全文获取类型
收费全文 | 94343篇 |
免费 | 1263篇 |
国内免费 | 1319篇 |
专业分类
测绘学 | 3062篇 |
大气科学 | 7167篇 |
地球物理 | 17836篇 |
地质学 | 36574篇 |
海洋学 | 7075篇 |
天文学 | 17454篇 |
综合类 | 2279篇 |
自然地理 | 5478篇 |
出版年
2020年 | 439篇 |
2019年 | 440篇 |
2018年 | 7275篇 |
2017年 | 6595篇 |
2016年 | 4679篇 |
2015年 | 1124篇 |
2014年 | 1420篇 |
2013年 | 2864篇 |
2012年 | 2974篇 |
2011年 | 6065篇 |
2010年 | 5422篇 |
2009年 | 6125篇 |
2008年 | 5150篇 |
2007年 | 6044篇 |
2006年 | 2047篇 |
2005年 | 2374篇 |
2004年 | 2417篇 |
2003年 | 2354篇 |
2002年 | 1988篇 |
2001年 | 1437篇 |
2000年 | 1381篇 |
1999年 | 1264篇 |
1998年 | 1202篇 |
1997年 | 1142篇 |
1996年 | 939篇 |
1995年 | 927篇 |
1994年 | 898篇 |
1993年 | 837篇 |
1992年 | 806篇 |
1991年 | 774篇 |
1990年 | 866篇 |
1989年 | 749篇 |
1988年 | 725篇 |
1987年 | 842篇 |
1986年 | 702篇 |
1985年 | 959篇 |
1984年 | 1107篇 |
1983年 | 1044篇 |
1982年 | 974篇 |
1981年 | 945篇 |
1980年 | 838篇 |
1979年 | 811篇 |
1978年 | 795篇 |
1977年 | 717篇 |
1976年 | 682篇 |
1975年 | 595篇 |
1974年 | 653篇 |
1973年 | 651篇 |
1972年 | 407篇 |
1971年 | 366篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
121.
This paper proposes a multi‐level parallelized substructuring–frontal combined algorithm for the analysis of the problem of thermo/hydraulic/mechanical behaviour of unsaturated soil. Temperature, displacement, pore water pressure and pore air pressure are treated as the primary variables in a non‐linear analysis. Details are given firstly of the substructuring–frontal combined approach. The incorporation of the algorithm in a multi‐level parallel strategy is then discussed. The parallel processing can thus be carried out at different substructural levels. The method thus developed impacts, in a positive way, on both computer storage requirement and execution time. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
122.
Due to the geological time scales required for observation of catchment evolution, surrogates or analogues of field data are necessary to understand long‐term processes. To investigate long‐term catchment behaviour, two experimental model catchments that developed without rigid boundaries under controlled conditions are examined and a qualitative and quantitative analysis of their evolution is presented. Qualitatively, the experimental catchments have the visual appearance of field scale data. Observation demonstrates that changes in catchment shape and network form are conservative. Quantitative analysis suggests that the catchments reach an equilibrium form while a reduction in the channel network occurs. While the catchments are laboratory scale models, the results provide insights into field scale behaviour. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
123.
Sarah Church Peter Ade James Bock Melanie Bowden John Carlstrom Ken Ganga Walter Gear James Hinderks Wayne Hu Brian Keating John Kovac Andrew Lange Eric Leitch Olivier Mallie Simon Melhuish Anthony Murphy Ben Rusholme Creidhe OSullivan Lucio Piccirillo Clem Pryke Andy Taylor Keith Thompson 《New Astronomy Reviews》2003,47(11-12):1083
QUEST on DASI is a ground-based, high-sensitivity, high-resolution (ℓmax2500) experiment designed to map CMB polarization at 100 and 150 GHz and to measure the power spectra from E-modes, B-modes from lensing of the CMB, and B-modes from primordial gravitational waves. The experiment comprises a 2.6 m Cassegrain optical system, equipped with an array of 62 polarization-sensitive bolometers (PSBs), located at the South Pole. The instrument is designed to minimize systematic effects; features include differencing of pairs of orthogonal PSBs within a single feed, a rotatable achromatic waveplate, and axisymmetric rotatable optics. In addition the South Pole location allows both repeatable and highly controlled observations. QUEST on DASI will commence operation in early 2005. 相似文献
124.
125.
126.
127.
128.
Pco2 of air and seawater samples from the East China Sea(ECS) were measured in situ in autumn, 1994,Ocean currents,terrestrial fluviation,biological activities,etc.,Pco2 char-acters in air and seawater were investigated,CO2 flux and its character in the East China Sea are discussed on the basis of the Pco2 profiles of air and seawater,It was clear that the nearshore was the source of CO2;and tht the oulter sea area was the sink of CO2; and that the shelf area of the EXS is a net sink for atmospheric CO2 in autumn. 相似文献
129.
JIANGDong WANGNai-bin YANGXIao-huan WANGJi-hua 《中国地理科学(英文版)》2003,13(1):62-65
Daily and ten-day Normalized Difference Vegetation Index(NDVI) of crops were retrieved from meteorological statellite NOAA AVHRR images ,The temporal variations of the NDVI were analyzed during the whole growing season,and thus the principle of the interaction between NDIV profile and the growing status of crops was discussed,As a case in point,the relationship between integral NDVI and winter wheat yield of Henan Province in 1999 had been analyzed.By putting integral NDVI values of 60 sample counties into the winter wheat yield-integral NDVI coordination,scattering map was plotted. It demonstrated that integral NDVI had a close relation with winter wheat yield.These relation could be described with linear,cubic polynomial ,and exponential regression,and the cubic polynomial regression was the best way,In general ,NDVI reflects growing status of green vegetation ,so crop monitoring and crop yield estimation could be realized by using remote sensing technique on the basis of time serial NDVI data together with agriculture calendars. 相似文献
130.