全文获取类型
收费全文 | 5350篇 |
免费 | 812篇 |
国内免费 | 892篇 |
专业分类
测绘学 | 155篇 |
大气科学 | 511篇 |
地球物理 | 670篇 |
地质学 | 2342篇 |
海洋学 | 1036篇 |
天文学 | 571篇 |
综合类 | 341篇 |
自然地理 | 1428篇 |
出版年
2024年 | 27篇 |
2023年 | 72篇 |
2022年 | 214篇 |
2021年 | 204篇 |
2020年 | 196篇 |
2019年 | 258篇 |
2018年 | 192篇 |
2017年 | 192篇 |
2016年 | 177篇 |
2015年 | 177篇 |
2014年 | 275篇 |
2013年 | 292篇 |
2012年 | 273篇 |
2011年 | 240篇 |
2010年 | 243篇 |
2009年 | 305篇 |
2008年 | 311篇 |
2007年 | 371篇 |
2006年 | 432篇 |
2005年 | 341篇 |
2004年 | 332篇 |
2003年 | 286篇 |
2002年 | 293篇 |
2001年 | 266篇 |
2000年 | 199篇 |
1999年 | 179篇 |
1998年 | 165篇 |
1997年 | 107篇 |
1996年 | 101篇 |
1995年 | 69篇 |
1994年 | 66篇 |
1993年 | 47篇 |
1992年 | 34篇 |
1991年 | 26篇 |
1990年 | 17篇 |
1989年 | 19篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 3篇 |
排序方式: 共有7054条查询结果,搜索用时 109 毫秒
11.
M. J. Carson J. C. Davies E. Daw R. J. Hollingworth V. A. Kudryavtsev T. B. Lawson P. K. Lightfoot J. E. McMillan B. Morgan S. M. Paling M. Robinson N. J. C. Spooner D. R. Tovey 《Astroparticle Physics》2004,21(6):667-687
Simulations of the neutron background for future large-scale particle dark matter detectors are presented. Neutrons were generated in rock and detector elements via spontaneous fission and (α,n) reactions, and by cosmic-ray muons. The simulation techniques and results are discussed in the context of the expected sensitivity of a generic liquid xenon dark matter detector. Methods of neutron background suppression are investigated. A sensitivity of 10−9–10−10 pb to WIMP-nucleon interactions can be achieved by a tonne-scale detector. 相似文献
12.
13.
14.
This paper describes the application of environmental isotopes and injected tracer techniques in estimating the contribution of storms as well as annual precipitation to groundwater recharge and its circulation, in the semi‐arid region of Bagepalli, Kolar district, Karnataka. Environmental isotopes 2H, 18O and 3H were used to study the effect of storms on the hydrological system, and an isotope balance was used to compute the contribution of a storm component to the groundwater. Some of the groundwater samples collected during the post‐storm periods were highly depleted in stable isotope content with higher deuterium excess relative to groundwater from the pre‐storm periods. Significant variation in deuterium excess in groundwater from the same area, collected in two different periods, indicates the different origin of air masses. The estimated recharge component of a storm event of 600 mm to the groundwater was found to be in the range of 117–165 mm. There was no significant variation in environmental tritium content of post‐storm and pre‐storm groundwater, indicating the fast circulation of groundwater in the system. After completion of the environmental isotope work, an injected radiotracer 3H technique was applied to estimate the direct recharge of total precipitation to the groundwater. The estimated recharge to the groundwater is 33 mm of the 550 mm annual precipitation during 1992. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
15.
Ignacio Ferreras Alessandro Melchiorri Domenico Tocchini-Valentini 《Monthly notices of the Royal Astronomical Society》2003,344(1):257-261
The age of the Universe has been increasingly constrained by different techniques, such as the observations of type Ia supernovae (SNIa) at high redshift or dating the stellar populations of globular clusters. In this paper, we present a complementary approach using the colours of the brightest elliptical galaxies in clusters over a wide redshift range ( z ≲ 1) . We put new and independent bounds on the dark energy equation of state parametrized by a constant pressure-to-density ratio w Q and by a parameter (ξ) which determines the scaling between the matter and dark energy densities. We find that accurate estimates of the metallicities of the stellar populations in moderate and high-redshift cluster galaxies can pose stringent constraints on the parameters that describe dark energy. Our results are in good agreement with the analysis of dark energy models using SNIa data as a constraint. Accurate estimates of the metallicities of stellar populations in cluster galaxies at z ≲ 2 will make this approach a powerful complement to studies of cosmological parameters using high-redshift SNIa. 相似文献
16.
17.
18.
19.
WANGWei-wu ZHULi-zhong WANGRen-chao SHIYong-jung 《中国地理科学(英文版)》2003,13(1):39-47
Urban heat environmental quality(UHEQ) is affected by the interacting of weather condition and underlying surface framework of urban area .In the last two decades,many researchers from domestic and overseas have studied many problems at the aspect of urban heat environment such as urban heat islands ,urban air temperature and their rela-tion with urban land cover,city population,air pollution etc,In the recent years,Hangzhou,acting as a center city of Zhejiang Province in China,its urbanization quantum and quantity have both changed greatly,in particular ,representing as business affairs building,resident real property and all kins of specialty market having arisen in built-up zone,Based on Landsat TM images data in 1991 and 1999,urban underlying surface temperature value and Normalized Difference Vegetation Index (NDVI) were calculated using image interpreting and supervised classification technique by remote sensing software ERDAS image 8.4,The relation model between urban underlying surface temperature (UUST )and urban air temperature was setup according to the certain correlation patten .Reference to the relational standard of assessing human comfort and other meteorology data of Hangzhou City in summer,the spatial distribution characteristic and the spatial varia-tion degree of human comfort of heat environmental quality are estimated and mapped on a middle scale,that is ,in six districts of Hangzhou City .Then the paper reveals the main characteristic of spatial variation from 1991 to 1999.Lastly,the change mechanism is analyzed and discussed from the viewpoint of city planning,construction and environmental protec-tion. 相似文献
20.
Using a set of compilations of measurements for extragalactic radio sources, we construct all-sky maps of the Faraday rotation produced by the Galactic magnetic field. In order to generate the maps, we treat the radio source positions as a kind of 'mask' and construct combinations of spherical harmonic modes that are orthogonal on the masked sky. As long as relatively small multipoles are used, the resulting maps are quite stable to changes in the selection criteria for the sources, and show clearly the structure of the local Galactic magnetic field. We also suggest the use of these maps as templates for cosmic microwave background (CMB) foreground analysis, illustrating the idea with a cross-correlation analysis between the Wilkinson Microwave Anisotropy Probe ( WMAP ) data and our maps. We find a significant cross-correlation, indicating the presence of a significant residual contamination. 相似文献