全文获取类型
收费全文 | 265630篇 |
免费 | 4466篇 |
国内免费 | 3504篇 |
专业分类
测绘学 | 7253篇 |
大气科学 | 19593篇 |
地球物理 | 55568篇 |
地质学 | 92917篇 |
海洋学 | 21902篇 |
天文学 | 57128篇 |
综合类 | 1119篇 |
自然地理 | 18120篇 |
出版年
2021年 | 2308篇 |
2020年 | 2662篇 |
2019年 | 2891篇 |
2018年 | 4171篇 |
2017年 | 3860篇 |
2016年 | 6211篇 |
2015年 | 4350篇 |
2014年 | 7124篇 |
2013年 | 14453篇 |
2012年 | 6865篇 |
2011年 | 8441篇 |
2010年 | 7459篇 |
2009年 | 10102篇 |
2008年 | 8802篇 |
2007年 | 8239篇 |
2006年 | 9734篇 |
2005年 | 7882篇 |
2004年 | 7724篇 |
2003年 | 7243篇 |
2002年 | 6862篇 |
2001年 | 6083篇 |
2000年 | 6011篇 |
1999年 | 5233篇 |
1998年 | 5277篇 |
1997年 | 5066篇 |
1996年 | 4736篇 |
1995年 | 4463篇 |
1994年 | 4144篇 |
1993年 | 3891篇 |
1992年 | 3679篇 |
1991年 | 3622篇 |
1990年 | 3784篇 |
1989年 | 3544篇 |
1988年 | 3318篇 |
1987年 | 3866篇 |
1986年 | 3424篇 |
1985年 | 4248篇 |
1984年 | 4765篇 |
1983年 | 4438篇 |
1982年 | 4351篇 |
1981年 | 3947篇 |
1980年 | 3664篇 |
1979年 | 3521篇 |
1978年 | 3516篇 |
1977年 | 3289篇 |
1976年 | 3063篇 |
1975年 | 2966篇 |
1974年 | 2932篇 |
1973年 | 3095篇 |
1972年 | 2030篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
861.
862.
The decline of the herring stocks and the gadoid outburst 总被引:2,自引:1,他引:2
863.
864.
Existing methods for the determination of the various forms of iodine present in seawater are laborious or unwieldy in use. This paper describes modified forms of the iodate and total iodine methods described by Barkley and Thompson (1960), a spectrophotometric procedure for iodate determination derived from Johannesson's (1958) work, and an automatic method for total iodine determination. Procedures for iodate and total-iodine determination which are suitable for use aboard ship, are recommended. Both procedures for iodate determination returned a standard deviation close to 0.5 μg/l when several replicate samples of a seawater containing approximately 30 μg/l of iodate-iodine were analysed. The automatic method for total iodine determination yielded a standard deviation of 0.8 μg/l by the repeated analysis of a seawater containing a total of approximately 50 μg/l of iodine. Suitable methods for the filtration and storage of seawater are also described. 相似文献
865.
Abstract. Benthic metabolism and standing stocks were investigated in the deep Red Sea between 21o and 27o N, Activity was assessed by the determination of respiration rates with a shipboard method and by calculating oxygen consumption from the activity in the electron transport system. We attempted to compare results from different latitudes within the warm Red Sea and with data from cold Atlantic environments. Our investigations were part of an environmental risk assessment to evaluate future mining of metalliferous sediments from the Atlantis II Deep. 相似文献
866.
OBS’s were deployed for 26 to 29 days in the eastern Bismarck Sea to investigate the back-arc spreading. Hypocenters of 186 shallow earthquakes were determined using P- and S-waves from at least five stations. In the western survey area, a transform fault zone is marked by a linear micro-earthquake activity striking N65°W and less than 5 km wide. The predominant type of their focal mechanisms is strike-slip. In the eastern area, several intermittent zones of micro-earthquakes and their strike-slip type focal mechanisms suggest the location of short-length transform faults separating en-echelon spreading ridges. 相似文献
867.
868.
This article deals with the analysis, synthesis and performance evaluation of the flow and dynamic characteristics of the new class of servo-controlled breathing regulators for underwater divers.Emphasis on such a class of regulators has been stimulated by their tremendous potential in extending the dive depth and duration because they reduce the diver breathing effort to a great extent. This would eliminate the unnecessary exhaustion of the diver under such extreme diving conditions and accordingly improve his work efficiency underwater.The study aims at developing rational design procedures and guides that would enable the regulator designers to select the optimal design parameters of this class of regulators. Such design guides are based on the analysis of the flow and dynamic characteristics of the servo-controlled regulator as well as the basic principle of the theory of optimum control.The study presents also experimental evaluation techniques of the dynamic characteristics of this class of regulators in order to provide common quantitative means for comparison with the conventional regulator designs.The presented results emphasize the merits and the potential of the servo-controlled regulators as essential tools of supporting the life of divers underwater. 相似文献
869.
870.