全文获取类型
收费全文 | 1338篇 |
免费 | 119篇 |
国内免费 | 20篇 |
专业分类
测绘学 | 23篇 |
大气科学 | 71篇 |
地球物理 | 371篇 |
地质学 | 648篇 |
海洋学 | 102篇 |
天文学 | 168篇 |
综合类 | 6篇 |
自然地理 | 88篇 |
出版年
2021年 | 23篇 |
2020年 | 18篇 |
2019年 | 33篇 |
2018年 | 47篇 |
2017年 | 46篇 |
2016年 | 57篇 |
2015年 | 43篇 |
2014年 | 48篇 |
2013年 | 89篇 |
2012年 | 57篇 |
2011年 | 65篇 |
2010年 | 67篇 |
2009年 | 75篇 |
2008年 | 62篇 |
2007年 | 36篇 |
2006年 | 52篇 |
2005年 | 60篇 |
2004年 | 42篇 |
2003年 | 53篇 |
2002年 | 40篇 |
2001年 | 30篇 |
2000年 | 26篇 |
1999年 | 23篇 |
1998年 | 19篇 |
1997年 | 15篇 |
1996年 | 15篇 |
1995年 | 18篇 |
1994年 | 16篇 |
1993年 | 8篇 |
1992年 | 13篇 |
1991年 | 23篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 13篇 |
1984年 | 20篇 |
1983年 | 20篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 12篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1971年 | 5篇 |
1970年 | 5篇 |
排序方式: 共有1477条查询结果,搜索用时 15 毫秒
921.
Collin Nkono Olivier Fmnias Annick Lesne Jean‐Claude Mercier Fadimatou Yamgouot Ngounouno Daniel Demaiffe 《Geological Journal》2016,51(5):748-759
As rock textures reflect the physical conditions and the mechanisms of formation of the rocks, new approaches are used for improving texture analyses, both qualitatively and quantitatively. Pioneer work has recently boosted interest in fractal analysis for quantifying and correlating patterns. Fractal‐like patterns relate to a degree of multiscale organization, and fractal dimensions (FD) and their potential variations can be used to infer the physical conditions of rock formation at various scales of observation. Here, we characterize quantitatively the shape and distribution of orthopyroxene grains in ultramafic xenoliths in terms of FD and their relation with temperature of equilibration. Fractal analysis has been applied to several populations of mantle xenoliths: 7 xenoliths collected in the vicinity of Pico Santa Isabel on Bioko Island, an alkaline basaltic volcano in oceanic domain (Gulf of Guinea, Equatorial Atlantic), 9 samples from Sangilen, in the Agardag alkaline lamprophyre dyke (Russia), and 11 samples form Śnieżnik (Lutynia, Poland), in the continental domain. Fractal analysis has been conducted to characterize the degree of complexity of the petrographic textures: it is indeed known that large values of FD are associated to more complex textures. The correlation here observed between the orthopyroxene fractal dimension and the temperature of equilibration suggests that FD captures a significant textural feature directly related to the temperature (i.e. generated by a temperature‐controlled process). The significant difference in the FD–T correlation observed for the continental and oceanic mantle domains suggests that the mechanical and rheological behaviour is distinct in the oceanic and continental lithospheres. These first promising results should be confirmed by analysing other mantle suites of rocks in different geodynamic settings. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
922.
There is a significant relationship between ambient temperature and mortality. In healthy individuals with no underlying co-morbid conditions, there is an efficient heat regulation system which enables the body to effectively handle thermal stress. However, in vulnerable groups, especially in elderly over the age of 65 years, infants and individuals with co-morbid cardiovascular and/or respiratory conditions, there is a deficiency in thermoregulation. When temperatures exceed a certain limit, being cold winter spells or heat waves, there is an increase in the number of deaths. In particular, it has been shown that at temperatures above 27 °C, the daily mortality rate increases more rapidly per degree rise compared to when it drops below 27 °C.This is especially of relevance with the current emergency of global warming. Besides the direct effect of temperature rises on human health, global warming will have a negative impact on primary producers and livestock, leading to malnutrition, which will in turn lead to a myriad of health related issues. This is further exacerbated by environmental pollution.Public health measures that countries should follow should include not only health-related information strategies aiming to reduce the exposure to heat for vulnerable individuals and the community, but improved urban planning and reduction in energy consumption, among many others. This will reduce the carbon footprint and help avert global warming, thus reducing mortality. 相似文献
923.
