全文获取类型
收费全文 | 1793篇 |
免费 | 231篇 |
国内免费 | 266篇 |
专业分类
测绘学 | 133篇 |
大气科学 | 156篇 |
地球物理 | 356篇 |
地质学 | 555篇 |
海洋学 | 372篇 |
天文学 | 20篇 |
综合类 | 136篇 |
自然地理 | 562篇 |
出版年
2024年 | 5篇 |
2023年 | 17篇 |
2022年 | 56篇 |
2021年 | 67篇 |
2020年 | 70篇 |
2019年 | 69篇 |
2018年 | 66篇 |
2017年 | 56篇 |
2016年 | 83篇 |
2015年 | 106篇 |
2014年 | 99篇 |
2013年 | 136篇 |
2012年 | 93篇 |
2011年 | 107篇 |
2010年 | 92篇 |
2009年 | 91篇 |
2008年 | 106篇 |
2007年 | 106篇 |
2006年 | 100篇 |
2005年 | 75篇 |
2004年 | 98篇 |
2003年 | 89篇 |
2002年 | 66篇 |
2001年 | 59篇 |
2000年 | 45篇 |
1999年 | 57篇 |
1998年 | 42篇 |
1997年 | 44篇 |
1996年 | 34篇 |
1995年 | 22篇 |
1994年 | 26篇 |
1993年 | 25篇 |
1992年 | 17篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1980年 | 4篇 |
1978年 | 3篇 |
排序方式: 共有2290条查询结果,搜索用时 15 毫秒
101.
Victoria Beach (Cadiz, Spain) comprises a rocky flat outcrop in its northern zone and a sand-rich southern zone. These natural features allowed for a 5-year monitoring period and subsequent analysis of two different profiles (one in each zone) based on differences in bottom contours. Topo-bathymetric data were analysed using empirical orthogonal functions (EOFs) to determine changes over the short-, medium- and long-term. Several morphologic phenomena were identified (generalised erosion, seasonal or summer–winter tilting of the profile around different hinge points, berm development and its posterior destruction, etc.) in terms of their importance in explaining the variability of the collected data for both profiles. It is worth mentioning that both profiles undergo parallel regression in the medium-term. Thus, the 1st eigenfunction enabled us to identify the true regression of the beach shoreline, independent of seasonal or summer–winter slope changes. Reconstruction of profiles using EOF components demonstrated that though accretion periods in the medium-term were similar for both types of profiles, the accretion speed was much faster in the sand-rich profile than in the reef-protected profile (1.01 m3/day versus 0.33 m3/day). Moreover, the seasonal erosion rate and the subsequent shoreline retreat for the sand-rich profile were much larger than for the reef-protected profile (121 m3/year versus 29 m3/year). Analysis in the short-term (changes induced by a single day's storm) showed an instantaneous tilting of the profile, with the mobilised sand volume being much greater for the sand-rich than for the reef-protected profile (68 m3/m versus 12 m3/m). 相似文献
102.
The Annualized Agricultural Non‐point Source (AnnAGNPS) pollution model has been widely used to assess and predict runoff, soil erosion, sediment and nutrient loading with a geographic information system. This article presents a case study of the effect of land‐use changes on nonpoint source (NPS) pollution using the AnnAGNPS model in the Xizhi River watershed, eastern Pearl River Delta of Guangdong province, China. The land‐use changes in the Xizhi River watershed between 1998 and 2003 were examined using the multitemporal remote sensing data. The runoff, soil erosion, sediment transport and nutrient loading 1998 and 2003 were assessed using AnnAGNPS. The effects of land‐use changes on NPS were studied by comparing the simulation results of each year. Our results showed that (i) the NPS loadings increased when forest and grass land converted into paddy, orchard and farmland land, and population size and gross domestic product size as well as the usage amounts of fertilizer and pesticide in the entire watershed were firmly correlated with the NPS loadings; (ii) the land‐use change during fast urbanization in particular when other land types were converted into the development land and buildup land led to increasing of NPS pollution; and (iii) urban land expansion showed more important effects on total organic carbon (TOC) loading compared with nitrogen and phosphorus loadings. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
103.
