全文获取类型
收费全文 | 9662篇 |
免费 | 1204篇 |
国内免费 | 3696篇 |
专业分类
测绘学 | 619篇 |
大气科学 | 1747篇 |
地球物理 | 3012篇 |
地质学 | 5839篇 |
海洋学 | 1041篇 |
天文学 | 411篇 |
综合类 | 740篇 |
自然地理 | 1153篇 |
出版年
2024年 | 69篇 |
2023年 | 199篇 |
2022年 | 157篇 |
2021年 | 233篇 |
2020年 | 98篇 |
2019年 | 150篇 |
2018年 | 202篇 |
2017年 | 84篇 |
2016年 | 170篇 |
2015年 | 184篇 |
2014年 | 295篇 |
2013年 | 275篇 |
2012年 | 303篇 |
2011年 | 365篇 |
2010年 | 238篇 |
2009年 | 314篇 |
2008年 | 306篇 |
2007年 | 458篇 |
2006年 | 500篇 |
2005年 | 552篇 |
2004年 | 558篇 |
2003年 | 389篇 |
2002年 | 440篇 |
2001年 | 485篇 |
2000年 | 529篇 |
1999年 | 263篇 |
1998年 | 201篇 |
1997年 | 225篇 |
1996年 | 174篇 |
1995年 | 227篇 |
1994年 | 176篇 |
1993年 | 401篇 |
1992年 | 348篇 |
1991年 | 432篇 |
1990年 | 380篇 |
1989年 | 416篇 |
1988年 | 447篇 |
1987年 | 376篇 |
1986年 | 264篇 |
1985年 | 356篇 |
1984年 | 298篇 |
1983年 | 214篇 |
1982年 | 174篇 |
1981年 | 122篇 |
1980年 | 178篇 |
1964年 | 90篇 |
1960年 | 52篇 |
1959年 | 109篇 |
1958年 | 121篇 |
1957年 | 128篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
181.
太平洋—南极海岭的新鲜玄武岩延伸到太平洋地球化学区域EllsaM.Ferguson等在最近对一部分太平洋—南极海岭(PAR)的地球物理调查期间,S.Cande、W.Haxby、C.Raymond和合作人员在大约64°S、171°W的破碎带Ⅶ两边海岭区... 相似文献
182.
Man-made defence structures (e.g., breakwaters, jetties) are becoming common features of marine coastal landscapes all around the world. The ecology of assemblages of species associated with such artificial structures is, however, poorly known. In this study, we evaluated the density and size of fish predators of echinoids (i.e., Diplodus sargus, Diplodus vulgaris, Sparus aurata), and the density of sea urchins (i.e., Paracentrotus lividus) at defence structures (i.e., breakwaters) inside and outside the marine protected area of Miramare (northern Adriatic Sea) in order to: (1) assess possible differences in fish predator density and size between protected and fished breakwaters; (2) assess whether fish predation may have the potential to affect sea urchin density in artificial rocky habitats. Surveys were carried out at four random times over a period of two years. Total density, and density of medium- and large-sized individuals of the three predatory fishes were generally greater at the protected than at the fished breakwaters, whereas no differences were detected in the density of small-sized individuals. Density of the sea urchin P. lividus did not show any difference between protected and fished breakwaters. The results of this study suggest that: (1) protection may significantly affect predatory fishes in artificial rocky habitats; (2) differences in predatory fish density, and size may be unrelated with the density of the sea urchin P. lividus; (3) protected artificial structures such as breakwaters, originally planned for other purposes, could represent a potential tool for fish population recovery and enhancement of local fisheries. 相似文献
183.
184.
杭州湾南岸潮滩的~(210)Pb分布及其沉积学意义 总被引:1,自引:0,他引:1
杭州湾南岸潮滩的~(210)Pb垂向分布具有随深度波动的特征。湖滩颗粒物在吸附模拟系统中的~(210)Pb分配系数,主要受颗粒物含量的影响。本文从潮滩沉积~(210)Pb初始比度在低于平衡点一侧波动的机理,以及被沉积间断所分隔的有效封闭段的存在出发,提出选择常态沉积层的高~(210)Pb比度窗口,建立以CIC模式估计潮滩沉积速率的方法。 相似文献
185.
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
186.
伊利诺斯盆地宾夕法尼亚纪沉积物季节性降雨的证据ErikP.Kvale等根据古纬度位置、动物群证据或气候敏感岩性的出现而恢复的古气候可表达一个地区相当长时期的气候格局,但气候的细节只有通过与目前条件相同地区的比较才能推断。由于时间的迁移、海洋和陆地的变... 相似文献
187.
太平洋西南部铁锰矿化的地球化学特征A.H等对克马德克和新赫布里底岛弧-海沟系不同地貌构造采集了海底样品(1990年科学考察船“A.H”院士号第17航次),在一系列测站上采集到不同的铁锰形成物(жMO)。在采自8个测站的38个样品分析资料的基础上研究了... 相似文献
188.
Trends in emigration from Ireland over time are reviewed. "During the eighteenth and nineteenth centuries overseas migration to the United States and seasonal harvest migration to Britain were the main types of movement, but over the past 100 years the Irish have developed a special affinity for settling in British towns. Although the outflow was halted for a time during the 1970s, when return migration took over, the 1980s have seen a renewal of the exodus. This time, however, the character of the flow has changed from predominantly low-skill construction and factory workers to embrace better-educated emigrants, including many graduates. This shift reflects Ireland's changing position in the international market for labour." 相似文献
189.
190.