全文获取类型
收费全文 | 5162篇 |
免费 | 951篇 |
国内免费 | 2165篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 15篇 |
地球物理 | 128篇 |
地质学 | 7428篇 |
海洋学 | 138篇 |
综合类 | 484篇 |
自然地理 | 74篇 |
出版年
2024年 | 57篇 |
2023年 | 139篇 |
2022年 | 181篇 |
2021年 | 202篇 |
2020年 | 183篇 |
2019年 | 194篇 |
2018年 | 161篇 |
2017年 | 197篇 |
2016年 | 247篇 |
2015年 | 246篇 |
2014年 | 345篇 |
2013年 | 271篇 |
2012年 | 295篇 |
2011年 | 301篇 |
2010年 | 268篇 |
2009年 | 235篇 |
2008年 | 235篇 |
2007年 | 303篇 |
2006年 | 280篇 |
2005年 | 257篇 |
2004年 | 330篇 |
2003年 | 288篇 |
2002年 | 301篇 |
2001年 | 390篇 |
2000年 | 348篇 |
1999年 | 344篇 |
1998年 | 318篇 |
1997年 | 289篇 |
1996年 | 261篇 |
1995年 | 214篇 |
1994年 | 185篇 |
1993年 | 135篇 |
1992年 | 97篇 |
1991年 | 76篇 |
1990年 | 32篇 |
1989年 | 30篇 |
1988年 | 22篇 |
1987年 | 14篇 |
1985年 | 4篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有8278条查询结果,搜索用时 0 毫秒
71.
72.
我国相继在多个盆地陆相页岩油勘探中获得突破,展示了良好的发展前景。基于现阶段勘探认识,本文认为陆相页岩油富集主要条件是:(1)稳定且有规模和适宜热成熟度的富有机质页岩是重要物质基础,以TOC含量>2%,最佳为3%~4%、母质类型Ⅰ和Ⅱ1型为主,Ro>0.9%或更高(咸化环境0.8%);(2)有一定容积规模的微纳米孔隙且具脆性的多类储层是重要条件,页岩储层有效孔隙度宜>3%~6%;成岩阶段偏低时,纯页岩段不是中高熟页岩油富集段,致密砂岩和混积岩黏土含量宜<20%;成岩阶段高时,页岩黏土含量可高至40%左右;(3)滞留烃数量大且品质好是重要保证,以S1>2 mg/g为门限,最佳>4~6 mg/g;气油比>80 m3/m3,最佳150~300 m3/m3;(4)顶底板具封闭性保持超压且滞留足够多轻-中组分烃类。陆相页岩油分布特征是:(1)有外物质注入的深-半深湖相是页岩油主要富集区;(2)具备“四高... 相似文献
73.
This work reveals the usefulness of the GIS (Geographic Information Systems) mapping techniques to show the distribution of pollutants along an estuarine environment, as the final stage of a thorough study. In the case of study, the environmental quality of the sediments in the Guadiana river estuary was determined by means of a complete geochemical characterization consisting on the calculation of enrichment factors for the most important metals and metalloids (compared with the local background of non-contaminated sediments). The obtained results were depicted in “enrichment distribution maps” which evidenced a distribution of the elements in two groups: Group-I, elements with natural origin (Al, Fe, Mn, Co, and Cr) distributed homogeneously along the basin, and Group-II, elements associated to anthropic origin (As, Cd, Cu, Pb, Ni and Zn) with clear punctual sources besides a high concentration all over the estuary. The enrichment factors for the elements of Group-II are indicative of the existence of a noticeable diffuse historical mining pollution associated with the acid mine drainage generated in the internal zones of the basin, which could overlap minor pollution inputs from other human activities. The obtained results lead us to a reconsideration of the traditionally thought “unpolluted” environment when it was compared to nearby estuaries. 相似文献
74.
在210Pb同位素测年的基础上,通过对乌梁素海沉积物元素含量的分析,研究了沉积物中元素的变化规律,探讨了沉积物中元素变化的影响因素,结果表明沉积物中Ca、Sr、Cu、Mn、P等元素随深度加深含量下降,其余元素含量随深度加深呈增加的趋势。通过对元素富集系数的变化规律进行研究后,发现Ca、Sr、Cu、Mn、P等元素的富集系数与其含量变化趋势基本相同,反映了该组元素主要受沉积通量的影响;Al、K、Be、Ba、Mg等富集系数与其含量的变化趋势具明显差异,与黏土含量变化一致;而Cr、Fe、Ni、V、Co、Pb、Zn等重金属元素可能受到黏土吸附作用影响。最后,应用有序样品聚类分析方法,对元素这一环境代用指标在研究湖泊历史演化中的作用进行了探讨,研究表明:在湖泊演化过程中,湖泊的形成、20世纪70年代入湖水量的急剧改变以及近年来河套灌区化肥用量逐年加大、大量生活污水和工业废水排入等人类活动的增强等事件,均在湖泊沉积物元素的变化中有所体现。 相似文献
75.
