全文获取类型
收费全文 | 1644篇 |
免费 | 44篇 |
国内免费 | 14篇 |
专业分类
测绘学 | 44篇 |
大气科学 | 122篇 |
地球物理 | 320篇 |
地质学 | 606篇 |
海洋学 | 122篇 |
天文学 | 344篇 |
综合类 | 3篇 |
自然地理 | 141篇 |
出版年
2021年 | 10篇 |
2020年 | 14篇 |
2019年 | 16篇 |
2018年 | 21篇 |
2017年 | 33篇 |
2016年 | 34篇 |
2015年 | 44篇 |
2014年 | 43篇 |
2013年 | 65篇 |
2012年 | 42篇 |
2011年 | 65篇 |
2010年 | 56篇 |
2009年 | 68篇 |
2008年 | 71篇 |
2007年 | 56篇 |
2006年 | 63篇 |
2005年 | 44篇 |
2004年 | 50篇 |
2003年 | 37篇 |
2002年 | 66篇 |
2001年 | 43篇 |
2000年 | 47篇 |
1999年 | 36篇 |
1998年 | 37篇 |
1997年 | 27篇 |
1996年 | 25篇 |
1995年 | 23篇 |
1994年 | 22篇 |
1993年 | 16篇 |
1992年 | 19篇 |
1990年 | 14篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 18篇 |
1986年 | 22篇 |
1985年 | 22篇 |
1984年 | 42篇 |
1983年 | 10篇 |
1982年 | 39篇 |
1981年 | 23篇 |
1980年 | 25篇 |
1979年 | 29篇 |
1978年 | 35篇 |
1977年 | 22篇 |
1976年 | 20篇 |
1975年 | 26篇 |
1974年 | 25篇 |
1973年 | 17篇 |
1972年 | 12篇 |
1971年 | 11篇 |
排序方式: 共有1702条查询结果,搜索用时 15 毫秒
71.
Policy-making in relation to sustainable development is usually at the national (or, in relation to climate change, the global)
level, yet the consumption it seeks to modify takes place at the household level. If households all ‘made ends meet’ in the
same way then the much-relied upon notion of per capita consumption would be valid and we could rely on ‘top-down’ modelling
to guide policy. Cultural Theory, however, predicts that there are five socially viable ways of making ends meet, and that
all of them will be found (in varying proportions) within any nation. This prediction has been tested on a sample of 220 British
households and shown to be well supported. Top-down modelling, it is argued, has to give way to a constructive interplay between
the reflexive policy-maker and a plurally responsive citizenry.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
72.
Woodrow B. Thompson Carol B. Griggs Norton G. Miller Robert E. Nelson Thomas K. Weddle Taylor M. Kilian 《Quaternary Research》2011,75(3):552-565
Excavations in the late-glacial Presumpscot Formation at Portland, Maine, uncovered tree remains and other terrestrial organics associated with marine invertebrate shells in a landslide deposit. Buds of Populus balsamifera (balsam poplar) occurred with twigs of Picea glauca (white spruce) in the Presumpscot clay. Tree rings in Picea logs indicate that the trees all died during winter dormancy in the same year. Ring widths show patterns of variation indicating responses to environmental changes. Fossil mosses and insects represent a variety of species and wet to dry microsites. The late-glacial environment at the site was similar to that of today's Maine coast. Radiocarbon ages of 14 tree samples are 11,907 ± 31 to 11,650 ± 50 14C yr BP. Wiggle matching of dated tree-ring segments to radiocarbon calibration data sets dates the landslide occurrence at ca. 13,520 + 95/−20 cal yr BP. Ages of shells juxtaposed with the logs are 12,850 ± 65 14C yr BP (Mytilus edulis) and 12,800 ± 55 14C yr BP (Balanus sp.), indicating a marine reservoir age of about 1000 yr. Using this value to correct previously published radiocarbon ages reduces the discrepancy between the Maine deglaciation chronology and the varve-based chronology elsewhere in New England. 相似文献
73.
A total of 268 thermal spring samples were analyzed for total soluble As using reduced molybdenum-blue; 27 of these samples were also analyzed for total Sb using flame atomic absorption spectrometry. At Yellowstone the atomic ratio is nearly constant among neutral-alkaline springs with Cl > 100 mg L?1, and within restricted geographic areas, indicating no differential effects of adiabatic vs. conductive cooling on arsenic. The ratio increases with silica and decreases with decreasing ; the latter relationship is best exemplified for springs along the extensively sampled SE-NW trend within the Lone Star-Upper-Midway Basin region. The relationship between and at Yellowstone suggests a possible rock leaching rather than magmatic origin for much of the Park's total As flux. Condensed vapor springs are low in both As and Cl. Very high ratios ( > 1000) are associated exclusively with highly diluted (Cl < 100 mg L?1) mixed springs in the Norris and Shoshone Basins and in the Upper White Creek and Firehole Lake areas of Lower Basin. The high ratios are associated with acidity and/or oxygen and iron; they indicate precipitation of As following massive dilution of the Asbearing high-Cl parent water.Yellowstone Sb ranged from 0.009 at Mammoth to 0.166 mg L?1 at Joseph's Coat Spring. Within basins, the ratio increases as the ratio decreases, in marked contrast to As. Mixed springs also have elevated ratios. White (1967) and Weissberg (1969) previously reported stibnite (Sb2S3), but not orpiment (As2S3), precipitating in the near surface zone of alkaline geothermal systems. 相似文献
74.
