全文获取类型
收费全文 | 1348篇 |
免费 | 49篇 |
国内免费 | 25篇 |
专业分类
测绘学 | 24篇 |
大气科学 | 115篇 |
地球物理 | 275篇 |
地质学 | 495篇 |
海洋学 | 119篇 |
天文学 | 214篇 |
综合类 | 15篇 |
自然地理 | 165篇 |
出版年
2023年 | 7篇 |
2021年 | 15篇 |
2020年 | 18篇 |
2019年 | 19篇 |
2018年 | 34篇 |
2017年 | 20篇 |
2016年 | 23篇 |
2015年 | 39篇 |
2014年 | 40篇 |
2013年 | 84篇 |
2012年 | 49篇 |
2011年 | 83篇 |
2010年 | 54篇 |
2009年 | 68篇 |
2008年 | 58篇 |
2007年 | 76篇 |
2006年 | 58篇 |
2005年 | 46篇 |
2004年 | 37篇 |
2003年 | 33篇 |
2002年 | 40篇 |
2001年 | 22篇 |
2000年 | 32篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 22篇 |
1996年 | 23篇 |
1995年 | 14篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 22篇 |
1988年 | 16篇 |
1987年 | 21篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 27篇 |
1983年 | 17篇 |
1982年 | 15篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 15篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 11篇 |
1975年 | 13篇 |
1974年 | 7篇 |
1973年 | 11篇 |
排序方式: 共有1422条查询结果,搜索用时 15 毫秒
951.
Heavy metal contamination in mangrove habitats of Singapore 总被引:1,自引:0,他引:1
Cuong DT Bayen S Wurl O Subramanian K Wong KK Sivasothi N Obbard JP 《Marine pollution bulletin》2005,50(12):1732-1738
952.
Chlorinated pesticides and PCBs in the sea-surface microlayer and seawater samples of Singapore 总被引:1,自引:0,他引:1
Sea-surface microlayer (SML) and seawater samples collected from Singapore's coastal marine environment were analyzed for selected chlorinated pesticides and polychlorinated biphenyls (PCBs). The SML is a potential site of enrichment of persistent organic pollutants (POPs) compared to the underlying water column. The concentration ranges of SigmaHCH, SigmaDDT and SigmaPCB in subsurface (1 m depth) seawater were 0.4-27.2 ng/l (mean 4.0 ng/l), 0.01-0.6 ng/l (mean 0.1 ng/l) and 0.05-1.8 ng/l (mean 0.5 ng/l) respectively. In the SML, the concentration ranges of SigmaHCH, SigmaDDT and SigmaPCB were 0.6-64.6 ng/l (mean 9.9 ng/l), 0.01-0.7 ng/l (mean 0.2 ng/l) and 0.07-12.4 ng/l (mean 1.3 ng/l) respectively. High spatial and temporal distribution was observed for all POPs measured. However, overall levels measured in the SML were lower than levels reported in the literature for SML samples from temperate coastal regions-possibly due to loss of semi-volatile compounds in the tropical climate of Singapore. Atmospheric wet deposition during the monsoon season may be an important source of POPs to the SML. This study provides the first scientific data on POP concentrations and enrichment factors in the SML for Southeast Asia. 相似文献
953.
Tectonic impact on the Lake Sevan environment (Armenia) 总被引:1,自引:0,他引:1
A. Karakhanian P. Tozalakyan J. C. Grillot H. Philip D. Melkonyan P. Paronyan S. Arakelyan 《Environmental Geology》2001,40(3):279-288
The geology of Lake Sevan is characterized by the structure of a pull-apart basin. Methane emission from the lake surface
correlates with evidence of physical and chemical water properties, remote sensing, etc., and suggests its possible emission
from active fault zones at the lake bottom, as well as emission of biogenic methane from the fermentation of bottom organic
remains. Correlation with anomalies in the lake bottom geochemistry suggests a high permeability of active fault zones and
suggests that geodynamic, seismic and geochemical activity across the fault zones during the buildup to the M=7.1 Spitak earthquake
led to plankton depression, which resulted in a large number of fish dying in 1984, and ended with a seismic disaster in 1988.
Received: 2 November 1999 · Accepted: 27 January 2000 相似文献
954.
955.
