全文获取类型
收费全文 | 90364篇 |
免费 | 22151篇 |
国内免费 | 46704篇 |
专业分类
测绘学 | 7476篇 |
大气科学 | 25440篇 |
地球物理 | 23298篇 |
地质学 | 57261篇 |
海洋学 | 21738篇 |
天文学 | 11140篇 |
综合类 | 5556篇 |
自然地理 | 7310篇 |
出版年
2023年 | 777篇 |
2022年 | 1698篇 |
2021年 | 2524篇 |
2020年 | 3265篇 |
2019年 | 6658篇 |
2018年 | 7167篇 |
2017年 | 6798篇 |
2016年 | 7107篇 |
2015年 | 6406篇 |
2014年 | 6197篇 |
2013年 | 7945篇 |
2012年 | 7187篇 |
2011年 | 7288篇 |
2010年 | 7171篇 |
2009年 | 7025篇 |
2008年 | 6222篇 |
2007年 | 6002篇 |
2006年 | 5548篇 |
2005年 | 4776篇 |
2004年 | 4822篇 |
2003年 | 4133篇 |
2002年 | 3958篇 |
2001年 | 3523篇 |
2000年 | 2993篇 |
1999年 | 2609篇 |
1998年 | 2555篇 |
1997年 | 2617篇 |
1996年 | 2057篇 |
1995年 | 1936篇 |
1994年 | 1773篇 |
1993年 | 1665篇 |
1992年 | 1442篇 |
1991年 | 1193篇 |
1990年 | 1140篇 |
1989年 | 1046篇 |
1988年 | 906篇 |
1987年 | 881篇 |
1986年 | 766篇 |
1985年 | 778篇 |
1984年 | 928篇 |
1983年 | 728篇 |
1982年 | 759篇 |
1981年 | 647篇 |
1980年 | 546篇 |
1979年 | 544篇 |
1978年 | 494篇 |
1977年 | 421篇 |
1976年 | 376篇 |
1975年 | 362篇 |
1973年 | 381篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
171.
172.
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
173.
K. Nagamine † M. Fukugita R. Cen J.P. Ostriker 《Monthly notices of the Royal Astronomical Society》2001,327(1):L10-L14
The luminosity function of galaxies is derived from a cosmological hydrodynamic simulation of a Λ cold dark matter universe with the aid of a stellar population synthesis model. At , the resulting B -band luminosity function has a flat faint-end slope of with the characteristic luminosity and the normalization in fair agreement with observations, while the dark matter halo mass function is steep with a slope of . The colour distribution of galaxies also agrees well with local observations. We also discuss the evolution of the luminosity function, and the colour distribution of galaxies from to 5. A large evolution of the characteristic mass in the stellar mass function as a result of number evolution is compensated by luminosity evolution; the characteristic luminosity increases only by 0.8 mag from to 2, and then declines towards higher redshift, while the B -band luminosity density continues to increase from to 5 (but only slowly at . 相似文献
174.
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
175.
176.
Historical Changes in the Flood Hazard at Khartoum, Sudan: Lessons and Warnings for the Future 总被引:1,自引:0,他引:1
The 1988 floods at Khartoum were frequently described as "unprecedented". However, an examination of evidence for floods caused by the Nile and rain storms during the nineteenth and twentieth centuries leads to the conclusion that neither the Nile flood nor the rain storms nor their coincidence in one season were unprecedented and that similar situations will recur.We argue that most problems were created by complacency, lack of planning and mismanagement. We conclude with some simple suggestions for flood amelioration in the future and warn that complacency is the single most important phenomenon likely to recur to the detriment of Greater Khartoum in the future. 相似文献
177.
本文讨论了河西走廊东部地区早二叠世地层研究的有关问题,认为甘肃山丹青羊泉下二叠统剖面是北祁连山—河西走廊地区的重要代表剖面之一。以该剖面研究为依据,提出走廊东部地区下二叠统的进一步划分方案,分析该区早二叠世地层岩性特征差异的原因,并与走廊西部地区同期地层进行对比,进一步明确了大黄沟组的含意。 相似文献
178.
Formation of saline groundwaters in the Baltic region through freezing of seawater during glacial periods 总被引:1,自引:0,他引:1
Typical Ca---Cl brines occur in crystalline and metamorphic rocks below freshwater horizons at various localities in Sweden and Finland. Total dissolved solids (TDS) range in concentration between 2 and 120 gl−1 and have long been thought to derive from water-rock interactions. The relationships between Na, Cl and Br in these brines suggest, however, that they were derived from freezing of seawater during glacial periods. The brines were subsequently diluted by meteoric waters and their Ca/Mg ratio was increased through water-rock interactions in the subsurface. The hydrogeological model for both the formation of freeze-derived marine brines and their lateral intrusion involves restricted inland marine basins in recent and subrecent polar climatic belts. Seawater in such basins gradually freezes in response to glaciation. The solutes which concentrate in the remaining water body are residual after precipitation of a sequence of minerals which include carbonates, mirabilite and hydrohalite. Hydraulic pressure of the growing ice sheet over the frozen seas is gradually added to the ambient hydrostatic pressure exerted on the brines. This, together with their increased density, increases the intrusional potential of the brines. As the land ice cannot exert hydraulic pressure on continental groundwater in the aquifers, the balance of pressure favours deep landward intrusion of brines. Post-glacial processes cause the subsurface dilution and replacement of the brines both by seawater and fresh waters. The presence of such brines also far from present-day coastal settings reflects the shifting of coastlines as a result of isostatic movements and eustatic sea-level changes associated with glaciation and deglaciation. 相似文献
179.
Pittichovâ J. Sekenina Z. Birkle K. Boehnhardt J. Engels D. Keller P. 《Earth, Moon, and Planets》1997,78(1-3):329-338
The Sekanina-Farrell particle fragmentation model for the striated tails of dust comets is successfully applied to two images
of comet Hale-Bopp to study the motions of 12 striae in a time span of March 12–15, 1997. There is evidence for recurring
outbursts with a periodicity of 11h21m, consistent with results based on analysis of dust jets. The ejecta in all the striae appear to have been released from one
source on the nucleus between the end of January and the second half of February 1997, some 60 to 40 days before perihelion.
The parent particles were subjected to a radiation pressure acceleration of βp ≃ 0.55 and their fragmentation lifetimes in 11 of the 12 striae were practically constant and equal to 13–15 days, when normalized
to 1 AU from the Sun. Brief analysis of Watanabe et al.'s measurements of striae on their images from March 5–9, 1997 shows
even shorter fragmentation lifetimes for the parent particles, mostly about 7–11 days at1 AU.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
180.