全文获取类型
收费全文 | 2074篇 |
免费 | 219篇 |
国内免费 | 148篇 |
专业分类
测绘学 | 48篇 |
大气科学 | 80篇 |
地球物理 | 631篇 |
地质学 | 601篇 |
海洋学 | 573篇 |
天文学 | 3篇 |
综合类 | 36篇 |
自然地理 | 469篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 26篇 |
2021年 | 56篇 |
2020年 | 55篇 |
2019年 | 82篇 |
2018年 | 66篇 |
2017年 | 91篇 |
2016年 | 80篇 |
2015年 | 79篇 |
2014年 | 110篇 |
2013年 | 162篇 |
2012年 | 66篇 |
2011年 | 130篇 |
2010年 | 86篇 |
2009年 | 177篇 |
2008年 | 155篇 |
2007年 | 156篇 |
2006年 | 118篇 |
2005年 | 87篇 |
2004年 | 64篇 |
2003年 | 68篇 |
2002年 | 78篇 |
2001年 | 45篇 |
2000年 | 52篇 |
1999年 | 32篇 |
1998年 | 43篇 |
1997年 | 45篇 |
1996年 | 28篇 |
1995年 | 40篇 |
1994年 | 19篇 |
1993年 | 18篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有2441条查询结果,搜索用时 46 毫秒
101.
The geometric signature: Quantifying landslide-terrain types from digital elevation models 总被引:11,自引:0,他引:11
Richard J. Pike 《Mathematical Geology》1988,20(5):491-511
102.
Monthly-mean winds and currents have been used to identify the driving mechanisms of seasonal coastal circulation in the North
Indian Ocean. The main conclusions are: (i) the surface circulation off Arabia is typical of a wind-driven system with similar
patterns of longshore current and wind stress; (ii) circulation off the west coast of India is consistent with the dynamics
of a wind-driven eastern boundary current only during the southwest monsoon. During the northeast monsoon it is possible that
the influence of the interior flow is important. (iii) There are at least three mechanisms that influence the surface circulation
off the east coast of India: wind-stress, influence of fresh-water run off and contribution of the interior flow. It is difficult
at present to assess the relative importance of these three processes. 相似文献
103.
R. M. Dargám 《International Journal of Salt Lake Research》1994,3(2):137-158
This paper reports on hydrochemical features of diluted waters in the source areas and the brine end-members dominant in the playa of the Salinas Grandes Basin, Córdoba, Argentina. Special emphasis was placed on the study of the relationship between geomorphology and the resulting hydrochemical fractionation. Inflow is from springs and mountain streams which disappear before reaching the saline complex. The playa and intermittent saline lakes are mainly fed by groundwater flow and a few moderately saline and perennial springs. Conversely, ephemeral lakes are fed by atmospheric precipitation and groundwater, whereas small ponds are only fed by atmospheric precipitation. The absence of a clear linkage between geomorphological units and water types was evident in the source areas. Up to four types of water were recognized in a given geomorphological unit. From the sandflat downward towards the playa, the correspondence between geomorphological units and water types was clear, coinciding with a decreased hydrochemical heterogeneity. In this subenvironment, I have recognized two dominant types of water (SO
4
2–
–Cl––HCO
3
–
–Na+ and Cl––SO
4
2–
–HCO
3
–
–Na+), which can be considered the original members of the neutral brine in the playa (Cl––SO
4
2–
–Na+ where Ca2++Mg2+ do not surpass 5 meq per cent), and an intermediate type in the mudflat (Cl––SO
4
2–
–Na+ where the contribution of Ca2++Mg2+ reaches up to 15 meq per cent). It seems evident that in the zone between the source areas and the sandflat, hydrochemistry is governed by chemical weathering. In stream floodplains and in the distal alluvial plain, close to the saline complex, the increase in water types as well as the increase of HCO
3
–
with respect to SO
4
2–
, were explained by the mixture of aquifers controlled by the Salinas Grandes-Salinas de Ambargasta fracture. In the saline complex, the more concentrated end-members are the result of evaporation of the two more frequent water-types in the sandflat subenvironment, and salt dissolution of ancient evaporite deposit. 相似文献
104.
105.
Results from a new model of river basin evolution 总被引:1,自引:0,他引:1
This paper briefly describes a model of the erosional development of catchments and their channel networks. The model differentiates between the dominant transport processes in hillslope and channels. The development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms. The growth of a river basin is qualitatively described. The model concepts are used to study the basin during periods of growth (transient periods), as well as during dynamic equilibrium. This leads to hypotheses about the relationship between slopes, relief, tectonic uplift, erodability, runoff, and catchment area. It is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation. 相似文献
106.
107.
Measurements were made of the water content in coastal rocks, by simulating tidal oscillations in the laboratory, and by field measurement in eastern Canada. If rapid freezing takes place upon exposure to the air, saturation levels may be high enough to permit frost weathering in fine grained rocks in the lower portions of the intertidal zone. Near the high tidal level, however, it may be dependent upon a supply of water from the ice foot and from melting snow. If freezing is slow, frost action may be inhibited by desorption of the rocks while they are exposed by the ebb tide. There was no evidence of a level of permanent sea water saturation within the intertidal zone. Ambient temperature and humidity may affect the rate of rock desorption. 相似文献
108.
Gordon E. Bigelow 《地球表面变化过程与地形》1984,9(4):383-390
Tumbler simulations of abrasion processes affecting rocks on basaltic marine benches have clarified the effects of mass and volume of rock fragments on their rate of wear. Several experiments indicate that rate of basalt wear increases with mass in the interval 1 g to 8 g, but is not related to volume of fragments abraded in seawater. Relatively small quantities of rock flour suspended in the immersant seawater substantially reduced the rate of basalt wear. Basalt and calcareous beachrock responded differently in systems with both rock types tumbling together. Examination of the cuttings from these low-energy encounters suggests that abrasion on elevated benches along exposed seacoasts reduces virtually all clastic material to particles of silt size or smaller, producing essentially no sand. 相似文献
109.
Stratigraphic and chemical data from the ice core of an ‘anthropogenic palsa’ at Toolik Lake, Alaska, indicate that the mound formed as a consequence of hydrostatic pressure developed in an isolated hydrologic system within the active layer. Survey data for five palsas over a three-year period suggest that growth was essentially complete at the time of the initial survey; a net decrease of summit elevation is apparent in all five mounds, but complete degradation of the palsas would require several decades at observed rates. Because accurate field measurements of thermal and hydrologic evolution in such features are extremely difficult, simulation of the environmental conditions and events involved in palsa growth is an important supplement to field observation. Both analytic and finite-element models yield results that are in substantial agreement with inferences drawn from observational data. 相似文献
110.
Weichselian geomorphological and fluvial evolution has been recorded in the valley fill of the Reusel, a small tributary of the lower Maas river. It has been studied by means of borehole sections. A first deep incision into the substratum occurred during the Early Weichselian-Lower Pleniglacial. This was followed by aggradation, at first by a braided river, at a later date by a meandering river, dating respectively from the Lower and Middle Pleniglacial. The Upper Pleniglacial aggradation again points to a braided river system. The end of the Pleniglacial is characterized by aeolian infilling of the valley and decreasing carrying capacity of the river. 相似文献