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81.
Christiane Neumann Julia Beer Christian Blodau Stefan Peiffer Jan H. Fleckenstein 《水文研究》2013,27(22):3240-3253
Exchange of groundwater and lake water with typically quite different chemical composition is an important driver for biogeochemical processes at the groundwater‐lake interface, which can affect the water quality of lakes. This is of particular relevance in mine lakes where anoxic and slightly acidic groundwater mixes with oxic and acidic lake water (pH < 3). To identify links between groundwater‐lake exchange rates and acid neutralization processes in the sediments, exchange rates were quantified and related to pore‐water pH, sulfate and iron concentrations as well as sulfate reduction rates within the sediment. Seepage rates measured with seepage meters (?2.5 to 5.8 L m‐2 d‐1) were in reasonable agreement with rates inverted from modeled chloride profiles (?1.8 to 8.1 L m‐2 d‐1). Large‐scale exchange patterns were defined by the (hydro)geologic setting but superimposed by smaller scale variations caused by variability in sediment texture. Sites characterized by groundwater upwelling (flow into the lake) and sites where flow alternated between upwelling and downwelling were identified. Observed chloride profiles at the alternating sites reflected the transient flow regime. Seepage direction, as well as seepage rate, were found to influence pH, sulfate and iron profiles and the associated sulfate reduction rates. Under alternating conditions proton‐consuming processes, for example, sulfate reduction, were slowed. In the uppermost layer of the sediment (max. 5 cm), sulfate reduction rates were significantly higher at upwelling (>330 nmol g‐1 d‐1) compared to alternating sites (<220 nmol g‐1 d‐1). Although differences in sulfate reduction rates could not be explained solely by different flux rates, they were clearly related to the prevailing groundwater‐lake exchange patterns and the associated pH conditions. Our findings strongly suggest that groundwater‐lake exchange has significant effects on the biogeochemical processes that are coupled to sulfate reduction such as acidity retention and precipitation of iron sulfides. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
82.
钽钼杂多酸—碱性染料多元缔合物体系的研究 总被引:1,自引:0,他引:1
在PVA、OP或Tween-60存在下,采用平衡移动法确定了碱性染料亚甲基蓝、耐尔蓝(NB)、罗丹明B(RB)、丁基罗丹明B(BRB)、结晶紫(CV)、乙基紫(EV)与Ta的摩尔比是1:1至7:1;考察了NB(或BRB)-钽钼杂多酸缔合物的红外光谱,初步探讨了反应机理:比较了几个碱性染料-钽钼杂多酸缔合物体系的光度特性,筛选出两个摩尔吸光系数>2×10~6的分析体系,并用于合金钢和地质标样中痕量Ta的测定,方法可行。 相似文献
83.
84.
Formic and acetic acids occurred in atmospheric condensate with concentrations similar to rainwater collected in Wilmington, North Carolina, during the sampling period from June to October of 1990. Atmospheric concentrations of these acids (calculated from the condensate concentrations) were higher in continental versus maritime air masses. Concentrations of formic and acetic acids were correlated with each other in both condensate and air. Traffic was a source of acetic acid and of bisulfite to atmospheric condensate in this study. 相似文献
85.
Numerical study of the oxidation process of dimethylsulfide in the marine atmosphere 总被引:1,自引:0,他引:1
A box model, involving simple heterogeneous reaction processes associated with the production of non-sea-salt sulfate (nss-SO
4
2–
) particles, is used to investigate the oxidation processes of dimethylsulfide (DMS or CH3SCH3) in the marine atmosphere. The model is applied to chemical reactions in the atmospheric surface mixing layer, at intervals of 15 degrees latitude between 60° N and 60° S. Given that the addition reaction of the hydroxyl radical (OH) to the sulfur atom in the DMS molecule is faster at lower temperature than at higher temperature and that it is the predominant pathway for the production of methanesulfonic acid (MSA or CH3SO3H), the results can well explain both the increasing tendency of the molar ratio of MSA to nss-SO
4
2–
toward higher latitudes and the uniform distribution with latitude of sulfur dioxide (SO2). The predicted production rate of MSA increases with increasing latitude due to the elevated rate constant of the addition reaction at lower temperature. Since latitudinal distributions of OH concentration and DMS reaction rate with OH are opposite, a uniform production rate of SO2 is realized over the globe. The primary sink of DMS in unpolluted air is caused by the reaction with OH. Reaction of DMS with the nitrate radical (NO3) also reduces DMS concentration but it is less important compared with that of OH. Concentrations of SO2, MSA, and nss-SO
4
2–
are almost independent of NO
x
concentration and radiation field. If dimethylsulfoxide (DMSO or CH3S(O)CH3) is produced by the addition reaction and further converted to sulfuric acid (H2SO4) in an aqueous solution of cloud droplets, the oxidation process of DMSO might be important for the production of aerosol particles containing nss-SO
4
2–
at high latitudes. 相似文献
86.
