全文获取类型
收费全文 | 2848篇 |
免费 | 76篇 |
国内免费 | 57篇 |
专业分类
测绘学 | 283篇 |
大气科学 | 273篇 |
地球物理 | 518篇 |
地质学 | 1296篇 |
海洋学 | 131篇 |
天文学 | 365篇 |
综合类 | 55篇 |
自然地理 | 60篇 |
出版年
2023年 | 17篇 |
2022年 | 54篇 |
2021年 | 61篇 |
2020年 | 64篇 |
2019年 | 67篇 |
2018年 | 253篇 |
2017年 | 237篇 |
2016年 | 227篇 |
2015年 | 135篇 |
2014年 | 199篇 |
2013年 | 261篇 |
2012年 | 161篇 |
2011年 | 154篇 |
2010年 | 137篇 |
2009年 | 135篇 |
2008年 | 124篇 |
2007年 | 75篇 |
2006年 | 67篇 |
2005年 | 48篇 |
2004年 | 41篇 |
2003年 | 36篇 |
2002年 | 24篇 |
2001年 | 20篇 |
2000年 | 31篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 21篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 18篇 |
1993年 | 17篇 |
1992年 | 7篇 |
1991年 | 26篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 13篇 |
1987年 | 23篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1975年 | 6篇 |
1974年 | 12篇 |
1973年 | 5篇 |
1972年 | 8篇 |
1971年 | 5篇 |
1969年 | 5篇 |
排序方式: 共有2981条查询结果,搜索用时 15 毫秒
811.
812.
Anil Kumar Y J Bhaskar Rao V M Padma Kumari A M Dayal K Gopalan 《Journal of Earth System Science》1988,97(1):107-114
Palaeomagnetic, geochemical and geochronological studies have been conducted on a set of dolerite dykes intruding the Peninsular
gneisses near Huliyurdurga town, Karnataka, as a reconnaissance survey indicated a Cretaceous age for them. The dykes are
mainly tholeiitic in composition with their 87Sr/86Sr ratios tightly clustered around 0·7045. Their palaeomagnetic data (D
m
=329°,I
m
=−55°) and the corresponding palaeopole coordinates (λ
p
= 34°S,L
p
=108°E) are strikingly close to those of the Deccan Traps to the north. Whole rock K-Ar ages of these dykes ranging between
69 and 84 Ma are also similar to the range of K-Ar ages of the Deccan basalts. The chemical, palaeomagnetic and temporal coherence
between the dykes and the Deccan basalts indicate that they may indeed be tectonically related events. 相似文献
813.
814.
In this paper, hydroclimatic fluctuations of the Upper Narmada catchment (upto Narmadasagar damsite) have been studied by
examining the time series (1901–80) of (i) 1-to 10-day annual extreme rainfall; (ii) seasonal total rainfall between May and
October; (iii) the precipitation concentration index (PCI); (iv) a modified version of PCI(MPCI); and (v) parameters of the
periods contributing specified percentages of rainfall to annual total. Most of these parameters followed the normal distribution
and did not show any significant long-term trend. However, some dominant long period oscillations have been noticed in extreme
rainfall, seasonal rainfall, PCI and MPCI series. Influence of break-monsoon days over India during July and August on the
rainfall activities of the Upper Narmada catchment has also been investigated and salient findings discussed. 相似文献
815.
Th, U and K abundances in four alkali granites of the Kerala region, south-west India, are presented. The plutons show high radioelement levels, correlatable with those of alkali granites in other regions. The nature of variation is consistent with the correlation of Th and U with accessory phases like sphene, zircon, allanite, apatite and monazite. A geochronologic correlation is also observed between the alkali granites and the Th-bearing beach placers of the region. The petrogenetic features of the alkali plutons, their taphrogenic association, Pan-African affiliation and high Th/U levels suggest that the alkali plutons are favourable locales for radioelement exploration. 相似文献
816.
817.
An attempt is made to reveal a geochemical compatibility with paleoenvironment to understand the genesis of bauxite deposits that are derived from two different parent rocks. For this purpose two in situ bauxite profiles, one developed over basalt and another over sandstone, have been taken. Gibbsite is the major mineral in all these bauxites with minor occurrences of goethite, hematite, anatase, kaolinite, etc. From the study it is evident that the paleoenvironment and geochemical processes are vital factors that could lead to the formation of bauxites. The significance of this is fully discussed. 相似文献
818.
Rock samples belonging to ten lithological types under different stages of weathering, were collected from different stratigraphical
horizons at Bhagalpur. Their densities and porosities were determined experimentally and the data obtained were fitted empirically
in a linear equation for each lithological type. The slopes of the curves, which were negative in each case, showed that the
increase in porosity for the same decrease in density were in the order, white sandstone > ferruginous sandstone > white claystone
> porphyritic gneiss > quartzite > pegmatite > amphibolite ≅ biotite gnejss > basalt ≅ dolerite. A new weathering potential
index based on the density-porosity data was proposed and the values for a specific stage of weathering for all the lithological
types studied fall within the same range. 相似文献
819.
Man has had to live with floods since the very inception of his existence. Fury of flood causes heavy damages to both life and property. Accurate flood inundation data is one of the essential requirements for effective management of flood problem. Remote Sensing methods are well suited for acquiring flood inundation data because of synoptic, repetitive coverage of the satellite data. This paper briefs on an attempt to map flood inundated areas in a part of Mahanadi river basin using remote sensing data. 相似文献
820.
The wave-induced nearshore circulation model suggested by Noda has been modified and applied for three small segments along
the coast of Goa. The present model incorporates the prevailing bottom topography and considers its variation along with the
radiation stress as the driving force for the circulation. We find that the flow pattern is strongly dependent on bottom topography.
While normal incidence of waves results in a cellular pattern of flow, meandering flows prevail for oblique incidence along
the coast. The shoreward flows are always located over shoals while the rip currents prevail over channels. The onshore/offshore
flows show magnitudes as high as 3·1 m/s, while those alongshore reach a maximum of 1·1 m/s. When compared with field observations
these values are slightly higher. 相似文献