全文获取类型
收费全文 | 1347篇 |
免费 | 292篇 |
国内免费 | 567篇 |
专业分类
测绘学 | 91篇 |
大气科学 | 188篇 |
地球物理 | 486篇 |
地质学 | 948篇 |
海洋学 | 193篇 |
天文学 | 49篇 |
综合类 | 152篇 |
自然地理 | 99篇 |
出版年
2020年 | 2篇 |
2016年 | 7篇 |
2015年 | 13篇 |
2014年 | 4篇 |
2013年 | 14篇 |
2012年 | 10篇 |
2011年 | 164篇 |
2010年 | 119篇 |
2009年 | 125篇 |
2008年 | 37篇 |
2007年 | 77篇 |
2006年 | 127篇 |
2005年 | 143篇 |
2004年 | 272篇 |
2003年 | 177篇 |
2002年 | 142篇 |
2001年 | 107篇 |
2000年 | 92篇 |
1999年 | 56篇 |
1998年 | 49篇 |
1997年 | 74篇 |
1996年 | 46篇 |
1995年 | 38篇 |
1994年 | 25篇 |
1993年 | 56篇 |
1992年 | 63篇 |
1991年 | 50篇 |
1990年 | 15篇 |
1989年 | 20篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 8篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 2篇 |
1965年 | 1篇 |
1962年 | 1篇 |
1950年 | 2篇 |
1942年 | 1篇 |
1940年 | 2篇 |
1937年 | 6篇 |
1934年 | 5篇 |
1931年 | 1篇 |
排序方式: 共有2206条查询结果,搜索用时 78 毫秒
991.
提出了一种基于空间微分块与动态球判定策略的k近邻快速搜索算法。该算法以空间包围盒为基础,首先对空间进行微分块,将离散点分配到子空间;然后,以计算点为球心建立动态球,确定k近邻候选点。球半径可根据空间包围盒的大小、离散点数量和k近邻点数进行估算和优化。实验结果表明,该算法可快速完成k近邻搜索,运行稳定可靠。 相似文献
992.
许家窑遗址是中国旧石器时代中期的一处重要考古遗址,按照地层古生物学常规判断,其地层为上更新统下部.许家窑遗址是泥河湾盆地乃至东亚地区发现的上更新统包含古人类及古哺乳动物化石和旧石器时代考古遗物最丰富的一个地层剖面.许家窑遗址的古地磁测年的分析存在重大理念误区,其"早更新世晚期至中更新世早中期"的断代结论令人难以置信. 相似文献
993.
在俄罗斯达吉斯坦共和国早白垩世地层中,极少见到菊石化石,但是可以利用地层中腕足动物化石组合为基础划分贝利阿斯阶(Berriasian)、凡兰吟阶(Valanginian)、上下欧特里夫维阶(Lower and Uppet Hauterivian)和下巴雷姆阶(Lower Barremian)地层. 相似文献
994.
995.
996.
A curve-fit model of the relationship between soil pH (A horizon) and climate forms the basis of a map of predicted pH for the conterminous United States. This map was produced with the aid of a large climatic data base, a computer mapping program and subroutines to map modeled values of soil pH. Patterns of pH follow well-recognized patterns of climate, although the pH of 7 line deviates greatly from Marbut's line dividing pedalfers from pedocals. The overall accuracy of the map and model was checked using a validation data set. Geographic patterns of pH are realistic, although land use, topography, and parent material may cause local variations about the predicted mean for a given region. Several apparently anamolous map patterns were also checked but found to be accurate. Prediction of the detailed pattern of pH will require variables in addition to climate. 相似文献
997.
SUN Haitao ZHONG Dakang ZHANG Simeng WANG Xingming.State Key Lab of Petroleum Resource Prospecting Faculty of Natural Resource Information Technology China University of Petroleum Beijing China.Exploration Development Research Institute of Dagang Oilfield Company PetroChina Tianjin China 《东北亚地学研究》2010,(1)
There are eighty sedimentary basins in five different types in African continent,i.e.craton sag basin,foreland basin,intermountain basin,passive margin basin and rift basin,which underwent the stress environment of stable depression-compression-extension.The first three types of basins had been intensely influenced by Hercynian and Alpine tectonic movement,while the later two types of basins always exist in a stable extension environment.Different basin evolution caused the obviously hydrocarbon distributio... 相似文献
998.
To gain a better understanding of water quality and eutrophication,we investigated the seasonal and spatial distribution of water quality at 17 stations in the Guangzhou Sea Zone (GZSZ).Nutrients,chlorophyll-a (Chl-a),salinity,chemical oxygen demand,and other physical and chemical parameters were determined in February,May,August and October from 2005 to 2007.The concentrations showed ranges of 93.2-530.4 μmol/L for dissolved inorganic nitrogen (DIN),0.62-3.16 μmol/L for phosphate (PO4-P) and 50-127 μmol/L ... 相似文献
999.
The future potential changes in precipitation and monsoon circulation in the summer in East Asia are projected using the latest generation of coupled climate models under Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A1B scenario (a medium emission scenario).The multi-model ensemble means show that during the period of 2010-2099,the summer precipitation in East Asia will increase and experience a prominent change around the 2040s,with a small increase (~1%) before the end of the 2040s and a large increase (~9%) afterward.This kind of two-stage evolution characteristic of precipitation change can be seen most clearly in North China,and then in South China and in the mid and lower Yangtze River Valley.In 2010-2099,the projected precipitation pattern will be dominated by a pattern of "wet East China" that explains 33.6% of EOF total variance.The corresponded time coefficient will markedly increase after the 2040s,indicating a great contribution from this mode to the enhanced precipitation across all East China.Other precipitation patterns that prevail in the current climate only contribute a small proportion to the total variance,with no prominent liner trend in the future.By the late 21st century,the monsoon circulation will be stronger in East Asia.At low level,this is due to the intensification of southwesterly airflow north of the anticyclone over the western Pacific and the SCS,and at high level,it is caused by the increased northeasterly airflow east of the anticyclone over South Asia.The enhanced monsoon circulation will also experience a two-stage evolution in 2010-2099,with a prominent increase (by ~0.6 m s-1) after the 2040s.The atmospheric water vapor content over East Asia will greatly increase (by ~9%) at the end of 21st century.The water vapor transported northward into East China will be intensified and display a prominent increase around the 2040s similar to other examined variables.These indicate that the enhanced precipitation over East Asia is caused by the increases in both monsoon circulation and water vapor,which is greatly different from South Asia.Both the dynamical and thermal dynamic variables will evolve consistently in response to the global warming in East Asia,i.e.,the intensified southwesterly monsoon airflow corresponding to the increased water vapor and southwesterly moisture transport. 相似文献
1000.
YIN XiaoBin WANG ZhenZhan & LIU YuGuang Center for Space Science Applied Research Chinese Academy of Sciences Beijing China Physical Oceanography Laboratory Ocean University of China Qingdao 《中国科学:地球科学(英文版)》2010,(6)
A new simple two-scale model on the polarimetric microwave emission of ocean surface is derived at first, which can be ex-pressed as an integral of weighting functions (M0 and M2) and ocean surface curvature spectrum coefficients (C0 and C2). This provides a simple way to investigate the effect of curvature spectrum on ocean emission. It is found that ocean waves with wavelengths both comparable to and much greater than the electromagnetic wavelength can contribute to the harmonics of ocean surface microwav... 相似文献