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   135篇
  免费   5篇
林业   3篇
农学   3篇
基础科学   5篇
  1篇
综合类   33篇
水产渔业   6篇
畜牧兽医   88篇
园艺   1篇
  2023年   1篇
  2020年   1篇
  2019年   2篇
  2017年   1篇
  2016年   4篇
  2015年   3篇
  2014年   2篇
  2013年   15篇
  2012年   3篇
  2011年   2篇
  2010年   5篇
  2009年   8篇
  2008年   10篇
  2007年   5篇
  2006年   1篇
  2005年   5篇
  2004年   3篇
  2003年   2篇
  2002年   4篇
  2001年   2篇
  2000年   3篇
  1999年   1篇
  1998年   2篇
  1997年   1篇
  1996年   4篇
  1994年   1篇
  1993年   1篇
  1992年   3篇
  1991年   7篇
  1990年   3篇
  1989年   1篇
  1988年   4篇
  1986年   4篇
  1985年   3篇
  1984年   6篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1970年   1篇
  1966年   1篇
  1924年   1篇
  1904年   3篇
  1902年   2篇
  1900年   2篇
  1896年   1篇
  1895年   1篇
  1893年   1篇
  1892年   1篇
排序方式: 共有140条查询结果,搜索用时 31 毫秒
1.
2.
The Atlantic meridional overturning circulation (MOC), which provides one-quarter of the global meridional heat transport, is composed of a number of separate flow components. How changes in the strength of each of those components may affect that of the others has been unclear because of a lack of adequate data. We continuously observed the MOC at 26.5 degrees N for 1 year using end-point measurements of density, bottom pressure, and ocean currents; cable measurements across the Straits of Florida; and wind stress. The different transport components largely compensate for each other, thus confirming the validity of our monitoring approach. The MOC varied over the period of observation by +/-5.7 x 10(6) cubic meters per second, with density-inferred and wind-driven transports contributing equally to it. We find evidence for depth-independent compensation for the wind-driven surface flow.  相似文献   
3.
4.
5.
6.
Mammary gland involution was morphologically evaluated 21 or 42 d after prevention of suckling of one udder half in 10 crossbred beef cows. Parenchymal tissue was taken from lower, middle and upper zones of each quarter from the teat to the ventral body wall. Udder halves, trimmed of extraparenchymal tissue, were weighed and used for DNA determination. DNA content was reduced 50 and 64% after 21 and 42 d of involution. However, the percentage of tissue occupied by epithelium was similar in suckled and nonsuckled glands. Well-differentiated cells, typical of suckled glands, were rarely observed in nonsuckled glands. Alveolar structure was evident in nonsuckled glands, but the number of cells per alveolar cross-section was reduced (30 vs 22). Unlike in suckled glands, there was a marked gradation in classification of epithelial cells across zones in involuting glands. For example, nearly 10% of the epithelium was well-differentiated in the tissue from the upper zone, whereas no well-differentiated cells were found in the lower zones. Regression of the mammary parenchyma does not occur uniformly through the udder, so use of single biopsy to study involution should be avoided. Presence of alveoli after 42 d indicates that redevelopment of the udder with subsequent lactations is less dramatic than suggested from study of other species.  相似文献   
7.
Toxin, one of the most important factors of plant fungal disease, has attracted much attention of many academicians who have been studying pathogen mycotoxin in deep research. The paper summarized chemical structures of some host-selective plant pathogen mycotoxins discovered in recent years and the correlation between biological activity and chemical structure of toxin.  相似文献   
8.
9.
10.
Body measurements on Angus- (n = 374) and Polled Hereford-sired (n = 438) calves were used to quantify calf shape via multivariate factor analysis, and measurements on Polled Hereford-sired calves were further used to investigate relationships between calf shape and sire expected progeny differences (EPD) for birth weight and first-calf calving ease. Calf birth weight, head circumference, shoulder width, hip width, heart girth, cannon bone circumference and length, and body length were recorded at 24 h postpartum. Sire birth weight EPD was positively associated (P less than .05) with all calf measures but only with head and cannon circumference after adjustment for phenotypic birth weight and gestation length. Thus, at constant birth weight, calves from higher birth weight EPD bulls tended to have larger cannon and head circumferences. Calving ease EPD was negatively related (P less than .05) to all calf measures except shoulder width. After adjustment for birth weight, only cannon circumference was associated with calving ease EPD, and this effect was removed by additional adjustment for birth weight EPD. Thus, at constant birth weight, bulls with higher EPD for calving ease sired calves with smaller cannon circumference, but at constant birth weight EPD, body measures were not associated with calving ease EPD. Factor analysis defined underlying skeletal width and frame components of shape (independent of birth weight) for both sire breeds. Calf shape differed among sires and was in part explained by birth weight EPD. No additional variation in shape was explained by calving ease EPD. Calf shape seemed to add no information for prediction of dystocia to that provided by birth weight EPD.  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