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   776篇
  免费   41篇
  国内免费   3篇
林业   21篇
农学   12篇
基础科学   7篇
  46篇
综合类   143篇
农作物   9篇
水产渔业   72篇
畜牧兽医   406篇
园艺   2篇
植物保护   102篇
  2023年   8篇
  2022年   16篇
  2021年   20篇
  2020年   16篇
  2019年   12篇
  2018年   12篇
  2017年   16篇
  2016年   22篇
  2015年   11篇
  2014年   14篇
  2013年   34篇
  2012年   23篇
  2011年   19篇
  2010年   31篇
  2009年   32篇
  2008年   29篇
  2007年   29篇
  2006年   25篇
  2005年   13篇
  2004年   14篇
  2003年   6篇
  2002年   11篇
  2001年   9篇
  1999年   18篇
  1998年   26篇
  1997年   26篇
  1996年   33篇
  1995年   17篇
  1994年   12篇
  1993年   26篇
  1992年   14篇
  1991年   13篇
  1990年   14篇
  1989年   21篇
  1988年   16篇
  1987年   14篇
  1986年   7篇
  1985年   9篇
  1984年   6篇
  1983年   5篇
  1982年   5篇
  1981年   11篇
  1980年   9篇
  1979年   9篇
  1978年   5篇
  1976年   6篇
  1958年   6篇
  1954年   4篇
  1947年   4篇
  1945年   5篇
排序方式: 共有820条查询结果,搜索用时 62 毫秒
61.
62.
Minimally displaced, spiral, radial fractures were diagnosed in three adult horses. Two horses had open fractures and in one horse the fracture was closed. A diagnosis was made on radiographs taken 24 h, 5, and 9 days after the fracture. There was minimal displacement of the fracture fragments despite the considerable time which had elapsed between fracture and diagnosis and an unfavourable prognosis with internal fixation, so conservative therapy was the preferred method of treatment. One horse developed a sequestrum and draining sinus, which was treated surgically under general anaesthesia 3 months after diagnosis of the fracture. Other complications were minimal and transient. Two horses were being used for pleasure riding 12 months after fracture and one horse was pasture sound at 8 months.  相似文献   
63.
64.
65.
66.
Comparative Earth History and Late Permian Mass Extinction   总被引:6,自引:0,他引:6  
The repeated association during the late Neoproterozoic Era of large carbon-isotopic excursions, continental glaciation, and stratigraphically anomalous carbonate precipitation provides a framework for interpreting the reprise of these conditions on the Late Permian Earth. A paleoceanographic model that was developed to explain these stratigraphically linked phenomena suggests that the overturn of anoxic deep oceans during the Late Permian introduced high concentrations of carbon dioxide into surficial environments. The predicted physiological and climatic consequences for marine and terrestrial organisms are in good accord with the observed timing and selectivity of Late Permian mass extinction.  相似文献   
67.
Magnetotactic bacteria are present in fresh water and marine sediments of Fortaleza, Brazil, situated close to the geomagnetic equator. Both South-seeking and North-seeking bacteria are present in roughly equal numbers in the same samples. This observation is consistent with the hypothesis that the vertical component of the geomagnetic field selects the predominant polarity type among magnetotactic bacteria in natural environments.  相似文献   
68.
69.
70.
The level of the plasma prothrombin in the circulating blood is decreased during its passage through the pulmonary capillaries. In 85 per cent. of samples, plasma prothrombin has been found to be less in the blood of the left ventricle than in that from the right ventricle. This difference averaged 10.6 per cent. and ranged from 4 to 19 per cent. In no instance was the level in the right ventricle lower than that in the left. In samples of blood taken from the arterial and venous supply of the head, liver, spleen, intestine, kidney and hind limbs, no significant difference in plasma prothrombin levels was found. A possible explanation of this role of the lung in the loss of plasma prothrombin is thought to be the production of blood platelets in this organ, as demonstrated by Howell and Donahue. Platelets, as they undergo disintegration, initiate the first stage of the clotting process by releasing thromboplastin, which, in the presence of calcium, changes prothrombin to thrombin.  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