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   10693篇
  免费   774篇
  国内免费   603篇
林业   2640篇
农学   633篇
基础科学   46篇
  1096篇
综合类   3477篇
农作物   480篇
水产渔业   1432篇
畜牧兽医   955篇
园艺   388篇
植物保护   923篇
  2024年   60篇
  2023年   188篇
  2022年   228篇
  2021年   336篇
  2020年   359篇
  2019年   398篇
  2018年   283篇
  2017年   446篇
  2016年   454篇
  2015年   395篇
  2014年   513篇
  2013年   671篇
  2012年   709篇
  2011年   759篇
  2010年   642篇
  2009年   634篇
  2008年   616篇
  2007年   661篇
  2006年   556篇
  2005年   459篇
  2004年   362篇
  2003年   308篇
  2002年   230篇
  2001年   222篇
  2000年   195篇
  1999年   171篇
  1998年   163篇
  1997年   132篇
  1996年   130篇
  1995年   143篇
  1994年   111篇
  1993年   103篇
  1992年   116篇
  1991年   96篇
  1990年   74篇
  1989年   55篇
  1988年   34篇
  1987年   18篇
  1986年   10篇
  1985年   4篇
  1983年   2篇
  1982年   5篇
  1981年   5篇
  1980年   1篇
  1979年   1篇
  1978年   3篇
  1977年   1篇
  1976年   2篇
  1963年   2篇
  1955年   3篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Since 1985, the U.S. Department of Agriculture, Animal and Plant Health Inspection Service has maintained the 'Port Information Network' (PIN) database for plant pests intercepted at the U.S. ports of entry. As of August 2001, PIN contained 6825 records of beetles (Coleoptera) in the family Scolytidae that had been intercepted during the years 1985–2000 from countries outside of North America. Of the 6825 scolytid interceptions, 2740 (40%) were identified to the species level, 2336 (34%) to only the genus level, and 1749 (26%) were identified to only the family level. Of the 49 identified scolytid genera, the 10 most common were Hypothenemus (821 interceptions), Pityogenes (662), Ips (544), Coccotrypes (520), Orthotomicus (461), Hylurgops (327), Hylurgus (266), Tomicus (194), Dryocoetes (166), and Hylastes (142). The 10 most common identified species were Pityogenes chalcographus (565 interceptions), Orthotomicus erosus (385), Hylurgops palliatus (295), Ips typographus (286), Hylurgus ligniperda (217), Ips sexdentatus (157), Tomicus piniperda (155), Hylastes ater (75), Hypothenemus hampei (62), and Polygraphus poligraphus (48). Of these 10 species, H. palliatus, H. ligniperda, and T. piniperda are known to be established in the continental U.S. The scolytids were intercepted from 117 different countries; the top 12 countries were Italy (1090 interceptions), Germany (756), Spain (457), Mexico (425), Jamaica (398), Belgium (352), France (261), China (255), Russia (247), India (224), U.K. (151), and Portugal (150). The scolytids were intercepted in 35 U.S. states and 97 port cities. In general, there was a positive relationship between the number of scolytid interceptions from individual countries and the value of the imports from those countries. Overall, 73% of the scolytids were found in solid wood packing materials, 22% in food or plants, and 5% in other or unspecified materials. The products most commonly associated with scolytid-infested wood packing materials were tiles, marble, machinery, steel, parts, ironware, granite, aluminum, slate, and iron. The food products and plants that were commonly infested with scolytids included nutmeg, palms, coffee beans, kola nuts, and macadamia nuts.  相似文献   
112.
This review deals with the biology and control of a biting pest species, Simulium posticatum, which has been responsible for a considerable degree of distress to the human population in the vicinity of the River Stour in Dorset. Each phase of the life cycle of the insect is considered in relation to possible control measures. An account is given of how this information has been combined with the use of Bacillus thuringiensis in a successful, precisely targeted attack on the pest.  相似文献   
113.
在云南中亚热带试验点,对8个禾本科饲草栽培种进行引种栽培试验,结果表明:墨西哥类玉米、8493墨西哥类玉米、大力士甜高粱、先锋高丹草和M-8IE甜高粱5个栽培种干物质产量高,适应性强,适宜在相似气候条件地区推广种植。  相似文献   
114.
福建黄兔开发利用及配套技术研究   总被引:2,自引:0,他引:2  
福建黄兔是福建省优良地方畜禽品种,2006年已被列入国家级畜禽遗传资源保护名录。福建黄兔具有耐粗饲、繁殖性能好、抗病力强等优点,其野性强,肉质口味好,药用价值高,但因其体型小,生长速度慢,影响了经济效益和保种利用。通过研究养殖配套技术:中草药免疫调节剂的研究应用、高产优质牧草栽培生产技术、福建黄兔的保健功效开发研究、实施“兔-沼-草(果)”工程模式,探索一条提高养兔经济效益,进而促进保种工作的新思路。  相似文献   
115.
