全文获取类型
收费全文 | 155篇 |
免费 | 11篇 |
国内免费 | 9篇 |
出版年
2024年 | 4篇 |
2023年 | 3篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 9篇 |
2012年 | 6篇 |
2011年 | 6篇 |
2010年 | 3篇 |
2009年 | 2篇 |
2008年 | 8篇 |
2007年 | 9篇 |
2006年 | 10篇 |
2005年 | 9篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有175条查询结果,搜索用时 281 毫秒
21.
22.
A new species of phocoenid cetacean Haborophocoena , collected from the Early Pliocene Embetsu Formation, in the close vicinity to the site where the holotype of the type species of the genus Haborophocoena was retrieved, improves our knowledge of the anatomy of this cetacean. The new species, represented by a skull, lacking distal half of the rostrum, ear bones, and teeth, is significantly smaller than, but morphologically similar to, the type species Haborophocoena toyoshimai Ichishima and Kimura 2005 . This new record of Haborophocoena confirms the veracity of the genus Haborophocoena as a biological entity, contributes to understanding the interspecific variation, and suggests that the genus diversified in the northwestern Pacific of early Pliocene time. The adult-like degree of ossification in this small skull precludes it from being a juvenile of Haborophocoena toyoshimai . Autapomorphies of Haborophocoena minutus include narrow premaxilla on the dorsal surface of the rostrum, the anterior position of the premaxillary foramen, and a distinct ridge dividing a fossa on the lateral face of the base of the zygomatic process into the dorsal and the ventral halves, the zygomatic process rectangular in lateral profile, and its small size, which is the most compelling feature, making it a distinct species. 相似文献
23.
24.
Jennifer A. Learmonth Sinead Murphy Patricia L. Luque Robert J. Reid I. Anthony P. Patterson Andrew Brownlow Harry M. Ross Jason P. Barley M. Begoña Santos Graham J. Pierce 《Marine Mammal Science》2014,30(4):1427-1455
Life history parameters were determined for stranded and bycaught harbor porpoises (Phocoena phocoena) from Scottish (UK) waters (1992–2005). Fetal growth rate was 84.4 mm/mo and mean size at birth was 76.4 cm (range 65–88 cm). Males and females had a similar range of body lengths (65–170 cm and 66–173 cm, respectively), although asymptotic lengths were higher in females than males (approximately 158 cm and 147 cm, respectively). Nonpregnant females were significantly lighter, in relation to their length than males. Maximum estimated age was 20 yr for both sexes. Age at sexual maturity (ASM) was estimated as 4.35 yr in females and 5.00 yr in males. Conception occurred mainly in July and August although reproductively active males were recorded during April to July. Gestation lasted 10–11 mo, with calving mainly between May and July. Lactating females were recorded during June to November, while small calves with solid food in their stomachs were found mainly during February to May. Estimated pregnancy rate (0.34–0.40) is lower than recorded elsewhere, but is likely underestimated due to the prevalence of mature females of poor health status in the sample. Nevertheless, cetacean strandings can be an essential source of data on demographic parameters. 相似文献
25.
26.
Between 1991 and 1993, Alaska harbor porpoise ( Phocoena phocoena ) abundance was investigated during aerial surveys throughout much of the coastal and offshore waters from Bristol Bay in the eastern Bering Sea to Dixon Entrance in Southeast Alaska. Line-transect methodology was used, and only those observations made during optimal conditions were analyzed. Survey data indicated densities of 4.48 groups/100 km2 , or approximately 3,531 harbor porpoises (95% C. I. 2,206-5,651) in Bristol Bay and 0.54 groups/100 km2 , or 136 harbor porpoises (95% C. I. 11-1,645) for Cook Inlet. Efforts off Kodiak Island resulted in densities of 1.85 groups/100 km2 , or an abundance estimate of 740 (95% C. I. 259-2,115). Surveys off the south side of the Alaska Peninsula found densities of 2.03 groups/100 km2 and an abundance estimate of 551 (95% C. I. 423-719). Surveys of offshore waters from Prince William Sound to Dixon Entrance yielded densities of 4.02 groups/100 km2 and an abundance estimate of 3,982 (95% C. I. 2,567-6,177). Combining all years and areas yielded an uncorrected density estimate of 3.82 porpoises per 100 km2 , resulting in an abundance estimate of 8,940 porpoises (CV = 13.8%) with a 95% confidence interval of 6,746-11,848. Using correction factors from other studies to adjust for animals missed by observers, the total number of Alaska harbor porpoises is probably three times this number. 相似文献
27.
