全文获取类型
收费全文 | 4510篇 |
免费 | 722篇 |
国内免费 | 965篇 |
专业分类
测绘学 | 115篇 |
大气科学 | 1052篇 |
地球物理 | 931篇 |
地质学 | 2515篇 |
海洋学 | 779篇 |
天文学 | 27篇 |
综合类 | 249篇 |
自然地理 | 529篇 |
出版年
2024年 | 17篇 |
2023年 | 67篇 |
2022年 | 149篇 |
2021年 | 174篇 |
2020年 | 155篇 |
2019年 | 205篇 |
2018年 | 128篇 |
2017年 | 162篇 |
2016年 | 182篇 |
2015年 | 176篇 |
2014年 | 273篇 |
2013年 | 280篇 |
2012年 | 232篇 |
2011年 | 296篇 |
2010年 | 243篇 |
2009年 | 311篇 |
2008年 | 363篇 |
2007年 | 353篇 |
2006年 | 399篇 |
2005年 | 278篇 |
2004年 | 240篇 |
2003年 | 213篇 |
2002年 | 181篇 |
2001年 | 155篇 |
2000年 | 127篇 |
1999年 | 146篇 |
1998年 | 129篇 |
1997年 | 104篇 |
1996年 | 83篇 |
1995年 | 67篇 |
1994年 | 70篇 |
1993年 | 50篇 |
1992年 | 37篇 |
1991年 | 21篇 |
1990年 | 20篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
排序方式: 共有6197条查询结果,搜索用时 265 毫秒
51.
本文根据1992年夏季对湄洲湾水质环境质量调查资料,对该海区海水中油的含量及分布特征进行了分析研究。结果表明:湄洲湾夏季表层海水油的含量为5-51μg/dm^3,平均值为19.8μg/dm^3。海水的混合系数较小,高潮和低潮时油含量分布的差异,除了与陆源污染源分布有关外,主要是由水文动力学条件所决定。 相似文献
52.
53.
54.
Cu2+、Zn2+、SDS、DBS对脊尾白虾的毒性试验 总被引:4,自引:0,他引:4
选用铜、锌2种常见重金属和十二烷基硫酸钠(SDS)、十二烷基苯磺酸钠(DBS)2种阴离子表面活性剂对脊尾白虾Palaemon carincauda仔虾进行96h急性毒性试验。结果表明,Cu2 、Zn2 、SDS、DBS对脊尾白虾仔虾的96h LC50分别为0.34、0.82、14.3和14.4 mg.L-1。将脊尾白虾仔虾对这4种毒物的敏感性与文献报道的其它动物进行了比较,结果认为可以将其作为毒性测试的标准试验生物。 相似文献
55.
56.
The tolerance of the oligochaete Monopylephorus rubroniveus and the polychaete Streblospio benedicti to sediment-associated fluoranthene was characterized under normoxic (>80% dissolved oxygen saturation) and moderately hypoxic ( approximately 50% dissolved oxygen saturation) conditions. Under both conditions, M. rubroniveus was highly tolerant of fluoranthene. Streblospio benedicti was considerably less tolerant of fluoranthene compared with M. rubroniveus. In addition, S. benedicti was less tolerant to fluoranthene under moderately hypoxic conditions, although no differences in sensitivity between the two oxygen conditions were observed based upon median lethal tissue residues. Bioaccumulation factors were higher for S. benedicti exposed to moderate hypoxia, suggesting that behavioral adaptations to compensate for the lower dissolved oxygen increased its bioaccumulation of fluoranthene. The results of the present laboratory study demonstrate that (1). changes in annelid tolerance to fluoranthene under varying oxygen conditions is a species-dependent phenomenon and (2). the differential tolerance of these two annelids to these combined stressors is consistent with their relative abundances in the field. 相似文献
57.
Nicolas Mazzella Josiane Molinet Agung Dhamar Syakti Jean-Claude Bertrand Pierre Doumenq 《Marine Chemistry》2007,103(3-4):304-317
This in situ study reports on the relevance of intact phospholipids as new biomarkers and highlights the limits of the classical fatty acid analysis after the hydrolysis of the polar lipid fraction. The analysis of polar lipid fractions revealed significant contributions of marine macrophytes with either non-phospholipid compounds (sulfoquinovosyl diacylglycerol) or with both non-bacterial phospholipid classes (phosphatidylcholine) and non-bacterial phospholipid molecular species (some molecular species of phosphatidylglycerol). The analysis of intact phospholipids showed also the predominance of gram-negative bacteria in sediments whereas the analysis of fatty acids alone cannot confirm such information. Lastly, as regard to the effects of petroleum hydrocarbons on the sedimentary bacterial communities, we observed a higher degree of saturation of the fatty acyl chains of the phospholipids extracted from sediment exposed to a massive and chronic crude oil contamination. Such a result was interpreted as an adaptive response resulting in higher membrane rigidity of the bacterial communities. 相似文献
58.
Determination of cadmium(II), copper(II), manganese(II) and nickel(II) species in Antarctic seawater with complexing resins 总被引:1,自引:0,他引:1
Raffaela Biesuz Giancarla Alberti Girolamo D'Agostino Emanuele Magi Maria Pesavento 《Marine Chemistry》2006,101(3-4):180-189
The strong species of cadmium(II), copper(II), manganese(II) and nickel(II) in an Antarctic seawater sample are investigated by a method based on the sorption of metal ions on complexing resins. The resins compete with the ligands present in the sample to combine with the metal ions. Two resins with different adsorbing strengths were used. Very stable metal complexes were investigated with the strong sorbent Chelex 100 and weaker species with the less strong resin, Amberlite CG-50. Strong species were detected for three of the considered metal ions, but not for Mn(II). Cu(II) is completely linked to species with a side reaction coefficient as high as log αM(I) = 11.6 at pH = 7.3. The ligand concentration was found to be similar to that of the metal ion, and the conditional stability constant was around 1020 M− 1. In the considered sample, only a fraction of the metal ions Cd(II) and Ni(II) is bound to the strong ligands, with side reaction coefficients equal to log αM(I) = 5.5 and 6.5 at pH = 7.3 for Cd(II) and Ni(II), respectively. These findings were confirmed by the test with the weaker sorbent Amberlite CG-50. It can be calculated from the sorption equilibria that neither Mn(II) nor Ni(II) is adsorbed on Amberlite CG-50 under the considered conditions and, in fact, only a negligible fraction of Mn(II) and Ni(II) was adsorbed. A noticeable fraction of Cd(II) was adsorbed on Amberlite CG-50, meaning that cadmium(II) is partially linked to weak ligands, possibly chloride, while no copper(II) was adsorbed on this resin, confirming that copper(II) is only combined in strong species. These results are similar, but not identical, to those obtained for other seawater samples examined in previous investigations. 相似文献
59.
60.
Particularly Sensitive Sea Areas (PSSAs) are a tool designed to protect vulnerable marine areas from vessel-source pollution through measures approved by the governing body, the International Maritime Organisation. Recent developments triggered by the proposal to designate, amongst others, a large part of the Western European Atlantic a PSSA have brought the instrument to a decisive stage. Although the proposal appears to be lawful, its implications for the concept, which this paper seeks to assess, are questionable. The significance of the instrument is at risk if it is overused. As a consequence, new protective mechanisms should be contemplated. 相似文献