全文获取类型
收费全文 | 117篇 |
免费 | 9篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 22篇 |
地球物理 | 18篇 |
地质学 | 49篇 |
海洋学 | 10篇 |
天文学 | 10篇 |
综合类 | 1篇 |
自然地理 | 18篇 |
出版年
2023年 | 4篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 11篇 |
2016年 | 11篇 |
2015年 | 4篇 |
2014年 | 7篇 |
2013年 | 8篇 |
2012年 | 6篇 |
2011年 | 5篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 10篇 |
2007年 | 5篇 |
2006年 | 1篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 4篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有130条查询结果,搜索用时 15 毫秒
1.
Johanna A. A. Bos Sjoerd J. P. Bohncke C. Roel Janssen 《Journal of Paleolimnology》2006,35(2):211-238
Late glacial changes in the vegetation were studied in and around a former lake on the southeastern side of a coversand ridge near Milheeze (southern Netherlands). Analyses of microfossils and macroremains and AMS 14C dating were performed on four sediment cores along a transect from sand ridge to the lake centre. Small-scale vegetation patterns and lake-level fluctuations were reconstructed in detail based on the information provided by the transect. For the first time in The Netherlands, cores along a transect within one lake were used to reconstruct the amplitude of late glacial lake-level fluctuations. Near Milheeze, a small and shallow lake was formed during the Bølling. The large increase in the water level during the Bølling and early Allerød, and the transition to more eutrophic conditions at the start of the Allerød, were probably related to the disappearance of permafrost. During the Allerød, open birch and pine woodlands developed in the area. In the lake, organic deposits accumulated, and the lake size and depth fluctuated. At the start of the Younger Dryas, higher lake water levels were recorded and woodlands became more open as a result of both a drop in the temperature and an increase in the effective precipitation. During the late Younger Dryas the lake water level dropped as the climate became drier and temperatures slightly increased. Accumulation of organic deposits in the lake ceased at the end of the Younger Dryas, which was caused by a drop in the water level in combination with the hydroseral succession process within the lake itself. The climatic signal reflected in the late glacial flora and lake-level fluctuations agree well with other published data from The Netherlands. 相似文献
2.
Natural Hazards - How have property buyouts and disaster recovery assistance programs been implemented in Canadian communities? This paper compares contrasting policies and programs in two Canadian... 相似文献
3.
Alida Bundy Johanna J. Heymans Lyne Morissette Claude Savenkoff 《Progress in Oceanography》2009,81(1-4):188
The facts: four Northwest Atlantic ecosystems, three cod stock collapses 15 years ago (plus one severely depleted), seals now top predator in all ecosystems, all had cod as a top predator before collapse, groundfish declines in all areas, forage base increased in most systems. No recovery in any system. Have these ecosystems fundamentally changed? Why? The challenge: compare and contrast these four ecosystems. The answer: using mass balance models, empirical data and a suite of ecosystem indicators, we explore how and why these systems have changed over time. At the ecosystem and community level, we see broad similarities between ecosystems. However, structurally and functionally these systems have shifted to an alternate state, with changes in predator structure, trophic structure and flow. 相似文献
4.
Johanna Wolf W. Neil Adger Irene Lorenzoni Vanessa Abrahamson Rosalind Raine 《Global Environmental Change》2010,20(1):44-52
It has been claimed that high social capital contributes to both positive public health outcomes and to climate change adaptation. Strong social networks have been said to support individuals and collective initiatives of adaptation and enhance resilience. As a result, there is an expectation that social capital could reduce vulnerability to risks from the impacts of climate change in the health sector. This paper examines evidence on the role social networks play in individuals’ responses to heat wave risk in a case study in the UK. Based on interviews with independently living elderly people and their primary social contacts in London and Norwich, we suggest that strong bonding networks could potentially exacerbate rather than reduce the vulnerability of elderly people to the effects of heat waves. Most respondents interviewed did not feel that heat waves posed a significant risk to them personally, and most said that they would be able to cope with hot weather. Bonding networks could perpetuate rather than challenge these narratives and therefore contribute to vulnerability rather than ameliorating it. These results suggest a complex rather than uniformly positive relationship between social capital, health and adaptation to climate change. 相似文献
5.
6.
Summary Seismograms recorded during the Trans-Scandinavian Profile of 1969 at the stations Kajaani, Oulu, Maaselkä and Sodankylä are used to determine theP wave velocities for distances from 400 km to 1300 km. An apparent velocity of 8.50 km/s was found. After making a correction due to the curvature of the earth the velocity of about 8.40 km/s was obtained at an approximate depth of 80 km. Some comparisons are made with other results from Fennoscandian area. 相似文献
7.
