全文获取类型
收费全文 | 1174篇 |
免费 | 377篇 |
国内免费 | 244篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 41篇 |
地球物理 | 364篇 |
地质学 | 1037篇 |
海洋学 | 182篇 |
天文学 | 1篇 |
综合类 | 81篇 |
自然地理 | 84篇 |
出版年
2024年 | 8篇 |
2023年 | 20篇 |
2022年 | 30篇 |
2021年 | 40篇 |
2020年 | 40篇 |
2019年 | 41篇 |
2018年 | 43篇 |
2017年 | 49篇 |
2016年 | 55篇 |
2015年 | 71篇 |
2014年 | 92篇 |
2013年 | 87篇 |
2012年 | 97篇 |
2011年 | 105篇 |
2010年 | 103篇 |
2009年 | 105篇 |
2008年 | 81篇 |
2007年 | 86篇 |
2006年 | 116篇 |
2005年 | 92篇 |
2004年 | 68篇 |
2003年 | 60篇 |
2002年 | 44篇 |
2001年 | 56篇 |
2000年 | 37篇 |
1999年 | 42篇 |
1998年 | 32篇 |
1997年 | 25篇 |
1996年 | 18篇 |
1995年 | 11篇 |
1994年 | 16篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1795条查询结果,搜索用时 15 毫秒
891.
林荣根 《中国海洋湖沼学报》1994,12(2):106-113
The degradability of particulate organic matter(POM)in the Gironde Estuary(France)was measuredusing the incubation technique.The influence of sample treatment and incubation conditions on the re-sults was evaluated.A mathematical model was successfully used to describe the various degradationcurves.Results showed that the upstream POM had very high degradability;the central estuaryPOM had low degradability;and that the mouth POM degradability was between that of central POM(low degradability)and marine POM(high degradability). 相似文献
892.
Based on the principle of synthesis, a new method was put forward to dispose Congo Red anion-containing dyestuff from wastewater
and its feasibility was also examined. The principle of the method is described as follows: Mg2+ and Al3+ are hydrolyzed to form Mg/Al-LDH by adding Mg2+, Al3+ and NaOH in wastewater containing anion dyestuff, which is selectively intercalated with the interlayer of LDH in order to
balance positive structural charge. While Mg2+ and Al3+ are co-precipitated to form LDH, the anion dyestuff in wastewater will be removed by LDH synthesized in-situ, as is confirmed by X-ray diffraction analysis of settlings and chemical analysis of aqueous samples. In this work, we studied
the influence of Mg/Al mole ratio, pH value, time and temperature of reaction on the removal of anion dyestuff and the use
of Mg and Al. The experimental results showed the maximum removal efficiency of anion dyestuff could be attained when pH value
was 9.0, and Mg/Al mol ratio was 2: 1, reaction duration was 2 hours, and the effect of temperature was not remarkable, and
the removal efficiency could reach 100%. Meanwhile, the Mg and Al added could be made good use of. This technology has the
advantage of extraordinary efficiency of wastewater disposal.
Foundation item: Project supported by the National Natural Science Foundation of China (40472026). 相似文献
893.
894.
Studies of groundwater following changes to the wastewater treatment plant and disposal field at Kinloch (Taupo area, New Zealand) showed increases in chloride (Cl) after 5 months, followed by increased calcium (Ca) and magnesium (Mg) concentrations arising as a result of cation exchange with sodium (Na) and potassium (K). Sodium (Na) and potassium (K) showed only small increases after 12 months of initial discharge, while phosphorus (P) was still being totally adsorbed by ion exchange in the aquifer. 相似文献
895.
Coal flotation studies were carried out in ultrasonically assisted flotation cells. Representative hard coal slime samples from Prosper-Haniel Coal Preparation Plant located in Bottrop, Ruhr Region of Germany were used for this purpose. A Wemco type flotation cell was fitted with transducers and tests were carried out at variable frequency and power. The reagent for coal flotation was Ekofol-440 with variable dosages during conventional and ultrasonic flotation experiments. The results showed that ultrasonic coal flotation yields more combustible recovery and lower ash values in concentrates than conventional flotation by using similar reagent dosages. These results are explained on the basis of efficient surface cleaning of the coal particles. 相似文献
896.
897.
898.
随着青藏高原工程强度的提高,冻土区斜坡稳定性成为工程建设必须面对和解决的问题,其中最为严重也是较难防治的斜坡失稳是热融滑塌.针对典型热融滑塌进行的温度监测资料表明,在滑塌的影响下,其下多年冻土地温年变化幅度趋小而年平均地温升高,导致产生这一现象的原因在于每年进入多年冻土的冷能有所降低.滑坡溯源侵蚀范围监测资料表明,滑塌范围的扩展随地温的周期变化波动进行,并主要集中在7~9月,最大扩展范围出现在沿坡体倾向方向.热融滑塌的产生与多年冻土条件和外因力的诱发关系密切,工程治理要考虑引起滑坡消亡的基本条件. 相似文献
899.
Sterols and their metabolites are recognized as hormonally active compounds in many earlier studies. Therefore, identification and quantification of selected phytosterols related to developments in pulping and wastewater treatment of pulp and paper industry were studied from sediment cores of two Finnish lakes. Indicating the period of maximal emissions, the highest total concentration of sterols, 1970 μg/g dry weight, was detected in the stratified sediment of central Lake Päijänne, dated to the mid-1970s (depth 12–15 cm). After notable changes in processes and effluent treatment, the amounts of sterols in effluents must have diminished, as shown by the sterol content in the sediment downstream from the mills. Therefore, the concentrations were about 10% of the historical maximum in the surface sediment (depth 0–3 cm) in both downstream sites investigated at Lake Päijänne. However, these concentrations were clearly over the natural background (10–50 μg/g) occurring in the subsamples of the pre-industrial phase (depth 36–44 cm) as well as in the reference site of southern Lake Saimaa, the second investigated lake. At a nearby site of a pulp and paper mill in southern Lake Saimaa, sterols were most abundant (1760 μg/g dry weight) in the sediment layer 0–5 cm despite the improved process control during last few decades. This study showed the abundance of ecotoxicologically harmful compounds in downstream sediment sites of pulp and paper industry. 相似文献
900.