全文获取类型
收费全文 | 759篇 |
免费 | 30篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 45篇 |
地球物理 | 160篇 |
地质学 | 255篇 |
海洋学 | 61篇 |
天文学 | 157篇 |
综合类 | 2篇 |
自然地理 | 95篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 15篇 |
2018年 | 25篇 |
2017年 | 23篇 |
2016年 | 19篇 |
2015年 | 19篇 |
2014年 | 24篇 |
2013年 | 32篇 |
2012年 | 18篇 |
2011年 | 27篇 |
2010年 | 31篇 |
2009年 | 45篇 |
2008年 | 37篇 |
2007年 | 39篇 |
2006年 | 33篇 |
2005年 | 21篇 |
2004年 | 38篇 |
2003年 | 23篇 |
2002年 | 18篇 |
2001年 | 24篇 |
2000年 | 22篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 14篇 |
1996年 | 5篇 |
1995年 | 9篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1975年 | 11篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有791条查询结果,搜索用时 27 毫秒
1.
2.
3.
4.
5.
Jennifer M. Galloway Christine T. Doherty R. Timothy Patterson Helen M. Roe 《第四纪科学杂志》2009,24(4):322-335
A pollen‐based study from Tiny Lake in the Seymour‐Belize Inlet Complex of central coastal British Columbia, Canada, permits an evaluation of the dynamic response of coastal temperate rainforests to postglacial climate change. Open Pinus parklands grew at the site during the early Lateglacial when the climate was cool and dry, but more humid conditions in the later phases of the Lateglacial permitted mesophytic conifers to colonise the region. Early Holocene conditions were warmer than present and a successional mosaic of Tsuga heterophylla and Alnus occurred at Tiny Lake. Climate cooling and moistening at 8740 ± 70 14C a BP initiated the development of closed, late successional T. heterophylla–Cupressaceae forests, which achieved modern character after 6860 ± 50 14C a BP, when a temperate and very wet climate became established. The onset of early Holocene climate cooling and moistening at Tiny Lake may have preceded change at more southern locations, including within the Seymour‐Belize Inlet Complex, on a meso‐ to synoptic scale. This would suggest that an early Holocene intensification of the Aleutian Low pressure system was an important influence on forest dynamics in the Seymour‐Belize Inlet Complex and that the study region was located near the southern extent of immediate influence of this semi‐permanent air mass. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
6.
Charles H. Nelson Douglas S. Hall Francis C. Fekel Robert E. Fried Richard E. Lines Helen C. Lines 《Astrophysics and Space Science》1991,182(1):1-17
Photometry of HD 155638=V792 Her has been analyzed to determine the elements of this totally eclipsing RS CVn binary. The light variation outside eclipse was found to have a period of 27d.07±0d.07, which is slightly different from the 27d.5384±0d.0045 orbital period. Analysis of the eclipses was achieved by a modification of the Russell-Merrill technique. With the aid of radial velocity measures, absolute elements were obtained for the hot and cool stars, respectively;R
h=2.58R
,R
c=12.28R
,M
h=1.40M
,M
c=1.46M
,i=80o.61 and velocity semi-amplitudesK
c=48.36 km s–1±0.79 km s–1, andK
h=50.50 km s–1±0.33 km s–1. The apparent magnitudes areV
h=9
m
.73 andV
c=8
m
.48. The distance to HD 155638 was estimated to be 310 parsecs. 相似文献
7.
8.
D. J. Mackey J. E. O'Sullivan R. J. Watson G. Dal Pont 《Deep Sea Research Part I: Oceanographic Research Papers》2002,49(12)
Profiles of total dissolvable Cd, Cu, Mn and Ni are reported for samples collected from the southwest Pacific in 1989, from the western equatorial Pacific along 155°E at 5°S, 0° and 5°N in 1990 and 1993, and along the equator from 143°E to 152°E and in the Bismarck Sea in 1997 and 2000. Profiles of Cd along 155°E in 1990 and along the equator were essentially the same but, in 1993, Cd values at 5°N were higher by a factor of about 1.5–2 than at 5°S over the depth range 500–1500 m. Similar, but less pronounced, differences were observed for PO4 and Ni. Cd and Ni were both strongly correlated with PO4, and an even stronger correlation was found between Ni and Cd. The concentration of Ni did not fall below ≈2 nmolkg−1, even in the nitrate-depleted waters of the western equatorial Pacific, where primary production is strongly dependent on recycled nitrogen (mainly ammonia and urea). It is proposed that this residual Ni is not bioavailable and that Ni could be biolimiting, since the metabolism of urea requires the nickel-containing enzyme urease. The impact of the Sepik River on Cd, Cu and Ni concentrations was small but elevated concentrations of Mn were observed near the Sepik River and close to the coast suggesting that the rivers and sediments on the north coast of New Guinea are a significant local source of Mn to the Bismarck Sea. Simple mass balance calculations show that the elevated levels of Mn observed in the Equatorial Undercurrent cannot be due to input from the rivers of New Guinea and they were attributed to the trapping of particulate matter due to strong current shear. A strong hydrothermal source of Mn was observed in the central Bismarck Sea. 相似文献
9.
10.
Watson W. Gregg Paul Ginoux Paul S. Schopf Nancy W. Casey 《Deep Sea Research Part II: Topical Studies in Oceanography》2003,50(22-26):3143
The JGOFS program and NASA ocean-color satellites have provided a wealth of data that can be used to test and validate models of ocean biogeochemistry. A coupled three-dimensional general circulation, biogeochemical, and radiative model of the global oceans was validated using these in situ data sources and satellite data sets. Biogeochemical processes in the model were determined from the influences of circulation and turbulence dynamics, irradiance availability, and the interactions among four phytoplankton functional groups (diatoms, chlorophytes, cyanobacteria, and coccolithophores) and four nutrients (nitrate, ammonium, silica, and dissolved iron).Annual mean log-transformed dissolved iron concentrations in the model were statistically positively correlated on basin scale with observations (P<0.05) over the eight (out of 12) major oceanographic basins where data were available. The model tended to overestimate in situ observations, except in the Antarctic where a large underestimate occurred. Inadequate scavenging and excessive remineralization and/or regeneration were possible reasons for the overestimation.Basin scale model chlorophyll seasonal distributions were positively correlated with SeaWiFS chlorophyll in each of the 12 oceanographic basins (P<0.05). The global mean difference was 3.9% (model higher than SeaWiFS).The four phytoplankton groups were initialized as homogeneous and equal distributions throughout the model domain. After 26 years of simulation, they arrived at reasonable distributions throughout the global oceans: diatoms predominated high latitudes, coastal, and equatorial upwelling areas, cyanobacteria predominated the mid-ocean gyres, and chlorophytes and coccolithophores represented transitional assemblages. Seasonal patterns exhibited a range of relative responses: from a seasonal succession in the North Atlantic with coccolithophores replacing diatoms as the dominant group in mid-summer, to successional patterns with cyanobacteria replacing diatoms in mid-summer in the central North Pacific. Diatoms were associated with regions where nutrient availability was high. Cyanobacteria predominated in quiescent regions with low nutrients.While the overall patterns of phytoplankton functional group distributions exhibited broad qualitative agreement with in situ data, quantitative comparisons were mixed. Three of the four phytoplankton groups exhibited statistically significant correspondence across basins. Diatoms did not. Some basins exhibited excellent correspondence, while most showed moderate agreement, with two functional groups in agreement with data and the other two in disagreement. The results are encouraging for a first attempt at simulating functional groups in a global coupled three-dimensional model but many issues remain. 相似文献