This paper reports results and analysis of210Pb-activity measurements in 51 lake-sediment cores from 32 lakes in the four PIRLA (Paleoecological Investigations of Recent Lake Acidification) project regions (Adirondack Mountains [New York], Northern New England, Northern Florida, and the Northern Great Lakes States). General application of the Constant Rate of Supply (Constant Flux) model for210Pb dating is valid for lakes in the PIRLA study, although application of the model is equivocal in a few lakes.210Pb inventories and profiles are replicable among closely spaced cores within a lake. Specific210Pb activity in surface sediments is negatively correlated with bulk sediment accumulation rate in seepage lakes, but not in drainage lakes. Drainage lakes with lower pH have lower unsupported210Pb inventories in sediments, but the relationship does not occur in seepage lakes.210Pb profiles in only seven of the cores, all from either the Adirondacks or the northern Great Lakes states, exhibit exponential decay curves. Deviations from an exponential profile include a flattening of the profile in the top few cm or excursions of one or a few measurements away from an exponential curve.210Pb dates typically agree with other chronostratigraphic markers, most of which are subject to greater uncertainty. Several hypotheses, including sediment mixing, hydrologic regime, sediment focusing, and acidification, are proposed to explain variation of210Pb distribution among lakes and regions. Hydrologic factors exert control on unsupported210Pb inventories in PIRLA lakes, and there is a strong focusing effect in drainage lakes but a weak focusing effect in seepage lakes.This is the third of a series of papers to be published by this journal following the 20th anniversary of the first application of210Pb dating of lake sediments. Dr P. G. Appleby is guest editing this series. 相似文献
87.
G. V. Triantaphyllidis T. J. Abatzopoulos R. M. Sandaltzopoulos G. Stamou C. D. Kastritsis 《International Journal of Salt Lake Research》1993,2(1):59-68
Cysts of two parthenogeneticArtemia strains from the Kalloni and Polychnitos saltworks on Lesbos Island were evaluated for their potential use in aquaculture.
The characterizations performed were: cyst and naupliar biometrics, cyst hatching characteristics, and fatty acid profile
of instar-I nauplii. Deactivation of diapause after treatment with H2O2 and/or decapsulation were applied in order to improve cyst hatchability. The evaluation revealed that the strains studied
exhibit acceptable hatching characteristics for parthenogeneticArtemia and that the fatty acid profile of the Kalloni strain is excellent for use in culturing marine fishes and crustaceans. Statistical
analyses on cyst and naupliar biometrics showed that the two populations characterized are almost identical and very similar
to other Greek parthenogenetic strains. 相似文献
88.
The development and first tests of a novel method for the direct, sensitive, selective, and fast detection of gaseous nitric acid in air are described. The detection method is based on the laser-photolysis fragment-fluorescence (LPFF) method using 193 nm (ArF) laser light. The photolysis process yielding OH fluorescence has been thoroughly investigated. Up to now, the method has been found to be practically free of interferences. The mixing ratio for nitric acid is measured on-line with a detection limit of about 0.1 ppbv for an accumulation time of the signal of 10–15 min. A number of tests and field measurements were performed to demonstrate the feasibility and limits of the described detection method. 相似文献
89.
A. Waltrop S. K. Mitra A. I. Flossmann H. R. Pruppacher 《Journal of Atmospheric Chemistry》1991,12(1):1-17
An experimental study involving the Mainz vertical wind tunnel is described where the rate of SO2 removed from the air by freely suspended water drops was measured for SO2 concentrations in the gas phase ranging between 50 and 500 ppb, and for various H2O2 concentrations in the liquid phase. In a first set of experiments, the pH inside the SO2 absorbing drops was monitored by means of colour pH indicators added to the drops. In a second set of experiments, the amount of SO2 scavenged by the drops was determined as sulfate by an ionchromatograph after the drops had been removed from the vertical air stream of the wind tunnel after various times of exposure to SO2. The results of our experimental study were compared with the theoretical gas diffusion model of Walcek and Pruppacher which was reformulated for the case of SO2 concentrations in the ppbv(v) range for which the main resistance to diffusion lies in the gas phase surrounding the drop. Excellent agreement between experiment and theory was obtained. Encouraged by this agreement, the theory was used to investigate the rate of sulfate production inside a drop as a function of pH. The sulfate production rate, which includes transport and oxidation, was compared with the production rate based on bulk equilibrium, as cited in the literature. 相似文献
90.
William R. Stockwell 《Journal of Atmospheric Chemistry》1994,19(3):317-329
The rates and mechanisms of both gas and liquid phase reactions for the oxidation of sulfur dioxide play an important role in the production of atmospheric acids and aerosol particles. Rhodeet al. (1981) concluded that sulfate production rates were highly non-linear functions of sulfur dioxide emission rates. Their modelling study used an HO
x
termination mechanism for the HO—SO2 reaction in the gas-phase. Stockwell and Calvert (1983) determined that one of the products of the overall reaction of HO with sulfur dioxide was an HO2 radical. The National Research Council (1983) using a version of the Rhodeet al. (1981) model modified to include HO2 production from the HO—SO2 reaction concluded that sulfate production becomes much more linear with respect to reductions in sulfur dioxide emissions. However, the cause of this increased linearity was not explained by the National Research Council report. It is demonstrated that the increased linearity is due to the coupling of gas-phases and aqueous phase chemistry. The gas-phase sulfur dioxide oxidation mechanism has a very significant effect on hydrogen perodide production rates. 相似文献