全文获取类型
收费全文 | 2146篇 |
免费 | 50篇 |
国内免费 | 31篇 |
专业分类
测绘学 | 60篇 |
大气科学 | 125篇 |
地球物理 | 440篇 |
地质学 | 782篇 |
海洋学 | 168篇 |
天文学 | 435篇 |
综合类 | 16篇 |
自然地理 | 201篇 |
出版年
2021年 | 10篇 |
2020年 | 25篇 |
2019年 | 25篇 |
2018年 | 39篇 |
2017年 | 30篇 |
2016年 | 43篇 |
2015年 | 32篇 |
2014年 | 50篇 |
2013年 | 94篇 |
2012年 | 67篇 |
2011年 | 89篇 |
2010年 | 102篇 |
2009年 | 127篇 |
2008年 | 107篇 |
2007年 | 84篇 |
2006年 | 77篇 |
2005年 | 69篇 |
2004年 | 72篇 |
2003年 | 80篇 |
2002年 | 67篇 |
2001年 | 41篇 |
2000年 | 49篇 |
1999年 | 35篇 |
1998年 | 26篇 |
1997年 | 26篇 |
1996年 | 35篇 |
1995年 | 31篇 |
1994年 | 40篇 |
1993年 | 28篇 |
1992年 | 28篇 |
1991年 | 12篇 |
1990年 | 27篇 |
1989年 | 29篇 |
1988年 | 33篇 |
1987年 | 29篇 |
1986年 | 27篇 |
1985年 | 42篇 |
1984年 | 40篇 |
1983年 | 38篇 |
1982年 | 33篇 |
1981年 | 46篇 |
1980年 | 28篇 |
1979年 | 22篇 |
1978年 | 20篇 |
1977年 | 22篇 |
1976年 | 19篇 |
1975年 | 16篇 |
1974年 | 21篇 |
1973年 | 22篇 |
1971年 | 9篇 |
排序方式: 共有2227条查询结果,搜索用时 375 毫秒
91.
Derek G. Turner Brent C. Ward Duane G. Froese Michel Lamothe Jeffrey D. Bond Nancy H. Bigelow 《Boreas: An International Journal of Quaternary Research》2016,45(3):521-536
At least five Middle to Late Pleistocene advances of the northern Cordilleran Ice Sheet are preserved at Silver Creek, on the northeastern edge of the St Elias Mountains in southwest Yukon, Canada. Silver Creek is located 100 km up‐ice of the Marine Isotope Stage (MIS) 2 McConnell glacial limit of the St Elias lobe. This site contains ~3 km of nearly continuous lateral exposure of glacial and non‐glacial sediments, including multiple tills separated by thick gravel, loess and tilted lake beds. Infrared‐stimulated luminescence (IRSL) and AMS radiocarbon dating constrain the glacial deposits to MIS 2, 4, either MIS 6 or mid‐MIS 7, and two older Middle Pleistocene advances. This chronology and the tilt of the lake beds suggest Pleistocene uplift rates of up to 1.9 mm a?1 along the Denali Fault since MIS 7. The non‐glacial sediment consists of sand, gravel, loess and organic beds from MIS 7, MIS 3 and the early Holocene. The MIS 3 deposits date to between 30–36 14C ka BP, making Silver Creek one of the few well‐constrained MIS 3‐aged sites in Yukon. This confirms that ice receded close to modern limits in MIS 3. Pollen and macrofossil analyses show that a meadow‐tundra to steppe‐tundra mosaic with abundant herbs and forbs and few shrubs or trees, dominated the environment at this time. The stratigraphy at Silver Creek provides a palaeoclimatic record since at least MIS 8 and comprises the oldest direct record of Pleistocene glaciation in southwest Yukon. 相似文献
92.
93.
H.J. O'Regan A. Turner L.C. Bishop S. Elton A.L. Lamb 《Quaternary Science Reviews》2011,30(11-12):1343-1352
Discoveries of fossil Homo outside Africa predating 1.0 Ma have generated much discussion about hominin dispersal routes. However, tool-using bipeds were only one element of the inter-continental mammalian dispersals that occurred during the climatic changes of the Pliocene and Pleistocene. This paper will place hominin movements in the context of those of the wider mammalian fauna, which includes carnivores, bovids and non-human primates. The distribution of these different taxa suggests that species moved individually when the environmental conditions were right for them, rather than in multi-species waves of dispersal, and allows evaluation of the contextual evidence for the newly emerging ‘Out of Asia’ paradigm as well as the established ‘Out of Africa’ model. 相似文献
94.
