全文获取类型
收费全文 | 680篇 |
免费 | 9篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 59篇 |
地球物理 | 154篇 |
地质学 | 221篇 |
海洋学 | 29篇 |
天文学 | 202篇 |
自然地理 | 19篇 |
出版年
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 12篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 13篇 |
2014年 | 15篇 |
2013年 | 17篇 |
2012年 | 28篇 |
2011年 | 20篇 |
2010年 | 12篇 |
2009年 | 24篇 |
2008年 | 16篇 |
2007年 | 30篇 |
2006年 | 29篇 |
2005年 | 27篇 |
2004年 | 30篇 |
2003年 | 20篇 |
2002年 | 22篇 |
2001年 | 9篇 |
2000年 | 9篇 |
1999年 | 21篇 |
1998年 | 16篇 |
1997年 | 16篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 6篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1971年 | 4篇 |
1964年 | 4篇 |
1962年 | 4篇 |
1958年 | 4篇 |
1955年 | 5篇 |
1954年 | 4篇 |
排序方式: 共有695条查询结果,搜索用时 0 毫秒
651.
Forest canopies alter the amount and isotopic composition of precipitation reaching the forest floor. Thus retention, evaporation and transport processes in forest canopies, and their effects on water isotopes, are key to understanding forest water cycling. Using a two-year isotope dataset from a mixed beech/spruce forest in Zurich, Switzerland, we assessed the isotopic offsets between precipitation, throughfall and stemflow. We also analysed how these offsets affect estimates of the fraction of soil water that is derived from winter precipitation. Throughfall was typically enriched in heavy isotopes compared to precipitation, but isotopically lighter than stemflow, with average δ2H of −64.3 ‰, −59.9 ‰ and − 56.3 ‰ in precipitation, throughfall and stemflow, respectively. The differences between beech and spruce were rather small compared to the seasonal differences in precipitation isotopes. Isotopic offsets between precipitation and throughfall/stemflow were smaller during the spring and summer months (March through August) than during fall and winter (September through February). Bulk and mobile soil waters at 10 and 40 cm showed smaller seasonal variations than those in precipitation, throughfall and stemflow, and were isotopically lighter than recent precipitation, with the largest offsets occurring during the summer months (June through August) for bulk soil waters. Thus, bulk soil waters at both depths contain a mixture of precipitation from previous events and seasons, with over-representation of isotopically lighter winter precipitation. Mobile soil waters were more similar to recent precipitation than bulk soil waters were. Throughfall isotopes were slightly heavier than precipitation isotopes, resulting in different sinusoidal fits for seasonal isotopic cycles in precipitation and throughfall. These differences lead to small underestimates in the fraction of soil water originating from winter precipitation, when open-field precipitation rather than throughfall is used as the input data. Together our results highlight the importance of isotope measurements in throughfall and stemflow for the assessment of precipitation seasonality and water cycling across forested landscapes. 相似文献
652.
P. Bertrand J. Giraudeau B. Malaize P. Martinez M. Gallinari T. F. Pedersen C. Pierre M. Th. Vnec-Peyr 《Marine Geology》2002,180(1-4):235-248
Concentration and mass accumulation rate profiles from Southeastern Atlantic sediment cores located off Namibia show that an exceptional episode in benthic carbonate dissolution occurred during early glacial isotope stage 6 (substages 6.6 and 6.5) between about 186 000 and 170 000 yr BP. Although this episode is restricted to or is more pronounced in this region than in other areas of the Atlantic Ocean, its exceptional character with respect to older and younger climatic episodes at the same site cannot be fully explained by local factors alone, but requires a combination of local and global influences. The onset of the carbonate dissolution episode is related to a more efficient transfer of organic matter from surface eutrophic areas to the lower and is due to low sea level, while its termination relates to a change in either global ocean alkalinity or bottom water circulation. An evaluation of the magnitude of this local carbonate dissolution episode suggests that its contribution to a global alkalinity change may have been significant. Carbonate dissolution was probably amplified by stronger upwelling activity of the Benguela System linked to an exceptional northern excursion of the boreal summer ITCZ during early glacial isotope stage 6. This low latitude global linkage may explain how this carbonate dissolution event as well as other ‘anomalies’ observed for early stage 6, like an important Dole effect minimum or a ‘cold’ Mediterranean sapropel, are related. 相似文献
653.
Th. Weimer 《Earth, Moon, and Planets》1979,20(2):163-167
Sans résuméPresented at the IAU-COSPAR Julius Schmidt Symposium on 100 Years of Lunar Mapping held at Lagonissi, Greece, 25–27 May, 1978. 相似文献
654.
