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   804篇
  免费   5篇
  国内免费   3篇
林业   78篇
农学   38篇
基础科学   3篇
  330篇
综合类   89篇
农作物   15篇
水产渔业   12篇
畜牧兽医   196篇
园艺   13篇
植物保护   38篇
  2023年   5篇
  2022年   7篇
  2021年   8篇
  2020年   8篇
  2019年   12篇
  2018年   12篇
  2017年   9篇
  2016年   15篇
  2015年   12篇
  2014年   12篇
  2013年   47篇
  2012年   39篇
  2011年   51篇
  2010年   23篇
  2009年   25篇
  2008年   41篇
  2007年   51篇
  2006年   52篇
  2005年   55篇
  2004年   33篇
  2003年   33篇
  2002年   40篇
  2001年   15篇
  2000年   26篇
  1999年   18篇
  1998年   13篇
  1997年   14篇
  1996年   14篇
  1995年   6篇
  1994年   12篇
  1993年   8篇
  1992年   7篇
  1991年   7篇
  1990年   8篇
  1989年   6篇
  1988年   9篇
  1987年   8篇
  1986年   2篇
  1985年   3篇
  1984年   3篇
  1978年   2篇
  1974年   3篇
  1973年   6篇
  1970年   3篇
  1969年   2篇
  1968年   3篇
  1966年   3篇
  1958年   2篇
  1955年   2篇
  1863年   1篇
排序方式: 共有812条查询结果,搜索用时 32 毫秒
21.
Summary Calosoma sycophanta L.(Col., Carabid.) andNabis apterus F.(Hemipt., Nabid.) were observed attacking and feeding onLymantria monacha, Bupalus piniarus andDiprion spec.-larvae and pupae in some pine stands in southern and northern Bavaria 1965. It is intended to investigate the two species in regard to their biology and importance for biological control measures. In the present paper the faunistical and biological data known until now are summarized.
Résumé Pendant l'année de 1965 les insectes prédateursCalosoma sycophanta L.(Col. Carab.) etNabis apterus F.(Hem. Nabid.) furent observés comme ennemies deLymantria monacha, Bupalus pinarius etDiprion frutetorum dans quelques forêts de pins en Bavarie. Les connaissances sur la biologie de ces deux espèces en Europe, quoique incomplètes, sont brièvement résumées pour faciliter des recherches futures.
  相似文献   
22.
The infestation of sweet cherry trees with Gnomonia erythrostoma has undergone an alarming increase. It leads to minor plant performance and fruit quality and may cause major problems for the fruit farmer up to existential problems. In order to thwart this development the Bavarian State Ministry of Agriculture and Forest Management has funded a three year pilot study to develop an effective control for this disease. Besides laboratory experiments investigating mechanisms of infection, field tests with new fungicides were performed. Our studies show that these fungicides are highly effective to eliminate infections with Gnomonia erythrostoma. In addition these substances have positive side effects such as controlling other diseases like the brown rot caused by Monilia.  相似文献   
23.
Association mapping identifies quantitative trait loci (QTLs) by examining the marker-trait associations that can be attributed to the strength of linkage disequilibrium between markers and functional polymorphisms across a set of diverse germplasm. In this study, association mapping was performed to detect QTL-linked and genome wide SSR markers linked to phenolic compounds of extraction meal in a population of 49 genetically diverse oilseed rape cultivars of dark-seeded, winter-type oilseed rape accessions. Correction for population structure was performed using 559 genome wide SSR markers. Results showed that seed colour is an important contributor to seed meal quality. Totally, 52 SSR markers linked to phenolic compounds were detected, five of them being QTL linked markers. Some of these markers were already mapped on Brassica napus chromosomes that contain known QTL controlling oilseed rape meal quality traits. Our results demonstrate that association mapping is a useful approach to complement and enhance previous QTL information for marker-assisted selection.  相似文献   
24.
25.
