全文获取类型
收费全文 | 10886篇 |
免费 | 765篇 |
国内免费 | 245篇 |
专业分类
测绘学 | 400篇 |
大气科学 | 1132篇 |
地球物理 | 3364篇 |
地质学 | 4054篇 |
海洋学 | 811篇 |
天文学 | 1090篇 |
综合类 | 209篇 |
自然地理 | 836篇 |
出版年
2021年 | 77篇 |
2020年 | 69篇 |
2019年 | 96篇 |
2018年 | 550篇 |
2017年 | 485篇 |
2016年 | 404篇 |
2015年 | 293篇 |
2014年 | 313篇 |
2013年 | 437篇 |
2012年 | 873篇 |
2011年 | 675篇 |
2010年 | 305篇 |
2009年 | 434篇 |
2008年 | 399篇 |
2007年 | 374篇 |
2006年 | 343篇 |
2005年 | 1011篇 |
2004年 | 1043篇 |
2003年 | 830篇 |
2002年 | 356篇 |
2001年 | 202篇 |
2000年 | 180篇 |
1999年 | 128篇 |
1998年 | 117篇 |
1997年 | 109篇 |
1996年 | 94篇 |
1995年 | 87篇 |
1994年 | 76篇 |
1993年 | 63篇 |
1992年 | 66篇 |
1991年 | 79篇 |
1990年 | 75篇 |
1989年 | 64篇 |
1988年 | 59篇 |
1987年 | 69篇 |
1986年 | 43篇 |
1985年 | 75篇 |
1984年 | 80篇 |
1983年 | 73篇 |
1982年 | 65篇 |
1981年 | 77篇 |
1980年 | 66篇 |
1979年 | 57篇 |
1978年 | 39篇 |
1977年 | 55篇 |
1976年 | 66篇 |
1975年 | 50篇 |
1974年 | 56篇 |
1973年 | 49篇 |
1972年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 54 毫秒
91.
92.
93.
We collected surface water along the 142nd E meridian from Tasmania to Antarctica in December 1999. We measured temperature,
salinity and total chlorophyll a; additionally, we collected suspended particle size fractions and used fluorometric analysis to determine the quantity of
chlorophyll a in each of four cell size classes: picoplankton (<3 μm), two nanoplankton fractions (3–10 μm and 10–20 μm) and microplankton
(> 20 μm). Changes in temperature and salinity show that we crossed 6 water masses separated by 5 fronts. We found low abundance
(<0.2 mg m−3) of chlorophyll in all size classes, with the exception of higher values near the continent (0.2 to 0.4 mg m−3). Lowest chlorophyll values (<0.1 mg m−3) were found in the Polar Frontal Zone (51° to 54°S). Microplankton made up the largest portion of total chlorophyll throughout
most of the region. We conclude that biomass of all phytoplankton fractions, especially pico-and nanoplankton, was constrained
by limiting factors, most probably iron, throughout the region and that ecosystem dynamics within a zone are not circumpolar
but are regionalized within sectors. 相似文献
94.
Daniel Jean Stanley Harrison Sheng Douglas N. Lambert Peter A. Rona David W. McGrail J.Stacy Jenkyns 《Marine Geology》1981,40(3-4):215-235
Analyses of DSRV “Alvin” core samples on the Cape Hatteras margin indicate major textural and compositional changes at depths of about 1000 and well below 2500 m. The distribution patterns of petrologic parameters correlate well with water mass flow and suspended-sediment plumes measured on this margin by other workers. Our study also shows: (a) vigorous erosion and sediment transport at depths of less than 400 m resulting from the NE-trending Gulf Stream flow; (b) deposition, largely planktonic-rich sediment released from the Gulf Stream, on the upper- to mid-slope, to depths of about 800–1200 m; (c) winnowing, resuspension and deposition induced by periodically intensified slope currents on the mid-slope to uppermost rise, between about 1000 and 2500 m; and (d) prevailing deposition on the upper rise proper (below 2500 m), from transport by the SW-trending Western Boundary Undercurrent. Sediments moved by bottom currents have altered the composition and distribution patterns of material transported downslope by offshelf spillover; this mixing of gravity-emplaced and bottom-current-transported sediment obscures depositional boundaries. Moreover, reworking of the seafloor by benthic organisms alters physical properties and changes erodability of surficial sediments by bottom currents. Measurement of current flow above the seafloor and direct observation of the bottom are insufficient to delineate surficial sediment boundaries. Detailed petrologic analyses are needed to recognize the long-term signature of processes and define depositional provinces. 相似文献
95.
96.
Identification of Danish North Sea trawl fisheries 总被引:1,自引:3,他引:1
97.
98.
Size-Fractionated Primary Production Estimated by a Two-Phytoplankton Community Model Applicable to Ocean Color Remote Sensing 总被引:3,自引:0,他引:3
In order to estimate primary production from ocean color satellite data using the Vertical Generalized Production Model (VGPM; Behrenfeld and Falkowski, 1997), we propose a two-phytoplankton community model. This model is based on the two assumptions that changes in chlorophyll concentration result from changes of large-sized phytoplankton abundance, and chlorophyll specific productivity of phytoplankton tends to be inversely proportional to phytoplankton size. Based on the analysis of primary production data, P
opt
B
, which was one parameter in the VGPM, was modeled as a function of sea surface temperature and sea surface chlorophyll concentration. The two-phytoplankton community model incorporated into the VGPM gave good estimates in a relatively high productive area. Size-fractionated primary production was estimated by the two-phytoplankton community model, and P
opt
B
of small-sized phytoplankton was 4.5 times that of large-sized phytoplankton. This result fell into the ranges observed during field studies. 相似文献
99.
The upper layer (above 140 m depth) temperature in the western Philippine Sea near Taiwan was sampled using a coastal monitoring
buoy (CMB) with 15 attached thermistors during July 28–August 7, 2005. The data were collected every 10 min at 1, 3, 5, 10,
15, and 20 m using the CMB sensors, and every 15 sec at 15 different depths between 25 m and 140 m. Internal waves and solitons
were identified from the time-depth plot of the temperature field. Without the internal waves and solitons, the power spectra,
structure functions, and singular measures (representing the intermittency) of temperature field satisfy the power law with
multi-scale characteristics at all depths. The internal waves do not change the basic characteristics of the multifractal
structure. However, the internal solitons change the power exponent of the power spectra drastically, especially in the low
wave number domain; they also break down the power law of the structure function and increase the intermittency parameter.
The physical mechanisms causing these different effects need to be explored further. 相似文献
100.