长江安庆段江豚主要栖息地鱼类群落结构 总被引:16,自引:3,他引:13
长江皖河交汇处(皖河口)是安庆江段江豚主要的栖息地之一。为了解江豚主要栖息地鱼类群落结构,于2013年9月—2014年8月对皖河口及其附近4个断面逐月进行了鱼类调查。研究结果表明,共采集鱼类35种,与历史资料相比,鱼类物种多样性已经严重下降,并且小型化趋势明显。5个断面当中,皖河口鱼类种数最多,为27种,且以中上层鱼类餐和油餐为主要优势种;其余4个断面分别为16、20、19和14种,且多数断面以底层鱼类黄颡鱼和长须黄颡鱼为主要优势种。方差分析结果表明,皖河口渔获物的总数量和总重量与其他断面无显著差异,但总种数却显著高于断面1和5。对中上层、中下层和底层鱼类的进一步分析发现,5个断面的显著差异仅存在于中上层鱼类,且皖河口中上层渔获物的数量和重量均显著高于其他断面。由此推断,江豚选择皖河口作为主要栖息地可能主要由于其更加丰富的中上层鱼类资源。研究结果不仅有助于了解鱼类资源的变化,还对江豚的原地和迁地保护具有重要意义。 相似文献
28.
长江江豚种群生存力分析 总被引:33,自引:5,他引:28
长江江豚是一个独立的种群,由于人类活动的影响,其数量呈下降的趋势,运用漩涡模型(VORTEX7.3)分析了长江江豚的种群生存力,预测了未来100a长江江豚的种群动态,比较了在假设环境条件下以及采取和不采取保护措施长江江豚种群的濒危程度,并模拟了江豚饲养群体的动态,主要结果显示,长江江豚在未来100a内灭绝的概率为0.01平均灭绝时间为100a,如长江环境状况进一步恶化,长江江豚的灭绝概率针大幅度提 相似文献
29.
长江江豚感染铜绿假单胞菌肺炎的诊治 总被引:1,自引:0,他引:1
本文记录了一例患急性铜绿假单胞菌肺炎的长江江豚诊断、治疗和预后观察过程。病原学鉴定采用鲜血琼脂平板对该江豚鼻腔拭子,在37℃下进行细菌需氧、厌氧培养和分离,并对所分离的细菌种类进行细菌学鉴定,结合血常规和血生化的检测结果,判定病原为铜绿假单胞菌(Pseudomonas aeruginosa,PA)。依据病原菌的药敏试验结果对患病江豚进行治疗,预后良好。通过对整个过程的资料分析以及预后观察,得到如下提示:1)应做好饲养环境的消毒措施,防止江豚出现获得性PA感染;2)对江豚日常呼吸道和粪便中PA的检测,有利于疾病的早期预防和控制;3)江豚呼吸系统疾病的治愈依赖于准确的病原鉴定和及时的治疗,药敏试验对于PA感染的治疗非常必要;4)行为学的改变在江豚呼吸道疾病发病初期以及预后有重要的指示作用。 相似文献
30.
铜陵长江大桥对豚类栖息地的影响 总被引:2,自引:0,他引:2
根据1987-2001年在铜陵江段所进行的18次豚类生态考察,统计历年考察记录中,在成德洲-梅埂段(以下称大桥河段)工作的天数及观察到的白Ji豚和长江江豚数量,分别计算其SPUE值(Sightings per unit of effort,以头/d计)。并于1989,2001年,在长江水位8.5m左右(吴淞 高程)测定了大桥河段断面A,B,C,D的深度(m)及流速(m/s)。根据汉道最大河宽(B),转折角(α),曲折率(S/L),以及汊道宽长比(B/S)的变化,分析河道与沙洲的变动对白Ji豚和长江江豚栖息地的影响。研究结果表明大桥建成后,河段平面变形小,汊道分流比稳定,滩槽很少变动,流态稳定,水势复杂多样,仍具备豚类栖息活动必要的水文条件,但铜陵大桥对其上下河道,沙洲也产生了一定的影响,主要表现为近期和悦洲与成德洲附近的滩槽冲淤明显,汇,分流区主流摆动不确定,不能形成稳定的水区,导致成德洲附近的白Ji豚和长江江豚活动次数明显减少,特别是白Ji豚的活动路线中(太阳洲→梅埂)的羊山矶,历次考察中未观察到白Ji豚,总而言之,白Ji豚在大桥河段的SPUE值降低与其种群急剧下降是一致的,但在梅埂活动的次数下降不明显;长江江豚在局部水域(梅埂,横港)的SPUE值有上升趋势,这些现象可能与近期的河床演变及桥墩挑流有关。 相似文献