全文获取类型
收费全文 | 918篇 |
免费 | 72篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 29篇 |
大气科学 | 63篇 |
地球物理 | 187篇 |
地质学 | 365篇 |
海洋学 | 83篇 |
天文学 | 133篇 |
综合类 | 1篇 |
自然地理 | 137篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 25篇 |
2020年 | 30篇 |
2019年 | 27篇 |
2018年 | 37篇 |
2017年 | 50篇 |
2016年 | 46篇 |
2015年 | 33篇 |
2014年 | 41篇 |
2013年 | 51篇 |
2012年 | 47篇 |
2011年 | 59篇 |
2010年 | 56篇 |
2009年 | 92篇 |
2008年 | 61篇 |
2007年 | 52篇 |
2006年 | 38篇 |
2005年 | 21篇 |
2004年 | 32篇 |
2003年 | 31篇 |
2002年 | 19篇 |
2001年 | 16篇 |
2000年 | 15篇 |
1999年 | 4篇 |
1998年 | 12篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1983年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1900年 | 2篇 |
1899年 | 2篇 |
1892年 | 6篇 |
1880年 | 1篇 |
1877年 | 1篇 |
排序方式: 共有998条查询结果,搜索用时 15 毫秒
51.
Enrique Macpherson Bertrand Richer de Forges Kareen Schnabel Sarah Samadi Marie-Catherine Boisselier Antoni Garcia-Rubies 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(2):228-238
We analyzed the distribution patterns of the galatheid squat lobsters (Crustacea, Decapoda, Galatheidae) of the Pacific Ocean. We used the presence/absence data of 402 species along the continental slope and continental rise (200–2000 m) obtained from 54 cruises carried out in areas around the Philippines, Indonesia, Solomon, Vanuatu, New Caledonia, Fiji, Tonga, Wallis and Futuna and French Polynesia. The total number of stations was ca. 3200. We also used published data from other expeditions carried out in the Pacific waters, and from an exhaustive search of ca. 600 papers on the taxonomy and biogeography of Pacific species. We studied the existence of biogeographic provinces using multivariate analyses, and present data on latitudinal and longitudinal patterns of species richness, rate of endemism and the relationship between body sizes with the size of the geographic ranges. Latitudinal species richness along the Western and Eastern Pacific exhibited an increase from higher latitudes towards the Equator. Longitudinal species richness decreased considerably from the Western to the Central Pacific. Size frequency distribution for body size was strongly shifted toward small sizes and endemic species were significantly smaller than non-endemics. This study concludes that a clear separation exists between the moderately poor galatheid fauna of the Eastern Pacific and the rich Western and Central Pacific faunas. Our results also show that the highest numbers of squat lobsters are found in the Coral Sea (Solomon-Vanuatu-New Caledonia islands) and Indo-Malay-Philippines archipelago (IMPA). The distribution of endemism along the Pacific Ocean indicates that there are several major centres of diversity, e.g. Coral Sea, IMPA, New Zealand and French Polynesia. The high proportion of endemism in these areas suggests that they have evolved independently. 相似文献
52.
Jayant A. Sathaye Larry L. Dale Peter H. Larsen Gary A. Fitts Kevin Koy Sarah M. Lewis André Frossard Pereira de Lucena 《Global Environmental Change》2013,23(2):499-511
Despite a clear need, little research has been carried out at the regional-level to quantify potential climate-related impacts to electricity production and delivery systems. This paper introduces a bottom-up study of climate change impacts on California's energy infrastructure, including high temperature effects on power plant capacity, transmission lines, substation capacity, and peak electricity demand. End-of-century impacts were projected using the A2 and B1 Intergovernmental Panel on Climate Change emission scenarios. The study quantifies the effect of high ambient temperatures on electricity generation, the capacity of substations and transmission lines, and the demand for peak power for a set of climate scenarios. Based on these scenarios, atmospheric warming and associated peak demand increases would necessitate up to 38% of additional peak generation capacity and up to 31% additional transmission capacity, assuming current infrastructure. These findings, although based on a limited number of scenarios, suggest that additional funding could be put to good use by supporting R&D into next generation cooling equipment technologies, diversifying the power generation mix without compromising the system's operational flexibility, and designing effective demand side management programs. 相似文献
53.
The Combined EMT/VES Geophysical Method for Siting Boreholes 总被引:2,自引:0,他引:2
54.
G2 theory calculations were performed on [H3SiO4]?, H4SiO4, [H3AlO4]2?, [H4AlO4]?, and [H5AlO4]. Molecular structures, atomic charges, and infrared spectra at the HF/6-31G* and MP2/6-31G* levels are compared. The influence of polarization and diffuse functions on the structure of [H3SiO4]? is also examined. Basis set and electron correlation effects on potential energies are assessed by comparing various levels of theory. Proton affinities of these gas-phase molecules and related mineral surface species are predicted based on corrections for cluster-size effects. 相似文献
55.
56.
57.
58.
