全文获取类型
收费全文 | 136篇 |
免费 | 2篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 13篇 |
地球物理 | 32篇 |
地质学 | 47篇 |
海洋学 | 8篇 |
天文学 | 10篇 |
自然地理 | 19篇 |
出版年
2023年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 12篇 |
2012年 | 4篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 8篇 |
2008年 | 9篇 |
2007年 | 10篇 |
2006年 | 5篇 |
2005年 | 10篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有139条查询结果,搜索用时 234 毫秒
111.
112.
The effect of changes in daily and interannual climatic variability on CERES-Wheat: A sensitivity study 总被引:4,自引:1,他引:4
We investigate the effect of changes in daily and interannual variability of temperature and precipitation on yields simulated by the CERES-Wheat model at two locations in the central Great Plains. Changes in variability were effected by adjusting parameters of the Richardson daily weather generator. Two types of changes in precipitation were created: one with both intensity and frequency changed; and another with change only in persistence. In both types mean total monthly precipitation is held constant. Changes in daily (and interannual) variability of temperature result in substantial changes in the mean and variability of simulated wheat yields. With a doubling of temperature variability, large reductions in mean yield and increases in variability of yield result primarily from crop failures due to winter kill at both locations. Reduced temperature variability has little effect. Changes in daily precipitation variability also resulted in substantial changes in mean and variability of yield. Interesting interactions of the precipitation variability changes with the contrasting base climates are found at the two locations. At one site where soil moisture is not limiting, mean yield decreased and variability of yield increased with increasing precipitation variability, whereas mean yields increased at the other location, where soil moisture is limiting. Yield changes were similar for the two different types of precipitation variability change investigated. Compared to an earlier study for the same locations wherein variability changes were effected by altering observed time series, and the focus was on interannual variability, the present results for yield changes are much more substantial. This study demonstrates the importance of taking into account change in daily (and interannual) variability of climate when analyzing the effect of climate change on crop yields.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
113.
The Cosmic Origins Spectrograph (COS) is an ultraviolet spectrograph scheduled for installation in the Hubble Space Telescope (HST) during HST Servicing Mission 4, currently planned to occur in August 2008. COS was designed to maximize sensitivity to faint point sources, and will provide limiting sensitivities at moderate spectral resolutions (R~20,000) that are a factor of 2 to >10 times better than those provided by previous ultraviolet spectrographs on HST. Here, we present an overview of the some of the science areas that will be addressed by COS observations and provide a summary of the capabilities of COS and the expected on-orbit performance. 相似文献
114.
115.
This work seeks to understand how the balance of abiotic and biotic kinetic processes in sediments control the residual concentration of TNT in marine systems after release from ocean-dumped source. Kinetics of TNT disappearance were followed using marine sediments at different temperatures and under both biotic and presumably abiotic conditions (through sodium azide addition). Sediments exhibiting the highest rate of TNT disappearance under biotic conditions also exhibited the highest sorption affinity for TNT under abiotic conditions. Significant temperature dependence in the abiotic processes was observed in the diffusion coefficient of TNT and not sediment sorption affinity. At higher temperature, kinetics of biotic processes outpaced abiotic processes, but at low temperature, kinetics of abiotic processes were much more significant. We concluded that the differential influence of temperature on the kinetics of abiotic and biotic processes could provide distinguishing predictions for the potential residual concentration of TNT contamination in marine-sediment systems. 相似文献
116.
Kamlesh P. Lulla Michael Helfert David Amsbury David Pitts Cynthia Evans Justin Wilkinson 《国际地球制图》2013,28(2):67-80
Abstract Many universities around the world are actively pursuing or have recently implemented professional graduate programs in geographic information science. However, the number of undergraduate programs focusing on geographic information science is far more limited. This is despite the rapid hiring of GIS faculty and the implementation of undergraduate program “specializations.” At first glance, this fact is surprising given the far greater number of undergraduate institutions. Unfortunately, undergraduate curriculum expansion is significantly more difficult than most graduate level, Master of Science/Arts programs. In particular, university administrators have been quite happy to approve professional Master of Science degree programs, seeing them for the financial stars they often are. Michigan State University created a similar, and now successful, MS‐GISc graduate program in 2000. Beginning in spring of 2003, the department of Geography began pursuing the development of a Bachelor of Science degree in Geographic Information Science. Expanding a traditional curriculum to include a BS‐GISc degree places an entirely different set of programmatic demands on both the department and faculty than the theoretically similar MS program. This paper outlines the challenges of establishing an undergraduate program in GISc, details the solutions employed, and provides recommendations for minimizing or mitigating the associated problems. 相似文献
117.
