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   452篇
  免费   38篇
林业   44篇
农学   14篇
基础科学   9篇
  66篇
综合类   11篇
农作物   82篇
水产渔业   110篇
畜牧兽医   89篇
园艺   8篇
植物保护   57篇
  2023年   8篇
  2022年   11篇
  2021年   19篇
  2020年   22篇
  2019年   30篇
  2018年   41篇
  2017年   34篇
  2016年   36篇
  2015年   15篇
  2014年   18篇
  2013年   53篇
  2012年   28篇
  2011年   38篇
  2010年   19篇
  2009年   11篇
  2008年   26篇
  2007年   11篇
  2006年   8篇
  2005年   4篇
  2004年   5篇
  2003年   5篇
  2002年   1篇
  2001年   1篇
  2000年   4篇
  1999年   3篇
  1998年   1篇
  1997年   2篇
  1996年   3篇
  1995年   2篇
  1994年   6篇
  1993年   4篇
  1992年   3篇
  1991年   1篇
  1990年   1篇
  1988年   3篇
  1987年   3篇
  1986年   2篇
  1984年   1篇
  1983年   1篇
  1981年   1篇
  1979年   2篇
  1978年   1篇
  1975年   1篇
  1965年   1篇
排序方式: 共有490条查询结果,搜索用时 421 毫秒
101.
Four spider species and the predacious mitePhytoseiulus persimilis (Athias-Henriot) were examined in the laboratory for their capacity to feed on the carmine spider mite,Tetranychus cinnabarinus (Boisduval). The adult females ofChiracanthium mildei L. Koch showed the highest capacity for feeding onT. cinnabarinus (27.5 mites/day) and differed significantly from all other spider species, including the immatureC. mildei which consumed an average of 18.9 mites/day — nearly equal to that of the Oxyopidae species (16.8 mites/day). The salticid (10.1 mites/day) and theridiid (9.5 mites/day) spider species had the lowest capacity, which was nearly equal to that of the predacious miteP. persimilis (11.3 mites/day). Results indicate that spiders play an important role as mite predators.  相似文献   
102.
The effects of Margosan-OTM, AzatinTM and RD9-Repelin on the phytophagous miteTetranychus cinnabarinus (Boisd.), the predacious miteTyphlodromus athiasae, and the predatory spiderChiracanthium mildei were studied and compared in laboratory experimentsr.-No toxic effect of any of these neem formulations was observed onC. mildei. Margosan-O and Azatin were not toxic to eitherT. cinnabarinus orT. athiasae, but RD9-Repelin was highly toxic to both the phytophagous and the predacious mite.  相似文献   
103.
Resistance of 37Citrullus lanatus L. lines to the carmine spider mite,Tetranychus cinnabarinus (Boisduval), was evaluated in three laboratory experiments, each including seven plants per line. Infestation with ten adult female mites per leaf, of each plant, was done at the three-leaf stage. In experiment A, average counts 10 days after infestation of three leaves ranged from 42 to 144 mites per leaf. In experiment B, average counts 8 days after infestation of two leaves ranged from 40 to 286 mites per leaf. In experiment C, average counts 8 days after infestation of two leaves ranged from 15 to 196 mites per leaf. The results suggest that a definite variation in resistance against mite infestation exists among watermelon lines. Contribution from the Agricultural Research Organization. No. 1082-E, 1993 series.  相似文献   
104.
The photostability of pirimicarb, (2-dimethylamino-5,6-dimethylpyrimidin-4-yl dimethylcarbamate) in aqueous media, under natural and artificial sunlight irradiation conditions, is reported. The pH of the irradiated solutions remained constant during degradation time. The photodegradation mechanism seemed to be similar under both conditions, but the half-life was found to be about three times longer under natural than under artificial conditions. Four main photo-products ( 1 , 2 , 3 and 4 ) were isolated and identified by spectroscopic methods. It is proposed that a common photodegradation pathway exists for pirimicarb under both irradiation conditions. The results obtained from the photodegradation of pirimicarb and of its four main products isolated on solid phase permit the construction of a possible photodegradation pathway. Photoproduct 4 (2-methyl-formylamino-5,6-dimethyl-4-hydroxypyrimidine) is here described for the first time.  相似文献   
105.