Remy Albrecht Jean Christophe GourryMarie-Odile Simonnot Corinne Leyval 《Journal of Applied Geophysics》2011,75(3):558-564
Several laboratory studies have recently demonstrated the utility of geophysical methods for the investigation of microbial-induced changes over contaminated sites. However, it remains difficult to distinguish the effects due to the new physical properties imparted by microbial processes, to bacterial growth, or to the development of bacterial biofilm. We chose to study the influence of biofilm formation on geophysical response using complex conductivity measurements (0.1-1000 Hz) in phenanthrene-contaminated media. Biotic assays were conducted with two phenanthrene (PHE) degrading bacterial strains: Burkholderia sp (NAH1), which produced biofilm and Stenophomonas maltophilia (MATE10), which did not, and an abiotic control. Results showed that bacterial densities for NAH1 and MATE10 strains continuously increased at the same rate during the experiment. However, the complex conductivity signature showed noticeable differences between the two bacteria, with a phase shift of 50 mrad at 4 Hz for NAH1, which produced biofilm. Biofilm volume was quantified by Scanning Confocal Laser Microscopy (SCLM). Significant correlations were established between phase shift decrease and biofilm volume for NAH1 assays. Results suggest that complex conductivity measurements, specifically phase shift, can be a useful indicator of biofilm formation inside the overall signal of microbial activity on contaminated sites. 相似文献
924.
M. Van Den Eeckhaut Jean Poesen Frans Gullentops Liesbeth Vandekerckhove Javier Hervás 《Quaternary Research》2011,75(3):721-733
Analysis of LiDAR-derived imagery led to the discovery of more than 330 pre-Holocene to recent landslides in Southern Flanders (4850 km2). The morphology of three landslides, including the 266.5 ha deep-seated gravitational slope deformation in Alden Biesen, was investigated in more detail. The analysis of the morphological and topographical characteristics (width–length relation, frequency–area distribution and topographical threshold) of the landslides revealed important differences compared to the characteristics reported in other landslide studies, and helped understanding possible landslide triggering mechanisms. Especially the possibility of a seismic origin of the landslides was investigated. Finally, a heuristic model for region-wide landslide susceptibility mapping was successfully tested. The susceptibility model and map allow prediction of future landslide locations and contribute to better understanding the role of individual causal factors on landslide location and spatial density. The results suggest that landslides on low-gradient, soil-mantled hills are a more important contributor to landscape evolution of hilly areas than was hitherto thought. The morphology of all hilly regions of Flanders is clearly marked by landslide processes and higher landslide densities often coincide with the presence of quaternary active faults. This study further shows that high-resolution topographical data such as LiDAR significantly contributes to a better detection of old, previously unknown landslides. 相似文献
925.
Bibhash Nath Jyoti Prakash Maity Jiin-Shuh Jean Gavin Birch Sandeep Kar Huai-Jen Yang Ming-Kuo Lee Rasmani Hazra Debashis Chatterjee 《Applied Geochemistry》2011,26(5):705-713
Major ion and trace element analyses were performed on groundwater samples collected from the Bengal Delta (Chakdaha municipality, West Bengal and Manikgonj town, Bangladesh) and Chianan Plains (SW Taiwan) to compare geochemical characteristics. Results showed that concentrations of Na, K, Mg, Cl and SO4 were generally higher in Chianan Plain (CNP) groundwaters, while high Ca was observed in Bengal Delta Plain (BDP) groundwater. Measured As concentrations in groundwaters of BDP and CNP showed large variations, with mean As concentrations of 221 μg/L (range: 1.1-476 μg/L) in Chakdaha, 60 μg/L (range: 0.30-202 μg/L) in Manikgonj, and 208 μg/L (range: 1.3-575 μg/L) in CNP groundwater. The Fe-reduction mechanism was found to be the dominant geochemical process in releasing As from sediment to groundwater in Chakdaha, West Bengal, however the Mn-reduction process was dominant in groundwaters of Manikgonj, Bangladesh. In Chianan Plain groundwater, a combination of geochemical processes (e.g., bacterial Fe-reduction, mineral precipitation and dissolution reactions) controlled release of As. Fluorescence spectral patterns of the groundwater showed low relative fluorescence intensity (RFI) of dissolved humic substances in BDP groundwater (mean: 63 and 72 QSU, Chakdaha and Manikgonj, respectively), while high RFI was observed in CNP groundwater (mean: 393 QSU). The FT-IR spectra of the extracted humic acid fractions from sediments of Chianan Plain showed a stronger aliphatic band at 2850-3000 cm−1 and a higher resolved fingerprint area (from 1700 to 900 cm−1) compared with BDP sediments. The geochemical differences between the study areas may play a crucial role in the clinical manifestation of Blackfoot disease observed only in Chianan Plain, SW Taiwan. 相似文献
926.
