全文获取类型
收费全文 | 126776篇 |
免费 | 2149篇 |
国内免费 | 1685篇 |
专业分类
测绘学 | 3052篇 |
大气科学 | 9001篇 |
地球物理 | 25108篇 |
地质学 | 45989篇 |
海洋学 | 11409篇 |
天文学 | 28000篇 |
综合类 | 478篇 |
自然地理 | 7573篇 |
出版年
2022年 | 877篇 |
2021年 | 1462篇 |
2020年 | 1540篇 |
2019年 | 1668篇 |
2018年 | 3375篇 |
2017年 | 3179篇 |
2016年 | 3773篇 |
2015年 | 2091篇 |
2014年 | 3679篇 |
2013年 | 6642篇 |
2012年 | 4144篇 |
2011年 | 5484篇 |
2010年 | 4891篇 |
2009年 | 6144篇 |
2008年 | 5365篇 |
2007年 | 5478篇 |
2006年 | 5183篇 |
2005年 | 3762篇 |
2004年 | 3650篇 |
2003年 | 3403篇 |
2002年 | 3331篇 |
2001年 | 2918篇 |
2000年 | 2853篇 |
1999年 | 2291篇 |
1998年 | 2372篇 |
1997年 | 2253篇 |
1996年 | 1934篇 |
1995年 | 1936篇 |
1994年 | 1672篇 |
1993年 | 1528篇 |
1992年 | 1494篇 |
1991年 | 1470篇 |
1990年 | 1510篇 |
1989年 | 1331篇 |
1988年 | 1260篇 |
1987年 | 1469篇 |
1986年 | 1263篇 |
1985年 | 1553篇 |
1984年 | 1758篇 |
1983年 | 1679篇 |
1982年 | 1573篇 |
1981年 | 1455篇 |
1980年 | 1392篇 |
1979年 | 1258篇 |
1978年 | 1206篇 |
1977年 | 1100篇 |
1976年 | 1066篇 |
1975年 | 1016篇 |
1974年 | 1014篇 |
1973年 | 1100篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
601.
602.
Summary All of the barium and marginal barium stars in the 1972 MacConnell, Frey, and Upgren (1972: MFU) list of such objects which
are located south of the celestial equator were examined for visual duplicity. Over 200 objects were observed, and a total
of six possible candidates for wide pair visual binaries were found. Of these, four are most likely optical in nature. These
data suggest that the incidence of wide binaries among barium stars is of the order of 1%. 相似文献
603.
604.
605.
The results of the electromagnetic studies, obtained on the North Pole drifting stations, are reviewed. These results are
still of current interest. The aspects of similar future works are discussed. 相似文献
606.
The present article is the second in a series of baseline water quality evaluation studies in parts of south-eastern Nigeria.
Study results indicate that the water samples from the study are generally acidic, soft and fresh in addition to low sodium
and salinity hazard. Regression equations indicate a good positive correlation between conductivity and Na, Ca, Mg and SO4. Ca-SO4 and Ca-Cl constitute the major facies in the area. Generally the waters in the area are good for most domestic and agricultural
purposes.
Received: 14 April 1997 · Accepted: 3 February 1998 相似文献
607.
The physicomathematical features of the plasma explosion region dynamics at altitudes higher than 100 km at the early stage of its development, which culminates in the transfer of a considerable portion of the initial plasma energy into the environment, are discussed in the first part of the work. The radiation gas dynamic, inertial, and shock stages of the disturbed region development are calculated. 相似文献
608.
The effect of highly saline oil-field water on soils and potable groundwater is considered. Three phases of the hydrochemical evolution of groundwater quality affected by transborder pollution and field development that has deteriorated potable groundwater in the two topmost aquifers are identified. 相似文献
609.
610.
We present simple analytic models which predict the peak X-ray emission measure and temperature attained in flares in which
the chromospheric evaporation process takes place either in a single ‘monolithic’ loop or in a loop consisting of several
filaments that are created successively as the energy release process proceeds in time. As possible mechanisms driving chromospheric
evaporation we consider both classical heat conduction from the loop top and non-thermal electron beams. The model predictions
are tested for a set of 18 well studied RHESSI microflares. The results suggest beam driven evaporation in filamented loops
as being capable of accounting for the observed emission measures and temperatures though there are issues with the very high
beam densities needed. On the other hand, estimates of the emission measures achieved by conductive evaporation which are
derived by using the Rosner – Tucker – Vaiana (RTV) scaling law are much larger than the observed ones. Possible reasons for
this discrepancy are discussed. 相似文献