Twenty-nine plant extracts of local species were evaluated for their potential as a source of bioactive ingredients with significant acaricidal activity that could lead to the development of new and safe bio-acaricides. The crude extracts (70% ethanol) of these plants were tested for their acaricidal activity against the carmine spider miteTetranychus cinnabarinus in a bioassay under controlled conditions. Mortality, repellency, and the number of eggs laid were measured. Extracts fromEucalyptus camaldulensis andInula viscosa caused more than 25% mortality. Sixteen plant extracts showed significant repellency compared with the control. The six best extracts, resulting in more than 75% repellency, were fromAllium sativum, Capparis spinosa, Cupressus sempervirens, Lupinus pilosus, Rhus coriaria andTamarix aphylla. Extracts from 16 plants were found to cause a significant reduction in the number of eggs laid compared with the control. The greatest reduction was achieved by extracts fromC. spinosa, Cyperus rotundus, E. camaldulensis, L. pilosus, Punica granatum, R. coriaria andT. aphylla. A relatively negative fit was found between the mean number of repelled mites and the number of eggs laid (r=−0.65), which might indicate that most repelled mites were unable to lay eggs before leaving the leaf discs of the bioassay. Our results show that several plant extracts have good potential for acaricidal activity and are worth further investigation. http://www.phytoparasitica.org posting Dec. 16, 2003.  相似文献   
106.
Faba bean necrotic yellows virus (FBNYV) was isolated from naturally infected faba bean plants in Jordan. The identification was based on host range, mode of transmission, symptomatology and serological properties. FBNYV occurred naturally in several leguminous crops including cultivated legumes and wild forage legumes, such as species of Medicago , Trifolium and Lathyrus . and infected other plant species belonging to the Malvaceae, such as Malva parviflora and Hibiscus esculentus . Such hosts may act as important natural reservoirs for both the virus and its aphid vectors. This is the first report of infection of M. parviflora and H. esculentus with FBNYV. The virus was not recovered from samples taken from some cultivated crops, including squash, cucumber, tomato, eggplant and pepper, growing near to faba bean fields. Also, it was not detected in commercial faba bean seeds collected from local companies or in seeds collected from infected faba bean plants. It was transmitted efficiently by Aphis craccivora . Serological testing of 1392 samples from faba beans showing virus-like symptoms and collected randomly from 16 locations (fields) in the Jordan Valley and Jarash areas showed that FBNYV occurred in 54.5% of the samples. These results indicate that FBNYV was an important pathogen of beans during the growing season of 1996 in Jordan.  相似文献   
107.
Field experiments in an apple orchard and in a citrus grove were carried out to evaluate the effect of four commercial pesticides in common use in Israel against apple and citrus pests, on the spider populations inhabiting the trees. The spider populations on apple were markedly suppressed by the pesticides, the order of toxicity being Talstar (biphenate) >Mavrik (fluvalinate) > Smash (fenpropathrin) > Dursban (chlorpyrifos). When grapefruit trees were treated with carbaryl + formothion, 232 spiders were sampled in the unsprayed plot, 55 days after treatment, as compared with only 11 spiders in the treated plot. Two and 7 days after treatment with chlorobenzilate, the sample from the treated plot numbered 68 and 55 spiders, respectively, as compared with 50 spiders collected 24 h before treatment. In addition, laboratory tests were carried out to determine the susceptibility of the spiderChiracanthium mildei L. Koch to 17 pesticides. When the spiders were exposed to grapefruit leaves which had been dipped 1 h previously for 5 sec in the aqueous emulsions of the pesticides, chlorpyrifos, fenpropathrin, fenvalerate, phosphamidon and biphenate caused 100%, and cypermethrin and fluvalinate 60% mortality, whereas all the other pesticides tested - acaricides, fungicides and herbicides - caused about 10-40% mortality.  相似文献   
108.
