全文获取类型
收费全文 | 231篇 |
免费 | 9篇 |
国内免费 | 25篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 9篇 |
地球物理 | 165篇 |
地质学 | 55篇 |
海洋学 | 15篇 |
天文学 | 7篇 |
综合类 | 6篇 |
自然地理 | 5篇 |
出版年
2023年 | 2篇 |
2021年 | 1篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 7篇 |
2012年 | 20篇 |
2011年 | 29篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 23篇 |
2007年 | 10篇 |
2006年 | 5篇 |
2005年 | 15篇 |
2004年 | 12篇 |
2003年 | 10篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1983年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有265条查询结果,搜索用时 15 毫秒
261.
262.
Halogenated aromatic hydrocarbons (HAHs) and polynuclear aromatic hydrocarbons (PAHs) are major environmental contaminants. Fish species that are chronically exposed to these compounds can develop resistance to their toxic effects. In all fish species studied to date, toxicant resistance has been accompanied by decreased inducibility of the xenobiotic metabolizing enzyme, cytochrome P450 1A (CYPIA). CYP1A induction is mediated through the Aryl Hydrocarbon Receptor (AHR). Although these compounds mediate their effects through this pathway, there have been resistant populations in which one chemical class cannot induce CYPIA expression (HAHs) while the other (PAHs) can. Resistance to PAHs was examined in a HAH-resistant population of Fundulus heteroclitus collected from a site contaminated with both compound classes (Newark Bay, NJ). Fish were injected intraperitoneally with the HAH 3,4,3',4'-tetrachlorobiphenyl (PCB77), benzo[a]pyrene (B[a]P, a PAH) or vehicle and sacrificed after 2 (B[a]P) or 5 days (PCB77, vehicle). We found no significant increase in CYP1A mRNA levels in resistant Newark Bay F. heteroclitus treated with either B[a]P or PCB77, while there was a 3.9 fold (PCB77) and 4.2 fold (B[a]P) increase in CYP1A mRNA in Flax fish relative to controls. AHR labeling studies revealed significantly (P < 0.05) lower levels of hepatic AHR in Newark fish (1,770 +/- 1,693.2 DPM) relative to Flax fish (6,082.5 +/- 1,709.9 DPM). Overall, these data suggest Newark F. heteroclitus are resistant to both PAHs and HAHs at the level of CYP1A mRNA, which might be mediated, in part, though lower expression of AHR. We are currently studying the promoter sequence to determine its role in chemical resistance. 相似文献
263.
Biomarker responses in Macoma nasuta (Bivalvia) exposed to sediments from northern San Francisco Bay
Our study investigates biomarker responses and survival of Macoma nasuta exposed to sediments collected from six locations in northern San Francisco Bay. Biomarkers analyzed were stress proteins (hsp70) in gill, mantle and digestive gland, lysosomal membrane damage and histopathologic lesions. Sediments and clam tissues were analyzed for a comprehensive suite of heavy metals and trace organic pollutants. Sediment grain size and organic carbon content were determined. Clams accumulated metals, polyaromatic hydrocarbons (PAHs) and organochlorine pesticides (aldrin and p,p(')-DDT and its metabolites p,p(')-DDD and p,p(')-DDE). Pearson and Spearman correlation analysis revealed that mortality, hsp70 in gill and histopathologic lesion scores in gonads, and lysosomal membrane damage were significantly correlated with tissue concentrations of DDT and/or its metabolites. Tissue concentrations of metals, in particular nickel, chromium, and copper, were associated with macrophage aggregates in digestive gland and germ cell necrosis. Cadmium was linked to mortality and lysosomal membrane damage. 相似文献
264.
A 400-year record of black carbon flux in the Xisha archipelago, South China Sea and its implication 总被引:2,自引:0,他引:2
Liu X Xu L Sun L Liu F Wang Y Yan H Liu Y Luo Y Huang J 《Marine pollution bulletin》2011,62(10):2205-2212
We reconstructed the first long-term (∼400 years) records of black carbon (BC) deposition flux from three ornithogenic sediment profiles, which were collected from three remote, isolated islets of the Xisha archipelago, South China Sea. The significant correlations between black carbon, organic matter and excess 210Pb suggested that black carbon was mainly derived from atmospheric deposition, and further enriched by plant-derived organic matter in sediments. During the past 400 years, the BC flux remained relatively low before the onset of 20th century; it started to increase from approximately 1900 AD, and peaked around the 1970s. In the recent 30 years, the BC flux seemed to display decreasing trend, very likely due to the change of energy structure and development of pollution control techniques. In comparison with marginal sea regions that are greatly impacted by anthropogenic activities, these pristine Xisha islands were not significantly influenced by black carbon of anthropogenic origin. 相似文献
265.
Newark Bay (NB) killifish (Fundulus heteroclitus) have been chronically exposed to environmental contaminants that activate the aryl hydrocarbon receptor (AHR) and are tolerant to toxic effects and CYP1A induction provoked by AHR ligands. Resistance to CYP1A induction could be due to an epigenetic mechanism such as DNA methylation. We measured in-ovo CYP1A catalytic activity (ethoxyresorufin-O-deethylase, EROD) in NB and reference site killifish embryos aqueously exposed to various concentrations of the de-methylating agent 5-azacytidine, 5-AC (5, 50 and 500 micro(micro)M) with or without 0.2 micro(micro)g/l of the CYP1A inducer 3,3',4,4',5 pentachlorobiphenyl (IUPAC PCB126). Neither PCB126 alone, nor PCB126 plus 5-AC, induced EROD above levels in vehicle treated Newark Bay fish. In reference site fish, the same PCB126 dose provoked a 7.4-fold EROD induction relative to controls. We conclude that Newark Bay killifish are resistant to CYP1A induction by co-planar PCBs during early embryological development and our data suggests that DNA methylation does not play a critical role in resistance to CYP1A induction in this model. 相似文献