  总被引:2,自引:0,他引:2  
With increasing agricultural and industrial use of rare earth elements (REEs), input of REEs into the pedosphere has risen in parallel. Since total REE budgets for soils in Germany are mainly unknown, this pilot study investigates the concentrations of REEs in three loess soil profiles under agricultural land use in the Wetterau region, Germany. There were no significant REE applications in the past, so the presented data can be considered as background concentrations of REEs in soils. In addition to the total REE contents (aqua regia digestion), potentially plant‐available (EDTA) and at actual conditions available, mobile (NH4NO3) REEs have been determined for each horizon. Interactions between REE availability and properties of soils are explained after assessing several chemical and physical properties. The results reveal a wide range of total REE contents, ranging from 222 to 423 mg kg–1. With 10.1% of total REE amounts, the potentially plant‐available proportions of REEs are generally low. In contrast, yttrium, which showed high available proportion of 24.8%, was found to be comparable with Cd. Cerium is the most abundant REE in aqua regia digests, whereas only small amounts in the potentially plant‐available fraction were found. Thus negative cerium anomalies could be concluded concerning its potential availability. Generally, bioavailability of REE had significant correlations between clay contents and Fe and Mn oxides for the majority of REEs. Due to moderately high pH (CaCl2) in soils (average 6.6) the mobile fraction for most of the elements was not detectible.  相似文献   
26.
27.
28.
    
Nitrogen (N) deposition can affect grassland ecosystems by altering biomass production, plant species composition and abundance. Therefore, a better understanding of the response of dominant plant species to N input is a prerequisite for accurate prediction of future changes and interactions within plant communities. We evaluated the response of seven dominant plant species on the Tibetan Plateau to N input at two levels: individual species and plant functional group. This was achieved by assessing leaf N : P stoichiometry, leaf δ15N and biomass production for the plant functional groups. Seven dominant plant species—three legumes, two forbs, one grass, one sedge—were analyzed for N, P, and δ15N 2 years after fertilization with one of the three N forms: NO$ _3^- $ , NH$ _4^+ $ , or NH4NO3 at four application rates (0, 7.5, 30, and 150 kg N ha–1 y–1). On the basis of biomass production and leaf N : P ratios, we concluded that grasses were limited by available N or co‐limited by available P. Unlike for grasses, leaf N : P and biomass production were not suitable indicators of N limitation for legumes and forbs in alpine meadows. The poor performance of legumes under high N fertilization was mainly due to strong competition with grasses. The total above‐ground biomass was not increased by N fertilization. However, species composition shifted to more productive grasses. A significant negative correlation between leaf N : P and leaf δ15N indicated that the two forbs Gentiana straminea and Saussurea superba switched from N deficiency to P limitation (e.g., N excess) due to N fertilization. These findings imply that alpine meadows will be more dominated by grasses under increased atmospheric N deposition.  相似文献   
29.
Langjährig unterlassene Kalkung führte bei mineralisch (NPK) und mit Stallmist gedüngtem Boden in den letzten 20 Versuchsjahren zu pH‐Werten von 4,2 bis 3,6. Die Relativerträge nahmen im Vergleich zur mineralischen Volldüngung (NPKCa) ab. Diese Abnahme war von der Pflanzenart abhängig und bei Sommergerste deutlicher als bei Kartoffeln und Mais. Kalkung des mit NPK gedüngten Bodens erhöhte die Erträge bei Mais bereits im ersten Jahr, bei Gerste und Kartoffeln erst nach mehreren Jahren auf das Niveau der Vergleichsvariante. Bei einer Umstellung von Stallmist auf Stallmist + NPKCa glichen sich die Erträge von Mais und Sommergerste im gleichen Jahr, bei Kartoffeln erst nach mehreren Jahren dem langjährig mit Stallmist + NPKCa gedüngten Prüfglied an.

Im langjährig ungedüngten Boden fielen pH‐Wert, KDL und PDL in den letzten 20 Versuchsjahren ebenfalls deutlich ab (pH 3,6 bis 4,1; KDL 2,2 bis 5,0 und PDL 3,5 bis 5,5 mg/100 g Boden). In deren Folge und durch N‐Mangel kam es bei Gerste zum Totalausfall und bei Mais nahezu zum Totalausfall. Bei Kartoffeln lag der Ertrag noch bei 15% der Vergleichsvariante NPKCa. Eine Düngung der Mangelparzellen mit NPKCa ließ den pH‐Wert bereits im ersten Jahr, KDL und PDL erst nach mehrmaliger Düngung in den anzustrebenden Bereich ansteigen. Eine Angleichung der Erträge an die Erträge des durchgehend mit NPKCa gedüngten Prüfgliedes dauerte drei bis vier Jahre.  相似文献   
30.
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