排序方式： 共有3条查询结果，搜索用时 15 毫秒
1
1.
Gross and light microscopic features of transitional cell carcinomas (TCC) of the urinary tract were examined in Beagle dogs used for the study of the long-term effects of low-dose, whole-body, 60Co gamma radiation. Thirty-eight cases of TCC occurred among 990 dogs that were from 0 to 14 years of age. There was no conclusive evidence of a radiation effect. The 38 TCC were equally divided between male and female dogs, but there was a significant difference in the sex distribution of urethra-origin TCC. Eleven males had a primary urethral TCC compared to only two females. There was no significant difference between the urethra-origin and bladder-origin TCCs in the number of tumors that caused clinical signs, metastasized, or that contributed to the death of the dog. All cases of urethral TCC in male dogs occurred in the prostatic urethra. The majority of these cases were not recognized to be neoplasms at gross necropsy, but microscopic examination revealed the TCC. Our findings differ from previous reports stating that TCC occurs more frequently in female than male dogs, and they especially differ from reports claiming that urethra-origin TCC is predominantly a disease of female dogs. 相似文献
2.
• Introduction
The interactive effects of water and nitrogen (N) on frost hardiness are not well known in broad-leaved trees. Furthermore, new environmental conditions may favour naturally generated hybrids between native and introduced tree species over native species. 相似文献3.
Effects of landscape structure and forest reserve location on old-growth forest bird species in Northern Finland 总被引：4，自引：0，他引：4
Brotons Lluís Mönkkönen Mikko Huhta Esa Nikula Ari Rajasärkkä Ari 《Landscape Ecology》2003,18(4):377-393
Old-growth forest birds in Fennoscandia have sharply declined in numbers during the last decades apparently due to commercial
forest harvesting and fragmentation of old-growth forests. Conservation measures have led to the establishment of a forest
reserve network to assure the persistence of forest birds at a regional scale. However, little is known about the effects
of landscape structure within and around the reserves on the distribution of old-growth forest birds. We used a hierarchical
approach to address the questions of how landscape structure and composition within forest reserves, landscape composition
of surrounding areas and reserve location affect the abundance of resident, old-growth forest birds in the Northern Finnish
forest reserve network. The positive role of particular landscape features on bird distribution indicates that both the proportion
of old-growth forests and the structure of boreal landscape mosaic has an important role in determining the distribution of
these birds. The landscape composition surrounding the reserves proved to be only a weak predictor in species distribution
models, which argues against the primary role of the surrounding matrix in determining species distribution within forest
reserves. Reserves located near the Russian border showed a higher abundance of old-growth birds than more western ones. Once
east-west gradients in overall landscape composition had been accounted for, however, reserves did not differ significantly
in the number of species present. These results suggest that landscape gradients, rather than ecological processes such as
the presence of source areas located along the border with Russia, are the main determinant of the distribution of old-growth
forest birds in the Finnish reserve network. We propose that to enhance regional persistence of old-growth forest birds, conservation
efforts should be primarily directed towards the protection and enhancement of forest habitat quality and natural heterogeneity
of landscapes within targeted areas.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
1