全文获取类型
收费全文 | 1234篇 |
免费 | 83篇 |
国内免费 | 12篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 85篇 |
地球物理 | 374篇 |
地质学 | 422篇 |
海洋学 | 138篇 |
天文学 | 168篇 |
综合类 | 6篇 |
自然地理 | 119篇 |
出版年
2024年 | 5篇 |
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 27篇 |
2020年 | 37篇 |
2019年 | 38篇 |
2018年 | 43篇 |
2017年 | 48篇 |
2016年 | 58篇 |
2015年 | 47篇 |
2014年 | 57篇 |
2013年 | 71篇 |
2012年 | 59篇 |
2011年 | 76篇 |
2010年 | 72篇 |
2009年 | 66篇 |
2008年 | 48篇 |
2007年 | 55篇 |
2006年 | 41篇 |
2005年 | 43篇 |
2004年 | 45篇 |
2003年 | 35篇 |
2002年 | 38篇 |
2001年 | 30篇 |
2000年 | 27篇 |
1999年 | 23篇 |
1998年 | 19篇 |
1997年 | 16篇 |
1996年 | 15篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 16篇 |
1980年 | 5篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 8篇 |
1971年 | 3篇 |
1966年 | 3篇 |
排序方式: 共有1329条查询结果,搜索用时 62 毫秒
991.
P. Worsley G. R. Coope T. R. Good D. T. Holyoak J. E. Robinson 《Geological Journal》1983,18(4):307-324
A thin sequence of in situ fossiliferous gravels and silts overlain by a glacigenic bed is described from a temporary exposure in a working silica sand quarry. The sequence directly overlies unweathered Mercia Mudstone. Locally the bedrock surface forms a shallow palaeovalley some 15 m deep and almost 1 km wide. The sequence in question lies close to the valley axis. The silts, pollen, plant macrofossils, Mollusca, Coleoptera, and Ostracoda assemblages each suggest a similar environment of sedimentation: a shallow pool within a treeless open landscape. Much of the bedrock within the working quarry appears to be draped by the Oakwood till and this unit is co-extensive with the glacigenic sediments over the silts and gravels. In parts at least, the till has been subject to redeposition and its upper surface has scattered ventifacts. Above this wind-deflation horizon lies the Chelford Sands Formation, in the middle of which is the Chelford Interstadial stratotype, the Farm Wood member. The biota preserved in the gravels and silts suggest a stadial prior to the Early Devensian Chelford Interstadial. This is the first unambiguous stratigraphic evidence from Cheshire of a glacial event antedating the Chelford Interstadial. 相似文献
992.
The effects of the scale of measurement, i.e., the field of view, on the interpretation of fracture properties from seismic wave propagation was investigated using an acoustic lens system to produce a pseudo-collimated wavefront. The incident wavefront had a controllable beam diameter that set the field of view at 15 mm, 30 mm and 60 mm. On a smaller scale, traditional acoustic scans were used to probe the fracture in 2 mm increments. This laboratory approach was applied to two limestone samples, each containing a single induced fracture and compared to an acrylic control sample. From the analysis of the average coherent sum of the signals measured on each scale, we observed that the scale of the field of view affected the interpretation of the fracture specific stiffness. Many small-scale measurements of the seismic response of a fracture, when summed, did not predict the large-scale response of the fracture. The change from a frequency-independent to frequency-dependent fracture stiffness occurs when the scale of the field of view exceeds the spatial correlation length associated with fracture geometry. A frequency-independent fracture specific stiffness is not sufficient to classify a fracture as homogeneous. A nonuniform spatial distribution of fracture specific stiffness and overlapping geometric scales in a fracture cause a scale-dependent seismic response, which requires measurements at different field of views to fully characterize the fracture. 相似文献
993.