927.
928.
Jean Wong Min Sun Guangfu Xing Xian-hua Li Guochun Zhao Kenny Wong Fuyuan Wu 《Gondwana Research》2011,19(1):244-259
The Jiangshan–Shaoxing Fault Zone (JSFZ) in Zhejiang Province has been proposed to represent a suture between the Yangtze and Cathaysia blocks in South China. In this study, in-situ zircon U–Pb and Hf isotopic analysis and whole-rock major- and trace-element measurement of early to middle Cretaceous felsic rocks across the fault zone were conducted to constrain the nature of the fault zone. Twelve Cretaceous granitoid bodies were sampled from the NW and SE sides of the fault zone, respectively, with composition ranging from diorite to granite (SiO2 = 56.2–76.6 wt.%). These granitoids yielded U–Pb ages ranging from 135–100 Ma, with a systematic variation in zircon Hf isotopic compositions (εHf(t) = + 6.9 to –7.0 in the NW side vs. + 1.9 to ? 12.9 in the SE side). The TDM2 values for the granitoids from the NW side are 0.34 to 1.33 Ga, with two peaks at ca. 876 and 1170 Ma respectively, whereas those from the SE side are 0.70 to 1.62 Ga, with a single peak at ca. 1126 Ma. The Hf isotopic disparity for the two sides may indicate a fundamental difference in the lower crustal compositions of the Yangtze and Cathaysia blocks, supporting that the JSFZ is possibly a suture zone between the two blocks. Our results together with the available geological data suggest that the Mesoproterozoic materials are important for both the Yangtze and Cathaysia basement and the Neoproterozoic magmatic activities were important in the Yangtze Block, possibly related to the break-up of the Rodinia supercontinent, but less significant in the Cathaysia Block. This may imply that the two blocks have not completely juxtaposed in the Neoproterozoic. 相似文献
929.
François Chabaux Mathieu Granet Philippe Larqué Jean Riotte Eugeni V. Skliarov Olga Skliarova Ludmilla Alexeieva François Risacher 《Comptes Rendus Geoscience》2011,343(7):462-470
The geochemical study of springs and lake waters from the Ol’khon Region, Siberia, confirms the strong chemical variability of these water samples, more particularly regarding their salinity. Such variability does not result from a simple mixing process between surface freshwaters and deeper saline waters. The variability, observed at the scale of a few square kilometers, would preferentially result from a secondary concentration processes (evaporation and/or cryogenesis) of lake waters of variable intensity from one lake to another. The U-disequilibria data suggest that the duration of the secondary process is certainly an important parameter to be considered to account for the variable salinity of these lakes. The data indicate that the lakes, however modest in size, could be as old as several ky, confirming therefore that the lake sedimentary deposits could represent relevant paleoenvironmental recorders for the last thousands years. 相似文献
930.
Patrice Brehmer Jean Guillard Pablo I. Caballero Pinzon Pascal Bach 《Estuaries and Coasts》2011,34(4):739-744
Fish school swimming speeds is essential for ecological and management studies. The multibeam sonar in horizontal beaming
provided dynamic echo traces of mobile fish schools. We used two school swimming speed indicators: the average of a series
of instantaneous speed values, and the exploratory speed. These swimming speeds were estimated for each fish school observed
on the basis of their Euclidian position within the sonar beams. The average ISS values per school ranged from 0.15 m s−1 to 4.46 m s−1, while the ESS values per school were lower, ranging from 0.04 m s−1 to 3.77 m s−1. Multibeam sonar technology makes it possible to measure fish school swimming speeds in their natural habitat at small spatio-temporal
scales. This methodology can therefore be used to analyse in situ their movements, and has a wide range of applications in
behavioural studies and management purposes. 相似文献