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101.
102.
Jun Hao Curtis Cleveland Eelin Lim Daniel R Strongin Martin AA Schoonen 《Geochemical transactions》2006,7(1):8-9
The chemolithoautotrophic bacterium, Acidithiobacillus ferrooxidans, commonly occurs in acid mine drainage (AMD) environments where it is responsible for catalyzing the oxidation of pyrite
and concomitant development of acidic conditions. This investigation reports on the growth of this bacterial species on the
pyrite surface and in the aqueous phase at a pH close to 2 as well as the role of adsorbed lipid in preventing pyrite dissolution.
Both acid washed pyrite and acid-washed pyrite coated with lipids were used as substrates in the studies. The choice of lipid,
1,2-bis(10,12-tricosadiynoyl)-sn-Glycero-3-Phosphocholine lipid (23:2 Diyne PC), a phosphocholine lipid, was based on earlier work that showed that this lipid
inhibits the abiotic oxidation rate of pyrite. Atomic force microscopy showed that under the experimental conditions used
in this study, the lipid formed ~4–20 nm layers on the mineral surface. Surface-bound lipid greatly suppresses the oxidation
process catalyzed by A. ferrooxidans. This suppression continued for the duration of the experiments (25 days maximum). Analysis of the bacterial population on
the pyrite surface and in solution over the course of the experiments suggested that the pyrite oxidation was dependent in
large part on the fraction of bacteria bound to the pyrite surface. 相似文献
103.
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105.
T. J. Whitmore M. Brenner Z. Jiang J. H. Curtis A. M. Moore D. R. Engstrom Y. Wu 《Environmental Geology》1997,32(1):45-55
Yungui Plateau lakes in southwestern China are economically important, although few have been studied previously. Water and
sediments of 24 lakes throughout Yunnan Province were sampled in October 1994. We describe the chemical and physical characteristics
of Yunnan lakes, and address effects of regional geology and human influences on water quality and sediment type. Water quality
differs between deep Yunnan lakes of tectonic origin and shallow solution basins. Shallow lakes generally have higher nutrient
concentrations and appear to be more susceptible to riparian disturbance than deeper lakes. Shallow lakes with high macrophyte
standing crops, nevertheless, exhibit nutrient-poor waters. Principal ions Ca2+, Mg2+, and HCO3
– reflect regional carbonate geology, except in Cheng Hai, which is a sodium bicarbonate lake. Specific conductance and δ18O are positively correlated, indicating that evaporation concentrates both solutes and 18O. Large, shallow lakes in southeastern Yunnan exhibit 18O-enriched waters because of substantial evaporation, whereas small, deep lakes are 18O-depleted. Lake waters are 18O-depleted in small, shallow basins that receive substantial rainwater input relative to their small volumes. 18O enrichment in Cheng Hai suggests that a recent 5-m water-level decline in this lake was caused by increased evaporation
or diversion of freshwater inflow. Yunnan watersheds have undergone substantial deforestation, agricultural cultivation, soil
erosion, and industrialization. Limnetic nutrient concentrations indicate that human activities have affected water quality.
Organic matter content is low in sediments because of increased non-carbonate, clastic sediment yield from watersheds. Environmental
policies are needed to balance ecological contraints with economic activities that impact water quality.
Received: 1 July 1996 / Accepted: 2 October 1996 相似文献
106.
Recent decades have seen changes in the pattern of rail traffic in the United States. This article describes the development of a United States railroad map depicting current levels of traffic on all rail lines handling over five million gross tons per year. This traffic pattern is compared with the 1929 traffic levels appearing on a similiar map developed by Edward Ullman. Revenue ton-miles have nearly doubled since 1929, with most of the increases concentrated on western and southern lines. Traffic on eastern lines has increased only slightly above 1929 levels. 相似文献
107.
A paleomagnetic study of the late Middle to possibly early Late Cambrian Liberty Hills Formation in the Ellsworth Mountains, Antarctica, reveals a stable magnetization with positive fold and reversal tests. The paleopole is based on 16 sites from volcanic and sedimentary rocks and lies at lat 7.3 degrees N and long 326.3 degrees E (A95=6.0&j0;). The new paleomagnetic data support the view that the Ellsworth Mountains are part of a microplate-the Ellsworth-Whitmore Mountains crustal block-that rotated independently of the main Gondwana continental blocks during breakup. The Liberty Hills pole differs from both previous poles recovered from Cambrian rocks in the Ellsworth Mountains and from the available Gondwana reference pole data. Our pole indicates a more northerly prebreakup position for the Ellsworth Mountains than previously suggested, contradicting the overwhelming geologic evidence for a prebreakup position close to southern Africa. The reasons for this are uncertain, but we suggest that problems with the Gondwana apparent polar wander path may be important. More well constrained, early Paleozoic paleomagnetic data are required from the Ellsworth Mountains and the Gondwana continents if the data are to constrain further the Middle-Late Cambrian location of the Ellsworth-Whitmore Mountains block. 相似文献
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Organization is recognized in the forereef–deep water slope–submarine fan system of the Burdigalian-Langhian Kaplankaya Formation. A basinwards transition from a prograding shelfal reef complex, through forereef talus, deep-water slope and laterally encroaching bypass deep-water clastic system is described, although the deep-water slope makes up the bulk of the succession. Considerable thickness variations occur between the reef and deep-water clastic complexes; these are controlled by sea-floor topography, carbonate foreslope gradient and degree of mass wasting off the platform and foreslope. The vertical and lateral heterogeneity of the Kaplankaya deep-water slope system is described from a number of localities along a 40-km-long and up to 3-km-wide exposed section of the northern margin of the Miocene Adana Basin, a foreland basin setting resulting from thrust sheet loading from the north during the Tauride Orogeny. Detailed field mapping is supplemented with vertical sedimentary logs, photomosaics, palaeontological and petrological data to investigate stratal variation, diagnostic architectural elements, controls on slope progradation, differential timing of basinward encroachment of the reefal complex and lateral onlap of the deep-water clastic system onto the slope. Three-dimensional models are presented showing the vertical and lateral facies associations in different parts of the deep-water slope system, and provide a basis for architectural prediction of geometry and relative position in such environments. 相似文献
110.