全文获取类型
收费全文 | 1260篇 |
免费 | 39篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 60篇 |
大气科学 | 103篇 |
地球物理 | 249篇 |
地质学 | 443篇 |
海洋学 | 88篇 |
天文学 | 232篇 |
综合类 | 1篇 |
自然地理 | 133篇 |
出版年
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 10篇 |
2017年 | 30篇 |
2016年 | 30篇 |
2015年 | 31篇 |
2014年 | 28篇 |
2013年 | 48篇 |
2012年 | 33篇 |
2011年 | 56篇 |
2010年 | 41篇 |
2009年 | 59篇 |
2008年 | 61篇 |
2007年 | 56篇 |
2006年 | 53篇 |
2005年 | 39篇 |
2004年 | 34篇 |
2003年 | 30篇 |
2002年 | 56篇 |
2001年 | 22篇 |
2000年 | 33篇 |
1999年 | 32篇 |
1998年 | 22篇 |
1997年 | 24篇 |
1996年 | 19篇 |
1995年 | 20篇 |
1994年 | 13篇 |
1993年 | 12篇 |
1992年 | 17篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 31篇 |
1981年 | 15篇 |
1980年 | 18篇 |
1979年 | 29篇 |
1978年 | 19篇 |
1977年 | 18篇 |
1976年 | 14篇 |
1975年 | 17篇 |
1974年 | 16篇 |
1973年 | 11篇 |
1972年 | 11篇 |
1971年 | 5篇 |
1966年 | 6篇 |
排序方式: 共有1309条查询结果,搜索用时 0 毫秒
1.
D.J. Curtis C.G. Galbraith J.C. Smyth D.B.A. Thompson 《Estuarine, Coastal and Shelf Science》1985,21(1):75-90
The number of black-headed gulls (Larus ridibundus) in the Clyde Estuary is large. In summer the average density has reached 1350 gulls km?2 and in winter 180 gulls km?2. This paper compares prey selection and feeding efficiency in gulls during summer and winter on tidal flats, and considers how seasonal differences may be adaptations to cope with seasonal changes in prey availability.Gross and net rates of energy intake were highest in summer because gulls captured more of the polychaete N. diversicolor than the amphipod C. volutator. In winter, gulls selected for C. volutator and therefore an energetically less profitable diet. Throughout the year gulls selected more C. volutator relative to N. diversicolor than expected on energetic grounds and so apparently did not maximize potential net rate of energy intake.Gulls used three techniques to capture prey and made most intensive use of the ‘crouch’ technique. Crouching gulls attained a much higher net rate of energy intake than ‘upright’ or ‘paddling’ gulls.A log-linear model showed that (a) season, water depth and gull density determined feeding technique and (b) feeding technique and season independently determined foraging success and prey selection. Thus gull density and water depth acted on prey selection through imposed variations in feeding technique.Reasons for gulls selecting energetically unprofitable C. volutator and for the use of several distinct feeding techniques are discussed. 相似文献
2.
When viewed from the air, Scottish ‘hummocky moraine’ can be resolved into a series of linear ridges that resemble those found at the margins of actively retreating glaciers today. Recent work has supported the interpretation of these linear ridges as ice-marginal landforms and the authors believe that the majority of ‘hummocky moraine’ deposits can be interpreted in this way. Consequently the pattern of deglaciation can be established fairly precisely from the pattern of linear ridges. This approach is applied to the landforms of the northern part of the Loch Lomond Stadial ice-field in order to reconstruct the regional pattern of deglaciation. This leads to important inferences about the significance of topographic control during deglaciation and more importantly it provides fresh insight into the environment of the British Isles during the Loch Lomond Stadial. 相似文献
3.
E. H. Thompson 《The Photogrammetric Record》1967,5(29):385-396
This paper discusses a simple method of computing independent strips under certain reasonable approximations. It is shown that, if the method is regarded as if it were computation by polynomials, the order of the polynomial is decided by the nature of the control provided and not by the number of controlled models. This conclusion should throw some light on the vexed (and perennial) problem of the choice of orders for polynomials. 相似文献
4.
5.
6.
Horiguchi T Li Z Uno S Shimizu M Shiraishi H Morita M Thompson JA Levings CD 《Marine environmental research》2004,57(1-2):75-88
Gastropods and bivalves were collected at 15 sites at Vancouver and Victoria, Canada between 24 May and 7 June, 1999, to establish tissue concentrations of butyltin and phenyltin compounds, to record imposex symptoms in gastropods, and to assess the present status of organotin contamination around Vancouver. No neogastropods (such as Nucella lima) were found around Vancouver. Neogastropod populations could have been extirpated by severe TBT contamination in Vancouver, as relatively high concentrations of TBT were detected in tissues of Mytilus trossulus from Vancouver, and the neogastropods distributed in Vancouver might be sensitive to TBT. Recovery from imposex, however, was observed in neogastropod populations from three sites at Victoria and Mission Point. TBT contamination has continued around Vancouver, arising from continuous use of TBT in antifouling paints for vessels larger than 25 m in length; however, TBT has decreased around Victoria and Mission Point. Different patterns of TBT accumulation in tissue were observed among the bivalve species from Vancouver. The highest TBT concentration detected in Tresus capax suggested some possible adverse effects. TBT was the most predominant butyltin component in almost all bivalve specimens surveyed, suggesting a low rate of TBT metabolism. Phenyltin compounds were not detected in any molluscan specimens in this study. 相似文献
7.
A 120 m thick section of the Cozy Dell Formation (middle Eocene), southem California, consists of a graylaminated mudstone and a tanungraded mudstone; sandstone beds are associated with the laminated mudstone. Sedimentary structures, stratification sequences, foraminiferal
distributions, and composition indicate that the ungraded mudstone is an upper slope hemipelagic deposit, while the laminated
mudstone is an overbank deposit associated with shallow channels or gullies in which the sandstone beds were deposited. This
depositional setting may be analogous to that of the modern Mississippi River delta front. 相似文献
8.
9.
The dissolution of opaline silica of diatom tests in sea water 总被引:3,自引:0,他引:3
Two different series of measurements have been made of the solubilities and rates of solution in sea water of acid-washed siliceous tests of the diatomsThalassiosira decipiens andRhizosolenia hebetata. The kinetic approach was carried out on the assumption that the tests behave as identical solid spheres. If the tests were present in considerable excess over that required for saturation of the water with respect to silica, the dissolution obeyed first order reaction kinetics and its rate was proportional to the surface area of the exposed tests. When the tests were not in excess the kinetics of dissolution appeared to be more complex. This was considered to be due to a decrease in specific surface area as dissolution proceeded. An expression developed to allow for the change of surface area as a sphere dissolves offers a partial explanation of the kinetics when the tests are not present in excess. 相似文献
10.