The infection process of hemibiotrophic isolates of Colletotrichum linicola (from flax, Linum usitatissimum ) and C . truncatum (from broad bean, Vicia faba and lentil, Lens culinaris ) was studied by light microscopy. Host surfaces were penetrated directly leading to a symptomless, biotrophic phase characterized by the elaboration of large multilobed, multiseptate, vesicular primary hyphae that were restricted to the initially infected epidermal cells. Biotrophy lasted for the first 48 h of the host-pathogen interaction and was rapidly succeeded by a necrotrophic phase during which narrow, secondary hyphae invaded the surrounding leaf tissues and water-soaked spreading lesions with sporulating, monosetate acervuli were produced on infected host surfaces. Molecular taxonomic analysis of the nucleotide sequences of the amplified D2 and ITS-2 regions of rDNA revealed very close similarities (97–99%) between these isolates and those of C . destructivum obtained from cowpea ( Vigna unguiculata ) and lucerne ( Medicago sativa ), and also of C . truncatum obtained from pea ( Pisum sativum ). This association was consistent with results from a comparative assessment of some in-planta and in-vitro morphological and growth characteristics of these hemibiotrophic fungi. It was concluded that localized hemibiotrophy is an infection strategy utilized predominantly by a closely-related group of pathogens comprising C . destructivum , C . linicola and C. truncatum , and the formation of multilobed primary hyphae restricted to the first penetrated cell might therefore be a key taxonomic character which correlates consistently with ITS sequence data.  相似文献   
116.
新疆天山大帽藓科植物的分类和分布   总被引:2,自引:1,他引:1  
根据作者十余年来在新疆天山地区所采的标本,对大帽藓科植物进行整理研究,现知该地区有本科植物7种,高山大帽藓,尖叶大帽藓,剑叶大帽藓,西藏大帽藓,大帽藓,钝叶大帽藓和天山大帽藓(新拟)其中的天山大帽藓为近年在我国西北发现的一个新种,文中简要概述了每种的识别行征,生境和地理分布,并根据标本编制了新疆大帽藓属植物分种检索表,凭证标本中存于河北师范大学生物系植物标本室(HBNU)和新疆大学生物系植物标本室  相似文献   
117.
本文报道了从上海动物园棕尾虹雉(Lophophorusimpejanus)体上所采集的鸟虱,经鉴定后,该虫神为头角亚目(Amblycera)短角鸟虱科(Menoponidae)短角鸟虱属(Menopon)一新种,文内对其所具有的分类特征进行了描述,并绘图。  相似文献   
118.
利用<农业科技成果经济效益计算方法>对"贵州主要地方优良草种选育及种子产业化研究"项目进行成果经济效益分析,结果表明:在计算年限内,该成果每年可增加纯收入926.96万元,科研经费与新增纯收益比为1:6.58,其成果效益明显,产生了較好的经济效益、社会效益和生态效益.该成果的进一步推广应用将有利于贵州省实施西部大开发和加快农业种植结构调整,尤其是对退耕还草种草畜、发展生态草地畜牧业及治理生态环境建设具有重要作用.  相似文献   
119.
三江源地区高寒草地群落特征研究   总被引:3,自引:3,他引:3  
选择三江源区针茅草原和高山嵩草草甸6处典型样地为研究对象,采用样方调查法,分析了该地区高寒草地群落特征。结果表明:1)达日县和曲麻莱县高寒草甸物种丰富度较高,分别为20种和15种;兴海县、玛多县和唐古拉山乡草地物种丰富度较低,均为8种,杂多县物种数最低,仅有5种(P0.05)。2)达日县和曲麻莱县物种多样性最高,分别为2.74和2.27;唐古拉山乡和杂多县最低,约为1.5;兴海县和玛多县针茅草原物种多样性均为1.87左右。唐古拉山乡和曲麻莱县均匀度指数稍低,分别为0.76和0.84,其余各县均匀度指数均较高。多样性指数与物种数极显著相关。3)聚类分析发现杂多县和曲麻莱县高山草甸首先被归为一类,接着将唐古拉山乡合为一类;然后依次是兴海县短花针茅草原和达日县高寒草甸,玛多县紫花针茅草原在最后被聚合为一类。  相似文献   
120.
The antifungal activity of the leaf extracts from 203 weed species was investigated by performing a bioassay using cucumber plants and Colletotrichum orbiculare. The leaf extracts from four families, namely, Urticaceae, Onagraceae, Commelinaceae, and Solanaceae, showed a relatively stronger inhibition of the anthracnose lesions in cucumber plants when compared with the other families investigated in the study. A remarkable inhibition of anthracnose infection in cucumber leaves was observed with the extracts from the following 19 weed species: Boehmeria nipononivea and Boehmeria longispica, Persicaria scabra, Ranunculus japonicus and Ranunculus sceleratus, Cardamine flexuosa, Oenothera biennis, Aeschynomene indica, Indigofera pseudo‐tinctoria, Torilis scabra, Calystegia japonica, Solanum americanum, Bidens pilosa, Gnaphalium japonicum, Kalimeris yomena, Bromus catharticus, Cynodon dactylon, Alopecurus aequalis, and Scirpus tabernaemontani. In particular, it is noteworthy that the extracts from C. dactylon, K. yomena, and S. americanum completely inhibited anthracnose infection in cucumber.  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