Colin R. O'Farrell Arjun M. Heimsath Daniel E. Lawson Laura M. Jorgensen Edward B. Evenson Grahame Larson Jon Denner 《地球表面变化过程与地形》2009,34(15):2008-2022
Glacial erosion rates are estimated to be among the highest in the world. Few studies have attempted, however, to quantify the flux of sediment from the periglacial landscape to a glacier. Here, erosion rates from the nonglacial landscape above the Matanuska Glacier, Alaska are presented and compare with an 8‐yr record of proglacial suspended sediment yield. Non‐glacial lowering rates range from 1·8 ± 0·5 mm yr?1 to 8·5 ± 3·4 mm yr?1 from estimates of rock fall and debris‐flow fan volumes. An average erosion rate of 0·08 ± 0·04 mm yr?1 from eight convex‐up ridge crests was determined using in situ produced cosmogenic 10Be. Extrapolating these rates, based on landscape morphometry, to the Matanuska basin (58% ice‐cover), it was found that nonglacial processes account for an annual sediment flux of 2·3 ± 1·0 × 106 t. Suspended sediment data for 8 years and an assumed bedload to estimate the annual sediment yield at the Matanuska terminus to be 2·9 ± 1·0 × 106 t, corresponding to an erosion rate of 1·8 ± 0·6 mm yr?1: nonglacial sources therefore account for 80 ± 45% of the proglacial yield. A similar set of analyses were used for a small tributary sub‐basin (32% ice‐cover) to determine an erosion rate of 12·1 ± 6·9 mm yr?1, based on proglacial sediment yield, with the nonglacial sediment flux equal to 10 ± 7% of the proglacial yield. It is suggested that erosion rates by nonglacial processes are similar to inferred subglacial rates, such that the ice‐free regions of a glaciated landscape contribute significantly to the glacial sediment budget. The similar magnitude of nonglacial and glacial rates implies that partially glaciated landscapes will respond rapidly to changes in climate and base level through a rapid nonglacial response to glacially driven incision. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
994.
Bayesian event tree for eruption forecasting (BET_EF) at Vesuvius,Italy: a retrospective forward application to the 1631 eruption 总被引:1,自引:0,他引:1
Laura Sandri Emanuela Guidoboni Warner Marzocchi Jacopo Selva 《Bulletin of Volcanology》2009,71(7):729-745
Reliable forecasting of the next eruption at Vesuvius is the main scientific factor in defining effective strategies to reduce
volcanic risk in one of the most dangerous volcanic areas of the world. In this paper, we apply a recently developed probabilistic
code for eruption forecasting to new and independent historical data related to the pre-eruptive phase of the 1631 eruption.
The results obtained point out three main issues: (1) the importance of “cold” historical data (according to Guidoboni 2008) related to pre-eruptive phases for evaluating forecasting tools and possibly refining them; (2) the BET_EF code implemented
for Vesuvius would have forecasted the 1631 eruption satisfactorily, marking different stages of the pre-eruptive phase; (3)
the code shows that pre-eruptive signals that significantly increase the probability of eruption were likely detected more
than 2 months before the event. 相似文献
995.
Cloelle G.S. Giddings Laura K. Jennings James M. Gossett 《Ground Water Monitoring & Remediation》2010,30(2):97-105
A molecular biological tool based on an organism-specific DNA sequence does not necessarily indicate in situ activity but serves important functions of evaluating the potential for biodegradation and mapping the distribution of an organism. Currently, DNA-based probes are accepted as evaluative tools for site assessment. However, these techniques are far from standardized, and information on precision is usually lacking. Here, we present the development and evaluation of a DNA probe for Polaromonas sp. strain JS666, a bacterium that couples growth to aerobic oxidation of cis-1,2-dichloroethene (cDCE), and is therefore a promising candidate for bioaugmentation at sites where cDCE has accumulated in aerobic zones. The DNA probe was used in conjunction with quantitative polymerase chain reaction to track the abundance of JS666 in microcosms. This series of studies has allowed explicit resolution of the accuracy and precision of the probe and its correlation with variations in microcosm performance. We determined that the method is sufficient to monitor distribution of JS666 at bioaugmented sites. We found within environmental, mixed cultures, that the DNA target does not persist long after cell death, demonstrating that positive result from the probe is a strong indicator that degradation can occur in suitable environmental conditions. Finally, in the absence of suspected predation, the probe accurately and precisely tracks growth. Collectively, the studies appear to validate the utility of the molecular probe for site assessment in a bioaugmentation context. 相似文献
996.
