全文获取类型
收费全文 | 90217篇 |
免费 | 1523篇 |
国内免费 | 995篇 |
专业分类
测绘学 | 2289篇 |
大气科学 | 7122篇 |
地球物理 | 18656篇 |
地质学 | 29782篇 |
海洋学 | 7975篇 |
天文学 | 20283篇 |
综合类 | 239篇 |
自然地理 | 6389篇 |
出版年
2020年 | 635篇 |
2019年 | 669篇 |
2018年 | 1348篇 |
2017年 | 1314篇 |
2016年 | 1969篇 |
2015年 | 1423篇 |
2014年 | 1966篇 |
2013年 | 4497篇 |
2012年 | 2166篇 |
2011年 | 3188篇 |
2010年 | 2734篇 |
2009年 | 4000篇 |
2008年 | 3618篇 |
2007年 | 3321篇 |
2006年 | 3303篇 |
2005年 | 2931篇 |
2004年 | 2978篇 |
2003年 | 2785篇 |
2002年 | 2654篇 |
2001年 | 2380篇 |
2000年 | 2340篇 |
1999年 | 2077篇 |
1998年 | 2001篇 |
1997年 | 1983篇 |
1996年 | 1744篇 |
1995年 | 1596篇 |
1994年 | 1466篇 |
1993年 | 1346篇 |
1992年 | 1265篇 |
1991年 | 1143篇 |
1990年 | 1292篇 |
1989年 | 1136篇 |
1988年 | 1050篇 |
1987年 | 1230篇 |
1986年 | 1112篇 |
1985年 | 1377篇 |
1984年 | 1565篇 |
1983年 | 1506篇 |
1982年 | 1384篇 |
1981年 | 1294篇 |
1980年 | 1140篇 |
1979年 | 1088篇 |
1978年 | 1145篇 |
1977年 | 1024篇 |
1976年 | 973篇 |
1975年 | 928篇 |
1974年 | 943篇 |
1973年 | 952篇 |
1972年 | 590篇 |
1971年 | 504篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Farmland on the Downs between Lewes and Brighton suffered severe erosion during the autumn of 1982. The erosion was widespread and affected a variety of topographic situations, but it was confined to areas of arable land and recently-sown grass leys. Erosion on the scale recorded during the autumn of 1982 has never previously been recorded from this area. Three major sites of erosion are described and explanations for the erosion are sought through an analysis of rainfall conditions experienced during autumn 1982 and in recent changes in agricultural land use on the Downs. It is concluded that, whilst total rainfall and the intensity of rainstorms were both unusually high, similar events are likely to recur several times a century. Evidence is presented which suggests that the ploughing up of permanent pasture, the removal of field boundaries and the increased adoption of autumn-sown cereals have all contributed to the onset of severe erosion. It appears that a major re-activation of erosion on the Downs may be commencing which threatens the long-term viability of farming in the area. 相似文献
932.
933.
In this article we make a case for a renewed emphasis upon some of the generic, albeit often tacit, spaces of practice that we share across our sub–disciplinary boundaries. In this we seek to emphasize the ways in which everyday actions make up the grander facades of institutional agendas, empirical projects and disciplinary schools of thought. To achieve this we trace the performance of disciplinary contours and identities across three important sites: the field, the body and the act of dissemination. There are, we will argue, significant commonalities that bind us as disciplinary practitioners in terms of how we perform within and across these sites, and indeed, how we join them up through our practices. 相似文献
934.
Hans J. Albrecht 《Meteorology and Atmospheric Physics》1958,11(1):84-92
Summary This paper presents new results of the author's investigations on ionospheric propagation in Australia from 1952 to 1957. Considerations on path attenuation are followed by a discussion on the propagation paths to North America and Western Europe. Conclusions are in agreement with the author's previous publications in this field.
