全文获取类型
收费全文 | 89389篇 |
免费 | 1765篇 |
国内免费 | 685篇 |
专业分类
测绘学 | 2295篇 |
大气科学 | 6988篇 |
地球物理 | 18435篇 |
地质学 | 30773篇 |
海洋学 | 7679篇 |
天文学 | 19467篇 |
综合类 | 206篇 |
自然地理 | 5996篇 |
出版年
2021年 | 571篇 |
2020年 | 729篇 |
2019年 | 757篇 |
2018年 | 1819篇 |
2017年 | 1819篇 |
2016年 | 2132篇 |
2015年 | 1424篇 |
2014年 | 2088篇 |
2013年 | 4413篇 |
2012年 | 2330篇 |
2011年 | 3245篇 |
2010年 | 2777篇 |
2009年 | 3863篇 |
2008年 | 3489篇 |
2007年 | 3224篇 |
2006年 | 3261篇 |
2005年 | 3060篇 |
2004年 | 3230篇 |
2003年 | 2876篇 |
2002年 | 2487篇 |
2001年 | 2241篇 |
2000年 | 2202篇 |
1999年 | 1848篇 |
1998年 | 1824篇 |
1997年 | 1853篇 |
1996年 | 1585篇 |
1995年 | 1525篇 |
1994年 | 1405篇 |
1993年 | 1259篇 |
1992年 | 1215篇 |
1991年 | 1063篇 |
1990年 | 1253篇 |
1989年 | 1102篇 |
1988年 | 1007篇 |
1987年 | 1202篇 |
1986年 | 1045篇 |
1985年 | 1344篇 |
1984年 | 1480篇 |
1983年 | 1429篇 |
1982年 | 1314篇 |
1981年 | 1230篇 |
1980年 | 1126篇 |
1979年 | 1054篇 |
1978年 | 1084篇 |
1977年 | 1006篇 |
1976年 | 937篇 |
1975年 | 889篇 |
1974年 | 893篇 |
1973年 | 897篇 |
1972年 | 567篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
571.
572.
573.
During a campaign of optical observations at high latitude, a bi-dimensional study of the wave structure of the OH layer has been performed in December 1981 from Sodankyla (Finland). This site is one of the three stations of the EISCAT ionosphere sounding system. It has been found that a wave field covering an area of 1 million km2 may extend to latitudes as high as 70°N. The OH wave structure shows many similarities with noctilucent clouds. The fairly large horizontal wavelength, of the order of 40 km cannot easily be explained by a wave motion at an interface. The observed wave structure seems to be a result of the propagation of an internal gravity wave in the 80–100 km region. This wave structure was often recorded during the same time as an active aurora was present. As a result, it appears that the perturbation might be correlated with particle precipitations at auroral latitudes. 相似文献
574.
Variables related to urban park awareness are identified and methods for relaxing assumptions of perfect information in park use models are discussed. Park awareness is related to park characteristics (age and degree of development of the park), population characteristics (race, age, length of residence, recreation participation), and distance. Park attributes are stronger predictors of both park awareness and use than is distance. These findings parallel similar research on the cognitive aspects of shopping decisions. 相似文献
575.
J. Teemu T. Mäkinen 《Icarus》2005,177(1):269-279
As a part of a project to study the cometary particle environment, a self-consistent ballistic rigid body particle colliding simulator, capable of producing fractal aggregates of icy particles modelled by hard or soft (metaball) spheres has been developed, to be used for creating test particles in future statistical studies of the cometary coma-particle interaction. Instead of a predefined sticking probability, actual surface interactions are modelled and a method for calculating internal stresses and fragmentation of an aggregate during the accretion phase is described. Simulations suggest that taking fragmentation into account has two major consequences, increase in the fractal dimension of resulting particles and a noticeable change in the mass spectrum of an ensemble. 相似文献
576.
577.
Methods of Hierarchical Control of Water Quality Taking into Account Manipulations of the Center and Countermoves of Enterprises 总被引:2,自引:1,他引:1
Methods of hierarchical control including manipulations of a Center and the countermove of enterprises are considered using as an example a dynamic two-level model of river water quality control in the presence of point pollution sources and in the absence of nonpoint sources. 相似文献
578.
J. van der Plicht B. van Geel S. J. P. Bohncke J. A. A. Bos M. Blaauw A. O. M. Speranza R. Muscheler S. Bjrck 《第四纪科学杂志》2004,19(3):263-269
Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric 14C; (ii) a temporary decline of atmospheric CO2; and (iii) an increase in the GRIP 10Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
579.
580.