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   1181篇
  免费   83篇
林业   43篇
农学   32篇
基础科学   9篇
  149篇
综合类   130篇
农作物   30篇
水产渔业   92篇
畜牧兽医   716篇
园艺   17篇
植物保护   46篇
  2023年   16篇
  2022年   14篇
  2021年   36篇
  2020年   29篇
  2019年   33篇
  2018年   32篇
  2017年   25篇
  2016年   35篇
  2015年   29篇
  2014年   29篇
  2013年   61篇
  2012年   43篇
  2011年   65篇
  2010年   35篇
  2009年   38篇
  2008年   51篇
  2007年   56篇
  2006年   53篇
  2005年   55篇
  2004年   52篇
  2003年   44篇
  2002年   38篇
  2001年   22篇
  2000年   26篇
  1999年   13篇
  1998年   15篇
  1997年   12篇
  1996年   11篇
  1995年   9篇
  1993年   10篇
  1992年   12篇
  1991年   13篇
  1990年   17篇
  1989年   10篇
  1988年   16篇
  1987年   17篇
  1986年   15篇
  1985年   15篇
  1984年   9篇
  1983年   11篇
  1980年   8篇
  1979年   12篇
  1978年   16篇
  1977年   9篇
  1976年   8篇
  1975年   8篇
  1973年   14篇
  1970年   9篇
  1967年   6篇
  1966年   7篇
排序方式: 共有1264条查询结果,搜索用时 15 毫秒
171.
CASE HISTORY: From 26 days of age, an Antipodes Island parakeet (Cyanoramphus unicolor) was noted to have a severe beak deformity and reduced bodyweight gain compared to its nest mate. The bird was euthanised at 43 days of age.

CLINICAL AND PATHOLOGICAL FINDINGS: The beak abnormality consisted of distortion of the right nares and severe shortening resulting in deviation of the upper maxilla to the right and cranially. On sectioning the head, copious mucoid material was found in the infraorbital sinus and the bony sinus architecture was disrupted. Histopathological examination of the infraorbital sinuses revealed a large focus of chronic but active inflammation, bony lysis on the right side and pockets of a mixed population of bacteria.

DIAGNOSIS: Severe beak deformity, likely secondary to bacterial sinusitis.

CLINICAL RELEVANCE: The case illustrates the need to look for underlying aetiologies to beak malformation, particularly in young parrots.  相似文献   
172.
AIMS: To assess the sensitivity and specificity of a bulk tank milk (BTM) antibody enzyme-linked immunosorbent assay (ELISA) to detect likely infection of a dairy herd with bovine vi- ral diarrhoea virus (BVDV). The ELISA was subsequently used to estimate the prevalence of likely infected herds in parts of the North Island of New Zealand.

METHODS: BTM samples from 724 randomly selected dairy herds in the Waikato, Bay of Plenty and Northland regions of New Zealand were tested for BVDV antibodies. From this group, 20 herds were again randomly selected from each of the quartiles of the ELISA percentage inhibition (%INH) result. From each participant herd, serum from 15 randomly selected calves aged 6–18 months and 15 cows was collected and tested using an indirect blocking ELISA for BVDV antibodies.

RESULTS: Among serum results from calves from 50 herds available for analysis, 34 (68%) herds were classified as likely non-infected (0-3 seropositive among 15 calves) and 16 (32%) as likely infected (5–15 seropositive among 15 calves). Receiver- operator characteristic (ROC) analysis identified an optimal cut-off for BTM of 80%INH associated with 81% sensitivity and 91% specificity for likely herd infection. The prevalence of BVDV antibodies in cows within herds and %INH for BVDV in bulk milk were positively correlated (p<0.01). The association between bulk milk %INH and the prevalence of BVDV antibodies in calves was stronger than the same association in cows. Based on the threshold of 80%INH, the 95% confidence interval (CI) for prevalence of likely infection in the 724 herds in the Waikato, Bay of Plenty and Northland regions of New Zealand was 12–17%. Vaccination against BVDV was not significantly associated with the likely infection status of the herd based on prevalence of BVDV antibodies among calves.

CONCLUSION: An ELISA test result for BVDV antibodies in BTM ≥80%INH can be used as a threshold to indicate the presence of likely infection with BVDV in dairy herds in New Zealand, with 81% sensitivity and 91% specificity.  相似文献   
173.
Micronised mebendazole has been shown to have anthelmintic activity against Fasciola hepatica in rats and sheep. Activity is higher against non-egg-producing F. hepatica in bile ducts than against the migrating larval stages. Parbendazole, cambendazole and thiabendazole have been shown to be much less active, or devoid of activity, against mature and immature F. hepatica in rats, at elevated dose rates.

