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   253150篇
  免费   15412篇
  国内免费   669篇
林业   23350篇
农学   13999篇
基础科学   2968篇
  42504篇
综合类   24293篇
农作物   16864篇
水产渔业   16606篇
畜牧兽医   98594篇
园艺   6296篇
植物保护   23757篇
  2021年   2454篇
  2020年   2864篇
  2019年   3635篇
  2018年   3963篇
  2017年   4358篇
  2016年   4761篇
  2015年   4306篇
  2014年   5672篇
  2013年   16199篇
  2012年   6135篇
  2011年   8089篇
  2010年   7293篇
  2009年   7869篇
  2008年   7490篇
  2007年   6469篇
  2006年   7245篇
  2005年   6436篇
  2004年   6274篇
  2003年   6031篇
  2002年   5403篇
  2001年   6022篇
  2000年   5785篇
  1999年   5385篇
  1998年   4142篇
  1997年   4215篇
  1996年   3941篇
  1995年   4555篇
  1994年   3969篇
  1993年   3641篇
  1992年   4501篇
  1991年   4710篇
  1990年   4307篇
  1989年   4271篇
  1988年   3839篇
  1987年   4005篇
  1986年   3943篇
  1985年   4167篇
  1984年   3781篇
  1983年   3577篇
  1982年   2913篇
  1981年   2770篇
  1980年   2775篇
  1979年   3280篇
  1978年   2991篇
  1977年   2740篇
  1976年   2544篇
  1975年   2391篇
  1974年   2630篇
  1973年   2648篇
  1972年   2383篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
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   
992.
993.
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   
994.
Erwinia amylovora has been spreading in the Czech Republic since 1986 regardless of emergency phytosanitary measures which have been taken. Its spread follows the predominant wind direction (west to east). The infested area now covers two thirds of the area of the country. Wild Crataegus spp. are the most important and widespread host plants. E. amylovora is still regulated as a quarantine pest, and areas free from fireblight are subject to special phytosanitary measures.  相似文献   
995.
996.
Long‐term experiments are a classical case of repeated measurements. Traits are measured on the same experimental unit over many years so that correlations arise between the observations made on the same plot in consecutive years. This paper describes the analysis of a three‐crop‐rotation long‐term experiment. We analysed the yields of the crops and the organic carbon content in the topsoil over 30 consecutive years. Several variance–covariance approaches are discussed and the trait‐specific best fit is interpreted. Mixed models are used to describe the structure of the experiment. Both yields and soil organic carbon show a more or less pronounced variance heterogeneity. Especially for yields, the heterogeneity of cycles and years is dominant. The consideration of correlations results in a better model fit in all cases.  相似文献   
997.
998.
999.
A. Wjtowicz 《EPPO Bulletin》2003,33(3):515-516
A computer system Agrogis has been developed to record information on pest infestation of plants in different regions of Poland. Data can be entered manually or from disks, and can be displayed in the form of charts and maps. Agrogis will be made available on the Internet.  相似文献   
1000.
糖类寄生螨快速分离检验方法   总被引:1,自引:0,他引:1  
本文对糖类寄生螨的快速分离检验方法进行了改进。将糖类溶解后,经过500目/英寸标准检验筛进行过筛分离。此方法对各种可溶性糖类中的寄生螨类能取得100%的快速分离检验结果。  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