全文获取类型
收费全文 | 1838篇 |
免费 | 68篇 |
国内免费 | 18篇 |
专业分类
测绘学 | 38篇 |
大气科学 | 139篇 |
地球物理 | 484篇 |
地质学 | 562篇 |
海洋学 | 141篇 |
天文学 | 362篇 |
综合类 | 1篇 |
自然地理 | 197篇 |
出版年
2021年 | 29篇 |
2020年 | 24篇 |
2019年 | 32篇 |
2018年 | 54篇 |
2017年 | 45篇 |
2016年 | 75篇 |
2015年 | 42篇 |
2014年 | 50篇 |
2013年 | 102篇 |
2012年 | 75篇 |
2011年 | 104篇 |
2010年 | 80篇 |
2009年 | 114篇 |
2008年 | 97篇 |
2007年 | 76篇 |
2006年 | 87篇 |
2005年 | 83篇 |
2004年 | 60篇 |
2003年 | 55篇 |
2002年 | 62篇 |
2001年 | 40篇 |
2000年 | 37篇 |
1999年 | 46篇 |
1998年 | 35篇 |
1997年 | 23篇 |
1996年 | 32篇 |
1995年 | 25篇 |
1994年 | 23篇 |
1993年 | 18篇 |
1992年 | 22篇 |
1991年 | 13篇 |
1990年 | 18篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 17篇 |
1983年 | 19篇 |
1982年 | 13篇 |
1981年 | 19篇 |
1980年 | 9篇 |
1979年 | 14篇 |
1978年 | 17篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1971年 | 7篇 |
排序方式: 共有1924条查询结果,搜索用时 15 毫秒
911.
912.
913.
914.
915.
916.
Michael P. Weinstein Larry Scott Steven P. O’Neil Robert C. Siegfried Stephen T. Szedlmayer 《Estuaries and Coasts》1984,7(4):444-450
Most populations of estuarine-dependent, early life stages of marine fishes are open. As a result, it has been difficult to apply conventional population models to most systems. In this study, a marked population of young-of-year spot (Leiostomus xanthurus) was released into a polyhaline tidal creek within the Guinea Marshes of the York River estuary, Virginia. Over a 90-day study period, 221 marked fishes were recaptured. Plots of the ratio of marked to unmarked individuals (mi/ni) in subsequent samples indicated that the population was resident in the creek for up to 162 days with the average individual present for 81 days. When this population turnover rate was compared to the total population decay rate (marked plus unmarked fish), it was determined that exchange between habitats (immigration/emigration) accounted for about 36.4% of the total decay rate, with the remainder attributed to natural mortality. By correcting the overall disappearance rate for population turnover due to emigration and using this adjusted value as a measure of instantaneous mortality (z), the estimated production (over 90 days) in this population was 23,630 cal (98,870 J) per m2. This figure agrees with a previously derived estimate for spot in the Guinea marshes and is nearly two orders of magnitude higher than other reported values for this species for all size classes over the entire growing season. 相似文献
917.
A sketch of some of the developments masterminded by Uki Helava during his years with Bendix Research Laboratories (1967–1979) and with his own company, Helava Associates, Inc., underlines the significance and breadth of his contribution. Although many of the leading edge developments were responses to US government contracts, the initial impetus behind the formation of Helava Associates was to supply to the commercial market-place and subsequent links with Leica are similarly aimed; thus the practicality of many of the developments is demonstrable. 相似文献
918.
919.
920.