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941.
942.
In unsaturated soil modelling, collapse is viewed as an ordinary response, whereas swelling upon an increase of moisture is
considered as a special class of problems. However, an investigation based on fundamentals of plasticity indicates that the
two seemingly opposite responses are unified within the same ordinary elastoplasticity framework. In fact, similar to the
well-known contractive and dilative responses in the critical state framework, the collapsive and expansive responses of unsaturated
soils differ only in the sign of the dissipative hydrostatic stress. For a soil with a low applied net stress, the dissipative
mean normal stress during wetting is likely to be negative, and the plastic volumetric strain is kept negative (swelling)
as well, such that the dissipation is always positive, complying with the second law of thermodynamics. When the applied net
stress is high, the dissipative mean normal stress may turn to be positive, resulting in a positive plastic volumetric strain
(collapse). This paper explains the concept of this ‘ordinary’ modelling framework, and uses a bounding surface triaxial model
to demonstrate the concept. The numerical results are compared with experimental observations reported in the literature. 相似文献
943.
944.
945.
946.
The glacier area changes in the Qangtang Plateau based on the multi-temporal grid method and its sensitivity to climate change 总被引:2,自引:1,他引:1
Glacier area changes in the Qangtang Plateau are analyzed during 1970-2000 using air photos,relevant photogrammetric maps and satellite images based on the multi-temporal grid method.The results indicate that the melting of glaciers accelerated,only a few of glaciers in an advancing state during 1970-2000 in the whole Qangtang Plateau.However,the glaciers seemed still more stable in the study area than in most areas of western China.We estimate that glacier retreat was likely due to air temperature warming during 1970-2000 in the Qangtang Plateau.Furthermore,the functional model of glacier system is applied to study climate sensitivity of glacier area changes,which indicates that glacier lifespan mainly depends on the heating rate,secondly the precipitation,and precipitation increasing can slow down glacier retreat and make glacier lifespan prolonged. 相似文献
947.
Pyrenoids found in green algae Order Ulvales have taxonomical significance.Their morphology,microstructure,and the location and number in the cells have been widely used as identification criteria. As these traits can be affected by environmental conditions,it is necessary to look for other different characteristics.Here pyrenoids in several algae species collected along the Qingdao coast were studied for such purpose. The morphology and distribution of pyrenoids in the cells,as well as their change in diff... 相似文献
948.
949.
鄂西渝东区志留系流体封存箱的演化与天然气成藏 总被引:1,自引:0,他引:1
因鄂西渝东区志留系勘探程度甚低,长期以来志留系一直被视为烃源层或盖层.随着建深1井在志留系钻获高压工业气流,曾经的"思维定式"发生了改变.通过对志留系油气成藏条件及碳、氧、锶稳定同位素追踪流体行为轨迹的分析认为,该区志留系具有自源供烃的特点以及流体相对封闭的独特性,这是形成志留系下统龙马溪组、小河坝组以及志留系中统韩家... 相似文献
950.
Siyuan Ye Edward A. Laws Xigui Ding Hongming Yuan Guangming Zhao Jin Wang 《Environmental Earth Sciences》2011,64(6):1641-1646
Samples of porewater and the edible tissue of mottled clams, Ruditapes variegatus, were collected simultaneously at each of 12 stations from Jiaozhou Bay near Qingdao, China, in June of 2003. Chemical analysis
focused on trace metals and major elements. Porewater concentrations of Cd, Cr, Pb, and Zn were distributed in a bimodal fashion
among the 12 stations, with mean concentrations at six of the stations being 8–32 times mean values at the other six stations.
The concentrations of the same metals in clams were remarkably similar among stations, the coefficients of variation being
only 12–37%. Calculations performed with the computer program PHREEQC indicated that Pb and Cr in porewater were present only
in the +2 and +3 states, respectively, and because dissolved Cd and Zn exist only in the +2 state, the bimodal distribution
of these four metals likely reflects secondary effects associated with their scavenging by Fe and/or Mn under oxidizing conditions
and subsequent dissolution in the reducing environment of the porewaters. Consistent with this hypothesis is the fact that
the distribution of high and low metal concentrations was closely correlated with the granularity of the sediment, with lower
metal concentrations associated with relatively coarse sediment. Comparison of published biological concentration factors
with the ratios of metal concentrations in the clams to porewater metal concentrations indicated that the porewaters were
not the primary sources of the metals in the clams. Mixing processes in the bay likely account for the rather uniform concentrations
of metals in clam tissue. 相似文献