T. Wang H. Guo D. R. Blake Y. H. Kwok I. J. Simpson Y. S. Li 《Journal of Atmospheric Chemistry》2005,52(3):295-317
We present a 16-month record of ozone (O3), carbon monoxide (CO), total reactive nitrogen (NOy), sulphur dioxide (SO2), methane (CH4), C2 – C8 non-methane hydrocarbons (NMHCs), C1 – C2 halocarbons, and dimethyl sulfide (DMS) measured at a southern China coastal site. The study aimed to establish/update seasonal
profiles of chemically active trace gases and pollution tracers in subtropical Asia and to characterize the composition of
the `background' atmosphere over the South China Sea (SCS) and of pollution outflow from the industrialized Pearl River Delta
(PRD) region and southern China. Most of the measured trace gases of anthropogenic origin exhibited a winter maximum and a
summer minimum, while O3 showed a maximum in autumn which is in contrast to the seasonal behavior of O3 in rural eastern China and in many mid-latitude remote locations in the western Pacific. The data were segregated into two
groups representing the SCS background air and the outflow of regional continental pollution (PRD plus southern China), based
on CO mixing ratios and meteorological conditions. NMHCs and halocarbon data were further analyzed to examine the relationships
between their variability and atmospheric lifetime and to elucidate the extent of atmospheric processing in the sampled air
parcels. The trace gas variability (S) versus lifetime (τ) relationship, defined by the power law, Slnx = Aτ− b, (where X is the trace gas mixing ratio) gives a fit parameter A of 1.39 and exponent b of 0.42 for SCS air, and A of 2.86 and b of 0.31 for the regional continental air masses. An examination of ln[n-butane]/ln[ethane] versus ln[propane]/ln[ethane] indicates that their relative abundance was dominated by mixing as opposed
to photochemistry in both SCS and regional outflow air masses. The very low ratios of ethyne/CO, propane/ethane and toluene/benzene
suggest that the SCS air mass has undergone intense atmospheric processing since these gases were released into the atmosphere.
Compared to the results from other polluted rural sites and from urban areas, the large values of these species in the outflow
of PRD/southern China suggest source(s) emitting higher levels of ethyne, benzene, and toluene, relative to light alkanes.
These chemical characteristics could be unique indicators of anthropogenic emissions from southern China. 相似文献
59.
Francine M. G. McCarthy John H. McAndrews Steve M. Blasco Sarah H. Tiffin 《Journal of Paleolimnology》2007,37(3):453-470
High-resolution seismic reflection profile data show that the modern sediment cover (over the last 150 years) in Georgian
Bay is thin and spatially discontinuous. Sediments rich in ragweed pollen, largely derived from siltation linked to land clearing
and European settlement, form a thin, discontinuous veneer on the lakebed. Much of the lakebed consists of exposed sediments
deposited during the late glacial or early postglacial. Accumulation rates of modern sediments range from < 0 mm/year (net
erosion) to ∼3.2 mm/year, often within a few hundred metres spatially. These rates are much lower than those reported for
the main basin of Lake Huron and the other Great Lakes, and are attributed to the low sediment supply. Only a few small rivers
flow into Georgian Bay, and most of the basin is surrounded by bedrock of Precambrian gneiss and granite to the east, and
Silurian dolostone, limestone and shale to the west. Thick deposits of Pleistocene drift, found on the Georgian Bay shoreline
only between Meaford and Port Severn, are the main sediment source for the entire basin at present. Holocene to modern sediments
are even absent from some deep basins of Georgian Bay. These findings have implications for the ultimate fate of anthropogenic
contaminants in Georgian Bay. While microfossil assemblages in the ragweed-rich sediments record increased eutrophication
over the last 150 years, most pollutants generated in the Georgian Bay catchment are not accumulating on the lakebed and are
probably exported from the Bay. 相似文献
60.
K. M. Tomkins G. S. Humphreys M. T. Wilkinson D. Fink P. P. Hesse S. H. Doerr R. A. Shakesby P. J. Wallbrink W. H. Blake 《地球表面变化过程与地形》2007,32(7):1013-1031
Short‐term (contemporary) and long‐term denudation rates were determined for the Blue Mountains Plateau in the western Sydney Basin, Australia, to explore the role of extreme events (wildfires and catastrophic floods) in landscape denudation along a passive plate margin. Contemporary denudation rates were reconstructed using 40 years of river sediment load data from the Nattai catchment in the south‐west of the basin, combined with an analysis of hillslope erosion following recent wildfires. Long‐term denudation rates (10 kyr–10 Myr) were determined from terrestrial cosmogenic nuclides, apatite fission track thermochronology and post‐basalt flow valley incision. Contemporary denudation rates average several times lower than the long‐term average (5·5 ± 4 mm kyr?1 versus 21·5 ± 7 mm kyr?1). Erosion of sediment following wildfires accounts for only a small proportion (5%) of the contemporary rate. Most post‐fire sediment is stored on the lower slopes and valley floor, with the amount transported to the river network dependent on rainfall–run‐off conditions within the first few years following the fire. Historical catastrophic floods account for a much larger proportion (35%) of the contemporary erosion rate, and highlight the importance of these events in reworking stored material. Evidence for palaeofloods much larger than those experienced over the past 200 years suggests even greater sediment export potential. Mass movement on hillslopes along valleys incised into softer lithology appears to be a dominant erosion process that supplies substantial volumes of material to the valley floor. It is possible that a combination of infrequent mass movement events and high fluvial discharge could account for a significant proportion of the discrepancy between the contemporary and long‐term denudation rates. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献