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   8087篇
  免费   393篇
  国内免费   57篇
林业   1303篇
农学   215篇
基础科学   65篇
  1305篇
综合类   735篇
农作物   246篇
水产渔业   358篇
畜牧兽医   3609篇
园艺   212篇
植物保护   489篇
  2023年   52篇
  2022年   71篇
  2021年   96篇
  2020年   131篇
  2019年   71篇
  2018年   208篇
  2017年   173篇
  2016年   209篇
  2015年   189篇
  2014年   163篇
  2013年   415篇
  2012年   383篇
  2011年   375篇
  2010年   236篇
  2009年   157篇
  2008年   306篇
  2007年   358篇
  2006年   320篇
  2005年   262篇
  2004年   256篇
  2003年   230篇
  2002年   222篇
  2001年   157篇
  2000年   156篇
  1999年   123篇
  1992年   95篇
  1991年   112篇
  1990年   129篇
  1989年   140篇
  1988年   117篇
  1987年   101篇
  1986年   104篇
  1985年   98篇
  1984年   93篇
  1983年   79篇
  1982年   50篇
  1979年   101篇
  1978年   73篇
  1977年   66篇
  1976年   51篇
  1975年   70篇
  1974年   91篇
  1973年   96篇
  1972年   73篇
  1971年   84篇
  1970年   78篇
  1969年   86篇
  1968年   69篇
  1967年   65篇
  1965年   56篇
排序方式: 共有8537条查询结果,搜索用时 140 毫秒
41.
42.
A new pest in oilseed rape the cabbage root fly (Delia radicum L.) has succeded to establish – at least regional –during the recent years. It is not easy to monitor the cabbage root fly. Although the usual yellow water trap works quite well, it is still difficult for the farmers to determine Delia radicum exactly. The amount of infestation can be assessed best in the middle of November by analysing the damages of the roots. In this article a classification scheme is proposed. It is also difficult to control this pest. While applications of Pyrethroids against the imagines and the use of Dimethoat against the larva mostly showed only little effect in the tests, some new dressing-substances proved better against the standard “Chinook” (Imidacloprid+beta-Cyfluthrin). To forward this research and to clarify factors, which influence the infestation, a project titled “Possibilities of defence and control of cabbage root fly in winter oilseed rape” has been started in November 2003. Eight crop-protection services at German Federal State level and the BBA are involved in this project, which is supported by UFOP.  相似文献   
43.
Five animals in a colony of cynomolgus monkeys (Macaca fascicularis) died or were euthanatized because of alveolar echinococcosis, during a period of 5 years. The remainder of the colony was screened for possible infection with Echinococcus multilocularis, using serology and ultrasonography. A total of 46 animals out of a group of 55 were examined. The presence of anti-Em2 antibodies analyzed with enzyme-linked immunosorbent assay was demonstrated in 3 monkeys. In 2 of these 3 monkeys, multilocular structures compatible with metacestodal cysts in the liver were identified, using ultrasonography. The presence of alveolar echinococcosis was subsequently confirmed at postmortem examination in 1 animal. The other animals are still alive. Two other monkeys were negative in the serological examination but had cystic structures in the liver, which were identified as bile duct cysts at postmortem examination in 1 animal. The other monkey is still alive. These findings suggest that serology for antibodies against the Em2 antigen may represent a useful method in identifying animals that might be infected with E. multilocularis and are therefore at risk of developing fatal alveolar echinococcosis.  相似文献   
44.
Samples of water and sediment were taken from drains, reservoirs and wells from four commercial hardy ornamental nurseries with water recirculation systems. The samples were taken on seven different dates throughout a single year from August 1994 to July 1995. The samples were screened for Phytophthora species using five different methods: direct plating, three bait tests (using lupin seedlings, apples and Rhododendron leaves) and a DAS-ELISA (double-antibody sandwich enzyme-linked immunosorbent-assay) with two antisera. In the nurseries with old water recirculation systems, Phytophthora species were detected in the drains and in the reservoirs. In the nursery with a new recirculation system, the pathogens were only present in the drains. None of the water samples from wells in any of the nurseries were contaminated. Phytophthora species were present in the water as well as in the sediment samples from drains and reservoirs. They were detected in the water recirculation systems irrespective of the season. The number of isolates increased about sevenfold between late summer and spring. At least 12 different Phytophthora species were identified: some isolates were previously unrecorded species. The epidemiology of the pathogens in outdoor water recirculation systems as well as the importance of the results for commercial nurseries is discussed.  相似文献   
45.
In a nematode survey of Tylenchida carried out in groundnut (Arachis hypogaea L.) growing areas in the Mediterranean region of Turkey, 15 species were determined as belonging to ten genera of eight families within the superfamilies Tylenchoidea, Dolichodoroidea, Hoplolaimoidea and Anguinoidea. Each of them constitutes a new record on groundnut in Turkey, andScutylenchus tumensis Skwiercz andPratylenchus brachyurus (Godfrey) are reported for the first time in the nematofauna of Turkey.  相似文献   
46.
47.
48.
49.
50.
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