H. Korhonen 《Pure and Applied Geophysics》1973,103(1):259-265
Summary In this study spectral development of microseisms at Oulu is discussed by means of power spectra computed from the recordings of a long period vertical seismograph. North Atlantic storm microseisms are found to be distinguished at peak frequencies in band 90–130 mHz while the main peaks of Norwegian microseisms occur at frequencies higher than 130 mHz. In both of these cases a low frequency side maximum is found at nearly the same frequencies as the main maximum in corresponding sea wave spectra. Fast moving storms associate with rapid changes in microseism spectra. A shift of peaks towards higher frequencies is found in connection with storm approach. 相似文献
8.
Per?WestmanEmail author Johanna?Borgendahl Thomas?S.?Bianchi Nianhong?Chen 《Estuaries and Coasts》2003,26(3):680-689
This study corroborates the hypothesis that nitrogen-fixing cyanobacteria have probably occurred as an important component
of the phytoplankton community in the Baltic Sea at least since brackish water conditions were initiated 8,50014C yr BP. Pigment analyses indicate that extensive occurrences started prior to a sharp increase in nutrient levels dated to
7,10014C yr BP. The cyanobacteria could have functioned as a natural trigger for eutrophication in the Baltic Sea by importing nitrogen.
This is also verified by a contemporaneous drop in the δ15N values from 4‰ to around 2‰. We further conclude that the spreading of cyanobacteria was probably caused by a decrease in
nitrogen∶phosphorus (N∶P) in the water mass that resulted from the intrusion of oceanic water with high P levels. The fractionation
of P in sediments indicated that iron-bound P was efficiently sequestered under anoxic conditions that occurred as a consequence
of the establishment of a stable stratification caused by the marine intrusion. This pool only showed minor variations around
3 μmol g−1 at the freshwater-brackish water transition. All P pools except the CaCO3 fraction showed a distinct increase around 9,30014C yr BP prior to the transition. We interpreted this increase as a change in preservation of organic matter or in the source
of the sediment. Slightly after 4,00014C yr BP there was a dramatic drop in all P pools without any corresponding decreases in total N and carbon. Total P decreased
from around 75 to 25–30 μmol g−1. The most dramatic drop occurred in the organic bound and the detrital apatite fractions, which decreased by a factor of
3–4. We explain this as a preferential regeneration of P, especially organic P, compared to other nutrients due to more prevalent
anoxic conditions. 相似文献
9.
The lithospheric models obtained for the Baltic Shield by using deep seismic soundings are discussed and results from different parts of the shield are compared with models achieved by the investigation of surface waves and of P to S converted waves. The results are found to agree rather well with each other particularly with regard to the first interface (at a depth of 10–15 km) and the whole thickness of the crust (c. 40 km). The macroseismic focal depth determinations of regional earthquakes are correlated with lithospheric structure. The main maximum in the focal depth distributions of Finnish earthquakes occur at a depth of 10–12 km. The geographical distribution of the earthquake epicentres suggests several seismo-active zones in the northern Baltic Shield. One new finding in this field concerns the Lapland zone, which runs in a north-westerly direction. 相似文献
10.
S. P. Jrvinen S. Hubrig M. Schller I. Ilyin T. A. Carroll H. Korhonen 《Astronomische Nachrichten》2016,337(3):329-338
Due to the knowledge of the rotation period and the presence of a rather strong surface magnetic field, the sharp‐lined young Herbig Ae star HD 101412 with a rotation period of 42 d has become one of the most well‐studied targets among the Herbig Ae stars. High‐resolution HARPS polarimetric spectra of HD 101412 were recently obtained on seven different epochs. Our study of the spectral variability over the part of the rotation cycle covered by HARPS observations reveals that the line profiles of the elements Mg, Si, Ca, Ti, Cr, Mn, Fe, and Sr are clearly variable while He exhibits variability that is opposite to the behaviour of the other elements studied. Since classical Ap stars usually show a relationship between the magnetic field geometry and the distribution of element spots, we used in our magnetic field measurements different line samples belonging to the three elements with the most numerous spectral lines, Ti, Cr, and Fe. Over the time interval covered by the available spectra, the longitudinal magnetic field changes sign from negative to positive polarity. The distribution of field values obtained using Ti, Cr, and Fe lines is, however, completely different compared to the magnetic field values determined in previous low‐resolution FORS 2 measurements, where hydrogen Balmer lines are the main contributors to the magnetic field measurements, indicating the presence of concentration of the studied iron‐peak elements in the region of the magnetic equator. Further, we discuss the potential role of contamination by the surrounding warm circumstellar matter in the appearance of Zeeman features obtained using Ti lines. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献