Reasons for the differences, in terms of molecular structure, are briefly discussed and the pitfalls of structure/activity analyses are considered.  相似文献   
174.
175.
Bud rot (BR) disease caused by Phytophthora palmivora is the most devastating disease in oil palm cultivation in America. Oil palms that survived BR epidemics were found in areas highly devastated by the disease; these palms were introduced into Cenipalma's in vitro micropropagation (cloning programme). A severity scale was developed for in vitro palms from five ortets inoculated with two different P. palmivora isolates. Then, eight ortets of Elaeis guineensis and two ortets of the OxG interspecific hybrid were evaluated in two inoculation trials under chamber growth conditions. The clone performance response was consistent with that reported in the field for the corresponding ortets, and two contrasting ortets, one susceptible (ortet 57) and one resistant (ortet 34) were identified. We monitored and compared defence responses to P. palmivora in the contrasting ortets. An increase in reactive oxygen species (ROS) production after inoculation with the pathogen was observed, with higher accumulation of H2O2 in the resistant plants. Catalase (CAT) activity in resistant plants increased after inoculation with the pathogen from 24 hr post‐infection (hpi) and remained high during the observation time. In the susceptible ortets, there was a significant increase on catalase activity only at 48 hpi. Peroxidase (POS) activity increased in clones from both susceptible and resistant ortets, but the increase was much greater in the susceptible ones. Phenylalanine ammonia lyase activity increased in response to inoculation, and these increases were greater in clones of the susceptible ortet than in clones of the resistant ortet.  相似文献   
176.
177.
Developing more stress‐tolerant crops will require greater knowledge of the physiological basis of stress tolerance. Here, we explore how biomass declines in response to salinity relate to leaf traits across 20 genotypes of cultivated sunflower (Helianthus annuus). Plant growth, leaf physiological traits and leaf elemental composition were assessed after 21 days of salinity treatments (0, 50, 100, 150 or 200 mM NaCl) in a greenhouse study. There was a trade‐off in performance such that vigorous genotypes, those with higher biomass at 0 mM NaCl, had both a larger absolute decrease and proportional decrease in biomass due to increased salinity. More vigorous genotypes at control were less tolerant to salinity. Contrary to expectation, genotypes with a low increase in leaf Na and decrease in K:Na were not better at maintaining biomass with increasing salinity. Rather, genotypes with a greater reduction in leaf S and K content were better at maintaining biomass at increased salinity. While we found an overall trade‐off between sunflower vigour and salt tolerance, some genotypes were more tolerant than expected. Further analysis of the traits and mechanisms underlying this trade‐off may allow us to breed these into high‐vigour genotypes in order to increase their salt tolerance.  相似文献   
178.
Laboratory-raised cotton rats (Sigmodon hispidus), outbred white mice (Mus musculus), and C57BL/6J-Lystbg-J/J mice (M. musculus) that were administered approximately 50 sporulated oocysts of Hepatozoon americanum (AF176836) by gavage developed inflammatory lesions containing parasitic cystozoites in cardiac and skeletal muscle, kidney, and lung. Sprague-Dawley rats (Rattus norvegicus) similarly exposed showed no evidence of infection. Cystozoites were first detected by histopathologic examination four weeks after exposure to oocysts. Globular, PAS-positive material accumulated around the cystozoites as the duration of infection lengthened. Nested PCR analysis of tissues collected 16 weeks post-exposure was positive for the 18S rRNA Hepatozoon sp. gene and the DNA sequence of the fragment amplified was 99.6% and 99.8% identical to H. americanum sequences previously reported from naturally-infected dogs (AF176836 and AY864676, respectively). Merogonous and gamontogonous stages of the parasite were not detected in any of the cystozoite-infected rodents.  相似文献   
179.
OBJECTIVE: To characterize heritability and mode of inheritance of cataracts and primary lens luxation in Jack Russell Terriers. ANIMALS: 872 Jack Russell Terriers from which buccal epithelial cells were collected and phenotypes for cataracts and lens luxation were determined and an additional 1,898 Jack Russell Terriers without phenotypic information used to complete pedigree relationships and that were included in the analyses. PROCEDURES: Narrow-sense heritabilities and genetic correlation for cataracts and lens luxation were modeled by use of threshold analysis, whereas complex segregation analysis was used to characterize mode of inheritance. For the analyses, dogs < 6 years old, unless confirmed as having cataracts or lens luxation, were classified as an unknown phenotype. The possible involvement of an HSF4 mutation in cataracts was determined by DNA sequencing. RESULTS: Cataracts and primary lens luxation were highly heritable and genetically correlated, and neither was controlled by a single gene. Cataracts were not associated with an HSF4 mutation. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis of the data indicated that concerted selection against both cataracts and primary lens luxation when choosing breeding animals can be used to improve ocular health in Jack Russell Terriers.  相似文献   
180.
Fresh meat retail cases in 104 supermarkets across 5 regions of the United States were audited for the use of packaging types and materials, branding, and cooking/nutritional information. Frequency means were separated for species of beef, ground beef, pork, chicken, turkey, lamb, and veal. Traditional polyvinyl chloride overwrap was used on 47.0% of packages in the fresh meat case nationwide and was the most frequent packaging type for beef, ground beef, pork, lamb, and veal. The use of modified atmosphere packaging was greatest (P < 0.001) in ground beef (33.2%) and turkey (45.1%) products. The 3 most common tray colors in the fresh meat retail case on a national level were white (39.6%), yellow (22.4%), and black (11.5%). Foam trays were used in 72.6% of all packages in the retail meat case. In 2004, 60.2% of all packages were case-ready. Chicken (94.8%) and turkey (95.6%) products utilized case-ready packaging systems more (P < 0.001) than any other species. On a national level, 50.1% of all products carried a national brand, 12.2% carried a store brand, and the remaining 37.7% of products in the fresh meat case in 2004 were not branded. Chicken was most (P < 0.001) likely to carry a natural brand label. Labels with cooking instructions were found most (P < 0.001) on pork (37.3%) and turkey products (48.1%). Chicken (20.4%) and turkey products (20.7%) were most (P < 0.001) likely to have the cooking instructions printed on the packaging material compared with all other species. Labels with nutritional information were most (P < 0.001) likely to be found on turkey products (55.7%) in the fresh meat case compared with any other species. On the national level, 6.1% of all packages reported in the fresh meat case in 2004 were value-added.  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