全文获取类型
收费全文 | 832篇 |
免费 | 121篇 |
国内免费 | 146篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 132篇 |
地球物理 | 255篇 |
地质学 | 381篇 |
海洋学 | 188篇 |
天文学 | 39篇 |
综合类 | 23篇 |
自然地理 | 77篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 13篇 |
2021年 | 15篇 |
2020年 | 21篇 |
2019年 | 30篇 |
2018年 | 15篇 |
2017年 | 49篇 |
2016年 | 42篇 |
2015年 | 35篇 |
2014年 | 43篇 |
2013年 | 34篇 |
2012年 | 22篇 |
2011年 | 66篇 |
2010年 | 29篇 |
2009年 | 74篇 |
2008年 | 74篇 |
2007年 | 56篇 |
2006年 | 61篇 |
2005年 | 50篇 |
2004年 | 42篇 |
2003年 | 37篇 |
2002年 | 36篇 |
2001年 | 36篇 |
2000年 | 38篇 |
1999年 | 33篇 |
1998年 | 23篇 |
1997年 | 20篇 |
1996年 | 23篇 |
1995年 | 15篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 5篇 |
排序方式: 共有1099条查询结果,搜索用时 15 毫秒
131.
J. Siepak 《洁净——土壤、空气、水》1999,27(5):282-285
This paper reports on total organic carbon (TOC) and its fractions dissolved organic carbon (DOC) and particulate organic carbon (POC) studied in different Polish rivers. The samples investigated came from the Vistula, Odra, and Warta rivers, and were compared with similar data on river waters available in the literature. The DOC concentrations ranged from 10.0 to 14.2 mg/L and did not vary during the vegetative season. The POC values considerably increased from May through September and reached a maximum in summer. Results for the years 1991τ1996 evidenced a significant increase in the POC value for the Polish rivers from 10.8 to 24.5 mg/L, in comparison with analogous values for West European rivers and North American ones. The enhanced values of TOC and POC were interpreted as being due to anthropogenic pollution. 相似文献
132.
The electrical conductivity of Posidonia black shales — from magnetotelluric exploration to rock samples
下载免费PDF全文
![点击此处可从《Geophysical Prospecting》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We carried out a magnetotelluric field campaign in the South–East Lower Saxony Basin, Germany, with the main goal of testing this method for imaging regional Posidonia black shale sediments. Two‐dimensional inversion results of the magnetotelluric data show a series of conductive structures correlating with brine‐saturated sediments but also with deeper, anthracitic Westphalian/Namurian coals. None of these structures can be directly related with the Posidonia black shale, which appears to be generally resistive and therefore difficult to resolve with the magnetotelluric method. This assumption is supported by measurements of electrical resistivity on a set of Posidonia shale samples from the Hils syncline in the Lower Saxony basin. These rock samples were collected in shallow boreholes and show immature (0.53% Ro), oil (0.88% Ro), and gas (1.45% Ro) window thermal maturities. None of the black shale samples showed low electrical resistivity, particularly those with oil window maturity show resistivity exceeding 104 Ωm. Moreover, we could not observe a direct correlation between maturity and electrical resistivity; the Harderode samples showed the highest resistivity, whereas the Haddessen samples showed the lowest. A similar trend has been seen for coals in different states of thermal maturation. Saturation of the samples with distilled and saline water solutions led to decreasing electrical resistivity. Moreover, a positive correlation of electrical resistivity with porosity is observed for the Wickensen and Harderode samples, which suggests that the electrical resistivity of the Posidonia black shale is mainly controlled by porosity. 相似文献
133.
134.
135.
136.
辽宁中部城市群大气能见度变化趋势及影响因子分析 总被引:38,自引:5,他引:33
通过分析辽宁中部相对集中分布的5个城市群1987-2002年间的大气能见度、影响能见度的气象因子和污染物的变化特征及能见度与气象因子、污染物浓度之间的相关关系等,得到以下结论:(1)各城市能见度有明显的月、季和年际变化特征,能见度月变化呈双峰型,第一个峰值在5月份,第二个峰值在9,10月份;冬季能见度的值最低,春、秋季高;本溪市的能见度在逐年变好;沈阳的能见度从1987-1997年逐年变好,1997年以后又逐年变差;其它城市的能见度呈逐年变差的趋势。(2)各城市影响能见度的气象因子的年际变化特征基本是一致的;5个城市TSP,SO2污染浓度年均值均呈下降趋势,NOx的年际变化趋势不明显。(3)能见度与湿度、雾的相关关系都呈负相关且非常显著;与降雨量、风速及温度之间的关系比较复杂;与各种污染物的相关都呈负相关。 相似文献
137.
