines for lunar surface operations. Our goal in this contribution is to inform the engineers and managers involved in mission planning, rather than the field geology community. Our results show that the exploration of the Haughton impact structure can be broken down into 3 distinct phases: (1) reconnaissance; (2) systematic regional-scale mapping and sampling; and (3) detailed local-scale mapping and sampling. This break down is similar to the classic scientific method practiced by field geologists of regional exploratory mapping followed by directed mapping at a local scale, except that we distinguish between two different phases of exploratory mapping. Our data show that the number of stops versus the number of samples collected versus the amount of data collected varied depending on the mission phase, as does the total distance covered per EVA. Thus, operational scenarios could take these differences into account, depending on the goals and duration of the mission. Important lessons learned include the need for flexibility in mission planning in order to account for serendipitous discoveries, the highlighting of key “science supersites” that may require return visits, the need for a rugged but simple human-operated rover, laboratory space in the habitat, and adequate room for returned samples, both in the habitat and in the return vehicle. The proposed set of recommendations ideally should be tried and tested in future analogue missions at terrestrial impact sites prior to planetary missions. 相似文献
82.
Myoung?Hak?Oh Ju?Hyung?Lee Gil?Lim?Yoon Junboum?ParkEmail author 《Environmental Geology》2003,45(2):181-189
The grid-net electrical conductivity measurement system for detecting exact locations of landfill leachate intrusion in the subsurface was developed in this study. Laboratory and pilot-scale field model tests were performed to evaluate the direct application of a grid-net electrical conductivity measurement system for the detection of landfill leachate. A significant increase in electrical conductivity of soil was observed by adding landfill leachate. This can be explained as an increase in electrical conductivity of pore fluid due to an increase in leachate constituents as charge carriers. In pilot-scale field model tests, leachate intrusion locations were accurately identified at the initial stage of landfill leachate release by the grid-net electrical conductivity measurement system. The electrical conductivity of the subsurface before leachate injection lay within a small range of 24.8–43.0 S/cm. The electrical conductivity values in detected points were approximately ten times more than the conductivity values of the subsurface without landfill leachate intrusion. The results in this study indicate that the grid-net electrical conductivity measurement method has a possible application for detecting locations of landfill leachate intrusion into the subsurface at the initial stage, and thus has great potential in monitoring leachate leakage at waste landfills. 相似文献
83.
84.
Larry R. Nittler Richard D. Starr Lucy Lim Timothy J. Mccoy Thomas H. Burbine Robert C. Reedy Jacob I. Trombka Paul Gorenstein Steven W. Squyres William V. Boynton Timothy P. Mcclanahan Jesse S. Bhangoo Pamela E. Clark Mary Ellen Murphy Rosemary Killen 《Meteoritics & planetary science》2001,36(12):1673-1695
Abstract— We report major element ratios determined for the S‐class asteroid 433 Eros using remote‐sensing x‐ray fluorescence spectroscopy with the near‐Earth asteroid rendezvous Shoemaker x‐ray spectrometer (XRS). Data analysis techniques and systematic errors are described in detail. Data acquired during five solar flares and during two extended “quiet Sun” periods are presented; these results sample a representative portion of the asteroid's surface. Although systematic uncertainties are potentially large, the most internally consistent and plausible interpretation of the data is that Eros has primitive Mg/Si, Al/Si, Ca/Si and Fe/Si ratios, closely similar to H or R chondrites. Global differentiation of the asteroid is ruled out. The S/Si ratio is much lower than that of chondrites, probably reflecting impact‐induced volatilization and/or photo‐ or ion‐induced sputtering of sulfur at the surface of the asteroid. An alternative explanation for the low S/Si ratio is that it reflects a limited degree of melting with loss of an FeS‐rich partial melt. Size‐sorting processes could lead to segregation of Fe‐Ni metal from silicates within the regolith of Eros; this could indicate that the Fe/Si ratios determined by the x‐ray spectrometer are not representative of the bulk Eros composition. 相似文献
85.
