全文获取类型
收费全文 | 54544篇 |
免费 | 5683篇 |
国内免费 | 7235篇 |
专业分类
测绘学 | 1987篇 |
大气科学 | 8393篇 |
地球物理 | 12415篇 |
地质学 | 23265篇 |
海洋学 | 5643篇 |
天文学 | 7748篇 |
综合类 | 3322篇 |
自然地理 | 4689篇 |
出版年
2023年 | 437篇 |
2022年 | 1263篇 |
2021年 | 1557篇 |
2020年 | 1412篇 |
2019年 | 1569篇 |
2018年 | 2148篇 |
2017年 | 2009篇 |
2016年 | 2371篇 |
2015年 | 1689篇 |
2014年 | 2402篇 |
2013年 | 2858篇 |
2012年 | 2290篇 |
2011年 | 2571篇 |
2010年 | 2628篇 |
2009年 | 2949篇 |
2008年 | 2576篇 |
2007年 | 2553篇 |
2006年 | 2312篇 |
2005年 | 1914篇 |
2004年 | 1696篇 |
2003年 | 1618篇 |
2002年 | 1563篇 |
2001年 | 1430篇 |
2000年 | 1656篇 |
1999年 | 2023篇 |
1998年 | 1770篇 |
1997年 | 1823篇 |
1996年 | 1477篇 |
1995年 | 1391篇 |
1994年 | 1302篇 |
1993年 | 1091篇 |
1992年 | 947篇 |
1991年 | 711篇 |
1990年 | 627篇 |
1989年 | 620篇 |
1988年 | 548篇 |
1987年 | 479篇 |
1986年 | 404篇 |
1985年 | 442篇 |
1984年 | 446篇 |
1983年 | 418篇 |
1982年 | 398篇 |
1981年 | 310篇 |
1980年 | 317篇 |
1979年 | 248篇 |
1978年 | 230篇 |
1977年 | 229篇 |
1976年 | 191篇 |
1975年 | 203篇 |
1974年 | 184篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
81.
82.
83.
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
84.
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
85.
86.
茅排金矿床属中-低温硫化物金矿床,矿体的分布严格受断裂构造控制.通过应用不同的物探方法来寻找控矿断裂,从而达到间接地寻找矿体分布的目的,取得了较好的效果。 相似文献
87.
G. A. GRAHAM P. G. GRANT R. J. CHATER A. J. WESTPHAL A. T. KEARSLEY C. SNEAD G. DOMÍNGUEZ A. L. BUTTERWORTH D. S. McPHAIL G. BENCH J. P. BRADLEY 《Meteoritics & planetary science》2004,39(9):1461-1473
Abstract— In 2006, the Stardust spacecraft will return to Earth with cometary and perhaps interstellar dust particles embedded in silica aerogel collectors for analysis in terrestrial laboratories. These particles will be the first sample return from a solid planetary body since the Apollo missions. In preparation for the return, analogue particles were implanted into a keystone of silica aerogel that had been extracted from bulk silica aerogel using the optical technique described in Westphal et al. (2004). These particles were subsequently analyzed using analytical techniques associated with the use of a nuclear microprobe. The particles have been analyzed using: a) scanning transmission ion microscopy (STIM) that enables quantitative density imaging; b) proton elastic scattering analysis (PESA) and proton backscattering (PBS) for the detection of light elements including hydrogen; and c) proton‐induced X‐ray emission (PIXE) for elements with Z > 11. These analytical techniques have enabled us to quantify the composition of the encapsulated particles. A significant observation from the study is the variable column density of the silica aerogel. We also observed organic contamination within the silica aerogel. The implanted particles were then subjected to focused ion beam (FIB) milling using a 30 keV gallium ion beam to ablate silica aerogel in site‐specific areas to expose embedded particles. An ion polished flat surface of one of the particles was also prepared using the FIB. Here, we show that ion beam techniques have great potential in assisting with the analysis and exposure of Stardust particles. 相似文献
88.
Using photoclinometry, topographic profiles across europan ridges have been produced. These profiles allow the identification of bulges in the terrain adjacent to the ridges. The bulges are assumed to have been produced by flexure of the elastic lithosphere due to the load of the ridges, which lie along cracks in the crust. The distance from the crack to these “fore-bulges” depends on the thickness of the elastic plate being flexed. Based on a survey of ridges in Galileo images with resolution <300 m/pixel, the thickness of the elastic lithosphere has been determined by this method at a wide variety of sites along the leading and trailing hemispheres of Europa. The average thickness is about 200 m. The elastic lithosphere underneath smooth dilational bands tends to be thicker than plains morphology, an effect that is pronounced at Thynia Linea and Astypalaea Linea. Among the ridges investigated here, more recent loading correlates with a thicker elastic lithosphere, which may either reflect an intrinsically thicker layer, or less viscous relaxation over the shorter time period. 相似文献
89.
90.
A new species,Clathrocorys gracilis nov. spec. of Tripocyrtidae (Radiolarians: Nassellaria) from surface water in northern South China Sea, is described in this
paper. The new species has four radial beams arising from the cephalic base centre, each foot with cup-shaped structure and
ramified bar in the proximal section (near cephalic base), and each wing with a large mesh in the middle, a medium mesh and
a small mesh on each side respectively.
Project supported by the NSFC (No. 40276044) and the Chinese Academy of Sciences (No. KSCX2-SW-101B). 相似文献