Emilio Palacios-Hernández Laura E. Carrillo Anatoliy Filonov Luis Brito-Castillo Carlos E. Cabrera-Ramos 《Ocean Dynamics》2010,60(1):81-91
Sea surface temperature (SST) harmonic and empirical orthogonal function (EOF) analyses covering 18 years were performed for the area located from 114° to 105° W and from 18° to 25° N. The results indicate that the influence of the annual signal predominates over the semi-annual signal, and the closer to the coast, the stronger the annual harmonic. Several interannual anomalies arose that are connected with the main global indexes, especially the Oceanic Niño Index. Pearson correlations between the first temporal mode of the SST and regional rainfalls in Nayarit indicate that maximum correlations (r?>?0.7) are observed when there is a +1-month lag between the series. However, this result indicates that SST is delayed with 1 month after rainfall occurrence, which shows that the dominant influence in this relationship is not the SST forcing. 相似文献
997.
Spatial mode estimation for functional random fields with application to bioturbation problem 总被引:1,自引:1,他引:0
Sophie Dabo-Niang Anne-Francoise Yao Laura Pischedda Philippe Cuny Franck Gilbert 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(4):487-497
This work provides a useful tool to study the effects of bioturbation on the distribution of oxygen within sediments. We propose
here heterogeneity measurements based on functional spatial mode. To obtain the mode, one usually needs to estimate the spatial
probability density. The approach considered here consists in looking each observation as a curve that represents the history
of the oxygen concentration at a fixed pixel. 相似文献
998.
Mobilisation of sedimentary monosulfidic black ooze (MBO) may result in rapid deoxygenation and acidification of surface waters, and release of potentially toxic metals. This study examines the extent and nature of MBO accumulation in the Geographe Bay area, Western Australia. MBO accumulations were found to be widespread in benthic sediments of the Geographe Bay area with acid-volatile sulfide (AVS) contents as high as 320 μmol g−1. The MBO materials often had unusually high dissolved sulfide (S−II) concentrations in their pore-waters (up to 610 mg L−1) and elevated elemental sulfur (S0) contents (up to 51 μmol g−1). Dissolved S−II is able to accumulate due to limited iron availability and S0 is largely its partial oxidation product. The availability of organic carbon and Fe limited MBO accumulation at many sites. A comparison of AVS and simultaneously extracted metal (SEM) concentrations has shown that metals are likely to be bound in sulfide complexes. 相似文献
999.
The life history of the amphipod Orchestia sp. cf. cavimana (Heller, 1865) was studied throughout the course of a year with monthly samplings and the use of pitfall traps along the shores of Lake Albano in central Italy. The data thus obtained showed two peaks in abundance (the first in June and the second in October) and a minimum capture frequency in February. Egg-bearing females were recorded in spring and late summer, whilst recruitment occurred from spring to autumn, with maximum in June and October. The data collected also indicated the presence of a positive correlation between the abundance of talitrids and both temperature and sediment moisture. Morphological analysis enabled the identification of four different cohorts (with a lifespan of the species of approximately 12–15 months) all four of which remained distinguishable throughout the course of the year. It, moreover, enabled sex determination in individuals of 5 or more millimetres. The subsequent distribution indicated that, when significant, the sex ratio was female biased and that maximum size was greater in males. In particular, maximum sizes were recorded in spring for both males and females and were of 17.5 and 13.0 mm, respectively. Furthermore, the total body length recorded for egg-bearing females was positively correlated with the number of eggs in their brood pouch. 相似文献
1000.
Laura S. Epp Kathleen R. Stoof Martin H. Trauth Ralph Tiedemann 《Journal of Paleolimnology》2010,43(4):939-954
Using molecular genetic methods and an ancient DNA approach, we studied population and species succession of rotifers of the
genus Brachionus in the Kenyan alkaline-saline crater lake Sonachi since the beginning of the 19th century as well as distribution of Brachionus haplotypes in recent and historic sediments of other lakes of the East African Rift System. The sediment core record of Lake
Sonachi displays haplotypes of a distinct evolutionary lineage in all increments. Populations were dominated by a single mitochondrial
haplotype for a period of 150 years, and two putatively intraspecific turnovers in dominance occurred. Both changes are concordant
with major environmental perturbations documented by a profound visible change in sediment composition of the core. The first
change was very abrupt and occurred after the deposition of volcanic ash at the beginning of the 19th century. The second
change coincides with a major lake level lowstand during the 1940s. It was preceded by a period of successively declining
lake level, in which two other haplotypes appeared in the lake. One of these putatively belongs to another species documented
in historical and recent Kenyan lake sediments. The analysis of plankton population dynamics through historical time can reveal
patterns of population persistence and turnover in relation to environmental changes. 相似文献