A safer, more effective adulticidal treatment and a safe method for reducing microfilaremia and breaking transmission of heartworm disease early in the treatment are needed. The present study evaluated efficacy of ivermectin (IVM) and doxycycline (DOXY) alone or together (with or without melarsomine [MEL]) in dogs with induced adult heartworm infection and assessed the ability of microfilariae from DOXY-treated dogs to develop to L3 in Aedes aegypti mosquitoes and subsequently to become reproductive adults in dogs. Thirty beagles were each infected with 16 adult heartworms by intravenous transplantation. Six weeks later, dogs were ranked by microfilarial count and randomly allocated to 6 groups of 5 dogs each. Beginning on Day 0, Group 1 received IVM (6 mcg/kg) weekly for 36 weeks. Group 2 received DOXY (10 mcg/(kgday)) orally Weeks 1-6, 10-11, 16-17, 22-25, and 28-33. Groups 3 and 5 received IVM and DOXY according to doses and schedules used for Groups 1 and 2. At Week 24, Groups 3 and 4 received an intramuscular injection of MEL (2.5 mg/kg), followed 1 month later by two injections 24h apart. Group 6 was not treated. Blood samples were collected for periodic microfilaria counts and antigen (Ag) testing (and later immunologic evaluation and molecular biology procedures). Radiographic and physical examinations, hematology/clinical chemistry testing, and urinalysis were done before infection, before Day 0, and periodically during the treatment period. At 36 weeks, the dogs were euthanized and necropsied for worm recovery, collection of lung, liver, kidney, and spleen samples for examination by immunohistochemistry and conventional histological methods. All dogs treated with IVM + DOXY (with or without MEL) were amicrofilaremic after Week 9. Microfilarial counts gradually decreased in dogs treated with IVM or DOXY, but most had a few microfilariae at necropsy. Microfilarial counts for dogs treated only with MEL were similar to those for controls. Antigen test scores gradually decreased with IVM + DOXY (with or without MEL) and after MEL. Antigen scores for IVM or DOXY alone were similar to controls throughout the study. Reduction of adult worms was 20.3% for IVM, 8.7% for DOXY, 92.8% for IVM + DOXY + MEL, 100% for MEL, and 78.3% for IVM + DOXY. Mosquitoes that fed on blood from DOXY-treated dogs had L3 normal in appearance but were not infective for dogs. Preliminary observations suggest that administration of DOXY+IVM for several months prior to (or without) MEL will eliminate adult HW with less potential for severe thromboembolism than MEL alone.  相似文献   
109.
Forty landraces of Damask rose were collected from 28 provinces (13 origin sites) in Iran and evaluated to determine the diversity among them. The investigated characters were: flower weight, flower diameter, peduncle length, number of petals, number of stamens and oil content. Pearson's coefficients showed that number of petals was positively correlated with flower weight (r = 0.642) and number of stamens (r = 0.630), while its correlation with peduncle length was negative (r = −0.53). A negative correlation was obtained between oil content and number of stamens (r = −0.60) which is useful for indirect selection of landraces with low number of stamens and therefore high amount of oil content. Cluster analysis based on five botanical characters and oil content separated the origin site 12, which included Guilan, Mazandaran and Golestan provinces with a specific climate condition of temperate humid, from other origin sites. This distinctiveness was already confirmed by the bi-plot of the principal components. The distribution of Damask rose landraces provided useful information for the future collection and for the genetic resource management in these origin sites.  相似文献   
110.
Immune modulation by Ostertagia ostertagi and the effects of diet   总被引:1,自引:0,他引:1  
IgG1 antibody responses to Ostertagia ostertagi third stage larvae (L3) and the third party antigen, keyhole limpet haemocyanin (KLH), and faecal egg counts were determined in calves infected with a single dose of O. ostertagi and in uninfected, pair-fed calves. The infected and uninfected calves were given diets either high (H) or low (L) in protein and energy. The diets were within the normal range of husbandry practice in the UK. IgG1 antibody responses to L3 antigen were significantly greater from 6 weeks post-infection in infected calves given the L diet than in infected calves given the H diet (P less than 0.05). The effects of diet and infection on anti-KLH IgG1 responses were independent of each other. IgG1 responses to KLH were decreased by infection and by the L diet compared with the H diet.  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