Shuttle radar images (SIR-A) of volcanic and impact craters were examined to assess their appearance on radar images. Radar characteristics were determined for: (a) 9 maarlike craters in the Pinacate volcanic field, Sonora, Mexico; (b) the caldera of Cerro Volcan Quemado, in the Bolivian Andes; (c) Talemzane impact crater, Algeria; and (d) Al Umchaimin, a possible impact structure in Iraq. SIR-A images were compared with conventional photographs and with results from field studies. Consideration was then given to radar images available for Venus, or anticipated from the Magellan mission. Of the criteria ordinarily used to identify impact craters, some can be assessed with radar images and others cannot be used; planimetric form — expressed as circularity — and ejecta-block distribution can be assessed on radar images, but rim and floor elevations relative to the surrounding plain and disposition of rim strata are difficult or impossible to determine. We conclude that it will be difficult to separate small impact craters from small volcanic craters on Venus using radar images, and suggest that it will be necessary to understand the geological setting of the areas containing in order to determine their origin.Department of Geology.Center for Meteorite Studies, Arizona State University, Tempe, Ariz., U.S.A. 相似文献
956.
Philip J. Stooke 《Earth, Moon, and Planets》1993,62(3):199-221
Topographic models of Saturn's F-Ring shepherd satellites Prometheus and Pandora were derived from the shapes of limbs and terminators in Voyager images, modified locally to accommodate large craters and ridges. The models are presented here in tabular and graphic form, including the first published maps of the satellites. The shape of Prometheus is approximated by a triaxial ellipsoid with axes of 145, 85 and 60 km. The volume is estimated to be 3.9 ± 1.0 × 105 km3, significantly smaller than previous estimates. A system of prominent ridges and valleys cross the north polar region. Prometheus appears to be less heavily cratered than the other small satellites near the edge of the rings, though this may be an artifact of the low resolution of available images. Pandora is approximated by a triaxial ellipsoid with axes of 114, 84 and 62 km. The volume is estimated to be 3.1 ± 1.0 × 105 km3. Its surface appears to be very heavily cratered. 相似文献
957.
Triangle based interpolation is introduced by an outline of two classical planar interpolation methods, viz. linear triangular facets and proximal polygons. These are shown to have opposite local bias. By applying cross products of triangles to obtain local gradients, a method designated slant-top proximal polygon interpolation is introduced that is intermediate between linear facets and polygonal interpolation in its local bias. This surface is not continuous, but, by extending and weighting the gradient planes, a C1
surface can be obtained. The gradients also allow a roughness index to be calculated for each data point in the set. This index is used to control the shape of a blending function that provides a weighted combination of the gradient planes and linear interpolation. This results in a curvilinear, C1,interpolation of the data set that is bounded by the linear interpolation and the weighted gradient planes and is tangent to the slant-top interpolation at the data points. These procedures may be applied to data with two, three, or four independent variables. 相似文献
958.
John T. Wasson William V. Boynton Chen-Lin Chou Philip A. Baedecker 《Earth, Moon, and Planets》1975,13(1-3):121-141
Siderophilic element/Ir ratios are higher in mature lunar soils from highlands sites than in those from mare sites. We infer that the population of materials responsible for the early intense bombardment of the Moon had high ratios, and that the population responsible for the essentially constant flux has low ratios. No group of chondrites has siderophile/Ir ratios identical to those in the mare or highlands soils; CM chondrites are the most similar, and CM-like materials may account for a major fraction of Earth-crossing materials during the past 3.7 b.y.Siderophile/Ir ratios may be used to determine the amount of highlands regolith in soils or breccias from the mare-highlands interface areas (Apollo 15 and 17), and to infer the time of formation of highlands breccias whose sideropbiles originated in mature soils. Arguments are summarized against the viewpoint that the siderophiles in most highlands breccias originated in basin-forming projectiles. Differences in mature soil siderophile concentrations at Apollo 14 and 16 indicate a substantially greater concentration at the latter site immediately following the Imbrium event.Siderophile concentrations are used to estimate mean regolith depths at the landing sites; as relative values these are more precise than estimates based on seismic or crater observations. The longlived flux is calculated to be 2.9 g cm–2 b.y.–1 averaged over the past 3.7 b.y. A consideration of the relationship between mass fluence and time indicates that the mass flux decreased with a half-life of about 40 m.y. immediately following the Imbrium event. 相似文献
959.
W.Philip Appleyard 《Marine Policy》1983,7(3):218-220
Fisheries have tended to be a relatively neglected aspect of aid to developing countries. In the article below, Philip Appleyard gives some reasons for this and indicates ways in which future fisheries aid could be usefully employed. 相似文献
960.