全文获取类型
收费全文 | 814篇 |
免费 | 134篇 |
国内免费 | 211篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 49篇 |
地球物理 | 64篇 |
地质学 | 645篇 |
海洋学 | 195篇 |
天文学 | 3篇 |
综合类 | 66篇 |
自然地理 | 130篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 20篇 |
2021年 | 30篇 |
2020年 | 24篇 |
2019年 | 35篇 |
2018年 | 25篇 |
2017年 | 29篇 |
2016年 | 24篇 |
2015年 | 27篇 |
2014年 | 63篇 |
2013年 | 56篇 |
2012年 | 57篇 |
2011年 | 64篇 |
2010年 | 41篇 |
2009年 | 56篇 |
2008年 | 50篇 |
2007年 | 42篇 |
2006年 | 45篇 |
2005年 | 45篇 |
2004年 | 31篇 |
2003年 | 41篇 |
2002年 | 20篇 |
2001年 | 33篇 |
2000年 | 34篇 |
1999年 | 39篇 |
1998年 | 30篇 |
1997年 | 31篇 |
1996年 | 29篇 |
1995年 | 22篇 |
1994年 | 36篇 |
1993年 | 11篇 |
1992年 | 15篇 |
1991年 | 19篇 |
1990年 | 9篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1984年 | 1篇 |
排序方式: 共有1159条查询结果,搜索用时 31 毫秒
1.
2.
Manoj K. Pandit Helga de Wall Narendra K. Chauhan 《Journal of Earth System Science》2008,117(3):201-209
A number of fine-grained sericite bearing pelitic, schistose lithologies occur along the Archean (Banded Gneiss Complex)-Proterozoic
(Aravalli Supergroup) contact (APC) in the Udaipur valley in NW Indian craton. These Al-rich lithologies (subsequently metamorphosed)
have been described as ‘paleosols’, developed over a 3.3 Ga old Archean gneissic basement and are overlain by Paleoproterozoic
Aravalli quartzite. The paleosol was developed between 2.5 and 2.1, coincident with the globally recognized Great Oxidation
Event (GOE). In previous studies these paleosol sections were interpreted to have developed under reducing environment, however,
the finding of a ‘ferricrete’ zone in the upper part of Tulsi Namla section (east of Udaipur) during the present study (in
addition to earlier reported lithologies) has led to an alternative suggestion of oxygen-rich conditions during paleosol development.
The Tulsi Namla paleosol section shows all the features characteristic of a complete paleosol section described from other
Archean cratons. The paleosol includes sericite schist with kyanite as the prevalent Al-silicate in the lower part of profile
while chloritoid and Fe-oxides typify the Fe-rich upper part. Alumina has remained immobile during the weathering process
while Fe and Mn show a decrease in the lower part of the section and an abrupt rise in the upper part, in the ferricrete zone.
The field and geochemical data indicate that the Tulsi Namla section is an in situ weathering profile and at least the upper part shows evidence of oxidizing conditions. 相似文献
3.
浙江省海岛沿岸水域微生物生态分布 总被引:2,自引:0,他引:2
文章报道了浙江海岛沿岸水域中异养细菌、氨化细菌和反硝化细菌的数量分布及异养细菌的种群组成。结果表明:本调查海区异养细菌的数量较多,其数量分布范围在2.04×104~8.36×106个/dm3之间;氨化细菌数量分布范围在3.0×103~1.1×106个/dm3之间;反硝化细菌的数量分布范围在3.0×102~1.1-106个/dm3之间。细菌的数量与环境中营养盐的浓度之间存在密切关系。在不同的海区异养细菌的种群组成存在一定的差异,在浙北海区,革兰氏阴性菌所占比例为41.6%,在浙中海区为46.9%,在浙南海区为64.9%。 相似文献
4.
