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   9486篇
  免费   539篇
  国内免费   493篇
林业   2198篇
农学   485篇
基础科学   742篇
  886篇
综合类   4286篇
农作物   305篇
水产渔业   283篇
畜牧兽医   712篇
园艺   144篇
植物保护   477篇
  2024年   44篇
  2023年   160篇
  2022年   270篇
  2021年   286篇
  2020年   338篇
  2019年   379篇
  2018年   154篇
  2017年   245篇
  2016年   330篇
  2015年   322篇
  2014年   517篇
  2013年   503篇
  2012年   780篇
  2011年   762篇
  2010年   627篇
  2009年   661篇
  2008年   590篇
  2007年   607篇
  2006年   550篇
  2005年   447篇
  2004年   362篇
  2003年   322篇
  2002年   257篇
  2001年   214篇
  2000年   154篇
  1999年   116篇
  1998年   116篇
  1997年   82篇
  1996年   67篇
  1995年   57篇
  1994年   45篇
  1993年   36篇
  1992年   35篇
  1991年   25篇
  1990年   18篇
  1989年   11篇
  1988年   11篇
  1987年   7篇
  1986年   2篇
  1984年   4篇
  1983年   1篇
  1980年   1篇
  1963年   1篇
  1962年   1篇
  1956年   1篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
991.
简要阐述了中国蛋禽产业的发展现状及其发展过程中存在的问题。通过对发展现状和存在问题的分析,初步论述了中国蛋禽业应沿着产业化和可持续化的方向发展。同时,还要充分利用先进的科研成果,处理好蛋禽产业的发展与环境保护的关系。  相似文献   
992.
该文旨在通过对土地整理与农村建设目标、内容及相互关系的分析,借鉴国外通过土地整理促进农村发展的经验,根据中国的实际,提出通过土地整理促进新农村建设的对策。研究发现,土地整理日趋成为农村建设的重要内容和手段,农村建设则成为土地整理的重要任务和目标。中国应从树立以新农村建设为目标的土地整理理念,完善政策导向、公众参与两个机制,构建法律、规划和科技支撑三个体系等方面推进土地整理与农村建设的结合,提高土地整理服务农村建设的能力,加快新农村建设进程。  相似文献   
993.
在提高农业生产力的同时,保护生态环境质量是我国生态农业的基本特点,本文分析了我国生态农业产生的背景、发展现状、功能及特色,并以黑龙江省拜泉县为例,阐明生态农业建设与生态环境保护的协调性关系。  相似文献   
994.
烧荒,是指人为地点燃田野上的牧草,使其成片焚烧。鉴于烧荒的危害性大,且在农村具有普遍性,针对这一问题,结合沂蒙山区的实际,作了一些探讨,以期能为解决烧荒问题提供一点借鉴。 就沂蒙山区来说,烧荒的主要表现形式有4种。(1)农民在野外上坟烧香燃纸时引起的烧荒,约占总烧荒数的40%;(2)农民在田头焚烧庄稼秸秆时引起的烧荒,约占25%;(3)有些少年在野外点火取乐时引起烧荒,约占15%;(4)农民在野外劳动或  相似文献   
995.
在分析了国内外畜牧业工程技术发展的基础上,提出吉林省畜牧业的发展将出现农户小规模饲养和企业大规模饲养并存的局面。农户小规模饲养以传统人工饲养为基础,其技术取向是“传统人工饲养+优良品种+配合饲料+简易生物环境工程”。企业大规模饲养要以“优种优料+机械技术+生物环境工程”为技术取向。对传统畜牧业要改善畜禽环境,并加强环境保护和资源的二次利用;大型畜牧企业要实现饮水、喂料、清粪自动化,畜禽棚舍环境要实现人为控制。战略重点是引进或开发简易清粪机械和粪肥处理设备,并在中小饲养场中进行推广;大型饲养场要引进机械化生  相似文献   
996.