The literatures on urban forestry, environmental justice, and Marxist urban political ecology are considered through empirical attention to the localized racial and ethnic politics which spatially differentiate urban socio-natural landscapes. In the American Southwest, urban landscapes reflect a history in which Anglo Whites were able to distance themselves from spaces of production while gaining access to superior residences and environmental amenities in spaces of reproduction; ethnoracially marginalized Others were treated as necessary yet disfavored populations, thus constituting a segregated mode of production. In this study, we investigate the association between tree canopy cover and the location of urban ethnic minority populations with a focus on the arid Southern High Plains city of Lubbock, Texas. Using data from color infrared aerial photography and block-group demographic indicators from the 2010 US Census, we analyze the city’s arboreal landscape with a mix of methods—hierarchical regression, archival research, and field observation. Results confirm that a lack of tree cover in minority neighborhoods is a symptom of broader environmental inequalities in which contemporary segregation patterns reflect a history of residential and land-use zoning with the socio-natural relations of planting and sustaining urban trees. 相似文献
118.
Seismology of the solar atmosphere 总被引:1,自引:0,他引:1
Wolfgang Finsterle Stuart M. Jefferies Alessandro Cacciani Paolo Rapex Cynthia Giebink Allister Knox Vincenzo DiMartino 《Solar physics》2004,220(2):317-331
We describe a new instrument for seismically probing the properties of the Sun's lower atmosphere, and present some first
results from an observational campaign carried out at the geographic South Pole during the austral summer of 2002/2003. A
preliminary analysis of the data (simultaneous, high-cadence observations of the velocity signals from the photosphere and
low chromosphere) shows that the well-known suppression of acoustic power in regions of strong magnetic field, and enhancement
of high-frequency power around active regions (acoustic halos), are both consistent with a spreading out of the magnetic field
lines with increasing height in the atmosphere. The data have also revealed some unexpected wave behavior. First, evanescent-like
waves are found at frequencies substantially above the acoustic cut-off frequency in regions of intermediate magnetic field.
Second, upward- and downward-propagating waves are detected in areas of strong magnetic field such as sunspots and plage:
even at frequencies below the acoustic cut-off frequency. Third, the wave behavior in regions of strong magnetic field can
change over periods of a few hours from propagating to evanescent. While we have no concrete explanation for the first two
results, the latter result opens up the question of whether sound waves are involved in short-term events such as flares or
CME's. 相似文献
119.
Cynthia S. Gorman 《Geographical review》2019,109(4):487-506
Through legal interpretation of immigration categories, such as the refugee definition, signatories to the UN Refugee Convention restrict access to political asylum. This paper examines how scalar logics are used in legal interpretation to filter out particular people from national space and control the number legally entitled to enter and remain in the U.S. Scalar logics shape access by requiring asylum seekers to prove they have been ‘singled out’ for persecution and by steering the meaning of the ‘particular social group’ provision of the refugee definition. The restrictive effects of these scalar logics are analyzed in relation to case law involving Central American asylum seekers fleeing gang‐related violence. These cases are often rejected on the basis that the asylum seekers possess identities and experiences exceeding the limited protection offered by asylum. Through analysis of these scalar logics, the paper highlights how interpretations of the refugee definition are an ongoing site of struggle over the scope of asylum protection. 相似文献
120.
Contemporary cartographic research on mapmaking and map use has a broad mandate and, as a consequence, researchers need a broad suite of methods. Consistent with research developments in other geographic subdisciplines, cartographic researchers now use qualitative methods. They offer the advantage of bringing research closer to the problem‐solving realms of mapmakers and map users. Our purpose here is to discuss an array of qualitative methods for mapmaking and map use. Questionnaires, interviews, and protocol methods are used to gather verbal data about mapmaking and map use. Ethnographies produce data from direct observation of mapmakers and users. Maps also are sources for document analysis. We use examples of published cartographic research to elaborate on each of these methods. 相似文献