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   140篇
  免费   10篇
林业   4篇
农学   4篇
基础科学   1篇
  29篇
综合类   11篇
农作物   4篇
水产渔业   9篇
畜牧兽医   65篇
园艺   2篇
植物保护   21篇
  2023年   1篇
  2022年   2篇
  2021年   3篇
  2020年   4篇
  2019年   6篇
  2018年   8篇
  2017年   12篇
  2016年   5篇
  2015年   3篇
  2014年   1篇
  2013年   10篇
  2012年   6篇
  2011年   16篇
  2010年   3篇
  2009年   4篇
  2008年   11篇
  2007年   16篇
  2006年   8篇
  2005年   8篇
  2004年   6篇
  2003年   4篇
  2002年   2篇
  2000年   2篇
  1999年   1篇
  1995年   1篇
  1992年   2篇
  1985年   1篇
  1984年   1篇
  1981年   2篇
  1964年   1篇
排序方式: 共有150条查询结果,搜索用时 0 毫秒
21.
The genetic structure of Azospirillum amazonense populations isolated from the rhizosphere soil and washed and surface-sterilised roots of rice, maize and sorghum plants, cropped simultaneously in two different soils (clay loam and sandy loam) was characterised. Genetic diversity was measured by restriction fragment length polymorphism of the amplified 16S–23S rDNA intergenic spacer region (RISA-RFLP) and cluster analysis. Four genetically distinct clusters of isolates were observed with 78% similarity, suggesting that the A. amazonense population was heterogeneous at the strain level regardless of the soil type or host plant. Analysis of molecular variance (AMOVA) demonstrated that the host plant had a highly significant selective effect on the genetic structure of this species, especially on those isolates intimately associated with them, but also to a lesser extent on isolates from the rhizosphere and washed roots. The soil type also had a highly significant selective effect on A. amazonense genetic diversity, especially for those isolates from the rhizosphere soil. The selective effect of the soil type combined with that of the host plant suggests that environmental factors, such as soil texture and composition of exudates provided by C3 or C4 plants, play major roles in the overall genetic structure of A. amazonense populations associated with these cereals.  相似文献   
22.
The reclamation of bauxite‐mined areas can be favored by the application of organic and/or chemical fertilization to restore the vegetation. Otherwise, the impact of fertilizations on soil microbiota or plant–microbe interactions as land reclamation progresses is less understood. To address this issue, we evaluated the impact of organic and chemical fertilization on plants and soil microbial community within the first 36 months of land reclamation in a bauxite‐mined site. The experiment was set up according to a split‐plot design in which the main plots received fertilizations [non‐fertilized control (NF), chemical fertilization (CF; NPK and rock phosphate), organic fertilization (OF; poultry litter), and CF+OF combined], and the subplots received cover crops [no cover crops (NC), grass (B; Brachiaria), legume (S, Stylosanthes), and B+S combined]. Cover crops biomass yield was assessed annually with five field campaigns per year. We used phospholipid fatty acids (PLFAs) to infer the impacts of mining and restoration practices on actinobacteria, Gram‐negative and Gram‐positive bacteria, arbuscular mycorrhizal fungi, and fungi. Accordingly, PLFAs were determined before bauxite mining (pre‐mining), six months after topsoil reconfiguration (post‐mining), and after 14 and 36 months following the application of the fertilizations and cover crops. PLFAs results indicated that in post‐mining, the living microbiota was significantly lower than in pre‐mining. Cover crops biomass yield was highest for B and B+S fertilized with CF+OF at 14 and 36 months. Both parametric and non‐parametric statistics showed a temporal variation in the response of living microbes to the treatments applied. After 14 months, living microbes showed greatest response to OF, while at 36 months their response was strongest in the treatments with highest plant biomass production (B and B+S). These results suggest that in the early stages of land reclamation, living microbial biomass benefit the most from organic fertilizers. As this initial boost decline, living microbes are more likely to thrive in areas undergoing reclamation where they can develop synergistic interactions with plants.  相似文献   
23.
