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991.
张敏 《中国地球化学学报》2005,24(3):228-231
Light hydrocarbons, especially C7 isoalkanes, cyclopentanes, cyclohexanes and n-heptane in 540 oils from the Tarim Basin were studied systematically. The results suggested the K1 values [ (2-MH+ 2,3-DMP)/(3-MH + 2,4-DMP) ] of crude oils vary from a lowest value of 0.78, to a highest value of 1.54, but the K1 values of the majority of oil samples (80%) range from 0.90 to 1.20. However, the absolute contents of ( 2-methylhexane + 2,3-dimethylpentane) and ( 3-methylhexane + 2,4-dimethylpentane) in the total light hydrocarbons ( C4-C7 ) show a similar variation trend. The variation of K1 values of crude oils can suggest a typical sedimentary environment for source rocks. Therefore, according to the compositional characteristics of C7 light hydrocarbons in light of the steady-state catalytic hypothesis, nonmarine oils from the Yingmaili area and marine oils from the Tazhong uplift in the Tarim Basin were genetically classified. 相似文献
992.
北京地区一次小雪天气过程造成路面交通严重受阻的成因分析 总被引:13,自引:1,他引:13
通过对2001年12月7日降雪天气过程与历史同期降雪过程的比较以及对降雪过程中不同物理介质路面温度变化的观测研究表明,"12·7"北京地区路面交通严重受阻是由于特殊的时间、特殊的城市和特定的路面状况等多种非气象因素与"落雪成冰"的气象环境条件共同作用造成的.这种气象环境条件的形成是由于降雪过程中,雪面、路面与近地面大气之间复杂的热量交换和相互影响的结果:降雪开始时,由于雪片的吸热作用,造成路面和紧贴地面的大气温度下降,而近地面层气温的下降,反过来造成路面温度进一步降低,在两者的共同作用下,地表落雪迅速形成冰面.冰面的反射作用又进一步加速了气温、尤其是近地面层气温的下降,不断降低的气温使得冰层硬度加强、厚度迅速增加.作者还通过天气诊断和数值模拟分析,对这次降雪天气过程的物理机制进行了简单的讨论,认为这次降雪天气很可能是由对流层中层快速移动的高空槽、地面弱倒槽和近地面层弱的偏东气流共同影响而产生的. 相似文献
993.
994.
结合一个具体工程应用实例,介绍了土钉墙与轻型井点联合基坑支护降水技术的设计方法,并初步总结了该技术的主要特点和应用注意事项。 相似文献
995.
During the spring seasons of 1983, 1986 and 1987 the development of phytoplankton in Lake Zürich was investigated (from February
to May) using samples taken at short term intervals. The aim was to describe the effects of the short term dynamics of environmental
factors on the algal growth. The results could then be used to discuss the existing theories to assess the start of phytoplankton
growth pulses in spring.
Only 7 to 10 days without wind driven vertical mixing were required in spring to start the first growth pulse, despite of
a still very unstable water column (sometimes inverse thermal stratification). Mainly flagellates andStephanodiscus hantzschii increased their biomass and achieved net growth rates of 0.1 and up to 0.65 d−1 respectively. During such a phase the mixing depth was always smaller than the euphotic depth. Later on, at the start of
the spring bloom (=last growth pulse in spring before the clear water stage), the intensity of vertical mixing as well as
the mixing depth were markedly reduced due to an increase in heat input and low wind. Then flagellates dominated (contribution
up to 75.5% of the areal biomass reaching 60 g fresh weight m−2) and the growth rate rose to a maximum of 0.65 d−1.
Standard models of critical depth considers that there is only a biomass increase if the mixing depth is smaller than the
depth of a water layer positive balanced between production and respiration. This model for determining the beginning of a
phytoplankton growth pulse in spring takes no account of the favorable light conditions for phytoplankton cells at calm and
sunny days in February and March. The newly developed threshold value model takes these situations into account: It assumes
that the phytoplankton biomass increases when the calculated effective light climate is equal or greater than a previously
fixed threshold. The calculations are based on the mean light intensity within the mixed layer at windy days or within the
euphotic depth (z
eu) at calm days. In Lake Zürich a minimum of 0.2 106 J m−2d−1 (=0.9 mol quanta m−2d−1) has to be reached or surpassed in at least 3 days before an exponential increase of algal biomass can occur. The value does
not depend on short term fluctuations in neither radiation nor mixing depth. It seems that this value is rather low comparing
with those of investigations in other water bodies (up to 0.8 106 J m−2 d−1) but high related to values from algal cultures (0.02 106 J m−2d−1). As the weather can only be forecasted a few days ahead with any certainty the period for a more or less accurate prediction
of an algal bloom is restricted to about 1 to 5 days. 相似文献
996.
FENG Wenhao LI Xin 《地球空间信息科学学报》2001,4(1):28-36
1 IntroductionInourcountry ,thesurveyingworkonindustrialobjectshave graduallyincreased .Thoseindustrialobjectsincluderailwayandhighwaytunnels,vari ousoilandgascans ,variousaircraft,shellofcars,largemilitaryantennausedforscoutingstealthplane ,ship ,internalst… 相似文献
997.
998.
应用GMS可见光和红外通道数值化资料,针对梅雨锋云系特点,选用云顶红外计数值、可见光计数值、红外计数值梯度等因子,用逐步回归法导得高层高积云、多层云和积雨云的降水与上述因子的关系。并将估计结果与理论、实测降水比较,表明该方法估计效果较好,采用云分类降水估计结果比无云分类的要好。 相似文献
999.
Dispersion of reflectances in air and oil between 400 and 700 nm of a suiteof scolecodont concentrates with known Conodont Alteration Index was determined using a reflected light microscope. Refractive and absorptive indices of these scolecodonts were calculated using their determined reflectances.Morphologically, scolecodonts in carbonate show similar granular morphology to that of graptolites. Fine structural details of scolecodonts can be observed under reflected light.Reflectances, refractive and absorptive indices of scolecodonts at 546 nm increase with increase of the Conodont Alteration Index, indicating that these properties of scolecodonts can be used to determine the maturity of sediments.Dispersion of the optical properties of scolecodonts follows similar trends to those for vitrinite, natural bitumen and graptolites, indicating similar molecular structural changes with increasing maturity. 相似文献
1000.
The Depth Limits of Red Sea Stony Corals: An Ecophysiological Problem (A Deep Diving Survey by Submersible) 总被引:2,自引:0,他引:2
Abstract. Along the Sinai coast of the Red Sea a deep diving survey with the research submersible GEO investigated the depth distribution of stony corals. 47 hermatypic species were identified below 50 m; 9 species extended below 100 m. Their depth distributions are related to light penetration. Observed changes in hermatype growth forms with depth were investigated and interpreted as photo-adaptations. 10 species of ahermatypic corals were found between 100–205 m. Ahermatype growth forms are adaptations to plankton feeding and do not change with depth. 相似文献