Several polar contaminants were found in screening analyses of 30 representative surface water samples collected from rivers, lakes, and canals in Berlin. Residues of pharmaceuticals and N-(phenylsulfonyl)-sarcosine originating from various sewage treatment plants effluents were found at concentrations up to the μg/L-level in the surface water, whereas the concentrations of polar pesticides such as dichlorprop and mecoprop were always below 0.1 μg/L. The pharmaceuticals most frequently detected in the surface water samples include clofibric acid, diclofenac, ibuprofen, propiphenazone, and two other drug metabolites. Additional investigations of groundwater wells of a drinking water plant have shown that polar contaminants such as drug residues or N-(phenylsulfonyl)-sarcosine easily leach through the subsoil into the groundwater aquifers when contaminated surface water is used for groundwater recharge in drinking water production. 相似文献
655.
656.
Richard Giot Albert Giraud Christophe Auvray Françoise Homand Théophile Guillon 《国际地质力学数值与分析法杂志》2011,35(3):329-359
In this paper, we investigate the pulse test, which is usually considered as efficient for measuring the permeability of weakly permeable porous media. The pulse is first analyzed and we show that it is a fully poromechanical coupled problem. Owing to those couplings, the problem is 2D‐axisymmetrical, rather than 1D as is usually considered to be the case. As a consequence, the 1D solutions, for example under constant mean stress hypothesis, although giving good approximates of permeability and storage coefficient, are not rigorous and an enhanced back analysis of the test requires 2D solutions. Therefore, no analytical solution exists, and the problem has to be solved using 2D‐axisymmetrical numerical modelings of the pulse test. The finite element method is considered in this paper. We then proceed to formulate the pulse test back analysis as a parameter identification problem, and we focus on intrinsic permeability, Biot coefficient, drained Young's modulus and reservoir compressibility levels. This parameter identification problem is solved by an inverse method consisting of the minimization of a cost‐functional, through a gradient‐based algorithm. This new method of interpretation of the pulse test is finally applied to laboratory tests on Meuse/Haute–Marne argillite and is shown to give encouraging results. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
657.
Large areas of Greece are seriously degraded and landscape deterioration is mainly influenced by climatic factors, geological factors, overgrazing, forest fires and urbanisation. The examined area of Saint Panteleimon is located in northern Greece on the foot-slope of Mt. Olympus and exhibits aesthetic beauty of significant value owed to specific ecological, historical and cultural conditions. Due to intensive erosion and other geological factors, the old village, which is characterised by unique architecture, was abandoned. In the study area is located the castle of Platamon, which is dated to 1222 a.d. Overgrazing, which was very common a few decades ago, has enhanced erosion and affected the surrounding landscape. Another case of degradation concerns forestland, where erosion and landslides have influenced the loss of surface soil layers resulting in vegetation decline. The erosion impact increased due to urbanisation and recreational activities. Management of degradation at a local scale is very complex and requires a multidisciplinary approach. Recent works for soil stabilisation in conjunction with efforts for maintaining and recovering the protective vegetation have increased the degree of protection. Priorities for environmental protection in the study area are proposed to focus on reforestation, rational management of rangeland and restoration of hydrologic conditions of the watersheds. 相似文献
658.
I.Th. Rosenqvist 《Engineering Geology》1966,1(6):445-450
The ultra-sensitive type of clay called quick clay has caused severe landslides in Scandinavia and on the east and west coast of Canada. Slides of this type were the mentioned in literature in the fourteenth century. Quick-clay properties were described in 1901. Later geologists at the Norwegian Geological Survey, the Norwegian Highway Laboratory and the Norwegian Geotechnical Institute carried out research on this material. The present opinion is that the peculiar properties are based upon colloidal-chemical phenomena. According to this the clays deposited and consolidated in a flocculated state. Later chemical changes increased the double layer potential, either by leaching of electrolyte or by addition of suitable anions. The flocculated structure remains, unstable though, until mechanical disturbances cause a breakdown. Thus the clay is transformed into a dispersed state. 相似文献
659.
This article describes the considerations which led to the current optical design of the new 1.5 m solar telescope GREGOR. The result is Gregorian design with two real foci in the optical train. The telescope includes a relay optic with a pupil image used by a high order adaptive optics system (AO). The optical design is described in detail and performance characteristics are given. Finally we show some verification results which prove that – without atmospheric effects – the completed telescope reaches a diffraction limited performance (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
660.
Dr. Th. Herzog 《International Journal of Earth Sciences》1914,5(5-6):353-371
Ohne Zusammenfassung 相似文献