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   84270篇
  免费   4714篇
  国内免费   57篇
林业   2930篇
农学   2286篇
基础科学   571篇
  9262篇
综合类   15040篇
农作物   3119篇
水产渔业   3915篇
畜牧兽医   45927篇
园艺   896篇
植物保护   5095篇
  2018年   1036篇
  2017年   1177篇
  2016年   1092篇
  2015年   945篇
  2014年   1179篇
  2013年   3079篇
  2012年   2138篇
  2011年   2713篇
  2010年   1668篇
  2009年   1763篇
  2008年   2619篇
  2007年   2418篇
  2006年   2427篇
  2005年   2155篇
  2004年   2117篇
  2003年   2103篇
  2002年   2002篇
  2001年   2710篇
  2000年   2813篇
  1999年   2142篇
  1998年   819篇
  1997年   825篇
  1996年   810篇
  1995年   1019篇
  1994年   890篇
  1993年   845篇
  1992年   1940篇
  1991年   2094篇
  1990年   1926篇
  1989年   1947篇
  1988年   1830篇
  1987年   1943篇
  1986年   1985篇
  1985年   1879篇
  1984年   1488篇
  1983年   1306篇
  1982年   887篇
  1979年   1372篇
  1978年   1126篇
  1977年   982篇
  1976年   942篇
  1975年   990篇
  1974年   1278篇
  1973年   1307篇
  1972年   1238篇
  1971年   1155篇
  1970年   1094篇
  1969年   971篇
  1968年   838篇
  1967年   876篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
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   
52.
The merits of integrated aquaculture farming (IAF) as a strategy for bolstering income for the rural poor have been recognized, but the economic efficiency and sustainability are yet to be determined. The effects of one species on another and the economic benefits, net of government support, have not been critically evaluated. The concept of a foodniche for alternative species in an aquatic environment has not been properly tested in an economic setting. Thus, this report reflects the results of applying the technique of mixed integer linear programming to determine the optimum combination of species within the context of a foodniche. The objective also included maximizing revenues, with minimal external input requirements, for a representative small Malaysian wet-rice farm. It was found that the foodniche concept permitted flexibility in stocking rates, and that farmers could actually stock species at the exact rate that was optimal for profit, instead of standard fixed rates. Also, government subsidies for pond construction were essential for IAF success. The net revenues from IAF were low without interest-free loans for pond construction.  相似文献   
53.
54.
55.
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   
56.
57.
58.
59.
60.
The paper describes pathomorphological findings in two dogs and one cat with the intention to clarify whether these animals died by drowning. The investigations are supplemented by experimental results of water instillation into the lung to induce signs of emphysema aquosum post mortem. Additionally, histopathology of the skin lesions due to water exposition after death are demonstrated by systematic investigations of four different localizations for 10 days. Critical evaluation of the results and literature references in human forensic pathology indicate that post mortem findings as described in this paper, especially those of the so called "drowning lung" can be attributed to death by drowning.  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