全文获取类型
收费全文 | 31355篇 |
免费 | 5484篇 |
国内免费 | 7140篇 |
专业分类
测绘学 | 3443篇 |
大气科学 | 5225篇 |
地球物理 | 7699篇 |
地质学 | 14894篇 |
海洋学 | 3866篇 |
天文学 | 1164篇 |
综合类 | 2753篇 |
自然地理 | 4935篇 |
出版年
2024年 | 132篇 |
2023年 | 386篇 |
2022年 | 916篇 |
2021年 | 1147篇 |
2020年 | 1266篇 |
2019年 | 1598篇 |
2018年 | 1145篇 |
2017年 | 1500篇 |
2016年 | 1467篇 |
2015年 | 1577篇 |
2014年 | 1994篇 |
2013年 | 2266篇 |
2012年 | 2062篇 |
2011年 | 2200篇 |
2010年 | 1805篇 |
2009年 | 2179篇 |
2008年 | 2128篇 |
2007年 | 2276篇 |
2006年 | 2206篇 |
2005年 | 1770篇 |
2004年 | 1604篇 |
2003年 | 1377篇 |
2002年 | 1107篇 |
2001年 | 1045篇 |
2000年 | 905篇 |
1999年 | 877篇 |
1998年 | 825篇 |
1997年 | 719篇 |
1996年 | 595篇 |
1995年 | 532篇 |
1994年 | 443篇 |
1993年 | 426篇 |
1992年 | 304篇 |
1991年 | 232篇 |
1990年 | 182篇 |
1989年 | 166篇 |
1988年 | 139篇 |
1987年 | 75篇 |
1986年 | 62篇 |
1985年 | 64篇 |
1984年 | 35篇 |
1982年 | 26篇 |
1981年 | 23篇 |
1980年 | 30篇 |
1979年 | 15篇 |
1978年 | 23篇 |
1977年 | 32篇 |
1976年 | 25篇 |
1973年 | 17篇 |
1971年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Olac Fuentes 《Experimental Astronomy》2001,12(1):21-31
In this article we show how machine learning methods can beeffectively applied to the problem of automatically predictingstellar atmospheric parameters from spectral information, a veryimportant problem in stellar astronomy. We apply feedforwardneural networks, Kohonen's self-organizing maps andlocally-weighted regression to predict the stellar atmosphericparameters effective temperature, surface gravity and metallicityfrom spectral indices. Our experimental results show that thethree methods are capable of predicting the parameters with verygood accuracy. Locally weighted regression gives slightly betterresults than the other methods using the original dataset asinput, while self-organizing maps outperform the other methods when significant amounts of noise are added. We also implemented a heterogeneous ensemble of predictors, combining the results given by the three algorithms. This ensemble yields better results than any of the three algorithms alone, using both the original and the noisy data. 相似文献
42.
应用地壳波浪与镶嵌构造学说对富氏谱分析法提取地壳垂直形变信息的科学性做了地质学意义上的阐释 ,并提出了根据多期形变资料提取特定波段上构造策应力的数学模型 相似文献
43.
PROPAGATION OF 30—60 DAY LOW FREQUENCY OSCILLATIONS AND THEIR INFLUENCE UPON THE SUBTROPICAL WESTERLIES JET STREAM DURING NORTHERN HEMISPHERE WINTER 下载免费PDF全文
Based on daily ECMWF gridpoint data of two winters during 1981—1983 including an ENSOyear,propagation of low frequency oscillations(LFO)during Northern Hemisphere winters andtheir influences upon 30—60 day oscillations of the subtropical jet stream are studied with the sta-tistical methods as complex empirical orthogonal function(CEOF)and so on.Results show that inthe winter of a normal year(1981—1982),30—60 day oscillations in the subtropical zone aremainly in the northern and southern flanks of exit region of jet stream.In the ENSO year(1982—1983),they are mainly in the vicinity of entrance and exit regions of jet stream.Intraseasonalchanges of subtropical jet stream manifested themselves as latitudinal fluctuation or longitudinalprogression or regression of about 40 day period.There are marked differences between propagat-ing passages of low frequency modes responsible for changes of subtropical jet stream in the normalyear(1981—1982)and in the ENSO year(1982—1983).Changes of oscillation amplitude showobvious phases.In general,the one in late winter is stronger than that in early winter,strongestone occurs in February. 相似文献
44.
We have analysed short-exposure high-resolution images obtained on the William Herschel Telescope (WHT), Big Telescope Azimuthal (BTA) and CanadaFranceHawaii Telescope (CFHT) in order to investigate mechanical vibrations that are capable of reducing the high angular resolution allowed by speckle-interferometric methods. After filtering the photon noise we have computed power spectra of the image centres of gravity. In these spectra we have found vibration features that differ from one telescope to another and that vary in particular with the zenith angle. In the case of the WHT we discuss these results in terms of possible causes and in terms of degradation of the transfer function. We present some means to improve the data. 相似文献
45.
46.
Measurements of salinity perturbations in a partially mixed estuary have been used to evaluate the usefulness of an inductive salinometer and to determine some of the characteristics of the salinity perturbations. The salinometer performed satisfactorily under most conditions. Although internal wave like effects were present, the turbulence fluctuations were dominant. The salinity fluctuations and the turbulent fluxes and were found to behave in a manner similar to the density fluctuations in a thermally stratified atmospheric boundary layer and a laboratory open channel flow. A quadrant analysis suggested that the contribution of each quadrant to the turbulent flux changed with Ri. The turbulence parameters ν and cγ were found to decrease and increase respectively as Ri increases. 相似文献
47.
1 INTRODUCTIONThe South China Sea (SCS) is a semi-enclosedmarginal sea in western North Pacific Ocean withvery complex topography and is the important pas-sage connecting the Pacific and Indian Oceans. Ithas great impact to the global climate and a greatinterest of many oceanography researchers. Twodominant surface hydrographic and circulation fea-tures in the northern SCS are a strong fresh waterexpansion and a warm and high-salinity seawaterintrusion such as the SCS Diluted Water… 相似文献
48.
49.
WEIHai-quan JINBo-lu LIUYong-shun 《东北亚地学研究》2004,7(1):28-35
A number of different lahars have been recognized from a systematic survey of a mapping project. The high setting temporamre feature of the deposits indicates a relationship between the lahar and the Millennium eruption event of Tianchi Volcano. The lahars caused a dramatic disaster. Recognize of the huge avalanche scars and deposits around Tianchi Volcano imply another highly destructive hazard. Three types of different texture of the avalanche deposits have been recognized. There was often magma mixing processes during the Millennium eruption of Tianchi Volcano, indicating a mixing and co-eruption regime of the eruption. 相似文献
50.
The UV spectra of mixture solutions consisting of tyrosine,tryptophane,phenylalanine,cystine,histidineand 3,4-dihydroxyl phenylalanine have been measured.The numbers,identities and concentrations of theamino acids in the mixtures have been determined successfully using target factor analysis.The effectsof the wavelength range and the selected sampling interval on the results are discussed.Twenty-fivesynthetic mixture samples have been analysed successfully.The average recoveries are 98·9 for Tyr,96·5for Trp,105·6 for Phe,98·1 for Cys,98·9 for His and 106·4 for Di-phe.The results obtained are ingood agreement with those obtained by the Kalman filter method. 相似文献