全文获取类型
收费全文 | 146305篇 |
免费 | 19157篇 |
国内免费 | 42793篇 |
专业分类
测绘学 | 5021篇 |
大气科学 | 28611篇 |
地球物理 | 34472篇 |
地质学 | 73723篇 |
海洋学 | 26203篇 |
天文学 | 27587篇 |
综合类 | 4234篇 |
自然地理 | 8404篇 |
出版年
2022年 | 1064篇 |
2021年 | 1867篇 |
2020年 | 3170篇 |
2019年 | 6770篇 |
2018年 | 8731篇 |
2017年 | 8221篇 |
2016年 | 8772篇 |
2015年 | 6409篇 |
2014年 | 7528篇 |
2013年 | 10800篇 |
2012年 | 8106篇 |
2011年 | 8778篇 |
2010年 | 8470篇 |
2009年 | 9044篇 |
2008年 | 7637篇 |
2007年 | 7567篇 |
2006年 | 6855篇 |
2005年 | 5635篇 |
2004年 | 5966篇 |
2003年 | 5485篇 |
2002年 | 5215篇 |
2001年 | 4623篇 |
2000年 | 4121篇 |
1999年 | 3631篇 |
1998年 | 3792篇 |
1997年 | 3774篇 |
1996年 | 3074篇 |
1995年 | 2992篇 |
1994年 | 2705篇 |
1993年 | 2494篇 |
1992年 | 2292篇 |
1991年 | 2051篇 |
1990年 | 2039篇 |
1989年 | 1761篇 |
1988年 | 1617篇 |
1987年 | 1719篇 |
1986年 | 1461篇 |
1985年 | 1694篇 |
1984年 | 1809篇 |
1983年 | 1732篇 |
1982年 | 1636篇 |
1981年 | 1467篇 |
1980年 | 1357篇 |
1979年 | 1290篇 |
1978年 | 1162篇 |
1977年 | 1032篇 |
1976年 | 987篇 |
1975年 | 956篇 |
1974年 | 958篇 |
1973年 | 1020篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
321.
322.
Jan Mangerud Valery I. Astakhov Andrew Murray John Inge Svendsen 《Global and Planetary Change》2001,31(1-4)
Beach and shoreface sediments deposited in the more than 800-km long ice-dammed Lake Komi in northern European Russia have been investigated and dated. The lake flooded the lowland areas between the Barents–Kara Ice Sheet in the north and the continental drainage divide in the south. Shoreline facies have been dated by 18 optical stimulated luminescence (OSL) dates, most of which are closely grouped in the range 80–100 ka, with a mean of 88±3 ka. This implies that that the Barents–Kara Ice Sheet had its Late Pleistocene maximum extension during the Early Weichselian, probably in the cold interval (Rederstall) between the Brørup and Odderade interstadials of western Europe, correlated with marine isotope stage 5b. This is in strong contrast to the Scandinavian and North American ice sheets, which had their maxima in isotope stage 2, about 20 ka. Field and air photo interpretations suggest that Lake Komi was dammed by the ice advance, which formed the Harbei–Harmon–Sopkay Moraines. These has earlier been correlated with the Markhida moraine across the Pechora River Valley and its western extension. However, OSL dates on fluvial sediments below the Markhida moraine have yielded ages as young as 60 ka. This suggests that the Russian mainland was inundated by two major ice sheet advances from the Barents–Kara seas after the last interglacial: one during the Early Weichselian (about 90 ka) that dammed Lake Komi and one during the Middle Weichselian (about 60 ka). Normal fluvial drainage prevailed during the Late Weichselian, when the ice front was located offshore. 相似文献
323.
IntroductionThe area of eastern Liaoning is an importantmetal and nonmetal metallogenetic district in China,and the Liaohe group is one of the most importantstrata that hosts Pb, Zn, Au, B and Mg etcstratabound deposits. Up to now many geo1ogistssuch as Z… 相似文献
324.
We report on SWS and LWS observations of the circumstellar disks of young stars of a few solar masses. The ISO spectra of
these objects present a diversity of emission features of carbon-rich and oxygen-rich grains. The similarity of the forsterite
spectra observed for Comet Hale-Bopp and the Haebe star HD100546 is particularly striking and provides a new argument that
huge comet swarms are formed in the disks surrounding young stars. While the data suggest that the formation of crystalline
silicates in the dust disks essentially occurs when a Haebe star has already reached the main sequence, no clear correlation
with stellar age only is apparent.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
325.
