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   545篇
  免费   30篇
林业   65篇
农学   17篇
基础科学   1篇
  50篇
综合类   63篇
农作物   9篇
水产渔业   15篇
畜牧兽医   304篇
园艺   2篇
植物保护   49篇
  2023年   5篇
  2021年   7篇
  2020年   15篇
  2019年   9篇
  2018年   11篇
  2017年   5篇
  2016年   10篇
  2015年   11篇
  2014年   14篇
  2013年   9篇
  2012年   24篇
  2011年   26篇
  2010年   15篇
  2009年   18篇
  2008年   23篇
  2007年   18篇
  2006年   24篇
  2005年   27篇
  2004年   18篇
  2003年   17篇
  2002年   9篇
  2001年   9篇
  2000年   10篇
  1999年   12篇
  1997年   4篇
  1996年   5篇
  1995年   5篇
  1994年   4篇
  1993年   7篇
  1992年   12篇
  1991年   19篇
  1990年   13篇
  1988年   11篇
  1987年   4篇
  1986年   7篇
  1985年   11篇
  1984年   6篇
  1983年   6篇
  1982年   4篇
  1980年   4篇
  1979年   8篇
  1974年   9篇
  1973年   8篇
  1972年   6篇
  1971年   8篇
  1970年   4篇
  1969年   6篇
  1967年   7篇
  1966年   4篇
  1942年   3篇
排序方式: 共有575条查询结果,搜索用时 15 毫秒
191.
Methylated N-methylol melamine (NMM) is known for its ability to enhance physico-mechanical properties, anti-fungal ability, and hydrophobicity and was therefore used to impregnate two less used and non-durable wood species from Myanmar, Bombax ceiba and Bombax insigne. Solution uptake, weight percent gain and nitrogen content were increased by increasing melamine concentrations with B. ceiba always achieving higher values compared with B. insigne. According to the leaching results, a higher degree of condensation after curing as well as a better crosslinking of NMM could be obtained at higher temperatures. However, both curing temperatures used (90 and 120 °C) resulted in almost the same amount of nitrogen fixed in the cell wall. UV microspectrophotometry confirmed the penetration of the NMM into different morphological regions of wood tissues, which was again supported by the analysis of point measurement spectra of treated and untreated specimens.  相似文献   
192.
Islands are insular environments that are negatively impacted by invasive species. In Hawai‘i, at least 21 non-native bees have been documented to date, joining the diversity of >9,000 non-native and invasive species to the archipelago. The goal of this study is to describe the persistence, genetic diversity, and natural history of the most recently established bee to Hawai‘i, Megachile policaris Say, 1831 (Hymenoptera: Megachilidae). Contemporary surveys identify that M. policaris is present on at least O‘ahu, Maui, and Hawai‘i Island, with the earliest detection of the species in 2017. Furthermore, repeated surveys and observations by community members support the hypothesis that M. policaris has been established on Hawai‘i Island from 2017 to 2020. DNA sequenced fragments of the cytochrome oxidase I locus identify two distinct haplotypes on Hawai‘i Island, suggesting that at least two founders have colonized the island. In their native range, M. policaris is documented to forage on at least 21 different plant families, which are represented in Hawai‘i. Finally, ensemble species distribution models (SDMs) constructed with four bioclimatic variables and occurrence data from the native range of M. policaris predicts high habitat suitability on the leeward side of islands throughout the archipelago and at high elevation habitats. While many of the observations presented in our study fall within the predicted habitat suitability on Hawai‘i, we also detected the M. policaris on the windward side of Hawai‘i Island suggesting that the SDMs we constructed likely do not capture the bioclimatic niche flexibility of the species.  相似文献   
193.
Journal of Plant Diseases and Protection - Using 30 winter wheat varieties, leaf symptoms indicating infection with common bunt (Tilletia tritici) as well as an enzyme-linked immunosorbent assay...  相似文献   
194.
In order to assess the effect of dietary pyridoxine supplementation on the growth performance of Nile tilapia and the haematological response under heat stress, 192 fingerlings (8.41 ± 0.22 g) were randomly distributed into eight tanks and fed practical diets supplemented with increasing levels of pyridoxine (0.0; 5.0; 10.0 and 20.0 mg of pyridoxal HCl kg?1 diet) for 91 days. The fish were then weighed and the diet was quantified to determine the growth performance [weight gain (WG), feed intake, feed conversion ratio, protein efficiency rate, protein retention (PR) and survival percentage]. Haematological analyses (red blood cell count, haematocrit, haemoglobin, total leucocyte and differentiation, mean corpuscular volume, mean corpuscular haemoglobin concentration, albumin, globulin and albumin/globulin ratio) were carried out and then 32 fish were transferred and subjected to heat stress (32 °C) for 3 days, after which the haematological parameters were analysed. The fish fed the unsupplemented diet showed the lowest WG and PR. For the normal growth and health of the Nile tilapia, the Pyridoxine requirement in a practical diet is 10.0 mg of pyridoxine HCl kg?1.  相似文献   
195.
196.
  • ? The secondary succession of wet grasslands to communities of alder carr dominated by Alnus glutinosa was recorded in different parts of Europe during the 20th century. However, knowledge of such development of alder carr remains insufficient.
  • ? The development of alder carr was reconstructed at five sites in the Czech Republic, using historical aerial photographs and methods of dendrochronology. The aims were to investigate the succession from wet grasslands to alder carr at sites previously intensively managed for agriculture and to find out the role of fluctuations in the groundwater table, caused by artificial drainage channels, in the observed stand dynamics and tree growth.
