全文获取类型
收费全文 | 5167篇 |
免费 | 959篇 |
国内免费 | 1386篇 |
专业分类
测绘学 | 504篇 |
大气科学 | 1576篇 |
地球物理 | 1291篇 |
地质学 | 2166篇 |
海洋学 | 1073篇 |
天文学 | 29篇 |
综合类 | 399篇 |
自然地理 | 474篇 |
出版年
2024年 | 24篇 |
2023年 | 45篇 |
2022年 | 139篇 |
2021年 | 168篇 |
2020年 | 183篇 |
2019年 | 263篇 |
2018年 | 184篇 |
2017年 | 248篇 |
2016年 | 220篇 |
2015年 | 246篇 |
2014年 | 284篇 |
2013年 | 352篇 |
2012年 | 286篇 |
2011年 | 291篇 |
2010年 | 268篇 |
2009年 | 361篇 |
2008年 | 341篇 |
2007年 | 408篇 |
2006年 | 324篇 |
2005年 | 323篇 |
2004年 | 312篇 |
2003年 | 233篇 |
2002年 | 230篇 |
2001年 | 217篇 |
2000年 | 226篇 |
1999年 | 188篇 |
1998年 | 156篇 |
1997年 | 164篇 |
1996年 | 167篇 |
1995年 | 124篇 |
1994年 | 128篇 |
1993年 | 96篇 |
1992年 | 83篇 |
1991年 | 60篇 |
1990年 | 35篇 |
1989年 | 34篇 |
1988年 | 28篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有7512条查询结果,搜索用时 140 毫秒
71.
Temporal change of clustered distribution in vertical profiles of three nutritional groups of planktonic ciliates, e.g. heterotrophic
naked ciliates, mixotrophic naked ciliates and heterotrophic loricated ciliates, was investigated by following a drifting
buoy in Toyama Bay on the Japan Sea coast of central Japan in summers of 1989 and 1990. Clustered distribution, represented
as the mode of population density in the vertical plane, occurred mainly in the oligotrophic upper layer (0–50 m depth) above
the subsurface chlorophyll-a maximum layer. Its clustered degree was stronger when the mode of population density in the vertical plane was formed at
shallower depth, while its longevity was shorter as mentioned above. Vertical distribution of ciliates during summer in Toyama
Bay is characterized by ephemeral clustered distribution, or in other wards, by rapid alternations of appearance and disappearance
of the clustered distribution. 相似文献
72.
湍流数值模拟中封闭模式应用的局限性 总被引:1,自引:0,他引:1
通过对琼州海峡的潮流场特征进行数值模拟,指出了选择不同的特征混合长度表达式对数值模拟结果的影响,表明了基于特征混合长度理论的流封闭模式在近海湍流数值模拟中应用的局限性。 相似文献
73.
对于含多资料三维分潮波模型建立了一种岸边资料运动学外推的潮波第一边值方法,并对渤海的四大原湖波进行试算。结果证实本方法可行,该方法使潮波方程既满足第一边值问题,充分利用岸边测站资料,又保证岸界法向流速为零条件,符合物理意义。并对复型病态矩阵的收敛问题提出了一种可行性处理。 相似文献
74.
75.