The results of prediction of occurrence of mining tremors and bursts in the course of the exploitation of the remaining part of the hard coal in seam 510 of the mine Pstrowski, Upper Silesia, have been presented in the paper. The exploitation has taken place under extremely difficult conditions hazardous for the mining crew.To predict the occurrence of mining tremors, bursts and direction of migration of increased elastic strain in the rock mass, the microgravity method has been applied.The microgravity observations were carried out in the measurement points located at mutual distances equal 20 m in three profiles of the lengths 700 m, 760 m and 260 m respectively. The profiles were located in mining workings in the vicinity of the exploited part of the bed. In the course of exploitation, lasting 25 months, 29 series of measurements including 3600 individual microgravity observations were carried out. Microgravity observations were made with a Worden-Master gravimeter.The observed time changes of gravity microanomalies were essential for prediction. Local negative changes of gravity microanomalies signalled the approaching mining tremor. The tremor would cover an area of the radius 60 m to 100 m. The regional time changes of the gravity microanomalies appearing as linear trends of these anomalies signalled the development of the fields of elastic strain in the whole investigated area and the approaching violent release of elastic strain energy from the rock mass.The values of the amplitudes AMP of the above-mentioned trend were the measure of this hazard. In the course of the investigations each shock was preceded by considerably increased values of AMP. 相似文献
104.
A. R. Wyatt 《International Journal of Earth Sciences》1993,82(2):185-188
Sediment yield from modern continental blocks is a function of the area (dissolved load) and hypsometry (mechanical load) of the blocks. Hypsographic curves for modern continental blocks show that the change in the percentage area flooded for any change in eustatic sea level depends on the size of the block and the absolute sea level. This allows predictions of changes in sediment yield around different sized blocks for any given eustatic change. The range in size of continental blocks is such that, for any given sea level change, the blocks will show different percentage changes in yield. Data from modern continental blocks are compared with theoretical results. Assuming that the rules governing modern hypsometries applied in the past, and a constant volume of continental crust, it is possible to estimate the hypsographic curves of former continental blocks. The implications of suggested past continental configurations and sea levels for sediment yield are discussed. 相似文献
105.
A profundal sediment core from Höllerer See frozen in situ was studied by means of diatom, microstratigraphical tape peel and pollen analyses. Varved sequences reflect eutrophication during mediaeval settlement and according to varve counts a recent eutrophic phase since the 1970's. Mesotrophication in-between coincides with regrowth of forests near the lake. 相似文献
106.
松辽盆地白垩纪古气候特征及其变化机制 总被引:5,自引:0,他引:5
本文综合研究了松辽盆地白垩纪古气候的沉积记录、孢份古植物群记录及碳、氧同位素地球化学特征,得出了松辽盆地白垩纪古气候的演变规律。并认为碳族国与古气候旋回有密切的对应关系,大气中CO_2含量的变化是古气候变化的根本原因。每一温暖时期的开始都与大气中CO_2含量的增加有关,随着固碳作用的增强,温室效应削弱。碳旋回是古气候变化的重要机制。 相似文献
107.
A. O. Ludwig 《International Journal of Earth Sciences》1994,83(4):799-810
Significant short-term fluctuations are characteristic of geological history since Precambrian times. Only the younger Quaternary climatic fluctuations are known in more detail as a result of a high grade time resolution. Climatic change can also be postulated with respect to older, cold periods during which polar inland ice sheets developed. From a discussion of endogene and exogene interpretations it is shown that global climatic changes, and the sea-level changes induced by them, as well as changes in the position and extent of climatic zones throughout the world provide a control mechanism for sedimentation which is consistent with cyclic sedimentation in Late Palaeozoic times, and also if the basin subsides non-cyclically. The model allows an explanation of the development of the Permo-Carboniferous sedimentary cycles without numerous short-term vertical oscillations of the earth's crust. In reality, exogene and endogene controls on sedimentation act together in great variety of combinations. 相似文献
108.
Although a traditional geological survey of terraced coastal slopes is an essential part of studies aimed to reconstruct relative sea-level changes, the stratigraphic and chronological data so obtained frequently prove inadequate to completely unravel the sometimes very complex history of sea-level fluctuation, especially where erosion has prevailed over deposition and/or deposits are difficult to date. On the basis of our experience we think that much additional information can be gained through geomorphological interpretation of the profiles of those slopes. In order to facilitate such interpretation, a computer simulation model is developed that is able to predict the morphogenic response to a variety of possible relative-sea-level histories. The results can be used to envisage some new interpretation keys for the analysis of real situations and, hopefully, as bases for the conception of general models of coastal slope evolution under the action of a variable sea level. Though preliminary, the results so far obtained permit identification of the geomorphological consequences (in terms of resulting slope profile) of ordered successions of transgressions and regressions of different amplitude, rate, order and style. Moreover they provide interesting insights into the role that different styles of tectonic uplift may play in the phenomenon of multiple terracing of coastal slopes. 相似文献
109.
110.
从更广泛和较高的层次对地质时期地球表层的生命活动和环境变化进行多学科的综合性研究,在全球系统分析的基础上为“协调人类与自然关系”的战略主题提供决策依据。以高分辨率地层学框架的研究的基础,综合多种学科对事件、间事件及其载体和介质的定量研究,为生物与环境的耦合机制的认识及有关模式的建立提供科学依据。化石燃料作为事件产物,其分布规律亦为重要研究内容之一。 相似文献