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We compared the distributions of 59 diatom species in surface sediments of 25 Costa Rican lakes with 21 environmental variables using canonical correspondence analysis (CCA). The distribution of taxa was related to the chemical and physical characteristics of the lakes. The most influential chemical variables were cation concentrations (especially magnesium) and related variables such as water hardness, pH, and temperature. Lake area and lake depth were among the most important physical variables.A number of taxa were identified as potential environmental indicators. The diatoms Brachysira serians var. brachysira and Frustulia rhomboides seem to be associated with low values of alkalinity, hardness, Ca, Mg, and SiO2. Cymbella minuta var. silesiaca is associated with low to moderate values of alkalinity, hardness, Ca, and Mg. Nitzschia cf. amphibia may be an indicator of moderate-to-high concentrations of Mg. Pinnularia braunii var. amphicephala seems to prefer low values of hardness, Ca, Mg, and SiO2.In many closed lakes, these environmental variables (Mg/Ca/hardness/alkalinity) increase with effective evaporation. Consequently, these diatoms may be indirectly tracking P:E ratios. Results from this initial, small data set indicate the potential of diatoms for inferring lake paleochemistry, and perhaps P:E ratios, in Costa Rica. 相似文献
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地震现场的通讯环境极为复杂,公共的网络接入模式在地震时往往很难保证现场与后方指挥中心之间的实时文件传输和视频通信。本文根据地震带来的破坏程度的不同,针对地震现场的具体通信情况,以及地震应急工作中现场网络通信的需求,提出多项确保地震现场局域网络和后方指挥中心之间通信畅通的解决方案。 相似文献
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本文介绍一种利用FY-4A成像仪遥感数据和全球预报系统(GFS)资料估算全天空地表长波辐射通量的反演方法。该方法通过辐射传输模拟和统计回归计算建立云天地表下行长波辐射通量的反演模式,并基于GFS资料处理云覆盖地区的地表上、下行长波辐射通量。这种全天空状况下两种通量的反演结合了FY-4A晴空地表长波辐射业务产品和本文反演模式处理的云天地表上、下行长波辐射通量。2018年9月1日的处理结果与Aqua/CERES同类产品相对比,精度为:RMSE=20.52 W·m^-2,R=0.9481,Bias=3.3 W·m^-2(夜间地表下行辐射通量对比);RMSE=25.58 W·m^-2,R=0.9096,Bias=5.4 W·m^-2(白天地表下行辐射通量对比);RMSE=10.97 W·m^-2,R=0.9762,Bias=-3.3 W·m^-2(夜间地表上行辐射通量对比);RMSE=19.97 W·m^-2,R=0.9283,Bias=5.0 W·m^-2(白天地表上行辐射通量对比)。这些结果表明本文发展的方法能够反演出精度较好的云天上下行长波辐射通量资料,为今后利用FY-4后续星处理生成全天空状况下的地表长波辐射通量产品奠定了理论基础。 相似文献
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The rates and altitudes for the dissociation of atmospheric constituents of Titan are calculated for solar UV, solar wind protons, interplanetary electrons, Saturn magnetospheric particles, and cosmic rays. The resulting integrated synthesis rates of organic products range from 102–103 g cm?2 over 4.5 × 109 years for high-energy particle sources to 1.3 × 104 g cm?2 for UV at , and to 5.0 × 105 g cm?2 if (acting primarily on C2H2, C2H4, and C4H2) is included. The production rate curves show no localized maxima corresponding to observed altitudes of Titan's hazes and clouds. For simple to moderately complex organic gases in the Titanian atmosphere, condensation occurs below the top of the main cloud deck at 2825 km. Such condensates comprise the principal cloud mass, with molecules of greater complexity condensing at higher altitudes. The scattering optical depths of the condensates of molecules produced in the Titanian mesosphere are as great as ~ 102/(particulate radius, μm) if column densities of condensed and gas phases are comparable. Visible condensation hazes of more complex organic compounds may occur at altitudes up to ~ 3060 km provided only that the abundance of organic products declines with molecular mass no faster than laboratory experiments indicate. Typical organics condensing at 2900 km have molecular masses = 100–150 Da. At current rates of production the integrated depth of precipitated organic liquids, ices, and tholins produced over 4.5 × 109 years ranges from a minimum ~ 100 m to kilometers if UV at is important. The organic nitrogen content of this layer is expected to be ~ 10?1?10?3 by mass. 相似文献
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Several directional discontinuities in the plasma tail of Comet Austin 1982g are apparent on photographs obtained by different observers between 1982 Augut 17.84 and August 21.85. Furthermore, anomalous changes in the orientation of the inner tail axis with respect to the projection on the sky of the prolonged radius vector are noticed. An analysis based on the wind-sock theory of plasma comet tail orientations shows that changes in the azimuthal component of the solar-wind velocity would have produced the observed anomalies. No satellite data on interplanetary conditions were available to check the existence of such a solar-wind event. A type II–IV solar radio event observed on August 17.64, followed by a geomagnetic storm in August 20.67, might denote, however, the existence of a solar flare-generated interplanetary disturbance. 相似文献