全文获取类型
收费全文 | 82856篇 |
免费 | 6528篇 |
国内免费 | 8812篇 |
专业分类
测绘学 | 4528篇 |
大气科学 | 10638篇 |
地球物理 | 18060篇 |
地质学 | 36638篇 |
海洋学 | 7032篇 |
天文学 | 8991篇 |
综合类 | 5283篇 |
自然地理 | 7026篇 |
出版年
2023年 | 623篇 |
2022年 | 1543篇 |
2021年 | 1868篇 |
2020年 | 1536篇 |
2019年 | 1804篇 |
2018年 | 6385篇 |
2017年 | 5554篇 |
2016年 | 4653篇 |
2015年 | 2237篇 |
2014年 | 2687篇 |
2013年 | 3275篇 |
2012年 | 3412篇 |
2011年 | 5333篇 |
2010年 | 4627篇 |
2009年 | 5033篇 |
2008年 | 4387篇 |
2007年 | 4667篇 |
2006年 | 2326篇 |
2005年 | 2222篇 |
2004年 | 2126篇 |
2003年 | 2078篇 |
2002年 | 1897篇 |
2001年 | 1623篇 |
2000年 | 1782篇 |
1999年 | 2121篇 |
1998年 | 1813篇 |
1997年 | 1757篇 |
1996年 | 1558篇 |
1995年 | 1406篇 |
1994年 | 1249篇 |
1993年 | 1174篇 |
1992年 | 973篇 |
1991年 | 815篇 |
1990年 | 732篇 |
1989年 | 635篇 |
1988年 | 644篇 |
1987年 | 562篇 |
1986年 | 514篇 |
1985年 | 615篇 |
1984年 | 664篇 |
1983年 | 640篇 |
1982年 | 525篇 |
1981年 | 529篇 |
1980年 | 524篇 |
1979年 | 448篇 |
1978年 | 421篇 |
1977年 | 376篇 |
1976年 | 407篇 |
1974年 | 400篇 |
1973年 | 390篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
WANGXie-kang HUANGEr CUIPeng 《中国地理科学(英文版)》2003,13(3):262-266
Debris flow is one of the most destructive phenomena of natural hazards. Recently, major natural haz-ard, claiming human lives and assets, is due to debris flow in the world. Several practical methods for forecasting de-bris flow have been proposed, however, the accuracy of these methods is not high enough for practical use because of the stochastic and non-linear characteristics of debris flow. Artificial neural network has proven to be feasible and use-fill in developing models for nonlinear systems. On the other hand, predicting the future behavior based on a time se-ries of collected historical data is also an important tool in many scientific applications. In this study we present a three-layer feed-forward neural network model to forecast surge of debris flow according to the time series data collect-ed in the Jiangjia Ravine, situated in north part of Yunnan Province of China. The simulation and prediction of debris flow using the proposed approach shows this model is feasible, however, further studies are needed. 相似文献
102.
The dunes in estuary of Tumen River in China lie to the area between the Jiushaping and Fangchuan in the left bank of Tumen River (Fig.1). The dis-tance is about 15~20 km between the dunes and the coast. It ranges from China to D. P. R. Korea and Russia. The range of the height of dunes is about 15~20 m and the width is 100~200 m. By the re-connaissance, we protracted 9 section planes of the dunes and collected 40 sand samples of the dunes, and identified the sedimentary environment … 相似文献
103.
Hong-Qi Zhang Xing-Ming Bao Yin Zhang Ji-Hong Liu Shu-Dong Bao Yuan-Yong Deng Wei Li Jie Chen Jin-Ping Dun Jiang-Tao Su Juan Guo Xiao-Fan Wang Ke-Liang Hu Gang-Hua Lin Dong-Guang WangNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(6):491-494
We analyze the magnetic configurations of three super active regions, NOAA 10484, 10486 and 10488, observed by the Huairou Multi-Channel Solar Telescope (MCST) from 2003 October 18 to November 4. Many energetic phenomena, such as flares (including a X-28 flare) and coronal mass ejections (CMEs), occurred during this period. We think that strong shear and fast emergence of magnetic flux are the main causes of these events. The question is also of great interest why these dramatic eruptions occurred so close together in the descending phase of the solar cycle. 相似文献
104.
本文讨论了彗星中尘埃粒子的充电机制 ,带电特性和平衡电势的变化规律 ,分析了彗星尘埃的破碎特性和临界半径 ,得出了很有意义的结果 相似文献
105.
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
106.
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
107.
108.
109.
YANGYong-liang SHITong-guang JLANGLU-guang LIYue 《中国地理科学(英文版)》2003,13(2):130-133
In recent years, many coal-producing countries have paid great attention to the land subsidence causedby coal cutting. In China, because of the dense population in coalfield areas, the land subsidence hazard is more seri-ous. After a brief analysis on the mechanism of land subsidence, this paper gives a comprehensive and systematical ac-count on all kinds of hazards caused by the land subsidence in China. The study shows that land subsidence has endan-gered land, buildings, traffic and communication lines, dykes and dams. It also causes damage to ecological and socialenvironment. In order to lessen the hazard of land subsidence, preventive measures should be taken to reduce the col-lapse amount, such as extraction with stowing, banded mining system, succession and coordination mining system, orhigh-pressure mudflow between rock strata. Measures of reinforcing or moving certain buildings should also be taken toreduce the destructive degree. In order to harness the subsidence land and bring them under control for fanning, mea-sures should be taken such as filling with spoil or fine breeze, excavating the deeper and covering the shallower land. 相似文献
110.
M.P. Collings J.W. Dever H.J. Fraser M.R.S. McCoustra 《Astrophysics and Space Science》2003,285(3-4):633-659
The interaction of carbon monoxide (CO) with vapour-deposited water(H2O) ices has been studied using temperature programmed desorption (TPD) and Fourier transform reflection-absorption infrared
spectroscopy (FT-RAIRS) over a range of astrophysically relevant temperatures. Such measurements have shown that CO desorption
from amorphous H2Oices is a much more complex process than current astrochemical models suggest. Re-visiting previously reported laboratory
experiments (Collings et al., 2003), a rate model has been constructed to explain, in a phenomenological manner, the desorption
of CO over astronomically relevant time scales. The model presented here can be widely applied to a range of astronomical
environments where depletion of CO from the gas phase is relevant. The model accounts for the two competing processes of CO
desorption and migration, and also enables the entrapment of some of the CO in the ice matrix and its subsequent release as
the water ice crystallises and then desorbs. The astronomical implications of this model are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献