全文获取类型
收费全文 | 88761篇 |
免费 | 1350篇 |
国内免费 | 839篇 |
专业分类
测绘学 | 2157篇 |
大气科学 | 6465篇 |
地球物理 | 16995篇 |
地质学 | 33871篇 |
海洋学 | 7562篇 |
天文学 | 18661篇 |
综合类 | 331篇 |
自然地理 | 4908篇 |
出版年
2021年 | 600篇 |
2020年 | 706篇 |
2019年 | 791篇 |
2018年 | 4004篇 |
2017年 | 3805篇 |
2016年 | 3142篇 |
2015年 | 1207篇 |
2014年 | 1780篇 |
2013年 | 3505篇 |
2012年 | 2986篇 |
2011年 | 5106篇 |
2010年 | 4582篇 |
2009年 | 5438篇 |
2008年 | 4581篇 |
2007年 | 5114篇 |
2006年 | 2723篇 |
2005年 | 2546篇 |
2004年 | 2386篇 |
2003年 | 2451篇 |
2002年 | 2120篇 |
2001年 | 1682篇 |
2000年 | 1646篇 |
1999年 | 1476篇 |
1998年 | 1409篇 |
1997年 | 1388篇 |
1996年 | 1212篇 |
1995年 | 1118篇 |
1994年 | 972篇 |
1993年 | 898篇 |
1992年 | 849篇 |
1991年 | 832篇 |
1990年 | 844篇 |
1989年 | 760篇 |
1988年 | 731篇 |
1987年 | 797篇 |
1986年 | 801篇 |
1985年 | 971篇 |
1984年 | 1056篇 |
1983年 | 1025篇 |
1982年 | 938篇 |
1981年 | 864篇 |
1980年 | 822篇 |
1979年 | 757篇 |
1978年 | 738篇 |
1977年 | 692篇 |
1976年 | 628篇 |
1975年 | 643篇 |
1974年 | 623篇 |
1973年 | 654篇 |
1972年 | 411篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
The potential of heterotrophs to degrade aromatic hydrocarbons derived from oil in water and sediments in the northern North Sea around the Brent, Beryl, Forties and Murchison oilfields and at a number of stations, from the Forties field to the Firth of Forth, was estimated using 1-14C naphthalene and 7, 10-14C benzo(a)pyrene. The degradation of uniformly labelled 14C mixed 1-amino acids was used as a measure of total heterotrophic activity. Results showed that microorganisms have the potential to degrade the smaller aromatic hydrocarbon molecules rapidly in the water column and in surface sediments. Close to the Beryl platform, where diesel-washed drill cuttings have been continuously dumped, the rate of input of hydrocarbons to the sediment has exceeded the rate of degradation. Mineralization of benzo(a)pyrene, estimated in the sediments only, was minimal. Close to production platforms the biodegradation rate of mixed 1-amino acids showed no increase comparable with that found for naphthalene, suggesting that existing microbial populations had not increased but adapted to degrade oil in water and sediments. 相似文献
992.
A. G. Matul T. A. Khusid V. V. Mukhina M. P. Chekhovskaya S. A. Safarova 《Oceanology》2007,47(1):80-90
The study of diatoms and benthic foraminifers from the southeastern shelf of the Laptev Sea shows that their most diverse and abundant recent assemblages populate the peripheral underwater part of the Lena River delta representing the marginal filter of the sea. This area is characterized by an intense interaction between the fresh waters of the Siberian rivers and the basin seawater, the Atlantic one included. Local Late Holocene (~last 2300 years) environments reflect the main regional and global paleoclimatic changes, the Medieval Warm Period (~600–1100 years B.P.) and the Little Ice Age (~100–600 years B.P.) inclusive. In addition, the composition and distribution of planktonic foraminifers implies a strong influence of the Atlantic water during the Holocene optimum ~5100–6200 years B.P. 相似文献
993.
994.
995.
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
996.
V. P. Dymnikov V. N. Lykosov E. M. Volodin 《Izvestiya Atmospheric and Oceanic Physics》2006,42(5):568-585
The properties of the climate system as a physical object are considered. Major concepts of the mathematical theory of climate are stated, and the problems of constructing mathematical climate models are discussed. The results of reproducing the present-day climate are analyzed, and the sensitivity of the climate system to changes in the content of greenhouse gases is considered. Major directions are formulated in which the development of the mathematical theory of climate and of modeling climate and climate change is possible. 相似文献
997.
Palynological characterization of the pollen assemblages from core ZV-01 offers a reliable age record of shallow ‘gas seal’
and ‘gas reservoir’ sediments from the Ría de Vigo (NW Spain). Gassy sediments show a direct correspondence with the palynological
assemblage zones (LPAZ) 2, 3 and 4, which range in age from 950 to 1510 a.d. for the interval 81–176 cm where gas is found. The facies acting as a seal would correspond to the sedimentation in the ria
starting from 1510 a.d. These assemblages also provide significant data which make it possible to reconstruct the palaeoenvironmental changes recorded
in the sedimentary infill of the Ría de Vigo. The gassy horizon corresponds to the phase when riparian and mesophilous forest
were better represented. This coincides with a relative high abundance of Lingulodinium machaerophorum, which indicates that the waters of the ria had been less renewed by oceanic waters and had a plentiful supply of continental
nutrients. At that time, anoxic conditions resulted from restricted vertical circulation of seawater and/or high biological
productivity. The dinocyst assemblages overlying and underlying the gassy horizon in core ZV-01 are clearly different from
those concomitant with the accumulation of the gassy sediments. This suggests that oceanographic conditions in the Ría de
Vigo may have changed several times during the time interval covered by our record. The weaker relationship between L. machaerophorum/Spiniferites spp., and simultaneous significant increases in Impagidinium spp. and Bitectatodinium tepikiense may indicate a greater intrusion of colder, more oceanic waters into the Ría de Vigo, which may have provoked intensification
in upwelling during two periods, ca. 700–850 a.d. and ca. 1500–1750 a.d. 相似文献
998.
999.
Seasonal variations in river discharge and nutrient export to a Northeastern Pacific estuary 总被引:1,自引:0,他引:1
Seasonal variations in dissolved nitrogen and silica loadings were related to seasonal variability in river discharge. Dissolved nutrient concentrations measured weekly at three stations in the Yaquina River, Oregon from 1999 through 2001, and then monthly in 2002 were used as the basis for developing a nutrient loading regression as part of a larger agency program for evaluating nutrient processes. Because realistic models of nutrient transport require dense data sets to capture both long and short term fluctuations in nutrient concentrations, data at one freshwater station also were collected hourly for the same years using an in-stream monitor.The effects of storm events on dissolved nutrient transport were examined during three storms, including one in a high rainfall-discharge year, and two in average years, one of which followed a drought year. During the drought year (WY2001), total dissolved nitrate input was considerably less than in wetter years. Dissolved nitrate concentrations, however, were unusually high in the first winter storm runoff after the drought. The freshwater dissolved nitrate nitrogen loads varied from 40,380 kg day−1 during a high-flow storm event to 0.11 kg day−1 during late summer, low flow conditions. Dissolved silica dynamics differed from those of nitrate because during storm events, silica concentrations in the Yaquina River decreased to near zero at the storm height, probably due to dilution by near surface or overland flow, and later recovered.During the time interval studied, over 94% of the dissolved nitrate and silica were transported from the watershed during the winter months of greater rainfall, indicating that seasonality and river flow are primary factors when considering nutrient loadings from this watershed system. 相似文献
1000.