全文获取类型
收费全文 | 1401篇 |
免费 | 37篇 |
国内免费 | 16篇 |
专业分类
测绘学 | 33篇 |
大气科学 | 98篇 |
地球物理 | 348篇 |
地质学 | 587篇 |
海洋学 | 116篇 |
天文学 | 162篇 |
综合类 | 5篇 |
自然地理 | 105篇 |
出版年
2022年 | 3篇 |
2021年 | 11篇 |
2020年 | 13篇 |
2019年 | 10篇 |
2018年 | 30篇 |
2017年 | 32篇 |
2016年 | 47篇 |
2015年 | 30篇 |
2014年 | 35篇 |
2013年 | 80篇 |
2012年 | 48篇 |
2011年 | 75篇 |
2010年 | 81篇 |
2009年 | 82篇 |
2008年 | 62篇 |
2007年 | 69篇 |
2006年 | 62篇 |
2005年 | 84篇 |
2004年 | 68篇 |
2003年 | 45篇 |
2002年 | 47篇 |
2001年 | 40篇 |
2000年 | 24篇 |
1999年 | 30篇 |
1998年 | 25篇 |
1997年 | 11篇 |
1996年 | 20篇 |
1995年 | 15篇 |
1994年 | 16篇 |
1993年 | 9篇 |
1992年 | 20篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 16篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 4篇 |
1974年 | 13篇 |
1973年 | 5篇 |
排序方式: 共有1454条查询结果,搜索用时 0 毫秒
41.
42.
Sediment infiltration can clog salmon nests and reduce egg survival. As a countermeasure, environmental managers often deploy infiltration traps to monitor sediment infiltration. Traps provide a repeatable means of measuring infiltration and enable comparisons to be made between sites. Results from infiltration rates measured with traps have also been used to estimate infilling rates into salmon nests. Application of these data is questionable, as the composition of the bed and the amount of fine sediment within the bed is known to affect infiltration rates. Thus, infiltration rates measured with infiltration traps may differ from the infiltration rates occurring in redd and riffle gravels. To examine how relationships between sediment infiltration rates varied between four watersheds, we continuously monitored suspended sediment transport, shear stress and infiltration rates at four sites over 5 months. We also compared infiltration rates measured with infiltration traps with changes in the hydraulic conductivity and subsurface grain size distribution of adjacent artificially constructed salmon nests and natural riffle gravels. Among the four watersheds, clear differences in sediment infiltration rates were observed. The differences correlated with the subsurface silt content but no strong relationship existed between land‐use or basin physiography/geology. Despite observing an average of 30 kg m−2 of sediment finer than 2 mm being deposited in the infiltration traps during the study, no change in redd or riffle substrate was observed. If the deposition rates measured with the traps reflect the processes in redds, enough sediment would have been deposited to inhibit egg emergence. However, no reduction in egg survival to the eyed stage was observed. In summary, our results show that infiltration traps with clean gravels can be used to detect intersite differences in sediment transport regimes. Extrapolations of sediment infiltration rates measured with such collectors to estimate infiltration rates in redds or riffles is, however, flawed. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
43.
44.
45.
Two-dimensional asymptotic iterative elastic inversion 总被引:3,自引:0,他引:3
Side Jin Raul Madariaga Jean Virieux Gilles Lambaré 《Geophysical Journal International》1992,108(2):575-588
46.
Mathieu Bringer Michel Boër Cedric Peignot Gérard Fontan Colette Mercé 《Experimental Astronomy》2001,12(1):33-48
We have developped a new method for the scheduling ofastronomical automatic telescopes, in the framework of theautonomous TAROT instrument. The MAJORDOME software canhandle a variety of observations, constrained, periodic,etc., and produces a timeline for the night, which may bemodified at any time to take into account the specificconditions of the night. The MAJORDOME can also handletarget of opportunity observations without delay. 相似文献
47.
In order to better identify the mineral phase which controls the rheology of the transition zone (between 410 and 660 km depth) transmission electron microscopy observations were made on several coexisting spinel-garnet assemblies: alkremite xenolith; pyrope-rich – MgO:1.1Al2 O3 spinel assembly deformed at 1173K, 800 MPa in a Griggs apparatus; (Mg,Fe)3 (Al,Mg,Si)2 Si3 O12 majorite – (Mg,Fe)2 SiO4 spinel assembly synthesized in a laser heated diamond anvil cell. It was found that garnet crystals systematically remain undeformed while spinel crystals are plastically deformed. These results are in accord with the assumption that the rheology of majorite is stronger than the rheology of spinel, in the conditions of the transition zone. 相似文献
48.
This article describes a method that determines the position of a point relative to a fixed boundary. Its advantage over the other existing algorithms described below is that in most cases it is necessary that only part of the algorithm be executed to determine the position of the point. A possible inconvenience of using this algorithm is that the contour boundary has to be entered as data. For problems where the boundary often changes the algorithm is not suitable in its present form. The applications envisaged here are to cases where the position of a very large number of points have to be determined relative to one fixed polygonal boundary whose shape is known in advance, for example, blanking out of contours in automatic contouring, or selecting drill holes which lie in the particular part of a mineral deposit. 相似文献
49.
50.
Minoru Koide Robert Michel Edward D. Goldberg Michael M. Herron Chester C. Langway 《Earth and Planetary Science Letters》1979,44(2):205-223
The annual fluxes of artificial radionuclides (238Pu,239+240Pu,241Am,137Cs,90Sr and3H) from the atmosphere to the Ross Ice Shelf in Antarctica were determined from measurements in strata dated by210Pb. Recognizable sources include the U.S. tests (Mike-Ivy and Castle Hill) in the early 1950s, the U.S.S.R. tests of the early 1960s, the SNAP-9A burnup of 1964 and the French and Chinese tests in the late 1960s and 1970s. There are several problems still awaiting resolution: the differences in atmospheric chemistries of fission products and of transuranics produced in weapons tests and the anomalous fluxes of238Pu to the ice shelf which do not appear to reflect a one-year stratospheric residence. There is no evidence for a smearing of the fallout record as a consequence of diffusion of these radionuclides in the glacial column. 相似文献