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   86236篇
  免费   4305篇
  国内免费   107篇
林业   4013篇
农学   2299篇
基础科学   527篇
  9577篇
综合类   15771篇
农作物   3642篇
水产渔业   3867篇
畜牧兽医   44891篇
园艺   1051篇
植物保护   5010篇
  2019年   736篇
  2018年   1244篇
  2017年   1407篇
  2016年   1233篇
  2015年   1137篇
  2014年   1390篇
  2013年   2778篇
  2012年   2556篇
  2011年   2885篇
  2010年   1728篇
  2009年   1809篇
  2008年   2664篇
  2007年   2456篇
  2006年   2332篇
  2005年   3058篇
  2004年   2850篇
  2003年   2662篇
  2002年   2044篇
  2001年   2492篇
  2000年   2471篇
  1999年   1987篇
  1998年   725篇
  1996年   715篇
  1995年   809篇
  1993年   745篇
  1992年   1646篇
  1991年   1867篇
  1990年   1775篇
  1989年   1766篇
  1988年   1613篇
  1987年   1631篇
  1986年   1718篇
  1985年   1646篇
  1984年   1253篇
  1983年   1127篇
  1982年   737篇
  1979年   1262篇
  1978年   978篇
  1977年   835篇
  1976年   722篇
  1975年   893篇
  1974年   1129篇
  1973年   1118篇
  1972年   1160篇
  1971年   1095篇
  1970年   1066篇
  1969年   991篇
  1968年   911篇
  1967年   904篇
  1966年   819篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
In a feeding trial lasting for months Halothane-positive fattening pigs were put on a diet containing different concentrations of vitamin E and selenium. After a Myostress application vitamin E and selenium were additionally injected in order to examine stress resistance (CK-test) and regenerative capacity (histological examination of Musculus longissimus dorsi) of skeletal muscle. The study revealed that neither high dietary levels of vitamin E/selenium nor a vitamin E/selenium treatment applied after stress are capable of preventing stress related myopathy nor can they influence its healing up favourably.  相似文献   
2.
3.
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   
4.
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   
5.
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   
6.
The isolation of (+)-totarol as active compound against Mycobacterium tuberculosis is reported from Chamaecyparis nootkatensis outerbark.  相似文献   
7.
8.
9.
Observations on transplacental infection with bluetongue virus in sheep   总被引:1,自引:0,他引:1  
Twenty-four ewes were inoculated with 1 of 2 strains of bluetongue virus type 4 at 40, 60, or 80 days of gestation. Two ewes aborted, 2 ewes died, and 1 was killed during the experiment, but their fetuses were recovered. At term, 2 mummified fetuses, 4 dead lambs, and 17 clinically healthy lambs were produced by 12 sheep, and the remaining 7 sheep were barren. Porencephaly and cerebellar dysgenesis were found in term lambs born to sheep inoculated at 40 and 60 days of gestation. Radiographic examination of 12 fetuses showed developmental ages far less than their chronologic age; 8 fetuses had skeletal growth-retardation lines, which were also observed in the dead lambs. A systemic lymphoreticular hyperplasia was observed in the dead lambs and in all lambs at 12 weeks of age; in 4 of the latter, granulomatous reactions were present in the liver and kidney. Lungs of the full-term lambs were reduced in weight and showed poor alveolar development and mononuclear cell infiltration, which persisted in the 12-week-old lambs. It was concluded that bluetongue virus is capable of causing not only gross abnormalities of the CNS, but also generalized growth retardation and fetal lymphoreticular hyperplasia.  相似文献   
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