全文获取类型
收费全文 | 388篇 |
免费 | 36篇 |
国内免费 | 62篇 |
专业分类
测绘学 | 2篇 |
地球物理 | 36篇 |
地质学 | 28篇 |
海洋学 | 367篇 |
天文学 | 1篇 |
综合类 | 42篇 |
自然地理 | 10篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 6篇 |
2020年 | 22篇 |
2019年 | 19篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 14篇 |
2015年 | 12篇 |
2014年 | 15篇 |
2013年 | 43篇 |
2012年 | 6篇 |
2011年 | 16篇 |
2010年 | 11篇 |
2009年 | 19篇 |
2008年 | 30篇 |
2007年 | 22篇 |
2006年 | 25篇 |
2005年 | 12篇 |
2004年 | 16篇 |
2003年 | 7篇 |
2002年 | 19篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 10篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有486条查询结果,搜索用时 656 毫秒
321.
介绍了新型绳索取心钻杆及新型机械传动不停车倒杆立轴岩心钻机的特点及应用效果。分析了提高岩心钻探施工效率、降低成本、节能降耗的技术措施,同时提出了未来地质岩心钻机的发展方向及建议。 相似文献
322.
Nest and feeding behaviour patterns were compared between two sympatric species, the bushy-tailed gerbilSekeetamys calurusand the golden spiny mouseAcomys russatus, in order to assess nest site and food as possible resources of competition. The way the species interact under laboratory conditions was also compared. WhileS. calurusused a nest into which they removed bedding material, only two out of sixA. russatusdid so, while in at least half of the studied cases they were found roosting outside of the nest inside the enclosure. When introduced into the same enclosure,S. caluruswas the dominant species and in five out of 12 casesS. calurusinhabited the nest abandoned byA. russatus, and in seven casesA. russatuswas found resting in the enclosure. UnlikeA. russatus,S. calurusaccumulated food inside its nest and also protected the food resource in the enclosure againstA. russatus. It seems that different nest and feeding behavioural patterns can reduce competition between these two sympatric species. 相似文献
323.
324.
325.
Abstract. When simultaneously presented with equal numbers of four sizes of clumped Mytilus californianus (20, 35, 55 and 85 mm shell length), Pisaster ochraceus (arm length of 70-110mm R) showed a preference for the medium sizes (35 and 55mm length). Prey-size preference was positively correlated with predator size. Mean prey-digestion times (insertion of the stomach, opening of the valves and digestive period) decreased significantly following fiiing of an artificial gape between the valves of mussels. When presented with different sizes of clumped filed mussels, starfish still chose medium mussels, indicating that stomach insertion, valve opening, and digestion rate may not be important constraints determining size selective predation. Measurements of the force required to dislodge mussels from the substratum and conspecifics showed an increasing exponential relationship with mussel size. Size selective feeding may be an energy maximizing and time minimizing strategy, where energy gained from choosing larger mussels is balanced against disproportionately increased costs in energy and time of removing large mussels from the substratum. 相似文献
326.
四种重金属离子对侧扁软柳珊瑚的毒性及其摄食行为的影响 总被引:1,自引:0,他引:1
本实验通过48h的急性毒性测试,来了解重金属Cu2 、Zn2 、Cd2 、Pb2 的污染环境对侧扁软柳珊瑚(Subergorgiasuberosa)的影响程度,以认知重金属对海洋生物尤其是柳珊瑚所造成的伤害.实验的结果显示,Cu2 的半致死浓度约为0.13mg/dm3,Zn2 为8.69mg/dm3,而Cd2 为10.84mg/dm3,Pb2 为8.49mg/dm3;亦即Cu2 污染对侧扁软柳珊瑚毒性影响最大.另外,在实验的观察中也发现,受到伤害的珊瑚中常会刺激黏液的分泌,在较高的浓度下则会造成其共肉组织的溃烂致使整株珊瑚部分或整体的死亡.在摄食影响的研究方面,侧扁软柳珊瑚在Cu2 浓度分别为0.02、0.05mg/dm3的污染环境下捕食丰年虫(Chirocephalus)的行为与正常珊瑚间有明显差异(p<0.01),经过Cu2 污染环境后的珊瑚虫(polyp)常常不能有效地捕食到丰年虫,甚至捕食到丰年虫却不能将其顺利吞咽而造成丰年虫从其触手中逃逸.数据显示正常珊瑚虫捕食丰年虫的成功率平均达85.42%,而受0.02mg/dm3Cu2 影响的珊瑚虫则为57.58%,受0.05mg/dm3Cu2 影响的则仅为24.24%. 相似文献
327.
We investigated the diel vertical migration of Euphausia pacifica in relation to molt and reproductive processes and feeding activity in April and September 2001 at fixed stations off northeastern
Japan. The vertical distribution of this species was shallower in April than in September during both day and night, which
was partly explained by a high surface temperature (19°C) and the existence of a subsurface chlorophyll maximum in September.
It has been demonstrated for the first time that diel vertical migration of this species is influenced by molt processes because
upward migration of molting individuals was restricted compared with non-molting ones. Feeding activity of molting individuals
was reduced throughout the day, being lower than or similar to the daytime feeding activity of non-molting ones. The percentage
of molting individuals was least (2–4%) among the gravid females, which suggests that gravid females molt less frequently
than other stages of females and males. Molt and reproductive processes therefore seemed to be coupled in this species. 相似文献
328.
329.
Japanese seaperch Lateolabrax japonicus migrate from Ariake Bay to the estuarine turbidity maximum (ETM) zone of the Chikugo River and inhabit there through the post-migration period (15–20 mm in standard length). The feeding, growth and mortality during the post-migration period of Japanese seaperch were analyzed in relation to seasonal changes in temperature and prey concentration. Larvae and juveniles were collected from ten sampling stations at 4–7 day intervals from 24 February to 24 April 2005 in the Chikugo estuary. Based on the otolith microstructure analysis the sampled fish were divided into nine cohorts, each cohort covering a 5 day hatch date period (22 December 2004 to 4 February 2005). The growth coefficient (G, day−1) was higher and the mortality coefficient (M, day−1) was lower in the later cohorts. The ratio of G to M as an index of stage-specific survival during the post-migration period significantly increased as the season progressed and exceeded 1.0 in the last cohort examined. Variability in abundance of the major prey organism, Sinocalanus sinensis, had a significant effect on the Japanese seaperch ingestion rate. Increase in temperature and spring bloom of S. sinensis is concluded to provide the later cohorts with a higher survival probability through increasing ingestion and growth rates during their post-migration period in spring 2005. 相似文献
330.
Test of a food consumption model for the Atlantic cod 总被引:3,自引:0,他引:3