全文获取类型
收费全文 | 510篇 |
免费 | 10篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 30篇 |
地球物理 | 26篇 |
地质学 | 347篇 |
海洋学 | 15篇 |
天文学 | 14篇 |
自然地理 | 94篇 |
出版年
2014年 | 6篇 |
2013年 | 25篇 |
2012年 | 7篇 |
2011年 | 11篇 |
2010年 | 17篇 |
2009年 | 8篇 |
2008年 | 14篇 |
2007年 | 16篇 |
2006年 | 14篇 |
2005年 | 14篇 |
2004年 | 6篇 |
2003年 | 9篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 20篇 |
1997年 | 27篇 |
1996年 | 25篇 |
1995年 | 16篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 20篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 15篇 |
1988年 | 16篇 |
1987年 | 18篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 12篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 2篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1967年 | 5篇 |
1963年 | 3篇 |
1942年 | 3篇 |
排序方式: 共有527条查询结果,搜索用时 15 毫秒
1.
PAUL COLE ANGUS DUNCAN JOHN GUEST 《Geology Today》1996,12(2):68-72
The 1957–58 eruption of Capelinhos, on Faial, in the Azores, built a new volcano at the west end of the island. Erosion by the sea has subsequently destroyed over two-thirds of this structure and will probably continue to remove much of the rest of the volcano over the next few decades. 相似文献
2.
3.
Oil-weathering processes in ice-free subarctic and Arctic waters include spreading, evaporation, dissolution, dispersion of whole-oil droplets into the water column, photochemical oxidation, water-in-oil emulsification, microbial degradation, adsorption onto suspended particulate material, ingestion by organisms, sinking, and sedimentation. While many of these processes also are important factors in ice-covered waters, the various forms of sea ice (depending on the active state of ice growth, extent of coverage and/or decay) impart drastic, if not controlling, changes to the rates and relative importance of different oil-weathering mechanisms. Flow-through seawater wave-tank experiments in a cold room at −35°C and studies in the Chukchi Sea in late winter provide data on oil fate and effects for a variety of potential oil spill scenarios in the Arctic. Time-series chemical weathering data are presented for Prudhoe Bay crude oil released under and encapsulated in growing first-year columnar ice through spring breakup. 相似文献
4.
MONA HENRIKSEN JAN MANGERUD ALEXEI MATIOUCHKOV REW S. MURRAY AAGE PAUS JOHN INGE SVENDSEN 《Boreas: An International Journal of Quaternary Research》2008,37(1):20-37
A 22 m long sediment core from Lake Yamozero on the Timan Ridge in northern Russia has provided evidence of intriguing climatic shifts during the last glacial cycle. An overall shallowing of the lake is reflected in the lower part of the cores, where pollen indicates a transition from glacial steppe vegetation to interstadial shrub-tundra. These beds are capped by a well-defined layer of compact clay deposited in relatively deep water, where pollen shows surrounding spruce forests and warmer-than-present summer temperatures. The most conservative interpretation is that this unit represents the last interglacial period. However, a series of Optical Stimulated Luminescence (OSL) dates suggests that it corresponds with the Early Weichselian Odderade interstadial (MIS 5a). This would imply that the Odderade interstadial was just as warm as a normal interglacial in this continental part of northern Europe. If correct, then pollen analysis, as a correlation tool, is less straightforward and the definition of an interglacial is more complex than previously thought. We discuss the validity and possible systematic errors of the OSL dates on which this age model is based, but conclude they really indicate a MIS 5a age for the warm period. Above the clay is an unconformity, most likely reflecting a period of subaerial exposure implying dry conditions. Deposition of silt under fluctuating cold climates in the Middle Weichselian continued until a second gap in the record at c . 40 kyr BP. The lake basin started to fill up again around 18 kyr BP. 相似文献
5.
Oolitic sediments occur over large portions of the outer continental shelf off northernmost Brazil and southern French Guiana. Carbon-14 dates, stable isotope values and analogies with similar deposits from other areas in the world indicate that the ooids were formed in shallow water (possibly protected hypersaline environments) during low stands of sea level. In contrast to both modern ooids and other relict ooids, however, the Amazon shelf ooids are composed entirely of magnesian calcite (12 mol % MgCO3) and possess radial crystal microstructures. A comparison of water depths and ages of the Amazon ooids with the generally accepted eustatic sea level curve indicates that the Amazon shelf subsided more than 100 m 16-21 thousand years ago. Prior to and subsequent to the subsidence, however, the outer shelf remained relatively stable. 相似文献
6.
7.
Origin of Geochemical Variability by Arc-Continent Collision in the Biru Area, Southern Sulawesi (Indonesia) 总被引:1,自引:0,他引:1
Analyses of igneous rocks from the Eocene calc-alkaline andMiocene potassic volcanic arc in southwest Sulawesi indicatethat magmas became more heterogeneous in their trace elementand PbSrNd isotopic signature following the collisionof the Buton microcontinent with the arc at 相似文献
8.
Experimental studies of the formation of planar laminae by migration of low-relief bed waves over aggrading upper-stage plane beds show that the average thickness of laminae at a point increases with both aggradation rate and the variance of the heights of bed waves passing that point. In general, the preserved laminae represent only a small proportion (generally less than 50%) of the height of the largest bed waves in the population. The theory developed by Paola & Borgman (1991), relating the probability density function of stratal thickness to that of bed wave height for the case of no net aggradation, was adapted for aggrading conditions and shown to agree well with data. These results suggest that the theory can be used to estimate, from the distribution of thickness of planar laminae, either the distribution of bed wave heights, mean aggradation rate, mean bed wave length or mean bed wave celerity, provided the other parameters can be estimated. 相似文献
9.
A study of the whole-rock geochemistry and mineral chemistry of high-TiO2 Upper Jurassic and medium-TiO2 Lower Cretaceous basalts from Kong Karls Land, Svalbard, is presented. Geochemical criteria indicate that the basalts are initial rifting tholeiites with weak signs of crustal contamination. The Upper Jurassic basalts appear to be associated with the Olga Rift, part of a trans-Barents rift system which failed to link the proto-Atlantic and proto-Arctic basins. The Lower Cretaceous basalts may be more closely related to initial rifting tholeiites on Franz Josef Land and Spitsbergen generated during the rifting stage of opening of the Canada Basin. During break-up of the Barents Shelf, the sequence of magma types corresponds to the pre-, syn- and post-rifting stages established in other areas of continental break-up. Evidence for a possible hot-spot or plume trail, extending from Siberia to the Yermak Plateau over 250 Ma, is assembled. 相似文献
10.
ABSTRACT. Contrary to much of the hype that posits cyberspace as the uncontested domain of rugged individualists, computer networks and traffic exhibit deeply social and political roots. The Internet is neither inherently oppressive nor automatically emancipatory; it is a terrain of contested philosophies and politics. After a brief review of the politics of electronic knowledge, we discuss the ways in which the Internet can be harnessed for counterhegemonic (antiestablishment) political ends. We focus on progressive uses, including the confrontation of nomadic power and rhizomic power structures, in which the local becomes the global. We also offer an encapsulation of right-wing uses. Throughout, we see cyberactivism as a necessary, but not sufficient, complement to real-world struggles on behalf of the disempowered. 相似文献