ObjectiveTo compare the effects of propofol and alfaxalone on respiration in cats.Study designRandomized, ‘blinded’, prospective clinical trial.AnimalsTwenty cats undergoing ovariohysterectomy.MethodsAfter premedication with medetomidine 0.01 mg kg−1 intramuscularly and meloxicam 0.3 mg kg−1 subcutaneously, the cats were assigned randomly into two groups: group A (n = 10) were administered alfaxalone 5 mg kg−1 minute−1 followed by 10 mg kg−1 hour−1 intravenously (IV) and group P (n = 10) were administered propofol 6 mg kg−1 minute−1 followed by 12 mg kg−1hour−1 IV for induction and maintenance of anaesthesia, respectively. After endotracheal intubation, the tube was connected to a non-rebreathing system delivering 100% oxygen. The anaesthetic maintenance drug rate was adjusted (± 0.5 mg kg−1 hour−1) every 5 minutes according to a scoring sheet based on physiologic variables and clinical signs. If apnoea > 30 seconds, end-tidal carbon dioxide (Pe′CO2) > 7.3 kPa (55 mmHg) or arterial haemoglobin oxygen saturation (SpO2) < 90% occurred, manual ventilation was provided. Methadone was administered postoperatively. Data were analyzed using independent-samples t-tests, Fisher's exact test, linear mixed-effects models and binomial test.ResultsManual ventilation was required in two and eight of the cats in group A and P, respectively (p = 0.02). Two cats in both groups showed apnoea. Pe′CO2 > 7.3 kPa was recorded in zero versus four and SpO2 < 90% in zero versus six cats in groups A and P respectively. Induction and maintenance dose rates (mean ± SD) were 11.6 ± 0.3 mg kg−1 and 10.7 ± 0.8 mg kg−1 hour−1 for alfaxalone and 11.7 ± 2.7 mg kg−1 and 12.4 ± 0.5 mg kg−1 hour−1 for propofol.Conclusion and clinical relevanceAlfaxalone had less adverse influence on respiration than propofol in cats premedicated with medetomidine. Alfaxalone might be better than propofol for induction and maintenance of anaesthesia when artificial ventilation cannot be provided.  相似文献   
24.
This study examined the effects of treatment with U0126, which inhibits MAPK by inhibiting MAPK kinase, during the first 2 hr of in vitro maturation on bovine developmental competence and on gap junction (GAPJ) communication between the oocyte and cumulus cells. The percentage of oocytes developing to the blastocyst stage in the group treated with 5 μM U0126 (28%) was significantly higher than that in controls (15%, < .05), while that in the group treated with 10 μM U0126 (18%) was not. Breakdown of the GAPJs was delayed in the group treated with 5 μM U0126 when compared to controls, as estimated by immunohistochemical examination of connexin 43, which is a primary constituent of the GAPJs. These results indicate that treatment with 5 μM U0126 during in vitro maturation delays GAPJ breakdown and improves bovine oocyte developmental competence.  相似文献   
25.
Porcine parvovirus (PPV) is a widespread DNA virus that causes reproductive failure in swine. The aim of the present study was to investigate the presence of PPV in sera of nursery piglets (healthy n = 191 and wasting n = 132) and regularly vaccinated sows (with different parity rank [PR] n = 129), collected from different herds. Altogether, 452 animals were sampled in 27 herds owned by five companies. All sera were analyzed for the presence of PPV DNA by nested-PCR. The samples from sows were in addition tested for the presence of antibodies by Hemagglutination Inhibition (HI). PPV DNA was detected in healthy piglets (15.7%), wasting piglets (18.2%) and sows (17.8%). 25 herds had at least one positive sample and four companies had positive animals. The serology revealed that 84.7% of the sows had detectable antibodies and the fourth PR sows had the highest mean PPV antibody titers. Thirteen sows (19.1%) were found to be positive for DNA detection in the presence of high levels of antibody titers (> 512). This finding indicates that PPV DNA can be detected in different swine production categories irrespective of antibody titers.  相似文献   
26.
