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   103665篇
  免费   5043篇
  国内免费   63篇
林业   4037篇
农学   3107篇
基础科学   633篇
  11253篇
综合类   21405篇
农作物   3749篇
水产渔业   4748篇
畜牧兽医   52834篇
园艺   1155篇
植物保护   5850篇
  2018年   1206篇
  2017年   1289篇
  2016年   1211篇
  2015年   994篇
  2014年   1208篇
  2013年   3399篇
  2012年   2326篇
  2011年   2879篇
  2010年   1940篇
  2009年   1874篇
  2008年   2875篇
  2007年   2748篇
  2006年   2648篇
  2005年   2523篇
  2004年   2502篇
  2003年   2556篇
  2002年   2346篇
  2001年   3149篇
  2000年   3142篇
  1999年   2469篇
  1998年   1008篇
  1997年   971篇
  1995年   1104篇
  1994年   989篇
  1992年   2252篇
  1991年   2356篇
  1990年   2405篇
  1989年   2375篇
  1988年   2236篇
  1987年   2247篇
  1986年   2215篇
  1985年   2161篇
  1984年   1784篇
  1983年   1557篇
  1982年   1050篇
  1981年   996篇
  1980年   950篇
  1979年   1627篇
  1978年   1331篇
  1977年   1176篇
  1976年   1099篇
  1975年   1233篇
  1974年   1543篇
  1973年   1470篇
  1972年   1556篇
  1971年   1422篇
  1970年   1355篇
  1969年   1240篇
  1968年   998篇
  1967年   1145篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
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   
142.
The influence of genotypic differences in resistance to infection from Lymphoid Leukosis (LL) on mortality and egg production was studied in three pairs of sublines. One subline of each pair had been selected for resistance and the other for susceptibility to infection. At 10 months of age, almost no hens with neutralising antibodies against LL were found in the resistant sublines, while in each susceptible subline more than 40% of the hens had LL antibodies. At 21 months of age, very few hens of the resistant sublines had group-specific (gs) antigen in their eggs. Susceptible sublines differed considerably in this respect, from 81% gs antigen-positive hens in one subline to 9% or no positive hens in the others. On the whole, the susceptible sublines had 6% higher mortality during the laying period (8 months) but the size of the difference was influenced by vaccination against Marek's disease (MD) and varied considerably between pairs of sublines. Significant interactions between strain and genotype of resistance to LL infection were observed for mortality from "other causes" in hens vaccinated against MD, as well as for mortality from "Leukosis" and from "MD" in non-vaccinated hens. The average rate of lay from 1 to 8 months was 8% lower in susceptible hens. In the subline with the highest frequency of eggs containing LL group-specific antigen in the albumen, the reduction of laying rate was twice as large as in the other susceptible sublines.  相似文献   
143.
A retrospective morbidity and mortality study was carried out on 125 case records of cattle involving xylazine/halothane anesthesia at the Ontario Veterinary College, Guelph between May 1979 and February 1983.  相似文献   
144.
145.
The complement fixation test (CFT), the enzyme labelled immunosorbent assay (ELISA) and the gel diffusion precipitin test (GD) were compared, for the diagnosis of Brucella ovis infection in rams. The sensitivities of the tests in 109 rams which were shedding B. ovis in their semen were: CFT 96.3%; ELISA 97.2%; GD 91.7%. The specificities of the tests in 141 rams from non-infected flocks were: CFI 99.3%; ELISA 98.6%; GD 100%. Predictive values of the three tests were measured in 285 rams from infected flocks. Thirty-eight percent of these rams were shedding B. ovis in their semen. Predictive values of positive tests were: CFT 75.5%; ELISA 66.7%; GD 72.5%. Predictive values of negative tests were: CFI 97.1%; ELISA 97.6%; GD 93.8%.  相似文献   
146.
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   
147.
Pleural effusions can cause dyspnea and cyanosis, and are caused by cardiomyopathy, pyothorax, FIP, FeLV-related disease and trauma. Thoracentesis is used to obtain fluid samples for cytologic examination and culture. Radiographs made after thoracentesis may reveal the cause. Lymphosarcoma causes a sterile exudate containing neoplastic cells. Congestive cardiomyopathy causes a transudate or modified transudate. The sterile exudate of FIP has a proteinaceous background on cytologic examination. The exudate of pyothorax is septic. Treatment depends on the cause but generally includes thoracentesis and supportive care. Cardiomyopathy causes dyspnea, cyanosis, murmurs, gallop rhythms and other arrhythmias. Radiography reveals a globoid heart in the congestive form and a "valentine-shaped" heart in the hypertrophic form. Treatment of congestive cardiomyopathy involves use of furosemide, but is usually unrewarding. Hypertrophic cardiomyopathy is treated with propranolol. Fever may be caused by infection, immune-mediated disease, neoplasia and unknown causes. Treatment is aimed at removal of the underlying cause.  相似文献   
148.
149.
150.
Of 32 calves given an unknown amount of a pluronic bloat mixture with their milk, 28 died in convulsions over 24 hours. Supportive therapy was unsuccessful. Concentrations of pluronic present in abomasal and rumenal contents supported a diagnosis of pluronic poisoning.  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