A new elastoplastic model called loading memory surface based on the critical state concept and the multi‐surface framework is proposed for geomaterials. The model uses a hypoelastic formulation and two plastic mechanisms. The formulations of the model are made in three‐dimensional stress–strain space and work under both monotonic and cyclic loadings. A newly introduced formalism makes it possible to obtain the cyclic response directly from the monotonic loading one. This formalism gives a three‐dimensional generalization of the well‐known Masing rule. The model has been validated against test results of Hostun sand under several conditions: monotonic and cyclic, drained and undrained, tests in compression and in extension, and at different confining pressures and different densities. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
95.
Intensification of Southern Hemisphere westerly winds 2000–1000 years ago: evidence from the subantarctic Campbell and Auckland Islands (52–50°S)
下载免费PDF全文
![点击此处可从《第四纪科学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
96.
David Nettle Galen P. Halverson Grant M. Cox Alan S. Collins Mark Schmitz James Gehling Peter R. Johnson Khalid Kadi 《地学学报》2014,26(2):120-129
The Ediacaran Jibalah Group comprises volcano‐sedimentary successions that filled small fault‐bound basins along the NW–SE‐trending Najd fault system in the eastern Arabian‐Nubian Shield. Like several other Jibalah basins, the Antaq basin contains exquisitely preserved sedimentary structures and felsic tuffs, and hence is an excellent candidate for calibrating late Ediacaran Earth history. Shallow‐marine strata from the upper Jibalah Group (Muraykhah Formation) contain a diversity of load structures and intimately related textured organic (microbial) surfaces, along with a fragment of a structure closely resembling an Ediacaran frond fossil and a possible specimen of Aspidella. Interspersed carbonate beds through the Muraykhah Formation record a positive δ13C shift from ?6 to 0‰. U‐Pb zircon geochronology indicates a maximum depositional age of ~570 Ma for the upper Jibalah Group, consistent with previous age estimates. Although this age overlaps with that of the upper Huqf Supergroup in nearby Oman, these sequences were deposited in contrasting tectonic settings on opposite sides of the final suture of the East African Orogen. 相似文献
97.
98.
99.
正China is one of the most prolific countries for dinosaur material in the world,from skeletons to footprints and eggs.At present,China has documented more than 160kinds of dinosaur,35 genera and 39 ichnospecies of dinosaur footprints,and 17 genera and 44 oospecies of dinosaur eggs.The dinosaur eggs in China are mainly distributed in Xinjiang,Inner Mongolia,Ningxia,Gansu, 相似文献
100.
Sibel Bargu Melissa M. Baustian Nancy N. Rabalais Ross Del Rio Benjamin Von Korff R. Eugene Turner 《Estuaries and Coasts》2016,39(5):1345-1356
The presence of domoic acid (DA) toxin from multiple species of Pseudo-nitzschia is a concern in the highly productive food webs of the northern Gulf of Mexico. We documented the Pseudo-nitzschia presence, abundance, blooms, and toxicity over three years along a transect ~100 km west of the Mississippi River Delta on the continental shelf. Pseudo-nitzschia were present throughout the year and occurred in high abundances (>104 cells l?1) in the early spring months during high Mississippi River (MSR) flow (~20,000 m3 s?1) but were most abundant (>106 cells l?1) when MSR discharge was relatively lower among the spring months. A high particulate toxin production (maximum reaching 13 μg DA l?1) was associated with the high cell abundances and exceeded, by an order of magnitude, prior reports of particulate DA concentrations in Louisiana coastal waters. Differences in Pseudo-nitzschia peak times and its toxicity were correlated mainly with the timing and magnitude of MSR discharge and changes in associated parameters such as nutrient stoichiometry and salinity. A negative relationship between high MSR discharge and Pseudo-nitzschia and particulate DA concentrations was documented. These riverine dynamics have the potential to influence DA contamination in pelagic and benthic food webs in the coastal waters of the northern Gulf of Mexico. 相似文献