全文获取类型
收费全文 | 80493篇 |
免费 | 1412篇 |
国内免费 | 542篇 |
专业分类
测绘学 | 1996篇 |
大气科学 | 5761篇 |
地球物理 | 15580篇 |
地质学 | 28203篇 |
海洋学 | 7072篇 |
天文学 | 18530篇 |
综合类 | 190篇 |
自然地理 | 5115篇 |
出版年
2021年 | 677篇 |
2020年 | 765篇 |
2019年 | 852篇 |
2018年 | 1708篇 |
2017年 | 1682篇 |
2016年 | 1972篇 |
2015年 | 1181篇 |
2014年 | 2038篇 |
2013年 | 3945篇 |
2012年 | 2123篇 |
2011年 | 2886篇 |
2010年 | 2661篇 |
2009年 | 3377篇 |
2008年 | 3083篇 |
2007年 | 3159篇 |
2006年 | 2942篇 |
2005年 | 2339篇 |
2004年 | 2348篇 |
2003年 | 2286篇 |
2002年 | 2119篇 |
2001年 | 1901篇 |
2000年 | 1765篇 |
1999年 | 1653篇 |
1998年 | 1593篇 |
1997年 | 1595篇 |
1996年 | 1322篇 |
1995年 | 1294篇 |
1994年 | 1201篇 |
1993年 | 1088篇 |
1992年 | 1029篇 |
1991年 | 1026篇 |
1990年 | 1109篇 |
1989年 | 997篇 |
1988年 | 935篇 |
1987年 | 1042篇 |
1986年 | 962篇 |
1985年 | 1215篇 |
1984年 | 1371篇 |
1983年 | 1335篇 |
1982年 | 1239篇 |
1981年 | 1162篇 |
1980年 | 1063篇 |
1979年 | 1003篇 |
1978年 | 995篇 |
1977年 | 931篇 |
1976年 | 862篇 |
1975年 | 794篇 |
1974年 | 864篇 |
1973年 | 872篇 |
1972年 | 554篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
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
992.
993.
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
994.
995.
996.
A simple and effective method of heating divers in extreme cold water has been developed. The local heating concept utilizes a uniformly distributed granular mixture of magnesium and iron particles packed in small sachets. Upon activation by sea water, the two metal mixture behaves as a multitude of short-circuited electrolytic cells, producing thermal energy rather than electrical energy. The 45 mm-square sachets may be placed where heating is required on the diver's body, thus giving rise to the term “local heating”, obviously, the heating system requires no pumping device, or distribution network. Heating rate and duration of output of the sachets are controlled by particle size, and mixture ratio of the constituent Mg and Fe particles.This paper described the development, testing and performance of the heating sachets. Results of live tests in different dive situations are also presented and discussed. 相似文献
997.
998.
Seismic reflection profiles from the equatorial Atlantic off Africa between 12°N and 1°N reveal remarkably widespread deformation of oceanic sediments in an area lacking teleseismic activity. Uplift of abyssal plain sequences has occurred along the eastern extensions of large-offset fracture zones on the Mid-Atlantic Ridge. Between the major transforms pervasive deformation is imaged in the sedimentary column. Diapirism and faulting may have been associated with extensive fluid migration and sediment mobilization. The deformation occurred during the late Cenozoic and was probably related to reactivation of Cretaceous transforms. 相似文献
999.
1000.
Effects of water-borne copper on metallothionein and lipid peroxidation in the marine amphipod Gammarus locusta 总被引:1,自引:0,他引:1
The aim of the current work was to determine over 10 days the effects of water-borne exposure of the marine amphipod Gammarus locusta to 4 microgCu l(-1) on the metallothionein (MT; measured by differential pulse polarography) protection system and lipid peroxidation (LP: thiobarbituric acid-reactive malondialdehyde equivalents) as a measure of oxidative damage. MT levels in exposed animals increased significantly at day 2 (36% > control; P < 0.001) and remained high at days 6 and 10 (55 and 38%, respectively, P < 0.001). The maximum level of MT at day 6 coincided with the highest Cu body-burden. LP increased within I day of exposure, indicative of Cu as an oxidative stressor. However, in contrast to MT, the highest LP level was seen at day 4 (68% > control, P < 0.001) before returning to control values by day 6, indicating a protective role of MT against the pro-oxidant effects of Cu. 相似文献