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91.
在祁连山冷龙岭南麓坡地进行不同海拔的土壤植被的整体双向移地实验,以探讨气候变化对土壤碳、氮含量及其比例的影响.结果表明: 土壤植被移植后土壤因原生状态不同而存在差异,移地后土壤有机质含量总体表现出随海拔升高而升高,部分移植后在海拔3 600~3 800 m处略有下降;土壤全氮变化比较复杂.从不同高度移植到各海拔后,除从海拔3 400 m移到各海拔的土壤碳氮比先升高后降低外,其它3个高度移植后土壤碳氮比随海拔升高而升高.受气候影响和原生植被类型差异,土壤碳、氮及碳氮比波动变化明显. 相似文献
92.
Steps are distinctive features for estimating the movement of the upper and lower block of faults. However, studies about the influence of steps as a special type of discontinuity on cracking behaviors and strength of rock masses are limited. In this research, rock-like samples with steps and preexisting flaws were fabricated. Step height h and the inclination angle of gentle slope of the step α were set to different values. Direct shear tests were conducted on these samples under different normal stresses. The experimental results reveal that the inclination angle of the gentle slope of the step α, step height h, and normal stress have an influence on the strength, crack initiation, and crack propagation of the samples. The experimental results show that crack behaviors and shear strength were affected by step inclination angles α and step height h. As the normal stress increases, the improvement of the strength of samples with a large step height is larger than that of samples with a small step height, the improvement of the strength of samples with α of 10° is larger than that of samples with α of 0° and-10°. The discrete element method was used to simulate the shear test. Numerical results show five different types of displacement vectors, which can be used to determine whether the cracks are tensile cracks or shear cracks. The above conclusions can provide help for estimating mechanical properties and failure modes of rock masses with steps of different geometries. 相似文献
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By employing the NCEP/NCAR reanalysis data sets(1 000 to 10 hPa,2.5°× 2.5°),the thermal forcing impacts are analyzed of an easterly vortex(shortened as EV) over the tropical upper troposphere on the quasi-horizontal movement of the Western Pacific Subtropical Anticyclone(shortened as WPS A) during 22-25 June 2003.The relevant mechanisms are discussed as well.It is shown that the distribution and intensity of the non-adiabatic effect near the EV result in the anomalous eastward retreat of the WPSA.The WPSA prefers extending to the colder region,i.e.,it moves toward the region in which the non-adiabatic heating is weakening or the cooling is strengthening.During the WPSA retreat,the apparent changes of non-adiabatic heating illustrate the characteristics of enhanced cooling in the east side of the EV.Meanwhile,the cooling in the west side exhibits a weakened eastward trend,most prominently at 300 hPa in the troposphere.The evidence on the factors causing the change in thermal condition is found:the most important contribution to the heating-rate trend is the vertical transport term,followed in turn by the local change in the heating rate term and the horizontal advection term.As a result,the atmospheric non-adiabatic heating generated by the vertical transport and local change discussed above is mainly connected to the retreat of the WPSA. 相似文献
95.
分析了1997—2006年辽宁境内能见度小于1000 m雾的时空分布特征。结果表明:就雾发生的频率而言,辽宁存在两个高值区和两个低值区,高值区分别位于黄海北部沿岸至辽宁东部山区和锦州北部至阜新一带,低值区分别位于辽宁中北部平原以及朝阳地区。从雾的日变化上看,近86%的雾出现在夜间,近69%的雾出现在02-08时,且多为辐射雾。地域不同但气候条件相近时,雾的日变化与雾发生的次数存在极其相似的特点。依据相似的地理环境和气候条件、雾的日变化特征以及雾发生次数等,将辽宁划分为5个预报区,对雾采取分区预报,以提高雾预报的准确率。 相似文献
96.
对照常规天气图实况资料,检验几种常用NWP产品对2008年7月5日山东一次强降水过程的形势场预报和降水预报,并对其物理量场进行诊断分析.结果表明,暴雨落区与诸多物理量场的配置紧密相关;暴雨区出现在低层水汽辐合中心移动路径上,位于与水汽通量散度强辐合中心和强上升运动中心接近处;暴雨区移动方向与水汽通量大值中心、△θse(500-850)负值中心长轴方向一致,水汽通量散度低层辐合、高层辐散两者均满足时有利于强降水发生;200 hPa高空辐散的抽吸作用远比仅有低层辐合更有利于上升运动发展;地面强降水区出现在200 hPa强辐散中心所在处. 相似文献
97.
98.
Robustness of Precipitation Projections in China:Comparison between CMIP5 and CMIP3 Models 下载免费PDF全文
Three sources of uncertainty in model projections of precipitation change in China for the 21st century were separated and quantified: internal variability,inter-model variability,and scenario uncertainty.Simulations from models involved in the third phase and the fifth phase of the Coupled Model Intercomparison Project(CMIP3 and CMIP5) were compared to identify improvements in the robustness of projections from the latest generation of models.No significant differences were found between CMIP3 and CMIP5 in terms of future precipitation projections over China,with the two datasets both showing future increases.The uncertainty can be attributed firstly to internal variability,and then to both inter-model and internal variability.Quantification analysis revealed that the uncertainty in CMIP5 models has increased by about 10%–60% with respect to CMIP3,despite significant improvements in the latest generation of models.The increase is mainly due to the increase of internal variability in the initial decades,and then mainly due to the increase of inter-model variability thereafter,especially by the end of this century.The change in scenario uncertainty shows no major role,but makes a negative contribution to begin with,and then an increase later. 相似文献
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100.