Species can become regionally rare when limited by the availability of suitable habitats or by limited dispersal ability. We tested if the presence of a rare bryophyte species (Sphagnum angermanicum) was dispersal or habitat limited and at the same time investigated the possibility of establishing new populations of this rare species. Further, we tested how propagule (fragment) size and small scale disturbances affected establishment success. All field experiments were performed by artificially transporting propagules (of various sizes) to new and old sites for the species in Sweden.We show that S. angermanicum is dispersal limited on a regional scale, as no significant differences in establishment success were found between new suitable sites and old occupied sites. The larger the propagule the better was the establishment success; the best establishment success was found when transplanting whole shoots. Disturbances did not increase establishment success, in contrary, when compared to controls success was reduced by the more intensive disturbance treatments. We suggest that disturbance maybe more important for increasing direct dispersal than for making the microhabitat more advantageous for establishment. However, an intermediate disturbance, which slightly reduces the Sphagnum-community length increment, might also be beneficial for the establishment success of S. angermanicum propagules.The reasonably high establishment success of S. angermanicum propagules in new suitable sites suggests that artificial introductions of fragments could be considered as an active management regime for the species if the number of localities continues to decrease.  相似文献   
997.
Earthworms are known to play a role in aggregate formation and soil organic matter (SOM) protection. However, it is still unclear at what scale and how quickly earthworms manage to protect SOM. We investigated the effects of Aporrectodea caliginosa on aggregation and aggregate-associated C pools using 13C-labeled sorghum (Sorghum bicolor (L.) Moench) leaf residue. Two incubations were set up. The first incubation consisted of soil samples crushed <250 μm to break up all macroaggregates with three treatments: (i) control soil; (ii) soil+13C-labeled residue and (iii) soil+13C-labeled residue+earthworms. Earthworms were added after 8 d and 12 d (days) later, aggregate size distribution was measured together with total C and 13C in each aggregate fraction. A second incubation was made to assay protected versus unprotected total C and 13C from 21-d laboratory incubations of intact and crushed large (>2000 μm) and small (250-2000 μm) macroaggregates and microaggregates (53-250 μm). Eight different pools of aggregate-associated C were quantified: (1) and (2) unprotected C pools in large and small macroaggregates, (3) unprotected C pools in microaggregates, (4) and (5) protected C pools in large and small macroaggregates, (6) protected C pool in microaggregates, and (7) and (8) protected C pools in microaggregates within large and small macroaggregates. In the presence of earthworms, a higher proportion of large macroaggregates was newly formed and these aggregates contained more C and 13C compared to bulk soil. There were no significant differences between the samples with or without earthworms in the C pool-sizes protected by macroaggregates, microaggregates or microaggregates within small macroaggregates. However, in the presence of earthworms, the C protected by microaggregates within large macroaggregates was a significant pool and 22% of this C pool was newly added C. In conclusion, these results clearly indicate the direct involvement of earthworms in providing protection of soil C in microaggregates within large macroaggregates leading to a possible long-term stabilization of soil C.  相似文献   
998.
In view of the remarkable interest of the flora, vegetation and landscape of Linosa island, a natural reserve should be suggested including protection of the traditional agriculture. Especially for the last aim completely new ways have to be elaborated. An integrated approach of nature protection and on-farm conservation could be the ideal conclusion.  相似文献   
999.
在分析农用电机烧损现象及研究现有保护方式的基础上,提出了选频振荡电路通过仪表的表针摆动实现采样、控制、保护的新方法,并研制了保护元件与仪表一体的装置,实现了对运行设备既能监视又能起到保护作用的一体化装置。  相似文献   
1000.
江河源区生物多样性问题研究   总被引:2,自引:0,他引:2  
江河源区西部、南部、东南部和东北部都毗邻生物多样性中心,生态系统多样,物种较丰富。这种生物多样性是随着青藏高原的隆起而产生和发展起来的并以其环境为生存条件,因而比较独特,不乏特有种、珍禽异兽、名贵药材和受到国家保护的物种。全面了解江河源区特殊的生物多样性将有利于该区的生态环境保护和区内自然保护区的建设。  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