  • ? The spread of forest (i.e., an increase in forest cover) predominated until the 1970s at all sites. This trend was disrupted by a large-scale dieback of forest stands in four of the five sites after the 1970s, followed by an increase in patch heterogeneity, as indicated by landscape metrics. The radial growth increment in Alnus glutinosa has been affected predominately by local environmental factors, probably including the changing degree of waterlogging. Forest dieback was presumably connected with a lesser extent of drainage channels.
  • ? Our results indicate that observed successional pathways at sites of alder carr were probably caused by local changes in the groundwater table.
  •   相似文献   
    197.
    RNA-based disease control has shown great potential for controlling pest and diseases in crop plants. While delivery of inhibitory noncoding double-stranded (ds)RNA by transgenic expression is a promising concept, it requires the generation of transgenic crop plants, which may cause substantial delay for application strategies depending on the transformability and genetic stability of the crop plant species. Focusing on agronomic important barley - Fusarium spec. pathosystems, we have sought for alternative strategies to apply dsRNAs for fungal control. Recently, we have demonstrated that a spray application of a long noncoding dsRNA termed CYP3RNA, which targets the three fungal Cytochrome P450 lanosterol C-14α-demethylase genes FgCYP51A, FgCYP51B, and FgCYP51C, inhibits Fusarium graminearum (Fg) on barley leaves (Koch et al., PLoS Pathogens, 12, e1005901, 2016). Here we show that another Fusarium species, F. culmorum (Fc), also is sensitive to CYP51-derived dsRNAs. Treating Fc with various dsRNAs targeting the genes FcCYP51A, FcCYP51B and FcCYP51C was destructive to the fungus and resulted in growth retardation in in vitro cultures. We discuss important consequences of this finding on future RNA-based disease control strategies. Given the ease of design, high specificity, and applicability to diverse pathogens, the use of target-specific dsRNA as an anti-fungal agent offers unprecedented potential for novel plant protection strategies.  相似文献   
    198.
    199.
    Aural plaques affect at least 22% of horses and can be asymptomatic or cause ear sensitivity. Immunohistochemical and electron microscopy studies have shown a strong association between aural plaques and papilloma virus. The purpose of this study was to investigate the efficacy of imiquimod 5% cream, an immune response modifier with potent antiviral activity, in the treatment of equine aural plaques. Twenty‐one horses were enrolled and 16 completed the study. Imiquimod 5% cream was applied three times a week, every other week. When both ears were affected only the worst affected ear was treated. Adverse effects in all horses included marked local inflammation, exudation and thick crust formation at the site of treatment and the adjacent skin. Removal of the crust before treatment was painful and required sedation in most horses. Complete resolution of lesions was noted in all horses immediately post‐treatment and the long‐term resolution rate was 87.5%. Duration of therapy ranged from 1.5 to 8 months (median: 2.9 mean: 3.5). All horses were followed‐up for 12–22 months after treatment was discontinued and only two horses had a recurrence of lesions. Clinical signs related to the aural plaques prior to treatment were reported in 11 of 16 (68.8%) horses and included resistance to touching the ears and bridling. Complete resolution of these signs was reported by the owners in all of the horses followed‐up for at least 12 months. In conclusion, the topical application of imiquimod 5% cream is an efficacious treatment for aural plaques in horses.  相似文献   
    200.
    To be profitable, producers must reduce diet costs, which can be as high as 80% of the variable costs of an aquaculture expense. As vitamin and mineral premixes represent a significant cost, eliminating addition of these premixes could reduce diet costs if no adverse effects were observed for growth and production parameters. A 105‐day feeding trial was conducted with juvenile Australian red claw crayfish (Cherax quadricarinatus) to evaluate the effects of growth, survival, body composition, processing traits and water quality when red claw were fed a supplemental diet containing 28% crude protein (CP) without vitamin and mineral premixes (and supplemented alfalfa hay) compared with red claw fed a diet (control diet) containing 42% CP, vitamin and mineral premixes, and with supplemented alfalfa hay, and compared with red claw only fed alfalfa hay when grown in ponds. Juvenile red claw (mean weight of 15.7 ± 1.0 g) were randomly stocked into nine 0.02‐ha ponds at a rate of 640 per pond (3.2 per m2), and each treatment was used in three ponds. There were two feedings per day, each consisting of one‐half of the total daily ration. At harvest, individual weight, percentage weight gain, specific growth rate, survival and total yield of red claw fed a control diet was significantly higher (P < 0.05) (83.0 g, 398%, 1.53% day?1, 65.1%,and 1708 kg ha?1 respectively) compared with red claw only fed alfalfa hay (44.9 g, 202%, 1.04% day?1, 30.3% and 431 kg ha?1, respectively), but not different (P > 0.05) from red claw fed the supplemental diet without vitamin and mineral premixes (76.2 g, 367%, 1.47% day?1, 57.2% and 1378 kg ha?1). There were no significant differences (P > 0.05) in feed conversion ratio (FCR) among treatments, which averaged 5.0 (based on prepared diet input). These results indicate that vitamin and mineral supplementation in a diet is not necessary when diet containing 28% CP and alfalfa hay are used in combination for pond grown red claw. These results may help reduce diet costs and possibly increase producers’ profits which might allow for industry expansion.  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