Joo Serdio Helena Coelho Snia Vieira Snia Cruz 《Estuarine, Coastal and Shelf Science》2006,68(3-4):547
The migratory response of intertidal microphytobenthos to changes in irradiance was studied on undisturbed estuarine sediments. Two non-destructive optical techniques were used to trace variations in vivo of surface biomass: PAM fluorometry, for measuring the minimum fluorescence level (Fo); and spectral reflectance analysis, for quantifying the normalized difference vegetation index (NDVI). Following the formation of a dense biofilm at the surface, replicated sediment samples were simultaneously exposed to six different irradiance levels, ranging from 50 to 1500 μmol m−2 s−1, during a period of 120 min. The migratory photoresponse of the biofilms was characterised by constructing biomass vs. light curves (BLC), relating the accumulation of microalgal biomass after that period (estimated by Fo or NDVI) to the irradiance level incident on the surface. BLCs allow characterising the main features of the migratory photoresponse of intact biofilms. Typical BLC showed a clear biphasic pattern, with an increase in microalgal accumulation under irradiances below 100 μmol m−2 s−1, maximum values under 100–250 μmol m−2 s−1, and a gradual decrease of surface biomass under higher irradiances, indicating a strong photophobic downward migratory response. Similar BLC patterns were obtained when measuring Fo or NDVI. The construction of BLCs for biofilms from intertidal sites with distinctive sediment characteristics and diatom taxonomic composition allowed to detected significant differences in the migratory photoresponse. Biofilms from a muddy sediment exhibited considerably larger amplitude in the migratory photoresponse than the biofilms from a sandy mud site, especially under high irradiances. The photophobic migratory response to high light was found to vary among diatom species, particularly in the case of the biofilms from the muddy sediments. 相似文献
76.
A numerical model to compute wave field is developed. It is based on the Berkhoff diffraction-refraction equation, in which an energy dissipation term is added, to take into account the breaking and the bottom friction phenomena. The energy dissipation function, by breaking and by bottom friction, is introduced in the Berkhoff equation to obtain a new equation of propagation.The resolution is done with the hybrid finite element method, where lagrangians elements are used. 相似文献
77.
Ana P. Mucha M. Teresa S. D. Vasconcelos Adriano A. Bordalo 《Estuarine, Coastal and Shelf Science》2004,59(4):663
Vertical distribution (0–15 cm) of the macrobenthic community and its relationships to natural sediment characteristics and trace metal contents and bioavailability were studied at five locations in the lower Douro estuary, Portugal. An analysis of vertical metal distribution, for the interpretation of anthropogenic impact on the estuarine sediments, was also investigated. Sediment characterisation included organic matter, grain size, metals (Al, Fe, Cu, Pb, Cr, Ni, Cd, Zn and Mn), acid volatile sulphide (AVS) and simultaneously extracted metals (SEM). The macrobenthic community had low diversity (14 species), was dominated by small size opportunists and seemed to be controlled mainly by natural factors such as grain size distribution, Al and Fe contents and sediment depth. The vertically heterogeneous distribution of macrobenthic community appears to affect redox status of the sediments and consequently metal bioavailability. Despite anthropogenic contamination in terms of Zn, Cu, Pb, Cr and Ni having already been detected in the north bank, the analysis of vertical distribution was essential for the identification of current anthropogenic contamination in terms of Zn, Pb and Cd in the south bank. 相似文献
78.
Detailed structural interpretation of the recently acquired deep seismic multichannel profiles along the Iberian Atlantic Margins (IAM Project) provides new results on the geodynamic evolution of the eastern part of the Azores-Gibraltar plate boundary. Thrusting and folding of the oceanic basement and of Mesozoic and Cenozoic sedimentary cover of the Gorringe Bank region are consistent with the N–S convergence of Iberia and Africa. Compressive structures in the Gorringe Bank region are spread over a wide area. Deformation under compression took place mainly in Tertiary times, as is evidenced by a basal unconformity and several discontinuities in Tertiary sediments, although some deformation has also been recorded in Quaternary sediments. The compressive structures in the Gulf of Cadiz are E–W oriented thrusts, folds and related diapiric structures. N–S oriented transpressive deformation is likely to occur in the western Portuguese platform. There is no continuity of structures from the oceanic to the continental domain, suggesting that deformation transfers from one side to the other through a transcurrent fault zone. The fault contact between the two domains is located in the ocean-continent transition zone. 相似文献
79.
80.
9012号热带气旋维持的卫星云图和垂直结构特征分析 总被引:2,自引:0,他引:2
本文根据卫星云图的演变和常规天气分析相结合,对9012号热带气旋登陆后维持水消的成因进行了分析。指出该热带气旋经久不消的重要原因为其西南侧对流云团和东北侧高空槽前对流云带与热带气旋云系相衔接在中低层东北气流引导下卷入,热带气旋内部的两条云带的维持,以及利有的环流条件。 相似文献