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991.
992.
993.
郑州市两次不同背景下特大暴雨诊断分析 总被引:1,自引:1,他引:0
利用NCEP资料,根据降水实况分布及各物理量分层平面分布,每隔6 h对特大暴雨中心区所在经、纬向带各物理量场作经、纬向垂直剖面图,结合高空观测图对郑州市两次特大暴雨发生的大环流形势场、触发特大暴雨发生的各物理量场进行诊断分析。结果表明:1)连续性特大暴雨区出现在低空急流轴的前方,一方面是由于低空急流前方水平辐合较强,另一方面低空急流对暖湿空气的输送,使大气不稳定度加强;局地短时性特大暴雨过程主要是冷空气侵入使冷暖湿空气团在郑州上空交汇,其对流不稳定能量释放所致。2)辐合线对暖湿空气的抬升运动起到动力加强作用,是触发中尺度雨团的根源,也是特大暴雨产生的根源。3)连续性暴雨发生、发展时,高空的反气旋起主导作用;局地短时性暴雨发生时,中低空的气旋辐合起主导作用。4)短时性特大暴雨天气,前期有较强的不稳定层结;连续性暴雨天气刚发生时,其前期存在较强的不稳定层结,在暴雨连续发生过程中不一定有强不稳定层结。5)连续性暴雨需要较强的水汽输送带,局地短时性暴雨不要求有明显的水汽输送。 相似文献
994.
Yonghong Yao Weidong Guo Yaoming Song 《Asia-Pacific Journal of Atmospheric Sciences》2010,46(4):475-481
Using data archived in the Coordinated Enhanced Observing Period (CEOP) project, comparisons between field observations undertaken at Tongyu CEOP reference site in China and model output from year 2003 to 2004 have been implemented, and in particular, the time series and diurnal cycles of precipitation, near-surface temperature, air temperature, and latent and sensible heat fluxes are presented. The results show that the ability of the model simulations on the temperatures, such as air temperature and the surface temperature, is satisfactory compared with the simulations on the land surface heat fluxes and the precipitation at Tongyu site. In addition, the multi-model ensemble exhibits better results over all items in comparison with the observations. The differences of the precipitation at the interannual and the seasonal time scales between the model results and observations indicate that some of the models are able to reproduce the larger amount of precipitation in 2003 than that in 2004, which is consistent with the trend of the observations at Tongyu site even though the mean square errors of models output calculated from daily precipitation during year 2003 and 2004 are even greater than the daily amount of the precipitation. The poor skill in the quantitative simulation of the precipitation indicates that the deficiency of the models in simulating the surface heat fluxes may be closely related to the biases of the precipitation simulations. In terms of the seasonal time series of the precipitation, there is an increase during summer, accompanied by the same increased trend of the latent heat flux and the decreased trend of the sensible heat flux from the insitu observations. 相似文献
995.
风电场风资源测量与计算的精度控制 总被引:3,自引:1,他引:2
根据多个复杂地形风电场观测操作实践和大量观测数据的计算分析,提出了对观测数据和计算质量精度控制的主要措施,包括:复杂地形测风站布设的5个原则,仪器的合理选型和设置;对由于测风仪固有的系统误差和缺测数据的插补订正可能引起的计算误差进行了定量估算,通过对大量实测数据的对比计算显示:①目前普遍采用的进口风速计的相对偏差在1.6%~5.25%之间,由此可导致轮毂高度附近的年平均风功率密度误差在5%以上,最大达13.8%;②在季风气候区、复杂地形和风的年变率较大的地区,进行缺测数据插补订正时,应选取同季或同一主导风向的数据作为插补订正的基础数据,否则可能导致其平均风功率密度相对误差达20%~50%. 相似文献
996.
从备份自动站数据文件的实际需要出发,通过实例由浅及深地介绍了用DOS批处理文件多目的地、多方式备份自动站数据的方法,包括本机备份、备份到局域网、备份到网络服务器以及自动备份等。 相似文献
997.
2008年初贵州低温雨雪凝冻灾害天气成因分析 总被引:5,自引:3,他引:2
利用NECP 2.5°×2.5°的日平均再分析资料和常规观测资料,对2008年1月12日-2月13日期间贵州省历史罕见的持续低温雨雪凝冻天气过程的环流特征及物理量进行了分析,并对中东部凝冻严重的前期和西部凝冻严重的后期做了对比.揭示了此次灾害天气的几个主要天气特征:(1)地面静止锋的位置关系着我省低温雨雪凝冻灾害的区域.(2)500 hPa环流前期和后期影响系统明显不同.过程期间欧亚大陆500 hPa高度场距平呈"北高南低"分布,亚洲区极涡南掉,面积偏大.(3)过程前期850 hPa冷舌明显,等温线密集;后期700 hPa 温降低,有冷舌活动,850 hPa冷舌明显减弱,低温维持.中东部和西部地区冷暖平流垂直方向上的配制不同.强盛的700 hPa暖湿气流是此次过程的主要水汽来源. 相似文献
998.
999.
The formation and evolution of elliptical galaxies (EGs) are still an open question. In particular, recent observations suggest that EGs are not only simple spheroidal systems of old stars. In this paper, we analyse a sample of EGs selected from the Sloan Digital Sky Survey in order to study the star-forming activity in local EGs. Among these 487 ellipticals, we find that 13 EGs show unambiguous evidence of recent star formation activity betrayed by conspicuous nebular emission lines. Using the evolutionary stellar population synthesis models and Lick absorption line indices, we derive stellar ages, metallicities and α-element abundances, and thus reconstruct the star formation and chemical evolution history of the star-forming elliptical galaxies (SFEGs) in our sample.
We find that SFEGs have relative younger stellar population age, higher metallicity and lower stellar mass, and that their star formation history can be well described by a recent minor and short starburst superimposed on old stellar component. We also detect 11 E+A galaxies whose stellar population properties are closer to those of quiescent (normal) ellipticals than to star-forming ones. However, from the analysis of their absorption line indices, we note that our E+A galaxies show a significant fraction of intermediate-age stellar populations, remarkably different from the quiescent galaxies. This might suggest an evolutionary link between E+As and star-forming ellipticals. Finally, we confirm the relations between age, metallicity, α-element abundance and stellar mass for local EGs. 相似文献
We find that SFEGs have relative younger stellar population age, higher metallicity and lower stellar mass, and that their star formation history can be well described by a recent minor and short starburst superimposed on old stellar component. We also detect 11 E+A galaxies whose stellar population properties are closer to those of quiescent (normal) ellipticals than to star-forming ones. However, from the analysis of their absorption line indices, we note that our E+A galaxies show a significant fraction of intermediate-age stellar populations, remarkably different from the quiescent galaxies. This might suggest an evolutionary link between E+As and star-forming ellipticals. Finally, we confirm the relations between age, metallicity, α-element abundance and stellar mass for local EGs. 相似文献
1000.
Using NSO/Kitt Peak synoptic charts from 1975 to 2003, we group the main solar magnetic fields into two categories: one for
active regions (ARs) and the other for extended bipolar regions (EBRs). Comparing them, we find that there exist three typical
characteristics in the variability of EBRs: First, there exists a correlation between ARs and EBRs. The phase of EBR flux
has a delay nearly two CRs. Second, we find that the EBR flux has two prominent periods at 1.79 years and 3.21 years. The
1.79-year period seems to only belong to large-scale magnetic features. Lastly, the North – South asymmetry of EBR flux is
not very significant on a time scale of one solar cycle. However, during solar maxima, its dominance is found to shift from
one hemisphere to the other. 相似文献