Models-3空气质量模式对兰州市污染物输送的模拟 总被引:23,自引:7,他引:16
较详细地介绍了美国环保总局的第三代空气质量模式系统Models-3的特点,并且针对兰州市冬季采暖期污染严重的特点,选取2002年12月份的个例,将兰州市最新的大气污染源资料加入模式中.对模式进行调试并检验了该模式对兰州污染的模拟性能。从模式对SO2,NO2和O3等几种大气污染物浓度的模拟结果与监测资料对比分析,表明该模式系统较好地模拟出了SO2,NO2的空间分布格局,模拟结果与监测结果比较吻合,而且模式模拟的污染物浓度场比较均匀;模式模拟的O3的日变化规律与资料分析结论基本一致,也符合O3的生成机理。因此该模式系统对于复杂地形条件下的城市污染物输送具有一定的模拟能力。 相似文献
138.
Mark Anglin Harris 《Environmental Geology》2009,56(8):1517-1522
Several years (7) after incidental lithification by added gypsum, the effect of crushing and phyto-organics on some physical
properties of red mud wastes (RMW) was examined under laboratory conditions. It was hypothesized that mechanically breaking
up the hardened masses would increase their permeability. However, on the contrary, crushing these rock-hard masses into <2-mm
particles did not increase permeability. A phyto-organic treatment on the other hand greatly improved permeability of the
crushed entities such that infiltration rates increased from 0 to 10 cm/h. After 24 weeks of incubation, the structure of
the newly formed phyto-organically treated gypsum-hardened RMW aggregates was also substantially improved over that of the
controls, as a >3-fold increase in resistance to disintegration during wet sieving was exhibited by the phyto-organically
treated samples. The increase in water infiltration by combining crushing with phyto-organic applications was ascribed to
a decrease in particle dispersion, creating more stable clay clusters, which in turn stabilized channels and pores. Conversely,
it was concluded that the singular crushing of gypsum-hardened bauxite waste in the waste dumps is potentially wasteful and
ineffective. 相似文献
139.
Mohamed A. Sakr Mohamed A. Shahin Yasser M. Metwally 《Geotechnical and Geological Engineering》2009,27(1):105-113
This paper presents the results of geotechnical and mineralogical investigations on lime-treated soft clay soil from Idku
City, Egypt, where high organic matters of about 14% exist. Lime was added in the order of 1%, 3%, 5% and 7% by weight and
laboratory experiments after 7, 15, 30 and 60 days were conducted including the mineralogical and microstructural examinations,
grain size analysis, plasticity limits, unconfined compressive tests, vane shear tests and oedometer tests. The results indicate
that soft clay soil of high organic content of 14% can be stabilized satisfactorily with the addition of 7% lime. The results
also demonstrate that the changes in the mineralogical contents and soil fabric of high organic lime-treated soft clay improve
soil plasticity, strength and compressibility. 相似文献
140.
Mineral constituents in common chanterelles and soils collected from a high mountain and lowland sites in Poland 总被引:1,自引:1,他引:0
This paper reported the results of the determination of Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Rb, Sr and Zn in Common Chanterelles (Cantharellus cibarius) Fr. and surface soil layer (0-10 cm) underneath the fruiting bodies. Mushrooms and soils were collected from a lowland site in the Hel Peninsula (Baltic Sea coast) and a high mountain site in the Tatra Mountains. The trace elements were determined using validated method and inductively coupled plasma - atomic emission spectroscopy (ICP-AES). Common Chanterelles that emerged at sites poor in mineral nutrients podzols of the Hel Peninsula forests efficiently bioconcentrated several essential trace elements (K, P, Co, Cu, Mn, Na, Zn), while the abundance of those elements in carpophores was around half less compared to specimens from Zakopane region and which emerged in soils much richer in minerals. Common Chanterelles collected at two spatially distant background areas in Poland were only weakly contaminated with metals such as Ag, Cd, Hg and Pb. The maximum tolerable Cd and Pb contents of certain cultivated mushrooms are regulated in the European Union by law and these hazardous metals in C. cibarius were far below tolerance limits set. 相似文献