The objective of this study was to identify the risk factors of stillbirth and foetal mummification in 565 farrowings of four commercial pig farms in Brazil. Stillborn piglets were observed in 31.3% of the litters and the stillborn risk was 5.6%. Mummified foetuses occurred in 42.1% of the litters and the mummification risk was 3.4%. The potential risk factors were included in multivariable logistic regression models as categories: herd (1–4); parity (1, 2–5 and >5); litter size (<10, 10–12 and >12 piglets); farrowing length (≤3 or >3 h); presence of mummified foetuses (yes or no); farrowing induction (yes or no); use of oxytocin (yes or no); use of vaginal palpation (yes or no); body condition score (<3, 3 and ≥4), and placental production index (PPI) (≤5 or >5) which was measured as the ratio of total foetal weight to total placental weight. Duration of farrowing and use of farrowing induction, oxytocin or vaginal palpation were not included in the model that investigated the risk factors of foetal mummification. Two models were used to investigate the risk factors of stillbirth, one with and the other without the inclusion of farrowing length. When compared to sows of parity 2–5, sows of parity >5 had 1.7- and 1.6-times higher odds (P < 0.05) for stillbirth in the models with and without the inclusion of farrowing length, respectively. In both models, sows with more than 12 piglets/litter had 3.6-times higher odds of stillbirth occurrence compared to sows with less than 10 piglets (P < 0.05). Sows with prolonged farrowing (>3 h) had 2.0-times higher odds of stillbirth occurrence than sows with short farrowing (P < 0.05). Sows with more than 12 piglets/litter had 14.5-times higher odds of mummification compared to sows with less than 10 piglets (P < 0.05). Sows of parities 1 and >5 had 3.5- and 2.0-times, respectively, higher odds of mummification in comparison to sows of parity 2–5 (P < 0.05). Sows with low PPI had 1.7-times higher odds of mummification compared to those with high PPI (P < 0.05). A large litter, a high-parity and a prolonged farrowing increased the risk of stillbirth. The probability of having a mummified foetus was increased in very young and older sows, when having a large litter and a litter with a less efficient placenta.  相似文献   
27.
Capture fisheries in the north‐east Atlantic account for approximately 10% of all fish consumed from capture fisheries globally. The literature shows that consumers show considerable interest in social sustainability of products in general and of fish specifically. This interest, however, has not yet been investigated for fish from the north‐east Atlantic. The first objective of this study, therefore, was to investigate whether consumers are interested in social sustainability issues of whitefish from the north‐east Atlantic by determining preferences for four social sustainability issues with distinct benefits in relation to a known reference point (i.e. approach to overfishing). The second objective of this study was to determine to what degree case‐specific and general psychographic consumer characteristics explain preferences for these issues. Choice modelling results from an online survey among 457 Dutch consumers show that consumers have the strongest preference for the environmental sustainability issue approach to overfishing. In addition, results on the social sustainability issues showed that consumers prefer fish welfare over product quality, worker safety and local employment, indicating that in this case, consumers place animal benefits over personal, worker and community benefits. The case‐specific psychographic characteristic concern contributed most to explaining preferences for the environmental sustainability issue, whereas the general psychographic characteristic personal relevance contributed most to explaining preferences for the social sustainability issues. This result is likely explained by the principal focus on MSC certification in markets for fish products, which caused consumers to form opinions (e.g. concern) on overfishing, but not on social sustainability.  相似文献   
28.
The concentrations of selected metals—Cr, Ni, Cu, Zn, Cd, and Pb—were determined in the samples of Hypogymnia physodes lichen and Pleurozium schreberi moss collected in Polish and Czech Euroregions Praded and Glacensis. More specifically, the samples were collected in Bory Stobrawskie, Bory Niemodlińskie, and Kotlina K?odzka (Poland) and in Jeseniki (Czech Republic). The concentration of metals in the samples was measured using the atomic absorption spectrometry (flame AAS technique and electrothermal atomization AAS technique). The results were used to calculate the comparison factor (CF) that quantifies the difference in concentration of a given bioavailable analyte × accumulated in lichens and mosses: CF?=?2 (c x,lichen ? c x,moss) (c x,lichen + c x,moss)?1. The values of CF greater than 0.62 indicate the most probable location of heavy metals deposited in the considered area. In this work, the method was used to show a significant contribution of urban emissions to the deposition of heavy metals in the area of Bory Stobrawskie and in the vicinity of K?odzko City.  相似文献   
29.
30.
We evaluated the humoral and cellular immune responses in pigs immunized intranasally with crude rhoptry proteins of Toxoplasma gondii plus Quil-A. The experiment used 13 mixed-breed pigs divided into the following three groups: G1 (vaccinated-challenged, n=6), which received the rhoptry vaccine (200(g/dose); G2 (adjuvant-challenged, n=4), which received PBS plus Quil-A; and G3 (unvaccinated-challenged, n=3), which was the control group. The treatments were performed intranasally at days 0, 21, and 42. Three pigs from G1 produced IgG and IgM antibody levels above the cut-off in the ELISA on the challenge day. Partial protection was observed in G1 at the chronic phase of infection when compared with G3. The preventable fractions were 41.6% and 6.5%, in G1 and G2, respectively. The results of this study suggest that rhoptry proteins plus Quil-A stimulated humoral, local, and systemic immune responses, which were able to partially protect the brain from cyst formation.  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