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   79976篇
  免费   4318篇
  国内免费   96篇
林业   3255篇
农学   2062篇
基础科学   467篇
  8689篇
综合类   15594篇
农作物   3161篇
水产渔业   3576篇
畜牧兽医   42239篇
园艺   870篇
植物保护   4477篇
  2019年   757篇
  2018年   1112篇
  2017年   1245篇
  2016年   1074篇
  2015年   922篇
  2014年   1211篇
  2013年   2673篇
  2012年   2171篇
  2011年   2633篇
  2010年   1659篇
  2009年   1766篇
  2008年   2654篇
  2007年   2456篇
  2006年   2345篇
  2005年   2180篇
  2004年   2131篇
  2003年   2188篇
  2002年   1984篇
  2001年   2412篇
  2000年   2454篇
  1999年   1889篇
  1998年   724篇
  1997年   717篇
  1996年   720篇
  1995年   816篇
  1993年   754篇
  1992年   1571篇
  1991年   1765篇
  1990年   1647篇
  1989年   1657篇
  1988年   1489篇
  1987年   1548篇
  1986年   1605篇
  1985年   1556篇
  1984年   1193篇
  1983年   1066篇
  1982年   710篇
  1979年   1163篇
  1978年   902篇
  1977年   758篇
  1975年   776篇
  1974年   1029篇
  1973年   1029篇
  1972年   1051篇
  1971年   998篇
  1970年   993篇
  1969年   908篇
  1968年   814篇
  1967年   806篇
  1966年   735篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
A systematic immunohistochemical study of the ultimobranchial tubule (UBT) has been carried out in 45 Wistar rats of different ages (0, 5, 10, 15, 20, 25, 30, 60 and 120 days). The existence of calcitonin immunoreactive cells in the UBT wall has been demonstrated in a 5-days old rat. In addition, immunohistochemical studies for thyroglobulin revealed positive staining in follicular cells connected to the UBT and, occasionally, in isolated cells lying within solid clusters from the UBT. These last results together with the continued and repeated existence of numerous mitosis and PAS (+) microfollicles, apparently rising from the UBT, support the hypothesis that the ultimobranchial body (UBB) may contribute partially to the formation of a part of the follicular component.  相似文献   
2.
3.
Abstract.— The freshwater mussel Elliptio complanata was provided water containing green algae and cyanobacteria delivered from the Partitioned Aquaculture System (PAS) at eight flow rates to determine algal filtration rates as mg of particulate organic carbon (POC)/kg wet tissue weight per h. The dominant taxon in cyanobacterial waters was Microcystis while the dominant taxa in green algal waters were Scenedesmus and Ankistrodesmus . The cell counts of Scenedesmus and Ankistrodesmus were the only algal taxa that were significantly different between the incoming water and water filtered by mussels. Filtration rates of POC obtained from green algal water were significantly greater than from cyanobacteria-dominated waters at all flow rates. A significant increase in mean filtration rate was observed as flow rates increased. The filtration rate of green algae increased as POC concentration increased, peaking at 28 mg C/L. A maximum filtration rate was not observed with cyanobacterial waters.  相似文献   
4.
The purpose of this study was to evaluate seasonal influences on thyroid hormone levels of healthy outdoor dogs in Hokkaido. We surveyed serum basal total thyroxine (tT4), free thyroxine (fT4), and canine thyroid-stimulating hormone (cTSH) levels, and tT4 levels after administration of TSH for a year. Basal tT4 levels decreased in January, and increased in August and September. fT4 levels increased in January and November. No significant seasonal variation was found in cTSH. tT4 levels after administration of TSH in August and November increased. These results suggested that the thyroid gland may have been activated in November. We should take seasonal variation into consideration when thyroid function is tested.  相似文献   
5.
The isolation of (+)-totarol as active compound against Mycobacterium tuberculosis is reported from Chamaecyparis nootkatensis outerbark.  相似文献   
6.
Prevention of renal carriage of leptospirosis in dogs by vaccination   总被引:1,自引:0,他引:1  
Dogs vaccinated with a Leptospira interrogans vaccine containing serogroups Canicola and Icterohaemorrhagiae and prepared from cultures grown in a protein-free medium resisted challenge with heterologous representatives of these serogroups. In contrast, control dogs were pyrexic and leptospires were isolated from the blood for nine days following Canicola challenge and six days after Icterohaemorrhagiae challenge. Leptospires were isolated from the urine of controls throughout the post challenge period and from kidneys at post mortem examination of six out of six and four out of six Canicola and Icterohaemorrhagiae challenged controls, respectively. There have been no reports of hypersensitivity reactions to this vaccine since its introduction in 1980.  相似文献   
7.
8.
9.
10.
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