全文获取类型
收费全文 | 5257篇 |
免费 | 198篇 |
国内免费 | 52篇 |
专业分类
测绘学 | 137篇 |
大气科学 | 418篇 |
地球物理 | 1230篇 |
地质学 | 1972篇 |
海洋学 | 360篇 |
天文学 | 900篇 |
综合类 | 17篇 |
自然地理 | 473篇 |
出版年
2022年 | 28篇 |
2021年 | 65篇 |
2020年 | 69篇 |
2019年 | 95篇 |
2018年 | 146篇 |
2017年 | 157篇 |
2016年 | 165篇 |
2015年 | 146篇 |
2014年 | 192篇 |
2013年 | 271篇 |
2012年 | 211篇 |
2011年 | 286篇 |
2010年 | 229篇 |
2009年 | 285篇 |
2008年 | 227篇 |
2007年 | 204篇 |
2006年 | 186篇 |
2005年 | 197篇 |
2004年 | 194篇 |
2003年 | 174篇 |
2002年 | 169篇 |
2001年 | 85篇 |
2000年 | 95篇 |
1999年 | 76篇 |
1998年 | 92篇 |
1997年 | 73篇 |
1996年 | 66篇 |
1995年 | 64篇 |
1994年 | 59篇 |
1993年 | 65篇 |
1992年 | 50篇 |
1991年 | 42篇 |
1990年 | 43篇 |
1989年 | 46篇 |
1988年 | 47篇 |
1987年 | 51篇 |
1986年 | 50篇 |
1985年 | 58篇 |
1984年 | 74篇 |
1983年 | 56篇 |
1982年 | 60篇 |
1981年 | 49篇 |
1980年 | 50篇 |
1979年 | 49篇 |
1978年 | 44篇 |
1977年 | 38篇 |
1976年 | 35篇 |
1975年 | 32篇 |
1974年 | 37篇 |
1973年 | 32篇 |
排序方式: 共有5507条查询结果,搜索用时 0 毫秒
1.
In the upper Chesapeake Bay (Maryland, U.S.A.) field surveys were conducted at 18 multiple longshore sand bar sites. The multiple bar systems were found in water depths less than approximately 2 m (mean sea level), and exhibited mild bottom slopes of 0·0052 or less. The number of bars composing each system ranged from four to 17 and the spacing between the crests typically increased in the offshore direction, ranging from 12 to 70 m. Bar height also typically increased with distance offshore and ranged from 0·03 to 0·61 m. A grain size analysis of crest and trough sediment did not reveal any significant differences and the sediment was categorized as ‘fine sand’. A review of the literature data indicated that the Chesapeake Bay multiple bars possessed similar characteristics to those found in Gelding Bay (Baltic Sea); similarities in fetch, wave height and tidal range between the two bays may account for this finding. The surf-scaling parameter indicated that the multiple bar systems were extremely dissipative with regard to wave energy, and wave height appeared to be an important factor in controlling bar spacing and bar height. A multiple wave break point hypothesis was discussed as a possible mechanism for the formation of Chesapeake Bay multiple longshore bars, and limited observational evidence appeared to support such a mechanism. 相似文献
2.
This paper proposes a multi‐level parallelized substructuring–frontal combined algorithm for the analysis of the problem of thermo/hydraulic/mechanical behaviour of unsaturated soil. Temperature, displacement, pore water pressure and pore air pressure are treated as the primary variables in a non‐linear analysis. Details are given firstly of the substructuring–frontal combined approach. The incorporation of the algorithm in a multi‐level parallel strategy is then discussed. The parallel processing can thus be carried out at different substructural levels. The method thus developed impacts, in a positive way, on both computer storage requirement and execution time. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
3.
4.
5.
S. Thomas Crough 《Marine Geophysical Researches》1982,5(3):263-271
Geoid height anomalies, as determined by satellite altimetry, suggest that the Cape Verde Rise is in local isostatic equilibrium, supported by a low-density root of altered lithosphere. A depth anomaly map shows the Cape Verde Rise to be approximately 1600 km wide and 2km high. Removal of a quadratic surface from the observed geoid heights leaves a residual positive anomaly with the same shape as the rise and an amplitude of about 8 m. The ratio of residual geoid height anomaly to depth anomaly is consistent with an isostatic root only 40 km deep on average. 相似文献
6.
Simon J. Walker Thomas A. Schlacher & Monika A. Schlacher-Hoenlinger 《Marine Ecology》2007,28(4):435-445
Artificial reefs are spatially complex habitats and serve as good model systems to study patterns of community succession and the response of epibiota to environmental clines over small spatial scales. Here, we quantified spatial heterogeneity in community composition and diversity of fouling communities across a number of environmental gradients that included water depth, surface orientation of habitats, exposure to currents, and shelter. Assemblage structure was quantified by spatially replicated photo transects on a recently scuttled large navy ship off the East Australian coast, lying in 27 m of water. A rich assemblage of epifauna had colonized the wreck within a year, dominated by barnacles, sponges and bryozoans. Community structure varied significantly over small spatial scales of meters to tens of meters. Depth, surface orientation and exposure were the major environmental drivers. Assemblages were substantially less diverse and abundant on the deepest (23 m near the seafloor) part of the hull with residual antifouling paint, on sheltered surfaces inside the wreck, and on the sediment‐laden horizontal surfaces. Overall, the wrecks’ habitat complexity corresponds with small‐scale heterogeneity in the fouling communities. This study supports the notion that wrecks enhance local diversity and biomass within the habitat mosaic of their location, and habitat complexity may be an important mechanism for this, as demonstrated by the large spatial variability in the assemblages documented here. 相似文献
7.
8.
9.
The methane abundance in the lower Jovian stratosphere is measured using Galilean satellite eclipse light curves. Spectrally selective observations in and between absorption bands are compared. An average mixing ratio at the locations measured is [CH4]/[H2] ~ 1.3 × 10?3, larger than the value 0.9 × 10?3 expected for a solar abundance of carbon. Some zenographic variation of the mixing ratio may occur. Observationally compatible values are 1.3–2.0 × 10?3 in the STZ, 1.3– 2.6 × 10?3 on the GRS/STrZ edge, and 0.7–1.3 × 10?3 in the GRS. 相似文献
10.
Thomas L. Duvall Jr. 《Solar physics》1982,76(1):137-143
The equatorial photospheric rotation rate has been observed on 14 days in 1978–1980. The resulting rotation rate, = 14.14±0.04°/day, is 2% slower than the rate as observed for long-lived sunspots.Stationed at Kitt Peak National Observatory.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation. 相似文献