全文获取类型
收费全文 | 1217篇 |
免费 | 30篇 |
国内免费 | 64篇 |
专业分类
测绘学 | 57篇 |
大气科学 | 47篇 |
地球物理 | 81篇 |
地质学 | 74篇 |
海洋学 | 65篇 |
天文学 | 917篇 |
综合类 | 20篇 |
自然地理 | 50篇 |
出版年
2024年 | 3篇 |
2023年 | 7篇 |
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 17篇 |
2019年 | 19篇 |
2018年 | 13篇 |
2017年 | 16篇 |
2016年 | 17篇 |
2015年 | 35篇 |
2014年 | 34篇 |
2013年 | 39篇 |
2012年 | 27篇 |
2011年 | 15篇 |
2010年 | 36篇 |
2009年 | 72篇 |
2008年 | 40篇 |
2007年 | 77篇 |
2006年 | 79篇 |
2005年 | 94篇 |
2004年 | 93篇 |
2003年 | 87篇 |
2002年 | 81篇 |
2001年 | 62篇 |
2000年 | 63篇 |
1999年 | 64篇 |
1998年 | 89篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1311条查询结果,搜索用时 8 毫秒
101.
102.
Peter Astrup T. Madsen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):132-142
Geografisk Tidsskrift, Danish Journal of Geography 97: 132–142, 1997. In the period 1971–90 the first admission rate to Danish psychiatric hospitals and wards decreased by approximately 45%. This might reflect the similar decrease in number of available psychiatric beds. Generally, the decrease of first admission rates was larger in the metropolitan area than in the rest of the country. Consequently, the disparity in admission rates between town and country was reduced. Number of available beds has gained increasing importance as a predictor of variations between counties and municipalities whereas the importance of distance to hospital and degree of urbanization has declined. As regards socio-demographic variables special importance should be attached to variables for social aid and the employment rate in the social and health sector. However, it is generally difficult to determine whether regional variations are due to differences in treatment facilities or morbidity differences. From a disaggregate analysis it will appear that the diagnoses schizophrenia and alcoholism are especially related to low status areas whereas a connection with social status regarding neuroses and manic-depressive psychoses is less obvious. 相似文献
103.
Environmental variables related to wheat yields in the semiarid pampa region of Argentina 总被引:1,自引:0,他引:1
The current paper analyses various environmental parameters in relation to wheat yields in Bordenave, Province of Buenos Aires, Argentina. The variables used are: precipitation (ppt), maximum (Tx) and minimum temperature (Tmi) as well as those obtained by applying the Palmer model. Decadic and phenological scales are used for data corresponding to the period 1977–2000. The stepwise method is used to obtain a multi-variate equation to calculate yield taking into account environmental variables only. For a five variates model the coefficient of determination, R2 equals 95.79% and the standard error of estimation is 129.0 kg ha−1. In the sample yields, the incidence of total variability for thermal variables is 42.7% and for hydrological variables, 53%. The value and sign of the correlation coefficients were analysed throughout the cultivation cycle. The α coefficient is mainly responsible for yield variance during tillering and stem elongation. There is good correlation with the values of Palmer's Drought Severity Index (PDSI) for the flowering and grain filling stages. 相似文献
104.
105.
《Marine Policy》2016
Globally, coastal aquaculture particularly shrimp farming has been under huge criticism because of its environmental impacts including devastating effects on mangrove forests. However, mangroves are ecologically and economically important forests, and the most carbon-rich forests in the tropics that provide a wide range of ecosystem services and biodiversity conservation. Carbon emissions are likely to have been the dominant cause of climate change and blue carbon emissions are being critically augmented through mangrove deforestation. Because of mangrove deforestation, different climatic variables including coastal flooding, cyclone, drought, rainfall, salinity, sea-level rise, and sea surface temperature have dramatic effects on coastal aquaculture. Mangrove forests have been instrumental in augmenting resilience to climate change. The “Reducing Emissions from Deforestation and forest Degradation (REDD)” program can help to restore mangroves which in turn increases options for adaptation to climate change. However, technical and financial assistance with institutional support are needed to implement REDD+. 相似文献
106.
107.
108.
109.
110.
L. Morales-Rueda P. J. Groot T. Augusteijn G. Nelemans P. M. Vreeswijk E. J. M. van den Besselaar 《Monthly notices of the Royal Astronomical Society》2006,371(4):1681-1692
We present the V -band variability analysis of the point sources in the Faint Sky Variability Survey on time-scales from 24 min to tens of days. We find that about one per cent of the point sources down to V = 24 are variables. We discuss the variability-detection probabilities for each field depending on field sampling, amplitude and time-scale of the variability. The combination of colour and variability information allows us to explore the fraction of variable sources for different spectral types. We find that about 50 per cent of the variables show variability time-scales shorter than 6 h. The total number of variables is dominated by main-sequence sources. The distribution of variables with spectral type is fairly constant along the main sequence, with 1 per cent of the sources being variable, except at the blue end of the main sequence, between spectral types F0 and F5, where the fraction of variable sources increases to about 2 per cent. For bluer sources, above the main sequence, this percentage increases to about 3.5. We find that the combination of the sampling and the number of observations allows us to determine the variability time-scales and amplitudes for a maximum of 40 per cent of the variables found. About a third of the total number of short time-scale variables found in the survey were not detected in either B or/and I band. These show a similar variability time-scale distribution to that found for the variables detected in all three bands. 相似文献