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   252536篇
  免费   15388篇
  国内免费   644篇
林业   24047篇
农学   14164篇
基础科学   2971篇
  43912篇
综合类   21421篇
农作物   17244篇
水产渔业   16997篇
畜牧兽医   97241篇
园艺   6355篇
植物保护   24216篇
  2021年   2550篇
  2020年   2981篇
  2019年   3726篇
  2018年   4205篇
  2017年   4628篇
  2016年   5011篇
  2015年   4452篇
  2014年   5832篇
  2013年   16508篇
  2012年   6403篇
  2011年   8212篇
  2010年   7382篇
  2009年   8006篇
  2008年   7606篇
  2007年   6560篇
  2006年   7107篇
  2005年   6416篇
  2004年   6180篇
  2003年   6043篇
  2002年   5312篇
  2001年   5728篇
  2000年   5367篇
  1999年   5143篇
  1998年   4111篇
  1997年   4185篇
  1996年   3895篇
  1995年   4478篇
  1994年   3864篇
  1993年   3564篇
  1992年   4199篇
  1991年   4398篇
  1990年   4116篇
  1989年   4094篇
  1988年   3638篇
  1987年   3672篇
  1986年   3632篇
  1985年   3928篇
  1984年   3689篇
  1983年   3430篇
  1982年   2870篇
  1981年   2762篇
  1980年   2741篇
  1979年   3265篇
  1978年   2911篇
  1977年   2765篇
  1976年   2549篇
  1975年   2388篇
  1974年   2606篇
  1973年   2574篇
  1972年   2314篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Landscape-ecological mapping of the Netherlands   总被引:1,自引:0,他引:1  
The Landscape-ecological Mapping of the Netherlands project (LMN project) started in 1983 with the aim of establishing a landscape-ecological database for use in developing and evaluating national land-use plans. The project, working with grid cells of 1 km2, has four working objectives: a) development of mapping potential for basic landscape-ecological data, b) assessment of susceptibility to interventions, c) evaluation of significance for nature conservation and d) production of vulnerability maps, as a combination of susceptibility and significance. In addition to information on soil, groundwater, ecotopes, flora and fauna, the database also incorporates information on physiographical features and entire landscapes. The resulting database is a geographic information system (GIS). This article describes the second phase of the project (1985–1989), covering the Randstad area, and focusses on the methods and the applications potential of the database.  相似文献   
992.
The efficacy of mixtures of respiration inhibitors and phenylamide fungicides (oxadixyl and metalaxyl) in controlling late blight was investigated using potato tuber disks. Results showed that uncoupling agents(e.g. DNP), inhibitors of ATP formation(e.g. oligomycin), ionophores(e.g, valinomycin) and inhibitors that block specific carriers in the electron transport chain(e.g. rotenone, antimycin A) increased significantly the control efficacy of both metalaxyl and oxadixyl towards populations ofPhytophthora infestons when applied to tuber slices pretreated with sublethal doses of both fungicides. When applied alone at the same doses, respiration inhibitors did not inhibit the development of the late blight fungus. Increased control efficacy of mixtures was not noted against phenylamide-sensitive populations of the fungus.  相似文献   
993.
A paper published byKniehase & Zoebelein (1990) describes a new laboratory method to test the side effects of pesticides on the predatory mitePhytoseiulus persimilis and criticizes the laboratory test developed by the International Working Group pesticides and beneficial organisms of the International Organization for Biological Control (IOBC), West Palaearctic Regional Section (WPRS). The present publication discusses the advantages and disadvantages of both methods, responds to the criticism and mention the overall concept of the IOBC/WPRS Working Group including semifield and field test methods.In einer Arbeit vonKniehase undZoebelein (1990) wird ein neues Laborverfahren zur Prüfung der Nebenwirkung von Pflanzenschutzmitteln auf die RaubmilbePhytoseiulus persimilis beschrieben. Die genannten Autoren äußern sich kritisch über das seither von der Arbeitsgruppe Pflanzenschutzmittel und Nutzorganismen der International Organization for Biological Control (IOBC), West Palaearctic Regional Section (WPRS) praktizierte Verfahren. In der vorliegenden Arbeit werden die Vor- und Nachteile der beiden Prüfmethoden diskutiert. Einer Reaktion auf die Kritik folgt eine kurze Beschreibung der gesamten Konzeption der genannten Arbeitsgruppe, die auf einer Kombination aus Labor-, Halbfreiland- und Feldprüfverfahren beruht.  相似文献   
994.
Data collected by the National Animal Health Monitoring System in Ohio for a 12-month period during 1986 and 1987 were used to determine the relative magnitude of costs associated with mastitis in the following categories: milk production loss, veterinary services, drugs, producer labor, and "other" factors. The cost of milk loss associated with mastitis that was reported by producers cooperating in the National Animal Health Monitoring System program was compared with estimates based on bulk tank somatic cell counts and individual cow milk somatic cell counts. Using producer-reported estimates, milk loss accounted for about one third of the total cost associated with mastitis. When estimates of milk loss were replaced by estimates based on bulk tank somatic cell counts, milk loss accounted for over 80% of the total cost of mastitis. Estimates of the cost of milk loss based on studies relating milk yield to somatic cell counts differed considerably. Consequently, it was unclear how to best estimate the relative magnitude of the milk loss component of mastitis costs.  相似文献   
995.
996.
997.
998.
999.
1000.
Vitamin E, selenium and polyunsaturated fatty acids (PUFAs) were determined in feed used at three piggeries over.a four week period and compared with corresponding concentrations in clinically normal grower pigs at slaughter. Mean values were vitamin E: 59 IU/kg (feed), 6 micromol/kg (liver), 1.7 micromol/l (serum); and selenium: 310 microg/kg (feed), 5200 nmol/kg (liver), 1700 nmol/l (blood). Alpha-tocopherol accounted for 80% of the mean vitamin E activity in the feed and over 95% that in the liver and serum. The mean ratio of PUFA to total fatty acid (FA) in the feed (38%) was similar to that in the serum (36%) and liver (39%), but the ratio of peroxidisable PUFA (PPUFA) to FA increased from 1.7% in the feed to 4.2% in the serum and 10.8% in the liver. The ratio of alpha-tocopherol (mmol) to PPUFA (mol) in the liver varied from 0.16 to 0.48. The relationship of these data to the VESD syndrome is discussed in the light of other published data.  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