全文获取类型
收费全文 | 2114篇 |
免费 | 136篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 45篇 |
大气科学 | 178篇 |
地球物理 | 609篇 |
地质学 | 778篇 |
海洋学 | 242篇 |
天文学 | 269篇 |
综合类 | 12篇 |
自然地理 | 128篇 |
出版年
2024年 | 7篇 |
2023年 | 7篇 |
2022年 | 24篇 |
2021年 | 57篇 |
2020年 | 61篇 |
2019年 | 40篇 |
2018年 | 109篇 |
2017年 | 85篇 |
2016年 | 163篇 |
2015年 | 114篇 |
2014年 | 118篇 |
2013年 | 149篇 |
2012年 | 99篇 |
2011年 | 131篇 |
2010年 | 136篇 |
2009年 | 130篇 |
2008年 | 126篇 |
2007年 | 73篇 |
2006年 | 81篇 |
2005年 | 59篇 |
2004年 | 56篇 |
2003年 | 60篇 |
2002年 | 49篇 |
2001年 | 30篇 |
2000年 | 27篇 |
1999年 | 27篇 |
1998年 | 30篇 |
1997年 | 20篇 |
1996年 | 16篇 |
1995年 | 20篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1978年 | 3篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1957年 | 2篇 |
1956年 | 3篇 |
1954年 | 2篇 |
1950年 | 2篇 |
排序方式: 共有2261条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
996.
997.
Jorge M. Navarro Waleska Labraña Oscar R. Chaparro Barbara Cisternas Alejandro Ortíz 《Estuaries and Coasts》2016,39(4):1133-1141
Frequent blooms of the dinoflagellate Alexandrium catenella in southern Chile encouraged undertaking the present study which uses the oyster Ostrea chilensis as a model for evaluating the feeding, growth, lipid storage and mortality responses to diets containing paralytic shellfish poisoning (PSP) produced by A. catenella. Medium-term (30 days) physiological responses of two groups of juvenile oysters were measured every 10 days. Five replicates were exposed to diets containing A. catenella and other five replicates were fed with a diet containing the non-toxic algae Isochrysis galbana. Diets were continuously supplied at a concentration of 2 mg L?1, in which the feeding and metabolic activity was measured, and the scope for growth calculated. Lipids storage, actual growth and mortality were also measured every 10 days. The results showed that the toxic diet has dramatic negative effects on feeding and metabolism of the juvenile individuals of O. chilensis, with high reduction of the lipid storage and growth. Mortality was also increased in individuals fed with the contaminated diet. This study supports the conclusion that the toxic dinoflagellate A. catenella restricts the energy acquisition in the juvenile O. chilensis, an important fishery and aquaculture resource in southern Chile. 相似文献
998.
999.
Iván A. Reyes Ister Mireles Francisco Patiño Thangarasu Pandiyan Mizraim U. Flores Elia G. Palacios Emmanuel J. Gutiérrez Martín Reyes 《Geochemical transactions》2016,17(1):3
Background
The presence of natural and industrial jarosite type-compounds in the environment could have important implications in the mobility of potentially toxic elements such as lead, mercury, arsenic, chromium, among others. Understanding the dissolution reactions of jarosite-type compounds is notably important for an environmental assessment (for water and soil), since some of these elements could either return to the environment or work as temporary deposits of these species, thus would reduce their immediate environmental impact.Results
This work reports the effects of temperature, pH, particle diameter and Cr(VI) content on the initial dissolution rates of K-Cr(VI)-jarosites (KFe3[(SO4)2 ? X(CrO4)X](OH)6). Temperature (T) was the variable with the strongest effect, followed by pH in acid/alkaline medium (H3O+/OH?). It was found that the substitution of CrO4 2?in Y-site and the substitution of H3O+ in M-site do not modify the dissolution rates. The model that describes the dissolution process is the unreacted core kinetic model, with the chemical reaction on the unreacted core surface. The dissolution in acid medium was congruent, while in alkaline media was incongruent. In both reaction media, there is a release of K+, SO4 2? and CrO4 2? from the KFe3[(SO4)2 ? X(CrO4)X](OH)6 structure, although the latter is rapidly absorbed by the solid residues of Fe(OH)3 in alkaline medium dissolutions. The dissolution of KFe3[(SO4)2 ? X(CrO4)X](OH)6 exhibited good stability in a wide range of pH and T conditions corresponding to the calculated parameters of reaction order n, activation energy E A and dissolution rate constants for each kinetic stages of induction and progressive conversion.Conclusions
The kinetic analysis related to the reaction orders and calculated activation energies confirmed that extreme pH and T conditions are necessary to obtain considerably high dissolution rates. Extreme pH conditions (acidic or alkaline) cause the preferential release of K+, SO4 2? and CrO4 2? from the KFe3[(SO4)2 ? X(CrO4)X](OH)6 structure, although CrO4 2? is quickly adsorbed by Fe(OH)3 solid residues. The precipitation of phases such as KFe3[(SO4)2 ? X(CrO4)X](OH)6, and the absorption of Cr(VI) after dissolution can play an important role as retention mechanisms of Cr(VI) in nature.1000.