Bong-Joo Jang Suk-Hwan Lee Sanghun Lim 《International journal of geographical information science》2014,28(4):763-779
With the increase in the number of applications using digital vector maps and the development of surveying techniques, a large volume of GIS (geographic information system) vector maps having high accuracy and precision is being produced. However, to achieve their effective transmission while preserving their high positional quality, these large amounts of vector map data need to be compressed. This paper presents a compression method based on a bin space partitioning data structure, which preserves a high-level accuracy and exact precision of spatial data. To achieve this, the proposed method a priori divides a map into rectangular local regions and classifies the bits of each object in the local regions to three types of bins, defined as category bin (CB), direction bin (DB), and accuracy bin (AB). Then, it encodes objects progressively using the properties of the classified bins, such as adjacency and orientation, to obtain the optimum compression ratio. Experimental results verify that our method can encode vector map data constituting less than 20% of the original map data at a 1-cm accuracy degree and that constituting less than 9% at a 1-m accuracy degree. In addition, its compression efficiency is greater than that of previous methods, whereas its complexity is lower for close to real-time applications. 相似文献
86.
Byung-Gu?Kim Changhoon?LeeEmail author Seokjun?Joo Ki-Cheol?Ryu Seogcheol?Kim Donghyun?You Woo-Sup?Shim 《Boundary-Layer Meteorology》2011,139(3):457-485
We conduct wind-tunnel experiments on three different uniform roughness arrays composed of sparsely distributed rectangular
cylinders for the estimation of surface parameters. Roughness parameters such as the roughness length z
0 and zero-plane displacement d are extracted using a best-fit approximation of the measured wind velocity. We also perform a large-eddy simulation (LES)
to confirm that four sampling points are sufficient to surrogate a space average above the canopy layer of the sparse roughness
arrays. We propose a new morphological model from a systematic analysis of experimental data on the arrays. The friction velocity
predicted by the proposed model agrees well with the peak value of the measured Reynolds shear stress ${(-\left<\overline{u'w'}\right>)^{0.5}}${(-\left<\overline{u'w'}\right>)^{0.5}}. The proposed model is further validated in an additional wind-tunnel experiment conducted on a scaled configuration of a
real urban area exposed to four wind directions. The proposed model is found to perform very well particularly in the estimation
of the friction velocity, readily leading to a better estimation of turbulence, which is essential for an accurate prediction
of pollutant dispersion. 相似文献
87.
The impact of the risk environment and energy prices to the budget of Korean households 总被引:2,自引:2,他引:0
Hyungho Youn Byung In Lim Eui Young Lee YongRok Choi 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(3):323-330
Energy is closely related to environmental risk. A rising fuel price in the 1970s had hurt consumers and caused disturbance
to the natural environment. Households could not afford high imported energy prices and thus resorted to fuel wood. Land competed
for fuel wood and agricultural crops, and thus high fuel prices strained the environment with respect to the use of land.
If human health and safe housing were included in environmental risk, a high energy price would induce broader environmental
risk. Households with limited income would not be able to use expensive fossil energy to warm their houses and would depend
on only electric mats or blankets to keep warm. Such insufficient warming methods would not only threaten their health but
would also worsen the condition of their houses. The abrupt increase in energy prices in 2007 and 2008 had significantly impacted
environmental risk. It forced low income households to spend more on energy, leaving less for other expenditure segments,
but had left high income households generally intact. This contrasting effect between different income groups had increased
the sustainability of the energy risks at the high prices. This study shows how risks associated with the household economy
have increased in response to the recent dramatic increases in energy prices. We develop a method for assessing risk by using
the variance of ratios of energy expenditure to current income. We then examine how differently the economic change has increased
risk across expenditure segments. We find energy expenditure as the biggest contributor to the risk. In addition, we illustrate
how energy expenditure has changed the risk profile for each income group, with the first group (i.e., the lowest income group)
experiencing the greatest increase. This group hurts the most during days of high energy prices. 相似文献
88.
