全文获取类型
收费全文 | 2344篇 |
免费 | 241篇 |
国内免费 | 503篇 |
专业分类
测绘学 | 350篇 |
大气科学 | 264篇 |
地球物理 | 655篇 |
地质学 | 1064篇 |
海洋学 | 279篇 |
天文学 | 86篇 |
综合类 | 225篇 |
自然地理 | 165篇 |
出版年
2024年 | 15篇 |
2023年 | 47篇 |
2022年 | 49篇 |
2021年 | 62篇 |
2020年 | 32篇 |
2019年 | 68篇 |
2018年 | 65篇 |
2017年 | 63篇 |
2016年 | 48篇 |
2015年 | 68篇 |
2014年 | 86篇 |
2013年 | 62篇 |
2012年 | 101篇 |
2011年 | 138篇 |
2010年 | 78篇 |
2009年 | 82篇 |
2008年 | 135篇 |
2007年 | 127篇 |
2006年 | 119篇 |
2005年 | 121篇 |
2004年 | 127篇 |
2003年 | 100篇 |
2002年 | 75篇 |
2001年 | 62篇 |
2000年 | 101篇 |
1999年 | 67篇 |
1998年 | 75篇 |
1997年 | 75篇 |
1996年 | 60篇 |
1995年 | 71篇 |
1994年 | 60篇 |
1993年 | 88篇 |
1992年 | 55篇 |
1991年 | 65篇 |
1990年 | 68篇 |
1989年 | 50篇 |
1988年 | 32篇 |
1987年 | 67篇 |
1986年 | 22篇 |
1985年 | 26篇 |
1984年 | 20篇 |
1983年 | 20篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 19篇 |
1978年 | 6篇 |
1959年 | 6篇 |
1957年 | 5篇 |
1937年 | 5篇 |
1935年 | 5篇 |
排序方式: 共有3088条查询结果,搜索用时 821 毫秒
31.
广西地区文蛤的遗传多样性研究 总被引:13,自引:3,他引:13
以随机扩增多态性DNA(RAPD)研究广西的山口、北海、犀牛角、东兴的文蛤种群的遗传多样性。结果表明,在筛选的60个引物中,23个呈阳性反应,其中10个引物可产生105条稳定、清晰的带。山口、北海、犀牛角、东兴的文蛤种群的遗传多样性指数分别为0.1995,0.2039,0.1773,0.1936;多态位点比例分别为86.32%,90.63%,81.05%,88.00%,4个种群间的遗传距离在0.050~0.070之间,相邻种群的遗传差距较小。除犀牛角种群以外,其它3个种群的遗传变异水平较高。 相似文献
32.
1nm锰矿相的金属阳离子交换能力的研究 总被引:6,自引:3,他引:6
人工合成的1nm锰矿相和铜、钴、镍等二价金属阳离子的交换实验表明,1nm锰矿相具有强烈的金属阳离子交换能力.正是这种金属阳离子的交换能力,使得大洋多金属结核大量地富集了铜、钴、镍等有价金属元素.1nm锰矿相对几种金属阳离子的交换的优先顺序为:Cu>Co>Zn≥Ni>Ca>Mg.多金属结核中镍的含量往往高于铜、钴、锌等元素,但在交换顺序中它却低于铜、钴、锌等,这种不一致性说明结核成矿后期的金属离子交换并非是有价金属结合进结核的唯一途径.多金属结核富含铜、钴、镍等有价金属可能是结核初始成矿和成矿后期金属离子交换等多种因素共同作用的结果. 相似文献
33.
Taban IC Bechmann RK Torgrimsen S Baussant T Sanni S 《Marine environmental research》2004,58(2-5):701-705
The single-cell microgel electrophoresis assay or the comet assay was used to evaluate DNA damage of dispersed crude oil on sea urchins (Strongylocentrotus droebachiensis) and mussels (Mytilus edulis L.). Sea urchins were exposed to 0.06 and 0.25 mg/L dispersed crude oil in a continuous flow system, while the mussels were exposed to 0.015, 0.06 and 0.25 mg/L dispersed crude oil. Sea urchin coelomocytes and mussel haemocytes were sampled after 4 and 5 weeks exposure, respectively. In the sea urchin coelomocytes, there was a significant concentration-related increase in the percentage of DNA in comet tail. In mussel haemocytes, there was a significantly higher percentage of DNA in comet tail for all treatments compared to the control. The responses were concentration-related up to 0.06 mg/L oil. The two highest exposure concentrations of mussels were not significantly different from each other. These results indicate that the comet assay can be used for biomonitoring of DNA damage in marine invertebrates following oil contamination. 相似文献
34.
35.
为获得河水及其悬浮物样品中痕量金属浓度的可比性数据,评价参加相互校准实验室的分析水平,联合国教科文组织政府间海洋学委员会和联合国环境规划署下属的“方法、标准和相互校准专家组”于1986年组织了对泰国曼谷的河水及其悬浮物样品中痕量金属分析互校工作。参加这次互校的有美国、加拿大、日本、菲律宾、南朝鲜、泰国和中国共7个国家的8个实验室。我国国家海洋局第三海洋研究所黄自强和李锦霞两位副研究员领导的科研小组参加了这次相互校准。他们采用洁净分析技术,分析了河水样品中痕量溶解态铜、铅、锌、镉、钴、镍、铁和锰,所有分析结果均落在定值的一倍标准偏差范围内,名列前茅,获得较高评价,为我国争得了荣誉。这标志着该所河 相似文献
36.
This study aimed to test the performance of the amphipod Gammarus locusta (L.) in chronic sediment toxicity tests. It constitutes part of a multi-level assessment of chronic toxicity of estuarine sediments, integrating organism and population-level endpoints with biochemical markers responses. Here we account for organism and population-level effects, while biomarker responses were reported in a companion article. Five moderately contaminated sediments from Sado and Tagus estuaries were tested, comprising 3 muddy and 2 sandy sediments. These sediments either did not show acute toxicity or were diluted with control sediment as much as required to remove acute toxicity. Subsequent chronic tests consisted of 28-day exposures with survival, individual growth and reproductive traits as endpoints. Two of the muddy sediments induced higher growth rates in the amphipods, and improved reproductive traits. This was understood to be a consequence of the amount of organic matter in the sediment, which was nutritionally beneficial to the amphipods, while concurrently decreasing contaminant bioavailability. Biomarker responses did not reveal toxicant-induced stress in amphipods exposed to these sediments. One of the sandy sediments was acutely toxic at 50% dilution, but in contrast stimulated amphipod growth when diluted 75%. This was presumed to be an indication of a hormetic response. Finally the two remaining contaminated sediments showed pronounced chronic toxicity, affecting survival and reproduction. The sex ratio of survivors was highly biased towards females, and offspring production was severely impaired. The particulars of the responses of this amphipod were examined, as well as strengths versus limitations of the sediment test. This study illustrates the utility of this chronic test for toxicity assessment of contaminated estuarine sediments, with potential application all along Atlantic Europe. 相似文献
37.
38.
39.
40.
迪尔闪石(deerite)是一种含水富铁的单双链复合结构链状硅酸盐矿物,其端员组分为Fe122++Fe62+(Si12O40)(OH) 10.最早由Agrell等在弗朗西斯科杂岩中发现,之后陆续在世界20余处蓝片岩地体的富铁石英岩中发现.迪尔闪石通常被认为是低温高压条件下富铁岩石的典型变质矿物,Lattard &Le Breton的实验岩石学证据表明:迪尔闪石只在小于10℃/km的地热梯度下稳定存在. 相似文献