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   6261篇
  免费   3351篇
林业   161篇
农学   424篇
基础科学   1篇
  1268篇
综合类   9篇
农作物   96篇
水产渔业   2484篇
畜牧兽医   3915篇
园艺   6篇
植物保护   1248篇
  2022年   4篇
  2021年   122篇
  2020年   462篇
  2019年   1014篇
  2018年   891篇
  2017年   932篇
  2016年   919篇
  2015年   807篇
  2014年   789篇
  2013年   951篇
  2012年   441篇
  2011年   456篇
  2010年   584篇
  2009年   241篇
  2008年   218篇
  2007年   60篇
  2006年   92篇
  2005年   85篇
  2004年   89篇
  2003年   82篇
  2002年   98篇
  2001年   67篇
  2000年   98篇
  1999年   7篇
  1997年   14篇
  1996年   5篇
  1995年   5篇
  1994年   5篇
  1993年   7篇
  1991年   3篇
  1990年   4篇
  1989年   2篇
  1986年   2篇
  1983年   2篇
  1982年   3篇
  1980年   2篇
  1978年   6篇
  1977年   5篇
  1975年   3篇
  1974年   2篇
  1972年   2篇
  1970年   5篇
  1969年   3篇
  1966年   2篇
  1962年   2篇
  1958年   1篇
  1956年   1篇
  1955年   1篇
  1936年   1篇
  1924年   1篇
排序方式: 共有9612条查询结果,搜索用时 15 毫秒
71.
The insecticidal activities of materials derived from the fruit of fennel, Foeniculum vulgare, against adults of Sitophilus oryzae, Callosobruchus chinensis and Lasioderma serricorne were examined using direct contact application and fumigation methods. The biologically active constituents of the Foeniculum fruits were characterized as the phenylpropenes (E)‐anethole and estragole, and the monoterpene (+)‐fenchone, by spectroscopic analysis. Responses varied with insect species, compound, dose and exposure time. In a filter paper diffusion test, estragole at 0.168 mg cm?2 caused 91% mortality to S oryzae adults within 1 day after treatment (DAT), whereas (+)‐fenchone and (E)‐anethole gave over 90% mortality at 2 and 4 DAT, respectively. Against C chinensis adults, all test compounds revealed potent insecticidal activities at 0.021 mg cm?2 at 2 DAT. Against L serricorne adults at 0.105 mg cm?2, (E)‐anethole gave 100% mortality at 1 DAT, whereas 90 and 60% mortality at 4 DAT was achieved with estragole and (+)‐fenchone, respectively. In a fumigation test, the test compounds were much more effective against adults of S oryzae, C chinensis and L serricorne in closed cups than in open ones, indicating that the insecticidal activity of test compounds was largely attributable to fumigant action. As naturally occurring insect‐control agents, the F vulgare fruit‐derived materials described could be useful for managing field populations of S oryzae, C chinensis and L serricorne. © 2001 Society of Chemical Industry  相似文献   
72.
73.
74.
Mammary gland problems occur incidentally in horses and one of the rarer conditions is botryomycosis (bacterial pseudomycosis, bacterial granuloma, staphylococcal pseudomycetoma). This article includes a short review of equine mammary gland problems inappropriate lactation, mastitis and neoplasia and botryomycosis, and additionally 2 clinical cases of botryomycosis of the udder resulting from Staphyloccocus aureus infection will be discussed. Both cases involved nonpregnant, nonlactating mares referred for chronic mammary inflammation with draining abcessation. In both mares, botryomycosis caused by S. aureus was confirmed by histopathology and a bacterial culture. Both mares recovered fully after surgical hemimastectomy under general anaesthesia.  相似文献   
75.
76.
Triploidization is an interesting tool to produce sterile fish. In the yellowtail tetra, Astyanax altiparanae, this can be applied for aquaculture and surrogate technologies. In this study, we compared the efficacy of cold (2 C) or heat shock (38 C, 40 C, and 42 C) on triploid induction in the yellowtail tetra. The eggs were treated with cold or heat shock, 2 min postfertilization (30 min in cold shock or 2 min in heat shock). Intact embryos served as the control group. Ploidy status was confirmed by karyotyping, flow cytometry, and nuclear diameter of erythrocytes. The hatching rate decreased after cold shock (12.69 ± 15.76%) and heat shock at 42 C (0.35 ± 0.69%) in comparison with the control group (63.19 ± 16.82%). At 38 C and 40 C, hatching rates (61.29 ± 17.73% and 61.75 ± 22.1%, respectively) were not decreased. Only one triploid arose at 38 C (1/80). At 40 C, a high number of triploids arose (72/78). At 42 C, very few embryos developed into the hatching stage. A large number of haploid individuals arose after cold shock (61/75), with only one triploid. Our results indicate that heat shocking of embryos at 40 C is optimum for triploid production in the yellowtail tetra.  相似文献   
77.
