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381.
Wilson Yetoh Fantong Hiroshi Satake Festus T. Aka Samuel N. Ayonghe Kazuyoshi Asai Ajit K. Mandal Andrew A. Ako 《Environmental Earth Sciences》2010,60(1):107-120
Unplanned exploitation of groundwater constitutes emerging water-related threats to MayoTsanaga River Basin. Shallow groundwater
from crystalline and detrital sediment aquifers, together with rain, dams, springs, and rivers were chemically and isotopically
investigated to appraise its evolution, recharge source and mechanisms, flow direction, and age which were used to evaluate
the groundwater susceptibility to contamination and the basin’s stage of salinization. The groundwater which is Ca–Na–HCO3 type is a chemically evolved equivalent of surface waters and rain water with Ca–Mg–Cl–SO4 chemistry. The monsoon rain recharged the groundwater preferentially at an average rate of 74 mm/year, while surface waters
recharge upon evaporation. Altitude effect of rain and springs show a similar variation of −0.4‰ for δ18O/100 m, but the springs which were recharged at 452, 679, and 773 m asl show enrichment of δ18O through evaporation by 0.8‰ corresponding to 3% of water loss during recharge. The groundwater which shows both local and
regional flow regimes gets older towards the basins` margin with coeval enrichment in F− and depletion in NO3
−. Incidentally, younger groundwaters are susceptible to anthropogenic contamination and older groundwaters are sinks of lithologenic
fluoride. The basins salinization is still at an early stage. 相似文献
382.
Samuel Nicolay Georges Mabille Xavier Fettweis Michel Erpicum 《Climate Dynamics》2009,33(7-8):1117-1129
A wavelet-based methodology is applied to relevant climatic indices and air temperature records and allow to detect the existence of unexpected cycles. The scale spectrum shows the presence of two cycles of about 30 and 43 months, respectively, in the air–temperature time series, in addition to the well-known cycles of 1 day and 1 year. The two cycles do not affect the globe uniformly: some regions seem to be more influenced by the period of 30 months (e.g. Europe), while other areas are affected by the period of 43 months (e.g. North-West of the USA). Similar cycles are found in the indices and the regions influenced by these indices: the NAO index and the Western Europe display a cycle of 30 months, while the cycle of 43 months can be found in the ENSO index and in regions where it is known to have an impact. 相似文献
383.
Indigenous knowledge related to climate variability and change: insights from droughts in semi-arid areas of former Makueni District,Kenya 总被引:1,自引:1,他引:0
Chinwe Ifejika Speranza Boniface Kiteme Peter Ambenje Urs Wiesmann Samuel Makali 《Climatic change》2010,100(2):295-315
This article describes the indigenous knowledge (IK) that agro-pastoralists in larger Makueni District, Kenya hold and how
they use it to monitor, mitigate and adapt to drought. It examines ways of integrating IK into formal monitoring, how to enhance
its value and acceptability. Data was collected through target interviews, group discussions and questionnaires covering 127
households in eight villages. Daily rainfall data from 1961–2003 were analysed. Results show that agro-pastoralists hold IK
on indicators of rainfall variability; they believe in IK efficacy and they rely on them. Because agro-pastoralists consult
additional sources, the authors interpret that IK forms a basic knowledge frame within which agro-pastoralists position and
interpret meteorological forecasts. Only a few agro-pastoralists adapt their practices in anticipation of IK-based forecasts
partly due to the conditioning of the actors to the high rainfall variability characteristic of the area and partly due to
lack of resources. Non-drought factors such as poverty, inadequate resources and lack of preparedness expose agro-pastoralists
to drought impacts and limit their adaptive capacity. These factors need to be understood and effectively addressed to increase
agro-pastoralists’ decision options and the influence of IK-based forecasts on their decision-making patterns. The limited
intergenerational transfer of IK currently threatens its existence in the longer term. One way to ensure its continued existence
and use is to integrate IK into the education curriculum and to link IK with formal climate change research through the participation
of the local people. However, further studies are necessary to address the reliability and validity of the identified IK indicators
of climate variability and change. 相似文献
384.
385.
Peter R. Gent Stephen G. Yeager Richard B. Neale Samuel Levis David A. Bailey 《Climate Dynamics》2010,34(6):819-833
A decadal climate projection between 1980 and 2030 using a nominal 0.5° resolution in the atmosphere and land components has
been performed using the Community Climate System Model, version 3.5. The mean climate is compared to a companion simulation
using a nominal 2° resolution in the atmosphere and land components. The increased atmosphere resolution has several benefits,
and produces a significantly better mean climate. The maximum sea surface temperature biases in the major upwelling regions,
including the West Coast of the USA, are reduced by more than 60%. Precipitation patterns are improved in the summer Asian
monsoon, mostly due to the better resolved orography, and in the eastern tropical Pacific Ocean south of the equator. The
improved precipitation patterns lead to better river flows in many rivers worldwide. The atmospheric circulation in the Arctic
also improves, which leads to a better regional sea ice thickness distribution in the Arctic Ocean. 相似文献
386.
Huntington Beach, California, one of the most popular surfing spots in the world, is plagued by sporadic, elevated levels of fecal bacteria. To assist with pollution source identification, we analyzed antibiotic resistance patterns (ARPs) of enterococci from four known sources (bird feces, urban runoff, coastal marsh sediment and sewage effluent from local sanitation district) and one unknown source (seawater) using seven antibiotics at four concentrations each. Of 2491 enterococci tested, all were resistant to at least one antibiotic at some level. Discriminant analysis indicated that the average correct classification rates for bird feces and urban runoff sources were above 80%. Sewage effluent contained mixed fecal sources. Sixty-four percent of the sewage isolates classified with the sewage category, while the other 35% of isolates were assigned evenly across the other three categories. When enterococci isolated from the seawater were classified using the known ARP database, it was evident that bird feces were the source of surf zone contamination on some days while the coastal salt marsh and sewage plume may have impacted the surf zone water quality to various degrees during other times. 相似文献
387.
