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   103311篇
  免费   5857篇
  国内免费   1988篇
林业   6223篇
农学   5867篇
基础科学   2146篇
  13394篇
综合类   18486篇
农作物   4134篇
水产渔业   5078篇
畜牧兽医   46989篇
园艺   1560篇
植物保护   7279篇
  2021年   1134篇
  2020年   1226篇
  2019年   1300篇
  2018年   1657篇
  2017年   1950篇
  2016年   1862篇
  2015年   1837篇
  2014年   2024篇
  2013年   4083篇
  2012年   3295篇
  2011年   3805篇
  2010年   2947篇
  2009年   2937篇
  2008年   3753篇
  2007年   3704篇
  2006年   3454篇
  2005年   3390篇
  2004年   2616篇
  2003年   2763篇
  2002年   2410篇
  2001年   3259篇
  2000年   3238篇
  1999年   2840篇
  1998年   1363篇
  1997年   1365篇
  1996年   1243篇
  1995年   1364篇
  1994年   1201篇
  1993年   1145篇
  1992年   2061篇
  1991年   2206篇
  1990年   2047篇
  1989年   1998篇
  1988年   1852篇
  1987年   1814篇
  1986年   1796篇
  1985年   1642篇
  1984年   1434篇
  1983年   1214篇
  1979年   1301篇
  1978年   971篇
  1977年   909篇
  1975年   898篇
  1974年   1100篇
  1973年   1129篇
  1972年   1065篇
  1971年   1010篇
  1970年   981篇
  1969年   960篇
  1967年   887篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
Eine Methode zur langfristigen Lymphsammlung aus der jejunalen Lymphbahn bei Schweinen und Schafen Es wird eine Methode zur langfristigen Lymphsammlung im Dünndarmbereich von Schweinen und Schafen vorgestellt. Mit Hilfe eines chirurgischen Eingriffs wurde ein Silikon-Katheder im truncus lymphaticus jejunalis implantiert. Zusätzlich wurde ein zweiter Katheter in die hintere vena cava in Richtung Herz eingesetzt. Beide Katheter wurden sofort miteinander verbunden, um die Wiedereinführung der jejunalen Lymphe in den Blutkreislauf zu gewährleisten. Der negative Druck in der hinteren vena cava im Thoraxteil förderte den Lymphfluß durch das Katheter im truncus lymphaticus jejunalis. Der preprandiale Lymphfluß des Jéjunums betrug bei Schweinen 0,3 ml/h/kg Körpergewicht und stieg postprandial auf 0,78 ml/h/kg an. Beim Schaf betrug der Basiswert 0,75 ml/h/kg. Er stieg nach intraduodenaler Infusion von Rapsöl auf 4,75 ml/h/kg. Eine mechanische Stimulation der intestinalen Receptoren durch 0,9% NaCl-Lösung stimulierte ebenfalls den Lymphfluß.  相似文献   
74.
Management of the lactating sow influences milk production and subsequent reproduction through changes in nutrient intake. The management goal during lactation is to maximize feed intake. Decreasing the effective environmental temperature, increasing the nutrient density of the lactation diet, maintaining fresh adequate supplies of feed and water, and preventing excess weight gain during the prior gestation period will increase nutrient intake during lactation. Effective environmental temperature of the lactating sow can be maintained in the thermoneutral zone by using drip cooling, increased ventilation rates and flooring materials with superior conductive properties. Sow parity, genetics, litter size, and disease level will also influence feed intake. Management practices must account for these factors and, thus, should be tailored to individual farm situations to ensure adequate nutrient intake and prevent aberrations in subsequent reproductive performance.  相似文献   
75.
Two-year field trials with winter wheat cultivars Batis and Toronto were conducted in Southern Bavaria, Germany, to investigate the possible causes of cultivar differences in response to N supply varying in total amount and time of application. Cultivar-related differences in grain yields were observed in treatments with low and medium N supply. High doses of N supply resulted in grain yield adjustment or grain yield advantage for cv. Toronto. The results of this study revealed a consistent, genotypic pattern in response to N fertilization in spite of strong seasonal effects. Systematic modifications in canopy growth rates in response to N supply were of particular relevance and a main factor for differences in tillering intensity resulting in modified stand densities. In the present study, cultivar differences in spike development and interactions with N supply related more to abortion than to initiation processes for number of spikelets and number of flowers per spikelet. High grain density (grains per m2) of cv. Toronto was evident during reproduction stages even under conditions of medium N supply. However, decreased growth rates during the later part of grain filling in combination with low 1000 grain weight, which was barely modified by N fertilization, allowed only partial utilization of this potential. It is assumed that sink limitations were of particular relevance for grain yield development in cv. Toronto, while cv. Batis combined a less intense response to N supply with more stability in the development of grain yield components.  相似文献   
76.
Reduced levels of total iron binding capacity and unsaturated iron binding capacity were observed in the blood of trichinous and iron-injected trichinous pigs. No change was observed in their serum iron and saturation concentration levels. Also, reduced iron concentration levels were observed in the livers of trichinous pigs, while increased iron concentration levels were observed in the spleens of trichinous pigs and the livers and spleens of iron-injected pigs. No difference was found with regard to weight gains, number of larvae per gram of tissues, or histologic characteristics of 'nurse cells'.  相似文献   
77.
Fifty six dogs of mixed age and sex were acquired from farms in the Otago/Southland region, and maintained at the Hydatid Research Unit, Taieri, where 43 were each fed two Tueniu ovis cysts. All were bled fortnightly for six or 12 weeks. Coded sera were sent to Wallaceville Animal Research Centre for testing using ELISA, with antigen from T. ovis scoleces. Dog treatments were identified after all tests were complete. A discriminant level was derived from the mean absorbance value plus three standard deviations of 56 sera taken at time zero and 78 sera from serially bled uninfected dogs. None of these 134 sera registered as a false positive using this discriminant level. The data showed no significant deviation from normality, and the expected frequency of the occurrence of false positives is therefore less than 0.14%. Four weeks after infection 63% of dogs proved to be infected were serologically positive, rising to 78% after 6 weeks. When worms were removed by anthelmintic treatment, ELISA absorbance levels decreased. Four weeks after removal 70% of previously infected dogs remained positive, decreasing to 30% after 6 weeks. Six weeks after infection the sensitivity of the test was 78%, and the specificity 63%. However, if dogs with positive ELISA absorbance levels, but which did not purge worms, were regarded as having had worms, the respective figures would be 82% and 100%. The latter figures are similar to our previously published laboratory results. The test is of comparable efficiency to arecoline purgation for surveillance, and has the additional advantage of detecting infection in the majority of those dogs that have been infected for three weeks or more but fail to pass worms on purgation, and a substantial proportion of those infected dogs that were treated by their owners prior to presenting them for purgation in order to avoid detection of infection.  相似文献   
78.
Two cases of noninfectious, nonerosive arthritis are presented. The diagnostic features, clinical course and treatment are reviewed. Potential etiologies are discussed in the light of relatively little current material on this subject in the veterinary literature.  相似文献   
79.
Ten out of eleven subcutaneous abscesses in cats harboured anaerobic bacteria. Seven of the ten abscesses contained a mixture of obligate anaerobes and facultative anaerobes or microaerophilic bacteria. All of the anaerobic isolates were sensitive to the antibiotic metronidazole, but were resistant to streptomycin. Three isolates from one abscess were resistant to penicillin and ampicillin. Clinical resolution of subcutaneous abscesses was poor when procaine penicillin was used alone as treatment.  相似文献   
80.
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