全文获取类型
收费全文 | 189篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 19篇 |
地球物理 | 43篇 |
地质学 | 69篇 |
海洋学 | 8篇 |
天文学 | 39篇 |
综合类 | 1篇 |
自然地理 | 19篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 10篇 |
2012年 | 10篇 |
2011年 | 14篇 |
2010年 | 6篇 |
2009年 | 13篇 |
2008年 | 11篇 |
2007年 | 11篇 |
2006年 | 8篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1980年 | 2篇 |
排序方式: 共有200条查询结果,搜索用时 15 毫秒
11.
12.
The active faults known and inferred in the area where the major Pacific, North American and Eurasian plates come together group into two belts. One of them comprises the faults striking roughly parallel to the Pacific ocean margin. The extreme members of the belt are the longitudinal faults of islands arcs, in its oceanic flank, and the faults along the continental margins of marginal seas, in its continental flank. The available data show that all these faults move with some strike-slip component, which is always right-lateral. We suggest that characteristic right-lateral, either partially or dominantly, kinematics of the fault movements has its source in oblique convergence of the Pacific plate with continental Eurasian and North American plates. The second belt of active faults transverses the extreme northeast Asia as a continental extension of the active mid-Arctic spreading ridge. The two active fault belts do not cross but come close to each other at the northern margin of the Sea of Okhotsk marking thus the point where the Pacific, North American and Eurasian plates meet. 相似文献
13.
14.
Andrei V. Sher Jacobo Weinstock Gennady F. Baryshnikov Sergey P. Davydov Gennady G. Boeskorov Vladimir S. Zazhigin Pavel A. Nikolskiy 《Quaternary Science Reviews》2011,30(17-18):2238-2249
For a long time, “spelaeoid” (cave-bear-like) bears, Ursus (Spelearctos) spp., were believed to be almost purely European animals. Their geographic range has recently been extended to the east, in southern Siberia, Transbaikalia, Kirghizia, Mongolia and Korea. Two unexpected new findings, presented here in detail, significantly change existing views on the distribution of cave bears; both were found in North-Eastern Siberia, far beyond the Arctic Circle, more than 1500 km to the north-east of the previously accepted range.One of the fossils is a mandible, found near the town of Cherskiy at 68.73°N, 161.38°E. The analysis of local geology and accompanying mammal fossils suggests that it comes from the Olyorian Fauna (Early to early Middle Pleistocene). Morphologically, the Cherskiy mandible is closest to Ursus savini, a small middle Pleistocene cave bear from the British Cromer Forest-bed Formation, but differs in having a slightly more advanced dentition, and thus it is described as a new subspecies Ursus savini nordostensis. Another newly recognized fossil of the “spelaeoid” bear is an astragalus found at the Oskhordokh site at 67.54°N, 135.67°E, on a large gravel bar on the right bank of the Adycha River. This specimen is attributed to Ursus cf. deningeri.The paper also presents an interesting example of the interaction between classical and “molecular” palaeontology.The new finds significantly change existing ideas on the ecology and evolution of cave bears, some of the most remarkable members of the extinct Pleistocene megafauna. 相似文献
15.
Frank Kienast Sebastian Wetterich Svetlana Kuzmina Lutz Schirrmeister Andrei A. Andreev Pavel Tarasov Larisa Nazarova Annette Kossler Larisa Frolova Viktor V. Kunitsky 《Quaternary Science Reviews》2011,30(17-18):2134-2159
Permafrost records, accessible at outcrops along the coast of Oyogos Yar at the Dmitry Laptev Strait, NE-Siberia, provide unique insights into the environmental history of Western Beringia during the Last Interglacial. The remains of terrestrial and freshwater organisms, including plants, coleopterans, chironomids, cladocerans, ostracods and molluscs, have been preserved in the frozen deposits of a shallow paleo-lake and indicate a boreal climate at the present-day arctic mainland coast during the Last Interglacial. Terrestrial beetle and plant remains suggest the former existence of open forest-tundra with larch (Larix dahurica), tree alder (Alnus incana), birch and alder shrubs (Duschekia fruticosa, Betula fruticosa, Betula divaricata, Betula nana), interspersed with patches of steppe and meadows. Consequently, the tree line was shifted to at least 270 km north of its current position. Aquatic organisms, such as chironomids, cladocerans, ostracods, molluscs and hydrophytes, indicate the formation of a shallow lake as the result of thermokarst processes. Steppe plants and beetles suggest low net precipitation. Littoral pioneer plants and chironomids indicate intense lake level fluctuations due to high evaporation. Many of the organisms are thermophilous, indicating a mean air temperature of the warmest month that was greater than 13 °C, which is above the minimum requirements for tree growth. These temperatures are in contrast to the modern values of less than 4 °C in the study area. The terrestrial and freshwater organism remains were found at a coastal exposure that was only 3.5 m above sea level and in a position where they should have been under sea during the Last Interglacial when the global sea level was 6–10 m higher than the current levels. The results suggest that during the last warm stage, the site was inland, and its modern coastal situation is the result of tectonic subsidence. 相似文献
16.
