全文获取类型
收费全文 | 2867篇 |
免费 | 83篇 |
国内免费 | 53篇 |
专业分类
测绘学 | 275篇 |
大气科学 | 278篇 |
地球物理 | 588篇 |
地质学 | 1279篇 |
海洋学 | 138篇 |
天文学 | 335篇 |
综合类 | 51篇 |
自然地理 | 59篇 |
出版年
2023年 | 16篇 |
2022年 | 54篇 |
2021年 | 63篇 |
2020年 | 63篇 |
2019年 | 67篇 |
2018年 | 253篇 |
2017年 | 237篇 |
2016年 | 226篇 |
2015年 | 138篇 |
2014年 | 204篇 |
2013年 | 264篇 |
2012年 | 169篇 |
2011年 | 154篇 |
2010年 | 135篇 |
2009年 | 142篇 |
2008年 | 119篇 |
2007年 | 78篇 |
2006年 | 68篇 |
2005年 | 49篇 |
2004年 | 38篇 |
2003年 | 33篇 |
2002年 | 28篇 |
2001年 | 19篇 |
2000年 | 27篇 |
1999年 | 21篇 |
1998年 | 18篇 |
1997年 | 17篇 |
1996年 | 11篇 |
1995年 | 10篇 |
1994年 | 22篇 |
1993年 | 13篇 |
1992年 | 6篇 |
1991年 | 23篇 |
1990年 | 18篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1975年 | 6篇 |
1974年 | 11篇 |
1972年 | 8篇 |
1971年 | 5篇 |
1969年 | 6篇 |
排序方式: 共有3003条查询结果,搜索用时 15 毫秒
961.
This is the second paper of the series where we have considered Brans-Dicke (B-D) theory as well as general scalar tensor
theory of gravitation in higher dimensional space-time model in the false vacuum state. We have examined whether inflationary
solutions are possible both for constant or variable coupling parameter ω. Also the nature of the scalar field and the coupling
parameter are discussed in the asymptotic limit.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
962.
A field study was conducted to assess variations in physico-chemical characteristics of water of the springs located within
the boundary of a Central Himalayan town where the springwater is used for drinking purposes. Monitoring of 12 springs was
carried out for three seasons (winter, summer and monsoon). The results indicate direct influence of unplanned sewage disposal
on the springwater quality as reflected by significant regional variations in the concentration of nitrates, chlorides, sulfates,
sulfides and electrical conductivity. Population density varies within the town from 3110 to 14 137 persons/km–2 and has direct relationship with water quality. Springs located in the densely populated area had higher concentrations of
all these compounds. Concentrations of nitrates up to 60 ppm were observed in some springs, making water unsuitable for human
consumption. No significant changes were observed in springwater quality during different seasons.
Received: 3 February 1995 · Accepted: 27 February 1996 相似文献
963.
The predicted occultation of the star No. 31 (Mink et al., 1981) by Neptune on September 12, 1983 was observed photoelectrically. Four secondary occultations were recorded before the immersion event. 相似文献
964.
High resolution FTS sunspot umbral spectra from NSO/Kitt Peak were used to detect rotational lines due to 11 electronic transitions of the molecule AlF, in the wavelength region 4400 – 9000 Å. The presence of lines due to bands C – A (0,0), (0,1), (0,2) and (1,2), D – A (0,0) and (0,1), F – A (0,0), G – A (0,0), and F – B (0,0) is confirmed. Further, the presence of lines due to C – A (1,0) and (1,1) transitions is treated as doubtful because of heavy blending in the region, by rotational lines of TiO. Among the identified lines, those which are well resolved were selected for measurement of equivalent widths. The measured values for the bands D – A (0,0) and F – A (0,0) were used to estimate the respective effective rotational temperatures to be 1240 ± 120 K and 2390 ± 400 K. 相似文献
965.
Shiv S. Kumar 《Astrophysics and Space Science》1972,16(1):52-54
Arguments are presented to show that Jupiter could not have been formed as a star of mass 0.001M
and that the observed excess energy is not due to gravitational contraction from an extended, gaseous state. 相似文献
966.
The morphotectonic features of the Central Indian Ocean Basin (CIOB) provide information regarding the development of the basin. Multibeam mapping of the CIOB reveals presence of abundant isolated seamounts and seamount chains sub-parallel to each other and major fracture zones along 73° E, 79° E and 75°45′ E. Morphological analyses were carried out for 200 seamounts that occur either as isolated edifies or along eight sub-parallel chains. The identified eight parallel seamount chains that trend almost north–south and reflecting the absolute motion of the Indian plate, probably originated from the ancient propagative fractures. Inspite of the differences in their height, the seamounts of these eight chains are morphologically correlatable. In the study area the seamounts are clustered north and south of 12° S latitude. Interestingly, in the area north of 12° S (area II: 9°–12° S) the seamounts are distinctly smaller (≤ 400 m height) whereas, the area south of 12° S (area I: 12°–15° S) has a mixed population of seamounts. The normalized abundance of the CIOB seamount is 976 seamounts/106 km2 but on a finer scale this value varies from 500 to 1600 seamounts/106 km2, which is less than the seamount concentrations of the Pacific and Atlantic oceans (9000 to 16,000 seamounts/106 km2). Three categories of seamounts are present in the CIOB e.g. (1) single-peaked (2) multi-peaked and (3) composite. The study indicate that single-peaked seamounts are dominant (89%) while multi-peaked is less (8%) and composite ones are rare (3%) in the CIOB.The progressive northward movement of the Indian continent caused collision between India and Asia at around 62 Ma ago. A majority of the near-axis originated seamounts in the CIOB seemed to have formed as a consequence of the temporally widespread (Cretaceous 65 Ma to late Eocene < 49 Ma) collision between India and Eurasia. The regional stress patterns in the Indian plate vary N to NE in the continent and N to NW in Indian Ocean areas. The combined effect of the regional stress patterns maintained the orientation of the seamount chains and the local stress regime helped in the upwelling of magma and formation of seamounts. The low heat flow, morphological features and geochemical signature indicate that the morphotectonic structures formed contemporaneously with the oceanic crust. 相似文献
967.
Santosh Sapkota Saurav Sarup Khadka Gautam Sabin Karki Monika Adhikari Binod Mishra Roshan Kumar Klausner Virginia Dhungana Beni Madhav 《Geomagnetism and Aeronomy》2022,62(1-2):125-137
Geomagnetism and Aeronomy - Electrodynamical coupling between the solar wind’s plasma and the Earth’s magnetosphere creates geomagnetic disturbances recorded on the ground. This work... 相似文献
968.
Ocean Dynamics - The performance of three different mixing schemes implemented in the HYbrid Coordinate Ocean Model (HYCOM), namely, K-Profile Parameterization (KPP), Goddard Institute of Space... 相似文献
969.
Hydrogeology Journal - Regional-scale estimates of groundwater recharge are inherently uncertain, but this uncertainty is rarely quantified. Quantifying this uncertainty provides an understanding... 相似文献
970.
Boroomandnia Arezoo Bozorg-Haddad Omid Bahrami Mahdi Goharian Erfan Singh Vijay P. Loiciga Hugo A. 《Hydrogeology Journal》2021,29(4):1379-1398
Hydrogeology Journal - A coupled simulation-optimization model (SOM) is developed in this work that links the US Environmental Protection Agency’s Storm Water Management Model (SWMM) with a... 相似文献