Peter Schürch Alexander L. Densmore Nicholas J. Rosser Michael Lim Brian W. McArdell 《地球表面变化过程与地形》2011,36(14):1847-1859
Detection of surface change is a fundamental task in geomorphology. Terrestrial laser scanners are increasingly used for monitoring surface change resulting from a variety of geomorphic processes, as they allow the rapid generation of high‐resolution digital elevation models. Irrespective of instrument specifics, survey design or data processing, such data are subject to a finite level of ambiguity in position measurement, a consideration of which must be taken into account when deriving change. The propagation of errors is crucial in change detection because even very small uncertainties in elevation can produce large uncertainties in volume when extrapolated over an area of interest. In this study we propose a methodology to detect surface change and to quantify the resultant volumetric errors in areas of complex topography such as channels, where data from multiple scan stations must be combined. We find that a commonly proposed source of error – laser point elongation at low incidence angles – has a negligible effect on the quality of the final registered point cloud. Instead, ambiguities in elevation inherent to registered datasets have a strong effect on our ability to detect and measure surface change. Similarly, we find that changes in surface roughness between surveys also reduce our ability to detect change. Explicit consideration of these ambiguities, when propagated through to volume calculations, allows us to detect volume change of 87 ± 5 m3, over an area of ~ ?4900 m2, due to passage of a debris flow down a 300 m reach of the Illgraben channel in Switzerland. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
89.
Guanie Lim 《Singapore journal of tropical geography》2016,37(2):176-194
This paper examines the Malaysian Chinese firms that have expanded into Vietnam. Based on research and qualitative personal interviews with Malaysian Chinese firms that have invested in Vietnam, the paper unpacks the entry modes that these firms have undertaken. It argues that the Malaysian Chinese firms prefer joint ventures in their Vietnamese businesses to wholly‐owned subsidiaries and personal direct investments. This paper also argues that such investments are often embedded in social and intraethnic ties, which connect Malaysian Chinese firms with Vietnam's ethnic Chinese businessmen. To this end, these firms tend to rely on informal ties and nonmarket institutions in the form of the ethnic Chinese business networks. Nevertheless, the Malaysian Chinese firms are not averse to collaborating with nonethnic Chinese firms that enjoy a good relationship with the Vietnamese state. This observation is especially marked in the property and construction, and finance sectors. 相似文献
90.
Donghyun Lee Seung-Ki Min Changyong Park Myoung-Seok Suh Joong-Bae Ahn Dong-Hyun Cha Dong-Kyou Lee Song-You Hong Seong-Chan Park Hyun-Suk Kang 《Asia-Pacific Journal of Atmospheric Sciences》2016,52(2):129-137
Time of Emergence (ToE) is the time at which the signal of climate change emerges from the background noise of natural climate variability, and can provide useful information for climate change impacts and adaptations. This study examines future ToEs for daily maximum and minimum temperatures over the Northeast Asia using five Regional Climate Models (RCMs) simulations driven by single Global Climate Model (GCM) under two Representative Concentration Pathways (RCP) emission scenarios. Noise is defined based on the interannual variability during the present-day period (1981-2010) and warming signals in the future years (2021-2100) are compared against the noise in order to identify ToEs. Results show that ToEs of annual mean temperatures occur between 2030s and 2040s in RCMs, which essentially follow those of the driving GCM. This represents the dominant influence of GCM boundary forcing on RCM results in this region. ToEs of seasonal temperatures exhibit larger ranges from 2030s to 2090s. The seasonality of ToE is found to be determined majorly by noise amplitudes. The earliest ToE appears in autumn when the noise is smallest while the latest ToE occurs in winter when the noise is largest. The RCP4.5 scenario exhibits later emergence years than the RCP8.5 scenario by 5-35 years. The significant delay in ToEs by taking the lower emission scenario provides an important implication for climate change mitigation. Daily minimum temperatures tend to have earlier emergence than daily maximum temperature but with low confidence. It is also found that noise thresholds can strongly affect ToE years, i.e. larger noise threshold induces later emergence, indicating the importance of noise estimation in the ToE assessment. 相似文献