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   229617篇
  免费   26384篇
  国内免费   28063篇
林业   13979篇
农学   11963篇
基础科学   9120篇
  54672篇
综合类   53258篇
农作物   11953篇
水产渔业   14429篇
畜牧兽医   93380篇
园艺   4553篇
植物保护   16757篇
  2022年   1769篇
  2021年   2169篇
  2020年   4055篇
  2019年   7789篇
  2018年   8599篇
  2017年   9599篇
  2016年   10253篇
  2015年   9859篇
  2014年   9425篇
  2013年   13610篇
  2012年   11674篇
  2011年   11612篇
  2010年   8637篇
  2009年   8002篇
  2008年   8952篇
  2007年   8866篇
  2006年   8127篇
  2005年   7388篇
  2004年   7360篇
  2003年   7148篇
  2002年   6390篇
  2001年   7282篇
  2000年   6964篇
  1999年   5808篇
  1998年   2976篇
  1997年   2924篇
  1996年   2636篇
  1995年   3043篇
  1994年   2716篇
  1993年   2521篇
  1992年   4314篇
  1991年   4315篇
  1990年   4134篇
  1989年   4099篇
  1988年   3734篇
  1987年   3623篇
  1986年   3552篇
  1985年   3213篇
  1984年   2659篇
  1983年   2342篇
  1982年   1613篇
  1979年   2193篇
  1978年   1741篇
  1975年   1575篇
  1974年   1825篇
  1973年   1883篇
  1972年   1854篇
  1971年   1603篇
  1970年   1627篇
  1969年   1562篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
953.
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   
954.
1. To test the preferences of hens for particular social conditions when laying, they were provided with choices of nest‐sites varying in seclusion. Three experimental conditions were used.

2. In Experiment 1, nest‐site selection by members of a group of light hybrids was studied in a complex pen‐system. Eggs were clumped in distribution ; only one individual laid in the most secluded part of the system.

3. Experiment 2 provided light hybrids with an extensive outdoor area, but similarly clumped laying was observed; there was no indication that hens attempted to find concealment for nesting.

4. In Experiment 3, hens from a group of light hybrids just coming into lay and from a group of mature medium hybrids were tested singly, in an area that included a cage containing some of their flockmates. Most subjects from both groups laid near the other birds rather than in isolation.

5. In semi‐intensive conditions, the majority of hens are apparently gregarious rather than solitary in their nesting behaviour.  相似文献   

955.
956.
957.
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   
958.
A nine year old Hereford crossbred cow with a history of progressive neurological signs was referred to the Western College of Veterinary Medicine, Saskatoon. A large intracranial mass, histologically identified as a schwannoma, was found to be compressing the left brain stem and appeared to have arisen from the left fifth cranial nerve.  相似文献   
959.
William osler and comparative medicine   总被引:2,自引:2,他引:0       下载免费PDF全文
During the last thirty years of the nineteenth century, comparative medicine deeply influenced veterinary education in Montreal, New York and Philadelphia. Of the many physicians and veterinarians involved in this movement, Sir William Osler has attracted the most biographical and historical attention. However, his contributions to comparative medicine have been characterized inexactly, partly because of his later prominence as a clinician and partly because little has been written about the history of veterinary education in Quebec.

Osler's teaching and research in comparative medicine as well as his efforts to promote a veterinary profession are described and set alongside the work of other physicians and veterinarians who were his contemporaries. As a result, Osler's contributions to comparative medicine are seen to be many and important but by no means unique. Other Quebec veterinarians, including Duncan McEachran, Orphyr Bruneau, Victor T. Daubigny and J.A. Couture, and such physicians as T. Wesley Mills and J. George Adami made as many, and in some cases greater, contributions to veterinary education in Quebec than did Osler. That they have not received the degree of recognition that Osler has received reveals Osler's ability to represent values and ideals and draws attention to some essential features of late nineteenth-century comparative medicine.

  相似文献   
960.
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