全文获取类型
收费全文 | 5009篇 |
免费 | 209篇 |
国内免费 | 93篇 |
专业分类
测绘学 | 157篇 |
大气科学 | 534篇 |
地球物理 | 1390篇 |
地质学 | 2156篇 |
海洋学 | 232篇 |
天文学 | 614篇 |
综合类 | 82篇 |
自然地理 | 146篇 |
出版年
2022年 | 42篇 |
2021年 | 72篇 |
2020年 | 64篇 |
2019年 | 42篇 |
2018年 | 162篇 |
2017年 | 151篇 |
2016年 | 234篇 |
2015年 | 162篇 |
2014年 | 244篇 |
2013年 | 299篇 |
2012年 | 249篇 |
2011年 | 207篇 |
2010年 | 244篇 |
2009年 | 258篇 |
2008年 | 195篇 |
2007年 | 152篇 |
2006年 | 135篇 |
2005年 | 130篇 |
2004年 | 107篇 |
2003年 | 85篇 |
2002年 | 90篇 |
2001年 | 93篇 |
2000年 | 87篇 |
1999年 | 85篇 |
1998年 | 104篇 |
1997年 | 65篇 |
1996年 | 83篇 |
1995年 | 65篇 |
1994年 | 65篇 |
1993年 | 47篇 |
1992年 | 39篇 |
1991年 | 39篇 |
1990年 | 42篇 |
1989年 | 44篇 |
1988年 | 28篇 |
1987年 | 45篇 |
1986年 | 34篇 |
1985年 | 39篇 |
1984年 | 45篇 |
1983年 | 61篇 |
1982年 | 43篇 |
1981年 | 40篇 |
1980年 | 40篇 |
1979年 | 45篇 |
1978年 | 45篇 |
1977年 | 39篇 |
1976年 | 28篇 |
1975年 | 44篇 |
1974年 | 38篇 |
1973年 | 40篇 |
排序方式: 共有5311条查询结果,搜索用时 15 毫秒
141.
142.
Jeremy D. Silver Jesper H. Christensen Michael Kahnert Lennart Robertson Peter J. Rayner Jørgen Brandt 《Journal of Atmospheric Chemistry》2016,73(3):261-302
Satellite retrievals of atmospheric composition provide a wealth of data on a global scale. These complement results from atmospheric chemistry-transport models (CTMs), and can be combined using data assimilation. We present two assimilation schemes coupled to the Danish Eulerian Hemispheric Model (DEHM), a three-dimensional, off-line CTM with full photochemistry: a variant on the ensemble Kalman filter and the three-dimensional variational scheme. The aim of this paper is to describe the two schemes and present an initial assessment of their impacts on model skill. Retrievals of multiple atmospheric trace gases are assimilated, namely: NO2 tropospheric column densities, CH4 total column densities, and partial column concentrations of O3, CO and CH4; these data are retrieved from four satellite sensors. Data for each species are assimilated independently of one another, and other species are only adjusted indirectly via the model’s chemistry and dynamics. Assimilation results are compared with measurements from surface monitoring stations and other satellite retrievals, and preliminary validation results are presented.Reference simulations (without assimilation) grossly underestimate surface CO concentrations, and both assimilation schemes eliminate this large and systematic model bias. The assimilation improves the spatial correlation of modelled CO with surface observations, and improves the spatial correlation between forecasts and retrievals for CO, NO2 and O3. Results for CH4 show a loss of skill due to a mismatch in model bias between two assimilated CH4 data-sets. Finally, we discuss differences in methodology and results between this paper and a recent study on multi-species chemical data assimilation. Joint optimisation of initial conditions and emission rates offers a promising direction for improving modelled boundary-layer concentrations. 相似文献
143.
144.
145.
146.
Long-term soil moisture dynamics derived from GNSS interferometric reflectometry: a case study for Sutherland,South Africa 总被引:3,自引:0,他引:3
Sibylle Vey Andreas Güntner Jens Wickert Theresa Blume Markus Ramatschi 《GPS Solutions》2016,20(4):641-654
Soil moisture is a geophysical key observable for predicting floods and droughts, modeling weather and climate and optimizing agricultural management. Currently available in situ observations are limited to small sampling volumes and restricted number of sites, whereas measurements from satellites lack spatial resolution. Global navigation satellite system (GNSS) receivers can be used to estimate soil moisture time series at an intermediate scale of about 1000 m2. In this study, GNSS signal-to-noise ratio (SNR) data at the station Sutherland, South Africa, are used to estimate soil moisture variations during 2008–2014. The results capture the wetting and drying cycles in response to rainfall. The GNSS Volumetric Water Content (VWC) is highly correlated (r 2 = 0.8) with in situ observations by time-domain reflectometry sensors and is accurate to 0.05 m3/m3. The soil moisture estimates derived from the SNR of the L1 and L2P signals compared to the L2C show small differences with a RMSE of 0.03 m3/m3. A reduction in the SNR sampling rate from 1 to 30 s has very little impact on the accuracy of the soil moisture estimates (RMSE of the VWC difference 1–30 s is 0.01 m3/m3). The results show that the existing data of the global tracking network with continuous observations of the L1 and L2P signals with a 30-s sampling rate over the last two decades can provide valuable complementary soil moisture observations worldwide. 相似文献
147.
148.
North-western Anatolia has been actively deformed since Pliocene by the right-lateral North Anatolian Fault (NAF). This transform fault, which has a transtensional character in its western end due to effects from the Aegean extensional system, is a major control on the regional geomorphologic evolution. This study applied some geomorphic analyses, such as stream longitudinal profiles, stream length-gradient index, ratio of valley floor width and valley height, mountain front sinuosity, hypsometry and asymmetry factor analyses, to an area just east of the Sea of Marmara in order to understand the tectonic effects on the area’s geomorphological evolution. The active and fastest northern branch of the NAF lies within a topographic depression connecting Sea of Marmara in the east to the Adapazar? Basin in the west. This depression filled with early Pleistocene and younger sediment after a series of pull-apart basins opened along the NAF. North of this depression lies the Kocaeli Peneplain, whose southern edge the NAF uplifted. Meandering streams on the central peneplain were incised possibly due to baselevel changes in the Black Sea. South of the depression, an E-trending mountainous area has a rugged morphology. Based on geomorphic analyses, uplifted Pliocene sediment, marine terraces, and recent earthquake activity, this area between northern and southern branches of the NAF is actively uplifting. The geomorphic indices used in this study are sensitive to vertical movements rather than lateral ones. The bedrock lithology that played an important role on the area’s geomorphologic evolution also affects the geomorphic indices used here. 相似文献
149.