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   67329篇
  免费   3721篇
  国内免费   104篇
林业   4398篇
农学   2486篇
基础科学   418篇
  8896篇
综合类   7528篇
农作物   2340篇
水产渔业   3653篇
畜牧兽医   36568篇
园艺   964篇
植物保护   3903篇
  2020年   598篇
  2019年   582篇
  2018年   1237篇
  2017年   1288篇
  2016年   1277篇
  2015年   1077篇
  2014年   1213篇
  2013年   2786篇
  2012年   2251篇
  2011年   2628篇
  2010年   1708篇
  2009年   1574篇
  2008年   2397篇
  2007年   2469篇
  2006年   2311篇
  2005年   2080篇
  2004年   1942篇
  2003年   1934篇
  2002年   1762篇
  2001年   2471篇
  2000年   2318篇
  1999年   1835篇
  1998年   721篇
  1997年   645篇
  1996年   636篇
  1995年   712篇
  1994年   595篇
  1993年   589篇
  1992年   1355篇
  1991年   1492篇
  1990年   1560篇
  1989年   1444篇
  1988年   1350篇
  1987年   1329篇
  1986年   1266篇
  1985年   1192篇
  1984年   998篇
  1983年   793篇
  1982年   566篇
  1979年   885篇
  1978年   686篇
  1976年   576篇
  1975年   568篇
  1974年   716篇
  1973年   703篇
  1972年   704篇
  1971年   693篇
  1970年   653篇
  1969年   608篇
  1967年   553篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
In a balance trial with 10 pigs (mean body mass 50 kg) the influence of a bacterial protein supplement (Alcaligenes eutrophus) on N-metabolism was investigated. The bacteria were included into the diet at levels of 7 and 14% at the expense of extracted soyabean meal. Thus bacterial "pure protein" (bacterial non-nucleic acid N X X 6.25) amounted to 30 and 60% of the protein of the ration. Consuming 2 kg of feed dry matter per day the animals of the control group (I) and the experimental groups (II and III) ingested 48 g, 52 g and 55 g of total N respectively. The difference in N-intake is explained by the additional nucleic acid-N, amounting to 19,8% of total bacterial N. Daily weight gain (on average 1054 g) and feed conversion efficiency (feed ingested/weight gain; on average 1,9) were relatively improved at the highest dietary level of bacterial cell mass. Faecal N-excretion was increased significantly, whereas renal N-excretion remained unchanged. Mean apparent N-digestibility was 87,4% showing no significant difference between the experimental groups. N-balance values were noticibly increased following the intake of the bacterial protein supplement. The excretion of urinary urea-N was slightly reduced whereas 4-6 times as much allantoin-N was excreted when bacteria were fed. It is calculated that about 80% of the bacterial purines are renally excreted as allantoin and uric acid.  相似文献   
102.
A two year old Thoroughbred gelding, presented with guttural pouch hemorrhage, had the internal and external carotid arteries ligated. Guttural pouch mycosis was detected on endoscopic examination. After one month of topical antifungal therapy, the horse was returned and euthanized because of recurrent epistaxis. A bacterial infection of the guttural pouch with associated ulceration and hemorrhage from the maxillary artery was found at necropsy.

A two year old grade gelding had ulceration and hemorrhage from the external carotid artery. Utilizing balloon-tipped catheters and arterial ligation, hemestasis was achieved in the internal carotid artery and the external carotid artery and its branches. Mycotic ulceration of the internal carotid artery was detected endoscopically and treated with local antifungal therapy for one month. Thirty-three days postoperatively the horse returned, bleeding from a lesion in the maxillary artery. The rationale for surgical intervention to prevent epistaxis associated with guttural pouch mycosis and possible etiologies for postsurgical epistaxis are discussed.

  相似文献   
103.
An enzyme-linked immunospecific assay (ELISA) for the serodiagnosis of Brucella ovis infection in sheep is described and compared with the cold complement fixation (CF) test. ELISA was performed in microtiter plates, using horse-radish peroxidase conjugated to anti-normal sheep serum globulins, and hydrogen peroxide plus o-phenylenediamine as substrate. A heated, cell-free B. ovis extract was used as antigen in both tests. ELISA was easier to perform, distinguished better between positive and negative sera, and did not need heat-inactivated sera.  相似文献   
104.
105.
The construction of a simple, portable restrainer for holding sheep in either the horizontal or vertical position for abdominal radiography is described. Examples of its use in locating slow-release pellets-and needles are given.  相似文献   
106.
An unusual combination of blood cytopenias and monocytic proliferation was observed in a dog. Initial hematologic findings included severe thrombocytopenia, neutropenia, mild nonregenerative anemia and apparently normal bone marrow. Subsequently, a severe persistent monocytosis developed and the bone marrow became populated with monocytes and cytophagic macrophages. Splenomegaly was due to reticuloendothelial hyperplasia and extramedultary hematopoiesis. Treatment consisted of splenectomy and azathioprine but the response was poor and the dog was euthanized. Postmortem examination revealed a hypocellular bone marrow which contained moderate numbers of monocytes and plasma cells. Neoplastic proliferation was absent in visceral organs. No definite diagnosis was established; chronic blood cell consumption, perhaps immune-mediated, may have been responsible for the extensive reticuloendothelial hyperplasia and cytophagia.  相似文献   
107.
108.
109.
110.
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