76.
Sven Petersen Peter M. Herzig Thomas Kuhn Leander Franz Mark D. Hannington Thomas Monecke 《Marine Georesources & Geotechnology》2013,31(3):175-193
ABSTRACT From September to October 2002, shallow drilling, using the submersible (5 m) Rockdrill of the British Geological Survey and the German R/V Sonne revealed critical information on the subsurface nature of two distinct hydrothermal systems in the New Ireland fore-arc and the Manus Basin of Papua New Guinea. Drilling at Conical Seamount significantly extends the known surface extent of the previously discovered vein-style gold mineralization (up to 230 g/t Au) at this site. Drilling the conventional PACMANUS volcanic-hosted massive sulfide deposit recovered complexly textured massive sulfide with spectacular concentrations of gold in several core sections including 0.5 m @ 28 g/t Au, 0.35 m @ 30 g/t Au, and 0.20 m @ 57 g/t Au. Shallow drilling is a fast and cost efficient method that bridges the gap between surface sampling and deep (ODP) drilling and will become a standard practice in the future study of seafloor hydrothermal systems and massive sulfide deposits. 相似文献
77.
78.
R. B. Williamson 《新西兰海洋与淡水研究杂志》2013,47(3):413-427
Water quality parameters associated with siltation (non‐volatile and volatile suspended solids), oxygen depletion (chemical and biochemical oxygen demand), nutrient enrichment (N, P), toxicity (Pb, Zn, Cu, Cr, Ni, Cd), and human pathogenic micro‐organisms (coliforms, faecal coliforms, faecal streptococci) were measured in baseflow and stormflow from a residential catchment in Hamilton, New Zealand, from November 1979 to December 1981. A macro‐invertebrate survey was conducted. All parameters, except nitrogen, were predominantly associated with particulate material, and closely followed suspended solids behaviour during storm runoff. The concentrations of these particulate parameters are linearly related to suspended solid concentrations, which implies a reasonable consistency in the particulate source material, probably attributable to the uniform stable land use. The runoff was enriched with nitrate (from septic tank seepage) and the particles by Zn, Pb, and Cu. There was little or no enrichment of the particulates with phosphorus, nitrogen, organic matter, Cr, or Ni relative to catchment soils. Ni, Cr, and Cd were generally below detection limits. Dissolved reactive phosphorus and NH4 +‐N levels were low and unimportant in total P or N leaving the catchment. Most organic matter was particulate and only slowly degraded, and consequently the biological oxygen demand was only a small fraction (c. 13%) of chemical oxygen demand. Interpretation of the water quality data allows some tentative predictions to be made of potential receiving water impacts. It is doubtful that urban runoff will cause significant oxygen depletion, although the high level of organic‐rich particulate material could lead to a deterioration of receiving water sediments and affect benthic invertebrates. Urban runoff may be an important source of nutrients, but (apart from nitrate) its importance depends on the amount of suspended material in the runoff rather than increased input of nutrients from urban‐related activities. Bacterial counts indicate a poor water quality. The impact of metals will depend largely on the bioavailability of the particulate‐bound fraction. The key to the understanding of transport, treatment, and impact of most potential pollutants in urban runoff is probably their association with particulate materials. 相似文献
79.
莱州湾东部滨海水域砂金分布特征 总被引:1,自引:0,他引:1
通过对莱州湾东部滨海水域地球物理和地质钻综合调查,业已查明该海区地质的构造和古地理环境特征,并发现区内砂金分布较普遍,本文从砂金分布的地貌单元,沉积物类型,砂金成因类型,物质来源,古气候,构造作用,砂金成因等诸方面,研究了该海域内砂金特征。 相似文献
80.
Gui-Peng Yang 《Marine Chemistry》1999,66(3-4)
A total of 22 sea surface microlayer samples collected from the Nansha Islands waters of the South China Sea were analyzed for dimethylsulfide (DMS), chlorophyll a and nutrients including nitrate, phosphate and silicate. The DMS concentrations in surface microlayer samples ranged from 82 to 280 ng S/l with a mean of 145 ng S/l. A significant correlation was found between DMS and chlorophyll a data both in the surface microlayer as well as in the subsurface water. However, no correlation was observed between DMS and nutrient concentrations in the surface microlayer. The DMS concentrations were higher in all surface microlayer samples, compared with subsurface samples. The enrichment factor (EF) of DMS in the surface microlayer varied from 1.21 to 3.08 with an average of 1.95. The EF of DMS was significantly correlated with that of chlorophyll a in the microlayer. The enrichment of DMS in the microlayer may be due to two factors, including the in situ production from phytoplankton and the transportation from the underlying seawater. The diel variations in DMS and chlorophyll a concentrations were studied at a fixed station. The highest concentrations of DMS in the surface microlayer and subsurface water were simultaneously observed in the late afternoon (1800 h), while the highest levels of chlorophyll a were simultaneously found at night (0200 h). 相似文献