A growth trial was conducted to evaluate the effect of a mixture of soybean meal and Chlorella meal (SCM) as a dietary fishmeal (FM) substitute on growth performance, apparent digestibility coefficients (ADCs), digestive enzymatic activities, and histology of juvenile crucian carp, Carassius auratus. Five isonitrogenous and isoenergetic diets were formulated to replace 0 (SCM0), 25 (SCM25), 50 (SCM50), 75 (SCM75), and 100% (SCM100) of protein from FM with SCM, respectively. The diets were fed to triplicate groups of juvenile crucian carp for 6 wk. Weight gain, specific growth rate, feed intake, protein efficiency ratio, and intestinal digestive enzymatic activities (amylase, trypsin, and lipase) tended to decline with increasing FM replacement levels (P > 0.05). Dietary SCM substitution significantly influenced dry matter content in muscle, and crude protein and lipid contents in liver (P < 0.05). ADCs for dry matter, protein, lipid, energy, and most amino acids showed no significant differences between the control and SCM25 group, but tended to decline with replacement levels over 25%. Higher SCM substitution (50–100%) caused karyopyknosis and necrosis in liver, but intestinal histology did not show noticeable pathological changes. The present study indicated that FM could be replaced by 25% of SCM, without significant adverse growth performance, feed utilization, and histology of crucian carp.  相似文献   
78.
Since its recent introduction into the Mediterranean area, Tuta absoluta (Meyrick) has become widespread and an important pest throughout the region, including in Tuscany, where it was first recorded in 2009. Although several studies have been conducted within controlled environments on the ecology and management of T. absoluta, limited information is currently available on the importance of this pest in open‐field cultivations, which may lead to ineffective management strategies. This study was carried out to monitor fluctuations in adult populations of T. absoluta in organic and conventional cultivations of processing tomatoes using pheromone lures, and to collect inter‐annual data on direct yield loss and fruit damage from larval feeding in two separate trials in Grosseto (Tuscany). The first trial included eight conventionally managed fields; the second trial was carried out in four organically managed fields. Results show relatively higher crop damage for tomatoes transplanted later in the season and harvested towards the end of August to early September, and limited fruit damage from this pest during the second year of the study for both conventional and organically managed fields. Finally, biological and chemical pest management strategies for the control of T. absoluta adopted by farmers within the region are reviewed and discussed.  相似文献   
79.
The incidence of sooty blotch/flyspeck (SBFS) and bitter and bull’s eye rots were assessed in a Fuji apple orchard during two seasons. Using a regular sampling design, 252 trees were selected and 20 fruits per tree were sampled at harvest and scored for disease incidence. For bitter and bull’s eye rots, additional assessments were made on all symptomless fruit after a 30‐day period of storage. Randomness in the spatial pattern was assessed using beta‐binomial analysis of incidence data for three sampling scales (one, three or six adjacent trees as sampling units) and using Spatial Analysis by Distance Indices (sadie ) for disease counts for the 3‐tree sampling scale. sadie was also used for testing spatial associations between a pair of diseases, between years for the same disease or between rotted and latently infected fruit. Using a toroidal‐shifts procedure, 360 maps of disease counts were created based on the observed data, which were further analysed using sadie . Most datasets showed an aggregated spatial pattern, which was more consistent for the two fruit rots than SBFS, which showed distinct patterns depending on the year or method of analysis. The two fruit rots were spatially associated in most situations but SBFS and bull’s eye rot were dissociated in one season. Results from virtual orchards showed that the patterns observed in the original maps may accurately represent those in similar apple‐growing areas. Hypotheses regarding aspects of ecology and epidemiology of pathogens studied and potential efficacy of control measures in the region are discussed.  相似文献   
80.
Bacterial canker, caused by Clavibacter michiganensis subsp. michiganensis (Cmm), can spread in commercial tomato greenhouses causing epidemics. Results of greenhouse experiments with Cmm‐contaminated tools demonstrated disease spread for only a limited distance (<4 plants) from infected plants. However, touching symptomless infected plants bearing guttation droplets prior to touching nearby plants spread the pathogen over longer distances within rows (>22 plants). The pathogen was exuded in large numbers in the guttation fluid of infected plants; its presence in the guttation fluid was not influenced by the inoculation procedures, leaf age or the volume of the guttation droplets. Population size of Cmm and the incidence of leaflets with epiphytic bacteria were significantly higher in plants placed in a guttation‐induction chamber than in those kept in a growth chamber with high humidity, suggesting exudation through guttation contributed to the formation of epiphytic populations on leaflets. This new knowledge may provide a simple and environmentally friendly means for decreasing the spread of the disease by avoiding contact with plants during periods when they bear guttation droplets.  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