全文获取类型
收费全文 | 10748篇 |
免费 | 803篇 |
国内免费 | 174篇 |
专业分类
测绘学 | 388篇 |
大气科学 | 922篇 |
地球物理 | 4250篇 |
地质学 | 3812篇 |
海洋学 | 480篇 |
天文学 | 1172篇 |
综合类 | 211篇 |
自然地理 | 490篇 |
出版年
2022年 | 47篇 |
2021年 | 116篇 |
2020年 | 102篇 |
2019年 | 87篇 |
2018年 | 649篇 |
2017年 | 581篇 |
2016年 | 563篇 |
2015年 | 387篇 |
2014年 | 389篇 |
2013年 | 457篇 |
2012年 | 890篇 |
2011年 | 663篇 |
2010年 | 340篇 |
2009年 | 352篇 |
2008年 | 308篇 |
2007年 | 301篇 |
2006年 | 298篇 |
2005年 | 931篇 |
2004年 | 994篇 |
2003年 | 747篇 |
2002年 | 263篇 |
2001年 | 165篇 |
2000年 | 108篇 |
1999年 | 73篇 |
1998年 | 82篇 |
1997年 | 80篇 |
1996年 | 59篇 |
1995年 | 52篇 |
1994年 | 59篇 |
1993年 | 53篇 |
1992年 | 53篇 |
1991年 | 74篇 |
1990年 | 69篇 |
1989年 | 84篇 |
1988年 | 45篇 |
1987年 | 66篇 |
1986年 | 50篇 |
1985年 | 57篇 |
1984年 | 48篇 |
1983年 | 50篇 |
1982年 | 54篇 |
1981年 | 48篇 |
1980年 | 52篇 |
1979年 | 52篇 |
1978年 | 56篇 |
1977年 | 47篇 |
1976年 | 44篇 |
1975年 | 51篇 |
1973年 | 52篇 |
1971年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
131.
Pilar Drake Alberto M. Arias Francisco Baldó José A. Cuesta Antonio Rodríguez Alfonso Silva-Garcia Ignacio Sobrino Diego García-González Carlos Fernández-Delgado 《Estuaries and Coasts》2002,25(3):451-468
The aquatic macrofauna of the Guadalquivir estuary were sampled (1 mm mesh persiana net) at 5 sampling sites located along the entire (except the tidal freshwater region) estuarine gradient of salinity (outer 50 km). A total of 134 fish and macroinvertebrate species was collected but only 62 were considered common or regularly present in the estuary. Univariate measures of the community structure showed statistically significant differences among sampling sites: species richness, abundance, and biomass decreased in the upstream direction, being positively correlated with the salinity. Temporal differences of these three variables were also statistically significant. While a clear seasonal pattern (minimum densities in winter and maximum in spring-summer) was observed for abundance and biomass, no such pattern existed for the number of species. Mysids was the most dominant group throughout the estuary (96% to 99% of abundance; 49% to 85% of biomass), although fish biomass was also important at the outer estuary (36% to 38%). Multivariate analyses indicated highly significant spatial variation in the macrofaunal communities observed along the salinity gradient. These analyses suggest that the underlying structure was a continuum with more or less overlapping distributions of the species dependent on their ability to tolerate different physicochemical conditions. There were also significant temporal (intermonthly + interannual) variation of the estuarine community; the relative multivariate dispersion indicated that monthly variation was more considerable (relative multivariate dispersion >1) at the outer part of the estuary during the wet year (last 20 km) and was higher in the inner stations during the dry year (32 to 50 km from the river mouth). Since a clear negative exponential relationship was observed between the freshwater input (from a dam located 110 km upstream) and water salinity at all sampling stations, it is concluded that the human freshwater management is probably affecting the studied estuarine communities. While the higher seasonal (long-term) stability of the salinity gradient, due to the human control of the freshwater input, may facilitate the recruitment of marine species juveniles during the meteorologically unstable early-spring, the additional (short-term) salinity fluctuations during the warm period may negatively affect species that complete their lifecycle within the estuary. 相似文献
132.
133.
Smoothing the Marmousi Model 总被引:1,自引:0,他引:1
K. Žáček 《Pure and Applied Geophysics》2002,159(7-8):1507-1526
134.
135.
136.
Gil A. J. Rodríguez-Caderot G. Lacy M. C. Ruiz A. M. Sanz de Galdeano C. Alfaro P. 《Studia Geophysica et Geodaetica》2002,46(3):395-410
The Granada Basin (Central Betic Cordillera), one of the most seismically active areas of the Iberian Peninsula, is currently subjected to NW-SE compression and NE-SW extension. The present day extension is accommodated by normal faults with various orientations but particularly with a NW-SE strike. At the surface, these active NW-SE normal faults are mainly concentrated on the NE part of the Basin. In this part we have selected a 15-km long segment where several active normal faults crop out. Using the marine Tortonian rocks as a reference, we have calculated a minimum extensional rate of 0.15-0.30 mm/year. The observed block rotation, the listric geometry of faults at depth and the distribution of seismicity over the whole Basin, indicate that this rate is a minimum value. In the framework of an interdisciplinary research project a non-permanent GPS-network has been established in the central sector of Betic Cordillera to monitor the crustal deformations. The first two observation campaigns were done in 1999 and 2000. 相似文献
137.
新时期我国区域经济地理学发展问题初探 总被引:4,自引:0,他引:4
我国新时期的区域经济地理学在取得全面发展的同时,在理论体系,研究方法和实践领域等方面还需要进一步的发展,文章根据学习和实践区域经济地理学的体会,初步提出基础理论和应用理论,思维方法和技术方法等方面发展见解,并指出区域创新系统和国际经济技术合作等学科应注意拓展的重要实践领域,最后提出我国区域经济地理学科发展的建议。 相似文献
138.
139.
成都市民消费结构与休闲活动关系研究 总被引:6,自引:0,他引:6
城市居民消费水平,消费结构会影响其休闲消费能力,消费意愿,消费方式,消费态度和休闲时空结构,文章以成都市7个城区歌舞,茶棋牌,电影及城市公园休闲活动调查为基础,探讨了城市居民消费结构及其变化与休闲活动特征的关系。研究结果表明,城市居民消费结构的改变对歌舞,茶棋牌娱乐活动影响最大。 相似文献
140.