With 1 Figure 相似文献
Zusammenfassung In dieser Arbeit behandelt der Verfasser neue Ergebnisse seiner Untersuchungen über ionosphärische Ausbreitung in Australien von 1952 bis 1957. Auf eine Betrachtung über die Signalschwächung folgt eine Diskussion über die Ausbreitungswege nach Nordamerika und Westeuropa. Die Folgerungen stimmen mit den früheren Veröffentlichungen des Verfassers auf diesem Gebiet überein.
Résumé L'auteur expose les nouveaux résultats de ses recherches sur la propagation ionosphérique en Australie de 1952 à 1957; il considère l'affaiblissement de la propagation des signaux et les chemins suivis par les ondes vers l'Amérique du Nord et vers l'Europe occidentale. Ces résultats concordent avec ceux qu'il a publiés précédemment.
With 1 Figure 相似文献
935.
936.
Daniel D. Riemer Eric C. Apel John J. Orlando Geoffrey S. Tyndall William H. Brune Eric J. Williams William A. Lonneman James D. Neece 《Journal of Atmospheric Chemistry》2008,61(3):227-242
As part of the 2000 Texas Air Quality Study (TexAQS), we studied the isoprene oxidation process under ambient conditions to
discern the presence of chlorine atom (Cl) chemistry in the Houston, Texas urban area. By measuring chloromethylbutenone (CMBO)
and an isomer of chloromethylbutenal (CMBA), we clearly observed sixteen episodes of active Cl chemistry during the 24-day
experiment. Estimated median Cl concentration during each of these episodes was between the detection limit of ~102 atoms cm−3 and 50 - 30 + 70 ×104 50_{ - 30}^{ + 70} \times {10^4} atoms cm−3. Cl concentration during all the episodes averaged 7.6 - 2.0 + 4.7 ×104 7.6_{ - 2.0}^{ + 4.7} \times {10^4} atoms cm−3 and thus amounted to less than 3% of the OH concentration during the same periods. During the episodes, the fraction of oxidation
chemistry initiated by Cl ranged from 3–43% and was strongly dependent on the quantity and type of hydrocarbons present in
the atmosphere. Because of its intermittent presence and low concentration, Cl is not a broadly influential oxidant in the
Houston, Texas urban area. 相似文献
937.
C.M. Penner 《大气与海洋》2013,51(1):14-22
Abstract Values of incoming solar and long‐wave radiation measured at the vessel Quadra during the three phases of GATE are used to assess the daily performance of three models, one for solar and two for long‐wave radiation. The solar radiation model, which uses data on precipitable water and cloud amount at three levels in the atmosphere performed satisfactorily during the first phase but gave poor results in the other two phases when cumulonimbus became more dominant. Both the flux‐emissivity approach using measured and interpolated Upper air data and Paltridge's empirical procedure produced estimates of long‐wave radiation which compared very closely with the measurements. 相似文献
938.
939.
Frequency response corrections for eddy correlation systems 总被引:27,自引:18,他引:27
C. J. Moore 《Boundary-Layer Meteorology》1986,37(1-2):17-35
Simplified expressions describing the frequency response of eddy correlation systems due to sensor response, path-length averaging, sensor separation and signal processing are presented. A routine procedure for estimating and correcting for the frequency response loss in flux and variance measurements is discussed and illustrated by application to the Institute of Hydrology's Hydra eddy correlation system.The results show that flux loss from such a system is typically 5 to 10% for sensible and latent heat flux, but can be much larger for momentum flux and variance measurements in certain conditions.A microcomputer program is included which, with little modification, can be used for estimating flux loss from other eddy correlation systems with different or additional sensors. 相似文献
940.
J. R. Garratt 《Boundary-Layer Meteorology》1986,36(1-2):101-105
The present note discusses one physical mechanism which may contribute to cold air channelling, manifest as a frontal bulge on a surface-analysis chart, in the coastal region of Victoria in southeast Australia. This involves the modification of boundary-layer air in both offshore (prefrontal) and onshore (postfrontal) flow, and the effect on cross-frontal thermal contrast. The problem is discussed in terms of a north-south-oriented cold front behaving as an atmospheric gravity current, propagating along an east-west-oriented coastline, in the presence of a prefrontal offshore stream. 相似文献