Larisa A. Savelieva Andrei A. Andreev Raphael Gromig Dmitry A. Subetto Grigory B. Fedorov Volker Wennrich Bernd Wagner Martin Melles 《Boreas: An International Journal of Quaternary Research》2019,48(2):349-360
The new pollen record from the upper 12.75 m of a sediment core obtained in Lake Ladoga documents regional vegetation and climate changes in northwestern Russia over the last 13.9 cal. ka. The Lateglacial chronostratigraphy is based on varve chronology, while the Holocene stratigraphy is based on AMS 14C and OSL dates, supported by comparison with regional pollen records. During the Lateglacial (c. 13.9–11.2 cal. ka BP), the Lake Ladoga region experienced several climatic fluctuations as reflected in vegetation changes. Shrub and grass communities dominated between c. 13.9 and 13.2 cal. ka BP. The increase in Picea pollen at c. 13.2 cal. ka BP probably reflects the appearance of spruce in the southern Ladoga region at the beginning of the Allerød interstadial. After c. 12.6 cal. ka BP, the Younger Dryas cooling caused a significant decrease in spruce and increase in Artemisia with other herbs, indicative of tundra‐ and steppe‐like vegetation. A sharp transition from tundra‐steppe habitats to sparse birch forests characterizes the onset of Holocene warming c. 11.2 cal. ka BP. Pine forests dominated in the region from c. 9.0 to 8.1 cal. ka BP. The most favourable climatic conditions for deciduous broad‐leaved taxa existed between c. 8.1 and 5.5 cal. ka BP. Alder experiences an abrupt increase in the local vegetation c. 7.8 cal. ka BP. The decrease in tree pollen taxa (especially Picea) and the increase in herbs (mainly Poaceae) probably reflect human activity during the last 2.2 cal. ka. Pine forests have dominated the region since that time. Secale and other Cerealia pollen as well as ruderal herbs are permanently recorded since c. 0.8 cal. ka BP. 相似文献
17.
In order to estimate a transient response of the local hydrological cycle and vegetation cover in the African monsoon area to global climate changes, a simple two-dimensional water vapor transport model coupled with a carbon cycle model for the soil was used. The key difference from other models is that we take into account a positive feedback between the precipitation and development of the vegetation root system in the underlying surface. As our calculation shows, this feedback is responsible for a long-term transient response of local hydrological cycles to the global temperature changes. In the case of a four component vegetation system - tropical forests, savannah, semi desert and desert, (and 2 °C ocean surface water warming), a new steady-state is reached in about 1500 years.In previous works of other authors, the increase of summer precipitations during Holocene or Last Interglacial could be explained only as a result of the surface temperature increase in the intracontinental parts of Africa. However, from paleodata indicates, the temperature in the intracontinental regions of Africa rather decreased during warm epochs of geological past: Holocene optimum, Last Interglacial and middle Pliocene climatic optimum. Our simple model simulations agree with both paleoprecipitation and paleotemperature data. 相似文献
18.
Tempos of Elderly Age and Geographical Concentration* 总被引:1,自引:0,他引:1
This paper presents a method to measure two types of tempos: 1) the tempo of elderly age concentration, the rate of change in the elderly proportion in a region; and 2) the tempo of elderly geographical concentration, the rate of change in a region's share of the national elderly population. The two measurements are applied to historical data for the United States. The results reveal that both tempos vary spatially and temporally. Relative tempos are also introduced to compare the indices between different age groups and regions. 相似文献
19.
Konstantin V. Kholshevnikov Andrei V. Elkin 《Celestial Mechanics and Dynamical Astronomy》2002,84(1):57-63
According to the classical theory of equilibrium figures surfaces of equal density, potential and pressure concur (let call them isobars). Isobars may be represented by means of Liapunov power series in small parameter q, up to the first approximation coincident with centrifugal to gravitational force ratio on the equator. A. M. Liapunov has proved the existence of the universal convergence radius q
: above mentioned series converge for all bodies if q < q
. Using Liapunov's algorithm and symbolic calculus tools we have calculated q
= 0.000370916. Evidently, convergence radius q
0 may be much greater in non-pathological situations. We plan to examine several simplest cases. In the present paper, we find q
0 for homogeneous liquid. The convergence radius turns out to be unexpectedly large coinciding with the upper boundary value q
0 = 0.337 for Maclaurin ellipsoids. 相似文献
20.