M. deCastro M. Gmez-Gesteira I. lvarez R. Prego 《Estuarine, Coastal and Shelf Science》2006,70(4):673
A quasi-permanent transverse asymmetry in the thermohaline properties of the Ria de Pontevedra (northwestern Spain) was measured from October 1997 to October 1998 during 23 cruises. On average, the density increased form north to south. This asymmetry was maintained by salinity during the wet season, and by salinity and temperature during the dry season. The density difference between coasts (Δσt = σtsouth − σtnorth) and the river discharge were positively correlated (correlation coefficient, approximately 0.6) throughout the year. The density difference was negatively correlated with the upwelling index during the wet season (correlation coefficient, approximately −0.45) and positively correlated during the dry season (correlation coefficient, approximately 0.55). 相似文献
5.
本文分析了当地前期气象要素——温度的演变特点与汛期降水量之间的关系,建立了两者之间的回归方程,并由此作出降水量的长期预报,从预报误差和试报结果看,效果是好的。 相似文献
6.
潮汐沉积率与沉积间断 总被引:16,自引:3,他引:16
在浙北奥陶系文昌组和长江三角洲开敞型淤泥质海岸非潮道潮汐纹层研究的基础上,得出与国外同类研究相近的沉积率。现代海岸进积速度和潮坪沉积的观察及测试证明,上述沉积率是难以置信的。现代潮坪观测表明,潮汐纹层在形成过程中即包含着改造,所保留的纹层占应形成数的不到10%,其余90%以上被侵蚀。小型层序是风暴和平静天气的产物,为风暴层序,与大小潮周期无关。其地层中保留的数量不到应生成数的10%,其余90%被改造。小型层序被侵蚀,其中的纹层随之消失。致使潮坪层序中保存的纹层数仅为应形成数的0.2%。被改造的纹层和单层留下的仅是侵蚀面,即小间断。在进行潮汐沉积高分辨率的研究时应充分重视沉积间断的作用 相似文献
7.
8.
Manuel Varela Ricardo Prego Yolanda Pazos ngeles Moroo 《Estuarine, Coastal and Shelf Science》2005,64(4):721-737
The first oceanographic research (hydrography, nutrient salts, chlorophyll, primary production and phytoplankton assemblages) in a Middle Galician Ria was carried out in Corme-Laxe during 2001, just a year before the Prestige oil spill, being the only reference to evaluate eventual changes in the phytoplankton community. Due to the small size of this ria (6.5 km2), oceanographic processes were driven by the continental water supplied by Anllons River during the wet season (20–30 m3 s−1 in winter), and the strong oceanic influence from the nearby shelf during the dry season. The annual cycle showed a spring bloom with high levels of chlorophyll (up to 14 μg Chl-a L−1) and primary production (3 g C m−2 d−1) and a summer upwelling bloom (up to 8 μg Chl-a L−1 and 10 g C m−2 d−1) where the proximity of the Galician upwelling core (<13.5 °C at sea surface) favors the input of upwelled seawater (up to 9 μM of nitrate and silicate) to the bottom ria layer, even during summer stratification events (primary production around 2 g C m−2 d−1). Thus, phytoplankton assemblages form a “continuum” from spring to autumn with a predominance of diatoms and overlapping species between consecutive periods; only in autumn dinoflagellates and flagellates characterized the phytoplankton community. In the Middle Rias as Corme-Laxe, the nutrient values, Chl-a, primary production and phytoplankton abundance for productive periods were higher than those reported for the Northern (Ria of A Coruña) and Southern Rias (Ria of Arousa) for year 2001; this suggests the importance of the hydrographic events occurring in the zone of maximum upwelling intensity of the Western Iberian Shelf, where a lack of annual cycles studies exists. 相似文献
9.
10.
M. Mistri 《Marine Ecology》1995,16(3):181-188
Abstract. The gorgonian Lophogorgia ceratophyta thrives in turbid water at Tinetto Rock, La Spezia Gulf, Ligurian Sea. Its age structure suggests that the population is in a steady state; nevertheless, it is difficult to discern whether the main factors controlling this population are biological or event-related. Secondary production was estimated by means of an increment-summation method and yielded 0.54 g ash-free dry weight (AFDW)*m-1 a-1 . This estimate does not take into account biomass losses due to reproductive output and non-lethal predation. Standing stock biomass was 5.44 g AFDW e m-2 . The annual P/B ratio was 0.10 and turnover time about 10a 相似文献