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991.
992.
丹宁棉分离富集—发射光谱法同时测定地质样品中微量铌钽锆铪 总被引:1,自引:1,他引:1
采用丹宁棉对地质样品溶液中的铌、钽、锆、铪进行分离富集,将写信后的丹宁棉在600℃灼烧30min,灰分用发射光谱法同时测定四元素。检出限与通常的发射光谱法相比降低约2个数量级,经国家级标准物质检验,结果与标准值相符,精密度试验,各元素的RSD(n=20)为2.6%-7.9%。 相似文献
993.
The strong motion displacement records available during an earthquake can be treated as the response of the earth as the a
structural system to unknown forces acting at unknown locations. Thus, if the part of the earth participating in ground motion
is modelled as a known finite elastic medium, one can attempt to model the source location and forces generated during an
earthquake as an inverse problem in structural dynamics. Based on this analogy, a simple model for the basic earthquake source
is proposed. The unknown source is assumed to be a sequence of impulses acting at locations yet to be found. These unknown
impulses and their locations are found using the normal mode expansion along with a minimization of mean square error. The
medium is assumed to be finite, elastic, homogeneous, layered and horizontal with a specific set of boundary conditions. Detailed
results are obtained for Uttarkashi earthquake. The impulse locations exhibit a linear structure closely associated with the
causative fault. The results obtained are shown to be in good agreement with reported values. The proposed engineering model
is then used to simulate the acceleration time histories at a few recording stations. The earthquake source in terms of a
sequence of impulses acting at different locations is applied on a 2D finite elastic medium and acceleration time histories
are found using finite element methods. The synthetic accelerations obtained are in close match with the recorded accelerations. 相似文献
994.
Geochemical processes controlling silica concentrations in groundwaters of the Salado River drainage basin, Argentina 总被引:1,自引:0,他引:1
Chemical analyses of dissolved silica in the shallow groundwater of the lower part of the Salado River drainage basin indicate that silica values averaged 60 ppm. The groundwaters are oversaturated in relation to quartz, Na-plagioclase, K-feldspar, and the weathering of quartz and aluminosilicates appear to have little control on silica concentrations in solution. Groundwater is undersaturated with respect to amorphous silica present in the loessic sediments, and these sediments are specially important in the control of the groundwater composition. The sources of amorphous silica are volcanic glass shards and biogenic silica derived from plant (silicophytoliths, diatom frustules) or animal remains (sponge spicules) also present in the Pampean loess. Silicophytoliths and diatoms have also been reported in A soil horizon samples. The dissolution of amorphous silica most likely controls the high dissolved silica concentrations in groundwater. 相似文献
995.
996.
D. W. Arlander D. Brüning U. Schmidt D. H. Ehhalt 《Journal of Atmospheric Chemistry》1995,22(3):243-249
A series of 72 measurements of the acetaldehyde (CH3CHO) mixing ratio were made in the lower troposphere during TROPOZ II. These measurements are the first ever made of the background level of this trace gas in the free troposphere. The data show a vertical decrease of the CH3CHO mixing ratio with increasing altitude and indicate higher CH3CHO concentrations in the Northern Hemisphere — in general agreement with a model-derived average CH3CHO distribution. Deviations of the observed CH3CHO mixing ratios from the modelled mean distribution are correlated with similar deviations in the corresponding HCHO mixing ratios. 相似文献
997.
Snow drift transport may cause avalanches on the roads during the periods of snowfall and strong wind. To better understand the factors influencing transport we have developed a theoretical model. This model is based on the boundary layer theory, where the particle mass conservation is considered. Assuming that the saturation is reached, the concentration profile can be represented by a negative exponential law. By means of this analysis, the influence of particle characteristics is explored through the roles of threshold friction velocity and fall velocity. Using fluid mechanics laws, an analysis of the concentration profile resulting from the effect of the wind on a particle bed was also developed. For several velocities of flow and for different kinds of particles an experimental determination of the concentration profile was achieved. We used a laser visualisation and image processing technique to carry out these experiments. The obtained results fit with the values predicted by the theoretical model. 相似文献
998.
Atmospheric concentrations and deposition of heavy metals over the North Sea: A literature review 总被引:2,自引:0,他引:2
A literature review of the atmospheric concentration rates and dry and wet deposition fluxes of particulate Cd, Cr, Cu, Pb and Zn to the North Sea and adjacent areas is given. The results of direct measurements of dry and wet deposition fluxes are compared to indirect estimates and to modelling values. This work points out the large uncertainties in results of different studies on atmospheric input of trace elements into the North Sea. The current knowledge about the dependence of the deposition velocity upon the particle size and about the processes controlling wet deposition fluxes, and the quality and completeness of the emission data are still inadequate for describing the environmental cycle and impact of heavy metals in the North Sea. 相似文献
999.
New laboratory measurements of NO2 absorption cross-sections have been performed between 300 and 500 nm at ambient temperature with improved experimental conditions: low gas pressures, long absorption paths, suitable absorbance values, narrow spectral bandwidths. The data, stored at 0.01 nm intervals, have been compared to those of the more recent studies and some reasons of disagreement are discussed.In the photolysis region below 400 nm, our absorption cross-sections are larger than those previously published, suggesting that the photodissociation coefficient calculated from the current data sets is underestimated. In the structured region of the spectrum above 400 nm, improvement of the resolution gives more precise values useful for optical measurements in atmosphere.Unité de Recherche Associée au CNRS. 相似文献
1000.
报道了P507-pMBP溶剂浸渍滤纸(SIFP)的制备及其吸附性质;提出含微量Zr、Hf的岩矿样品经碱熔分解后用强阳离子交换树脂静态吸附分离大量干扰元素,再用P507-PMBPSIFP富集Zr与Hf,然后用XRF光谱直接测定SIFP上Zr、Hf的方法;考察了阳离子交换树脂分离干扰元素的条件,以及在残留干扰元素存在下P507-PMBPSIFP对Zr、Hf的富集情况等;对分析误差的来源,样品分析的精密度,SIFP样片的稳定性等也进行了讨论;所拟方法经用GSR及GSS系列部分地质标准样品分析验证,其结果与推荐值符合。 相似文献