首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   169篇
  免费   36篇
  国内免费   1篇
林业   3篇
农学   6篇
基础科学   3篇
  13篇
综合类   26篇
农作物   4篇
水产渔业   23篇
畜牧兽医   116篇
园艺   1篇
植物保护   11篇
  2023年   1篇
  2022年   1篇
  2021年   3篇
  2020年   8篇
  2019年   5篇
  2018年   15篇
  2017年   10篇
  2016年   7篇
  2015年   8篇
  2014年   5篇
  2013年   13篇
  2012年   10篇
  2011年   12篇
  2010年   11篇
  2009年   11篇
  2008年   10篇
  2007年   13篇
  2006年   3篇
  2005年   7篇
  2004年   2篇
  2003年   3篇
  2002年   2篇
  2001年   6篇
  2000年   2篇
  1999年   1篇
  1998年   10篇
  1997年   5篇
  1996年   7篇
  1995年   2篇
  1994年   1篇
  1993年   3篇
  1992年   4篇
  1991年   2篇
  1990年   1篇
  1988年   1篇
  1987年   1篇
排序方式: 共有206条查询结果,搜索用时 0 毫秒
201.
Lake Victoria is the largest lake in Africa and harbors more than 300 endemic species of haplochromine cichlid fish. Seismic reflection profiles and piston cores show that the lake not only was at a low stand but dried up completely during the Late Pleistocene, before 12,400 carbon-14 years before the present. These results imply that the rate of speciation of cichlid fish in this tropical lake has been extremely rapid.  相似文献   
202.
Recent discoveries of fossil vertebrates from the Late Cretaceous of Madagascar include several specimens of a large theropod dinosaur. One specimen includes a nearly complete and exquisitely preserved skull with thickened pneumatic nasals, a median frontal horn, and a dorsal projection on the parietals. The new materials are assigned to the enigmatic theropod group Abelisauridae on the basis of a number of unique features. Fossil remains attributable to abelisaurids are restricted to three Gondwanan landmasses: South America, Madagascar, and the Indian subcontinent. This distribution is consistent with a revised paleogeographic reconstruction that posits prolonged links between these landmasses (via Antarctica), perhaps until late in the Late Cretaceous.  相似文献   
203.
Commercially valuable sea cucumbers are potential co‐culture species in tropical lagoon environments, where they may be integrated into established aquaculture areas used for seaweed farming. In the current study, wild‐caught juvenile sea cucumbers, Holothuria scabra, and red seaweed Kappaphycus striatum were co‐cultured on Zanzibar, United Republic of Tanzania. Sea cucumbers (97 g ± 31 SD,= 52) were cultured in mesh enclosures at initial cage stocking densities of 124 ± 21 SD and 218 ± 16 SD g m?2 under seaweed culture lines. Over 83 days, individual growth rate (1.6 g d?1 ± 0.2 SD) of sea cucumbers at low stocking density was significantly higher (χ2 = 8.292, d.f. 1, P = 0.004) than at high‐stocking density (0.9 g d?1 ± 0.1 SD). Seaweed individual growth rates [6.27 (±0.3 SE) g d?1] were highest in co‐culture with sea cucumber at low density but did not differ significantly from high sea cucumber density or seaweed monoculture treatments (χ2 = 3.0885, d.f. = 2, = 0.2135). Seaweed growth varied significantly (χ2 = 35.6, d.f. = 2, < 0.0001) with sampling period, with the final sampling period resulting in the highest growth rate. Growth performance for seaweed and sea cucumbers (χ2 = 3.089, d.f. = 2, = 0.21 and χ2 = 0.08, d.f. = 1, = 0.777 respectively), did not differ significantly between monoculture and co‐culture treatments, yet growth in co‐culture was comparable with that reported for existing commercial monoculture. Results indicate H. scabra is a highly viable candidate species for lagoon co‐culture with seaweed. Co‐culture offers a more efficient use of limited coastal space over monoculture and is recommended as a potential coastal livelihood option for lagoon farmers in tropical regions.  相似文献   
204.
AIMS: The principle aim of this study was to examine the association between infection with Theileria orientalis Ikeda type and growth rates of suckled beef calves on four beef farms. In addition, associations between calf sex, sampling time, and individual farm and T. orientalis Ikeda type infection intensity and haematocrit (HCT) were investigated.

METHODS: The study was a prospective longitudinal study in which 240 calves from four purposively selected beef farms in the North Island of New Zealand were blood sampled and weighed in late spring, mid-summer and early autumn. Two farms were from high-risk (A and B) and two from low-risk (C and D) tick areas. Blood samples were analysed to determine HCT, and the number of T. orientalis Ikeda type organisms/µL of blood (infection intensity) using a quantitative PCR assay. A calf was defined as infected if >415 organisms/µL were detected in a blood sample. Linear mixed models were used to examine associations between infection intensity, mean daily liveweight gain (MDG), HCT, calf sex and time of sampling on the four farms.

RESULTS: On Farms A and B nearly all calves were infected at each sampling time, on Farm C <30% were infected at any sampling and on Farm D infection prevalence increased from 32 to 79% between late spring and early autumn. On Farms C and D, from mid-summer to early autumn, mean MDG was 0.127 (95% CI=0.072–0.183) kg/day less for infected than uninfected calves (p<0.001). On all farms MDG was negatively associated with infection intensity for mid-summer and early autumn sampling times (p=0.037). The relationship between time of sampling and infection intensity varied between farms (p<0.001), and between male and female calves (p=0.018). Females had a higher infection intensity than males at the mid-summer and early autumn samplings. The association between HCT and infection intensity varied with sampling time and farm (p=0.018). There was a strong negative association between infection intensity and HCT at the late spring sampling, but in mid-summer there was no association, and in early autumn only a weak association.

CONCLUSIONS AND CLINICAL RELEVANCE: This study has shown that beef farmers in the North Island of New Zealand should be concerned about the welfare effects and economic impacts of T. orientalis Ikeda type infection in suckled beef calves.  相似文献   

205.
206.
In this study, two unusual presentations of canine prostatitis are described; in the first case a 10‐years‐old neutered Boxer dog was presented to the Veterinary Teaching Hospital of the University of Extremadura with a complaint of anorexia, apathy and preputial discharge. In the second case, a local veterinarian referred an 8‐years‐old male Labrador to the Veterinary Teaching Hospital of the University of Extremadura. The dog had a history of pain in the caudal abdomen and preputial oedema. The final diagnosis in both cases was acute prostatitis. It is concluded that although canine prostatitis is a common disease, sometimes can have presentations that may differ from those classically described in the literature.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号