全文获取类型
收费全文 | 117篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 4篇 |
地球物理 | 42篇 |
地质学 | 46篇 |
海洋学 | 4篇 |
天文学 | 19篇 |
综合类 | 1篇 |
自然地理 | 9篇 |
出版年
2023年 | 1篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 7篇 |
2012年 | 6篇 |
2011年 | 14篇 |
2010年 | 5篇 |
2009年 | 5篇 |
2008年 | 4篇 |
2007年 | 6篇 |
2006年 | 4篇 |
2005年 | 6篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有128条查询结果,搜索用时 162 毫秒
121.
122.
Microconchids are a group of tiny, encrusting tubeworms. They appeared in the Late Ordovician, some 450 Myr ago, flourished during the rest of Palaeozoic and Triassic, and became extinct in the Middle Jurassic. Their morphological resemblance to the sedentary polychaete genus Spirorbis, very common in marine environments, misled various authors for decades. This mistake originally gave the genus Spirorbis an enormous stratigraphical range, from Ordovician to Recent. Indeed, microconchids provide an excellent example of evolutionary convergence with respect to both their morphology and ecology. In the late 1970s these ‘spirorbids’ were interpreted as vermetid gastropods on the basis of the inner architecture and microstructure of their tubes. This idea, however, was challenged in the 1990s when detailed microstructural investigation showed them to be neither polychaetes nor gastropods, but closely related to an extinct Palaeozoic enigmatic group of organisms called tentaculitids. No thorough investigation of their origin, phylogeny and ecology has ever been conducted, but new data concerning their palaeobiology has come to the light during the last few years. 相似文献
123.
A whitefish population considered to consist of two morphologically similar subpopulations is analyzed. Since a reproductive
barrier existing earlier between the two subpopulations has lost its effectiveness, only one population exists today, having
a very long reproductive period.
相似文献
124.
C. A. Ruhl D. H. Schoellhamer R. P. Stumpf C. L. Lindsay 《Estuarine, Coastal and Shelf Science》2001,53(6):801
Analysis of suspended-sediment concentration data in San Francisco Bay is complicated by spatial and temporal variability. In situ optical backscatterance sensors provide continuous suspended-sediment concentration data, but inaccessibility, vandalism, and cost limit the number of potential monitoring stations. Satellite imagery reveals the spatial distribution of surficial-suspended sediment concentrations in the Bay; however, temporal resolution is poor. Analysis of thein situ sensor data in conjunction with the satellite reflectance data shows the effects of physical processes on both the spatial and temporal distribution of suspended sediment in San Francisco Bay. Plumes can be created by large freshwater flows. Zones of high suspended-sediment concentrations in shallow subembayments are associated with wind-wave resuspension and the spring-neap cycle. Filaments of clear and turbid water are caused by different transport processes in deep channels, as opposed to adjacent shallow water. Crown 相似文献
125.
Quaternary deformation, river steepening, and heavy precipitation at the front of the Higher Himalayan ranges 总被引:9,自引:0,他引:9
Kip V Hodges Cameron Wobus Katharine Ruhl Taylor Schildgen Kelin Whipple 《Earth and Planetary Science Letters》2004,220(3-4):379-389
New geologic mapping in the Marsyandi Valley of central Nepal reveals the existence of tectonically significant Quaternary thrust faults at the topographic front of the Higher Himalaya. The zone of recent faulting is coincident with an abrupt change in the gradient of the Marsyandi River and its tributaries, which is thought to mark the transition from a region of rapid uplift in the Higher Himalayan ranges to a region of slower uplift to the south. Uplift of the Higher Himalaya during the Quaternary is not entirely due to passive uplift over a deeply buried ramp in the Himalayan sole thrust, as is commonly believed, but partially reflects active thrusting at the topographic front. The zone of active thrusting is also coincident with a zone of intense monsoon precipitation, suggesting a positive feedback relationship between focused erosion and deformation at the front of the Higher Himalayan ranges. 相似文献
126.
During the Last Glacial Maximum (LGM), long valley glaciers developed on the northern and southern sides of the High Tatra Mountains, Poland and Slovakia. Chlorine-36 exposure dating of moraine boulders suggests two major phases of moraine stabilization, at 26–21 ka (LGM I — maximum) and at 18 ka (LGM II). The dates suggest a significantly earlier maximum advance on the southern side of the range. Reconstructing the geometry of four glaciers in the Sucha Woda, Pańszczyca, Mlynicka and Velicka valleys allowed determining their equilibrium-line altitudes (ELAs) at 1460, 1460, 1650 and 1700 m asl, respectively. Based on a positive degree-day model, the mass balance and climatic parameter anomaly (temperature and precipitation) has been constrained for LGM I advance. Modeling results indicate slightly different conditions between northern and southern slopes. The N–S ELA gradient finds confirmation in slightly higher temperature (at least 1 °C) or lower precipitation (15%) on the south-facing glaciers during LGM I. The precipitation distribution over the High Tatra Mountains indicates potentially different LGM atmospheric circulation than at the present day, with reduced northwesterly inflow and increased southerly and westerly inflows of moist air masses. 相似文献
127.
Secondary metabolites protect many marine sponges (Phylum: Porifera) from settlement by fouling organisms. Previous studies on the subtidal demosponge Axinella verrucosa collected in the Western Mediterranean led to the isolation of compounds that inhibited the settlement of cyprids larvae of the intertidal barnacle Balanus amphitrite, and the enzyme chitinase, which plays a key role in the molting cycle of crustaceans. However, in a field survey conducted at three locations in Israel, Eastern Mediterranean Sea, we observed that A. verrucosa is fouled by the subtidal barnacle Balanus trigonus, a previously unknown association. Settlement inhibition assays using B. amphitrite with chemical extracts from Israeli A. verrucosa and Axinella polypoides, a sympatric, congeneric sponge that seems not to be fouled by B. trigonus, showed that cyprid larvae of B. amphitrite were inhibited by the extracts of both sponges from settlement at concentrations several magnitudes lower than natural volumetric extract concentration in the sponges. These results indicate that, unlike the intertidal barnacle B. amphitrite, the subtidal B. trigonus is unaffected by the compounds from A. verrucosa, stressing and underlining the importance of using suitable target organisms (i.e. from the same habitat) to test for ecologically relevant antifouling activities. 相似文献
128.
The goal of the research was to demonstrate the impact of thin porous interfacial transition zones (ITZs) between aggregates and cement matrix on fluid flow in unsaturated concrete caused by hydraulic/capillary pressure. To demonstrate this impact, a novel coupled approach to simulate the two-phase (water and moist air) flow of hydraulically and capillary-driven fluid in unsaturated concrete was developed. By merging the discrete element method (DEM) with computational fluid dynamics (CFD) under isothermal settings, the process was numerically studied at the meso-scale in two-dimensional conditions. A flow network was used to describe fluid behaviour in a continuous domain between particles. Small concrete specimens of a simplified particle mesostructure were subjected to fully coupled hydro-mechanical simulation tests. A simple uniaxial compression test was used to calibrate the pure DEM represented by bonded spheres, while a permeability and sorptivity test for an assembly of spheres was used to calibrate the pure CFD. For simplified specimens of the pure cement matrix, cement matrix with aggregate, and cement matrix with aggregate and ITZ of a given thickness, DEM/CFD simulations were performed sequentially. The numerical results of permeability and sorptivity were directly compared to the data found in the literature. A satisfactory agreement was achieved. Porous ITZs in concrete were found to reduce sorption by slowing the capillary-driven fluid flow, and to speed the full saturation of pores when sufficiently high hydraulic water pressures were dominant. 相似文献