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941.
In the present paper, the boundary element method with exterior collocation was applied to two-dimensional elastodynamic problems. The stability of the numerical solution was discussed and the collocation rule of source points outside the region being studied was investigated in the frequency domain by means of the computed error in the boundary displacement and the condition number of the coefficient matrix for two typical wave propagation problems. The achieved results are helpful to the practical application of this method to earthquake ground motion analysis. 相似文献
942.
By the measurement of the wind directional indicator of the Cretaceous desert in Ordos Basin, the regularity of the paleoprevailing
wind directions and pattern of the paleowind belts are revealed. It is considered that the desert was controlled by a planetary
wind system. In the early stage, the subtropical high pressure zone drifted south and northwards with short cycles, resulting
in the alternation of westerlies and northeast trades; in the late stage, the subtropical high pressure zone drifted southwards
with a long cycle, placing the desert under the westerly belt and making the desert completely controlled by the westerly
belt. The reconstruction of the paleowind belts has provided the evidence of the general circulation of the atmosphere for
the pattern of the circulation before the uplift of the Tibetan Plateau 相似文献
943.
川滇地区7级大震前中强震震源机制变化 总被引:7,自引:0,他引:7
分析了 70年代以来 ,川滇地区发生的 8次 7级大震前 5年内 ,发生在大震孕震区和震源区内的中强震震源机制解时空分布。结果表明 ,最早中强震发生在大震震源区或其附近 ,其发震应力场与区域构造应力场一致 ,与大多数大震发震应力场一致或接近。大多数中强震震源破裂特征与大震明显不同。之后有多次中强震发生在距大震震源区较远的大震孕震区内其他地方 ,它们的发震应力场往往经历了与区域构造应力场和大震应力场一致与不一致的多次交替变化。大震前最后 1个中强震也发生在距大震震源区较近的地方 ,其发震应力场与大震发震应力场明显不一致 ,偏转了 30°~ 5 0° ,或更多 ,大多数也与区域构造应力场不一致 ,有的中强震发震断裂破裂特征与大震不一致。大震前中强震震源机制的变化 ,反映了大震孕育过程的不同阶段 ,区域构造应力场的时空调整变化和增强过程 ,以及由此引发的构造断裂异常活动 ,揭示出与大震发生有关的应力场和震源破裂特征信息 相似文献
944.
945.
946.
Sea fog is typically formed and developed under a set of favorable environmental conditions, which are associated with the station pressure changes, sea level pressure, winds, temperature, water vapor supply, and sea surface temperature. Understanding of these environmental factors during the evolution of a sea fog episode is crucial for forecasting the occurrence and severity of sea fogs over the ocean and adjacent coastal areas. In this study, the large-scale environment variability of six fog events over the Yellow Sea was investigated. It was realized in the present study that the northwest Pacific Ocean high (NPH) is vital to fog formation over the Yellow Sea. In our study, six fog cases can be basically divided into two types: (1) pressure-weakening type, (2) pressure-strengthening type. The former type happened in spring and the latter type in summer. Prevailing southerly winds, accompanied with the well-positioned NPH, may supply a large amount of warm water vapor for the fog formation and maintenance. The intensity of the air temperature inversion is stronger in summer cases than that in spring ones. The wind direction change from south to north and the unstable lower atmosphere may lead to fog’s dissipation. This study may provide a comprehensive understanding of sea fog’s onset, maintenance, and dissipation over the Yellow Sea. 相似文献
947.
A Comparison Study Between Spring and Summer Fogs in the Yellow Sea-Observations and Mechanisms 总被引:1,自引:0,他引:1
Suping Zhang Man Li Xiangui Meng Gang Fu Zhaopeng Ren Shanhong Gao 《Pure and Applied Geophysics》2012,169(5-6):1001-1017
New observations from buoys and soundings reveal the discrepancies in air–sea interface and in vertical structures between spring (April to May) and summer (July) fogs in the Yellow Sea. Spring fogs are shallow with a robust temperature inversion, dry layer and cold phase (surface air temperature or SAT is lower than sea surface temperature or SST); summer fogs are deep with weaker stability, indistinct fog top and warm phase (SAT?>?SST). Along with numerical simulations, conceptual models for the mechanisms of temperature inversion are suggested. The land–sea contrast is responsible for the robust temperature inversion in spring, and the deep southerlies derived from the east Asian summer monsoon and the adiabatic sinking from the western Pacific subtropical high contributes to the weaker inversion in summer. The dry layer above the sea fog top intensifies the longwave radiative cooling effect to lead to the cold phase in spring fogs. The radiative cooling is weaker in summer fogs resulting in SAT?>?SST. 相似文献
948.
Global mean sea level is a sensitive factor of climate change. Global warming will contribute to worldwide sea‐level rise from thermal expansion of ocean water, melting of glaciers and polar ice. Consideration of global soil erosion, water vapor cycle, and hydraulic actions suggests that soil erosion is another important factor contributing to sea‐level rise in addition to global warming. Much terrestrial sediment flows into the rivers each year but cannot be replenished, resulting in land surface declines. Moreover, sediment flow into rivers and oceans contributes to rising sea level. Ecological protection measure was proposed to prevent rising sea levels caused by soil erosion. This commentary should be useful to attract attention on rising sea levels caused by soil erosion. 相似文献
949.
950.
Yunfeng Li Jiangxia Wang Yaoguo Wu Zhonghua Xu Xiaogang Fu Guangcai Hou 《Environmental Geology》2007,52(4):739-745
Groundwater flow fields in aquifers are often determined by water level data measured in monitoring wells. The flow field
can be further refined by mass balance simulations, especially when groundwater level data is limited. The mass balance simulation
is based on the principle of mass conservation and relies on water quality data in the same aquifer. The approach is applied
to the Luohe aquifer in the Binchang area, China. The water-rock interactions and the hydrogeochemical evolution were studied
along four typical flow paths. The study indicates that groundwater in the Luohe formation flows from the southern border
to the interior of the Ordos Basin. The southern border, approximately 1,400 km2, is a recharge zone, where the Luohe formation outcrops. The total dissolved solids of the groundwater in the southern boarder
are less than 1 g/l, and the hydrochemistry type is HCO3–Na. This new finding refines the flow field of the water-bearing formation, and an additional 1,400 km2 is included in the water resource planning of the area. 相似文献