A. Kučinskas 《Astrophysics and Space Science》1997,251(1-2):231-234
We have calculated terminal gas outflow velocities from the circumstellar shells of the AGB stars. Our results confirm that,
in case of the stationary dust driven winds, the dynamics of the outflow is governed essentially by the dust properties and
stellar luminosities, while only marginally by other stellar parameters. Although being far from comprehensive, our calculations
also indicate that the dust driven winds may only occur in cool, luminous, low mass objects.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
326.
An optoelectronic instrument has been developed to analyze the scales and scale patterns of chum salmon. This device, with specially developed software, has been used to study populations of salmon. Fish from two different rivers approximately 200 km apart from each other were grouped with an accuracy of 82% or more. Machine-measured ages coincided with those derived from visual estimation in approximately 80% of the fish sampled. These results suggest the proposed system could be of practical use for measuring and analyzing the scale patterns that allow one to accurately measure both natural and farmed populations of salmon 相似文献
327.
Published in Astrofizika, Vol. 38, No. 4, pp. 677–680, October–December, 1995. 相似文献
328.
J. M. Gregory J. A. Church G. J. Boer K. W. Dixon G. M. Flato D. R. Jackett J. A. Lowe S. P. O'Farrell E. Roeckner G. L. Russell R. J. Stouffer M. Winton 《Climate Dynamics》2001,18(3-4):225-240
Sea-level rise is an important aspect of climate change because of its impact on society and ecosystems. Here we present
an intercomparison of results from ten coupled atmosphere-ocean general circulation models (AOGCMs) for sea-level changes
simulated for the twentieth century and projected to occur during the twenty first century in experiments following scenario
IS92a for greenhouse gases and sulphate aerosols. The model results suggest that the rate of sea-level rise due to thermal
expansion of sea water has increased during the twentieth century, but the small set of tide gauges with long records might
not be adequate to detect this acceleration. The rate of sea-level rise due to thermal expansion continues to increase throughout
the twenty first century, and the projected total is consequently larger than in the twentieth century; for 1990–2090 it amounts
to 0.20–0.37 m. This wide range results from systematic uncertainty in modelling of climate change and of heat uptake by the
ocean. The AOGCMs agree that sea-level rise is expected to be geographically non-uniform, with some regions experiencing as
much as twice the global average, and others practically zero, but they do not agree about the geographical pattern. The lack
of agreement indicates that we cannot currently have confidence in projections of local sea-level changes, and reveals a need
for detailed analysis and intercomparison in order to understand and reduce the disagreements.
Received: 1 September 2000 / Accepted: 20 April 2001 相似文献
329.
We study the solar cycle evolution during the last 8 solar cycles using a vectorial sunspot area called the LA (longitudinal asymmetry) parameter. This is a useful measure of solar activity in which the stochastic, longitudinally evenly distributed sunspot activity is reduced and which therefore emphasizes the more systematic, longitudinally asymmetric sunspot activity. Interesting differences are found between the LA parameter and the more conventional sunspot activity indices like the (scalar) sunspot area and the sunspot number. E.g., cycle 19 is not the highest cycle according to LA. We have calculated the separate LA parameters for the northern and southern hemisphere and found a systematic dipolar-type oscillation in the dominating hemisphere during high solar activity times which is reproduced from cycle to cycle. We have analyzed this oscillation during cycles 16–22 by a superposed epoch method using the date of magnetic reversal in the southern hemisphere as the zero epoch time. According to our analysis, the oscillation starts by an excess of the northern LA value in the ascending phase of the solar cycle which lasts for about 2.3 years. Soon after the maximum northern dominance, the southern hemisphere starts dominating, reaching its minimum some 1.2–1.7 years later. The period of southern dominance lasts for about 1.6 years and ends, on an average, slightly before the end of magnetic reversal. 相似文献
330.
The distribution of perihelion distances of nearly periodic comets was studied using different assumptions about comet discovery probabilities. It was shown that the concentration of perihelia at small heliocentric distances cannot be explained solely by the influence of visibility conditions. 相似文献