Organic ligands affect the sorption and mobility of radionuclides in soils. Batch desorption experiments on goethite particles reveal the extent of uranyl desorption and hence bioavailability with different organic acids. The desorptive strength increases in the following order: background electrolyte < Na-alginate < desferrioxamine B (DFO-B) < oxalate. The sequence is consistent with decreasing molecular size and mass from alginate via DFO-B to oxalate. The concomitant Fe release in the desorption experiments indicates that desorption from goethite and not dissolution of goethite governs the mobility of adsorbed U(VI). A compilation of DFO-B surface excesses on goethite from our experiments together with literature values indicate that DFO-B adsorbs at a constant ∼3% to the goethite surface. It is surprising that such a small fraction suffices to account for the considerable uranyl desorption and thus remobilization of a radionuclide into solution. Oxalate displays higher surface concentrations but still lower than the determined uranyl surface excess. It follows that based on the high U(VI) stability constants, both organic ligands induce the desorption of uranyl species by increasing the chemical affinity of the aqueous phase. In the case of alginate, desorption of uranyl is weak and adsorbed alginate hampers any considerable detachment of U(VI) in the presence of the more potent ligands, DFO-B and oxalate. This inhibition is based on biosorption and in this respect polysaccharides in soils may retard and even halt the advance of actinides through the soil column. This hypothesis calls for further studies into the interaction of siderophores and polysaccharides with soil adsorbents and their role in the mobilization of contaminant metals. 相似文献
388.
Saralees Nadarajah Samuel Kotz 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(3):164-170
Motivated by environmental applications, we derive the exact distributions of R = X+Y, P = X
Y and W = X/(X+Y) and the corresponding moment properties when X and Y follow Downton’s bivariate exponential distribution. The expressions turn out to involve several special functions. For practical
purposes, we also provide extensive tabulations of the percentage points associated with the distributions. 相似文献
389.
Bellie Sivakumar Wesley W. Wallender William R. Horwath Jeffrey P. Mitchell Samuel E. Prentice Brian A. Joyce 《水文研究》2006,20(8):1723-1736
This study investigates the dynamic nature of rainfall observed at the Sustainable Agriculture Farming Systems (SAFS) site in California's Sacramento Valley, which was established to study the benefits of winter cover cropping in Mediterranean irrigated‐arid systems. Rainfall data of four different temporal scales (i.e. daily, weekly, biweekly, and monthly) are analysed to determine the dynamic nature of precipitation in time. In an arid climate with seasonal precipitation this has large implications for land and water management, both in the short term and in the long term. A nonlinear dynamic technique (correlation dimension method) that uses the phase‐space reconstruction and dimension concepts is employed. Bearing in mind the possible effects of the presence of zeros (i.e. no rain) on the outcomes of this analysis, an attempt is also made to compare the dynamic nature of all‐year rainfall and winter rainfall. Analysis of 15 years of data suggests that rainfall dynamics at this site are dominated by a large number of variables, regardless of the scales and seasons studied. The dimension results also suggest that: (1) rainfall dynamics at coarser resolutions are more irregular than that at finer resolutions; (2) winter rainfall has a higher variability than all‐year rainfall. These results are indeed useful to gain information about the complexity of the rainfall process at this site with respect to (temporal) scales and seasons and, hence, the appropriate model (high‐dimensional) type. However, in view of the potential effects of certain rainfall data characteristics (e.g. zeros, measurement errors, scale effects) on the correlation dimension analysis, the discussion also emphasizes the need for further verification, and possibly confirmation, of these results. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
390.
Recent advances in U–Pb geochronology allow unprecedented levels of precision in the determination of geological ages. However, increased precision has also illuminated the importance of understanding subtle sources of open-system behavior such as Pb-loss, inheritance, intermediate daughter product disequilibria, and the accuracy of the model assumptions for initial Pb. Deconvolution of these effects allows a much richer understanding of the power and limitations of U–Pb geochronology and thermochronology. In this study, we report high-precision ID-TIMS U–Pb data from zircon, baddelleyite, titanite and apatite from the McClure Mountain syenite, from which the 40Ar/39Ar hornblende standard MMhb is derived. We find that excess 206Pb in zircon due to inclusions of high-Th minerals and elevated Th/U in titanite and apatite jeopardize the utility of the 238U–206Pb system in this rock. Strongly air-abraded zircons give dates that are younger than chemical-abraded zircons, which yield a statistically robust 207Pb/235U date of 523.98±0.12 Ma that is interpreted as the crystallization age. We explore the best method of Pbc correction in titanite and apatite by analyzing the U–Pb isotopes of K-feldspar and using 2-D and 3-D regression methods—the latter of which yields the best results in each case. However, the calculated compositions of Pbc for titanite, apatite and K-feldspar are different, implying that using a single Pbc correction for multiple U–Pb thermochronometers may be inaccurate. The U–Pb thermochronological results are used to predict a closure time for Ar in hornblende of 522.98±1.00 Ma. Widely cited K–Ar and 40Ar/39Ar dates overlap with the U–Pb date, and relatively large errors make it impossible to verify whether U–Pb dates are systematically ≤1% older than K–Ar and 40Ar/39Ar dates. 相似文献