The quantitative significance of organic matter degradation in bringing about the early diagenetic mobility of anthropogenic trace metals (Cu, Zn, Pb) is assessed specifically in relation to the use of estuarine sediments as historical records of pollution. A 1,500 mm salt-marsh sediment depth profile from Tites Point, Severn Estuary, England, was sampled at 10-mm intervals. Organic carbon determinations were carried out by a wet oxidation technique, and ‘organic fraction’ metals were separated by sequential leaching. Results demonstrated that organic phase metals are quantitatively significant in Severn Estuary sediments, particularly Cu and Zn (Cu>Zn), and that metals are probably released from this fraction during early diagenesis. The degree of release, and the apparent loss of the released trace metals from the sediment, would suggest that the use of estuarine sediments as historical records of pollution requires qualification. 相似文献
75.
It is suggested that Bouvet Island is the surface manifestation of a mantle plume which has resulted in the creation of a chain of seamounts in the South Atlantic and a general shoaling of the region.The strike of two newly defined large fracture zones borth and south of the Bouvet Island pedestal have been utilized to determine a pole of rotation at 12.5°S, 12.5°W for the Africa-Antarctica motion. A pole at 75°S, 13°E has been calculated for the South America-Antarctica motion. At the triple junction the South America-Africa relative motion is 3.3 cm yr-1 (whole rate) at 075°. The Africa-Antarctica motion is 1.7 cm yr-1 at 065° and the South America-Antarctica motion is 1.6 cm yr-1 at 085. 相似文献
76.
Chung-Lin SHIE Long S. CHIU Robert ADLER Eric NELKIN I-I LIN Pingping XIE Feng-Chin WANG R. CHOKNGAMWONG William OLSON D. Allen CHU 《大气科学进展》2009,26(6):1071-1080
Accurate sea surface flux measurements are crucial for
understanding the global water and energy cycles. The oceanic
evaporation, which is a major component of the global oceanic fresh
water flux, is useful for predicting oceanic circulation and
transport. The global Goddard Satellite-based Surface Turbulent
Fluxes Version-2 (GSSTF2; July 1987--December 2000) dateset that was
officially released in 2001 has been widely used by scientific
community for global energy and water cycle research, and regional
and short period data analyses. We have recently been funded by NASA
to resume processing the GSSTF dataset with an objective of
continually producing a uniform dataset of sea surface turbulent
fluxes, derived from remote sensing data. The dataset is to be
reprocessed and brought up-to-date (GSSTF2b) using improved input
datasets such as a recently upgraded NCEP/DOE sea surface
temperature reanalysis, and an upgraded surface wind and microwave
brightness temperature V6 dataset (Version 6) from the Special
Sensor Microwave Imager (SSM/I) produced by Remote Sensing Systems
(RSS). A second new product (GSSTF3) is further proposed with a
finer temporal (12-h) and spatial (0.25ox0.25o)
resolution. GSSTF2b (July 1987--December 2008) and GSSTF3 (July
1999--December 2009) will be released for the research community to
use by late 2009 and early 2011, respectively. 相似文献
77.
C.A. Lindemer N.G. Plant J.A. Puleo D.M. Thompson T.V. Wamsley 《Coastal Engineering》2010,57(11-12):985-995
Tropical cyclones that enter or form in the Gulf of Mexico generate storm surge and large waves that impact low-lying coastlines along the Gulf Coast. The Chandeleur Islands, located 161 km east of New Orleans, Louisiana, have endured numerous hurricanes that have passed nearby. Hurricane Katrina (landfall near Waveland MS, 29 Aug 2005) caused dramatic changes to the island elevation and shape. In this paper the predictability of hurricane-induced barrier island erosion and accretion is evaluated using a coupled hydrodynamic and morphodynamic model known as XBeach. Pre- and post-storm island topography was surveyed with an airborne lidar system. Numerical simulations utilized realistic surge and wave conditions determined from larger-scale hydrodynamic models. Simulations included model sensitivity tests with varying grid size and temporal resolutions. Model-predicted bathymetry/topography and post-storm survey data both showed similar patterns of island erosion, such as increased dissection by channels. However, the model under predicted the magnitude of erosion. Potential causes for under prediction include (1) errors in the initial conditions (the initial bathymetry/topography was measured three years prior to Katrina), (2) errors in the forcing conditions (a result of our omission of storms prior to Katrina and/or errors in Katrina storm conditions), and/or (3) physical processes that were omitted from the model (e.g., inclusion of sediment variations and bio-physical processes). 相似文献
78.
A riparian ecosystem downstream of a small dam in central Texas was instrumented for sap flow, soil moisture content, and stream level from 2001. Stable isotopes in water (D and 18O) were analysed from rainfall, stream, lake, and cored sapwood cellulose from cedar elm (Ulmus crassifolia). The isotope signature of water source to cedar elm was identified by back calculation starting with the water isotopes in cellulose, and accounting for leaf‐water evaporation and biological fractionation during cellulose synthesis. The estimated mean isotope of the source water to cedar elm was enriched above rainfall in similarity to stream water during 2002. Flow paths that may have contributed to estimated variability from regional base flow and recharge water were identified using the variably saturated HYDRUS‐2D model. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
79.
80.