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   373篇
  免费   24篇
  国内免费   1篇
林业   25篇
农学   3篇
基础科学   5篇
  61篇
综合类   63篇
农作物   9篇
水产渔业   20篇
畜牧兽医   196篇
园艺   3篇
植物保护   13篇
  2023年   3篇
  2021年   5篇
  2020年   7篇
  2019年   4篇
  2018年   6篇
  2017年   7篇
  2016年   9篇
  2015年   4篇
  2014年   5篇
  2013年   8篇
  2012年   25篇
  2011年   24篇
  2010年   5篇
  2009年   10篇
  2008年   11篇
  2007年   13篇
  2006年   16篇
  2005年   13篇
  2004年   8篇
  2003年   18篇
  2002年   11篇
  2001年   14篇
  2000年   10篇
  1999年   15篇
  1998年   3篇
  1997年   3篇
  1995年   3篇
  1993年   3篇
  1992年   9篇
  1991年   6篇
  1990年   12篇
  1989年   5篇
  1987年   3篇
  1986年   5篇
  1985年   6篇
  1984年   9篇
  1983年   3篇
  1982年   4篇
  1979年   3篇
  1977年   8篇
  1974年   5篇
  1972年   6篇
  1970年   3篇
  1967年   2篇
  1966年   3篇
  1957年   2篇
  1941年   2篇
  1938年   2篇
  1912年   2篇
  1904年   2篇
排序方式: 共有398条查询结果,搜索用时 15 毫秒
11.
A retrospective study evaluated cases of feline esophageal dysfunction. Cats identified had contrast esophagrams performed during a six-year period. Of 56 cases undergoing esophagography, 51 had complete records available for review. Forty-four cases were felt to be abnormal and were included in the study. Cases were analyzed for signalment, presenting complaints, and identifiable causes of abnormal esophageal motility. Response to treatment and case outcome were also reviewed. The signalment of the cases varied widely, especially in age. The occurrence of esophageal motility dysfunction was low, comprising only 0.05% of all feline cases seen in a six-year period. Forty-three percent of cases were considered idiopathic, and 57% were congenital or diagnosed with conditions known to cause esophageal motility dysfunction. The causative disease states included myasthenia gravis, mediastinal masses, vascular ring anomalies, dysautonomia, and esophageal stricture. Seventy-eight percent of those treated with medical therapy (i.e., combinations of sucralfate, H2 receptor antagonists, and either metoclopramide or cisapride) showed clinical improvement.  相似文献   
12.
Sequence comparisons and phylogenetic analysis of the 16S rRNA genes and the 16S/23S spacer regions of the phytoplasmas associated with Australian grapevine yellows, papaya dieback and Phormium yellow leaf diseases revealed minimal nucleotide differences between them resulting in the formation of a monophyletic group. Therefore, along with Australian grapevine yellows, the phytoplasmas associated with Phormium yellow leaf and papaya dieback should also be considered as Candidatus Phytoplasma australiense.  相似文献   
13.
Stimulatory effects of selenium on mitogen responses in lambs   总被引:2,自引:0,他引:2  
Separated lymphocytes from untreated and selenium-supplemented lambs were tested in culture against phytolectins (phytohaemagglutinin and pokeweed mitogen). Levels of response varied considerably among individuals, and this tended to mask the effects of selenium. However, cells from both groups were more active in the presence of serum from supplemented animals, and a similar stimulatory effect was achieved by adding sodium selenite in vitro. Thus selenium could exert a direct influence on the performance of immunocompetent cells.  相似文献   
14.
15.
Ohne Zusammenfassung  相似文献   
16.
A computer model characterizing the performance of a u-tube oxygen absorption system was developed based on finite difference-mass transfer calculations. Performance was assessed in terms of oxygen utilization, transfer efficiency and economy. The system evaluated was unique in that oxygen not absorbed initially (off-gas) was captured and recycled. Mass transfer coefficients derived from pilot-scale test data were used to calibrate the computer model. A separate series of tests served to verify the effects of off-gas recycling as predicted by the program. Simulation data indicate off-gas recycling can result in substantial savings in variable and total costs of oxygen transfer with only a minor increase in capital expenditures, both initially and when amortized. The benefits achieved will increase with lower oxygen flow rates, deeper shaft depths, and low influent dissolved oxygen concentrations. Performance algorithms developed should be useful to those establishing design conditions for pure oxygen u-tube systems.  相似文献   
17.
ABSTRACT

Shrimp farmers in Alabama who produce the Pacific white shrimp, Litopenaeus vannamei, have recently reported abnormally low survival at harvest. Farmers have hypothesized that this phenomenon may be due to disease, toxic algae, shrimp source, or reduced shrimp robustness in later stages of production. To compare performance of shrimp from different sources, postlarvae were obtained from three different hatcheries and stocked on the same day in on-levee tank systems (TS) on two farms (Farm 1-TS; Farm 2-TS1; Farm 2-TS2). Following 104 days of culture on Farm 2-TS1 and Farm 2-TS2, there were no differences in survival (72.8%–91.2%) or final weight (19.8–24.6 g). At Farm 1-TS following 107 days of culture, there were differences in survival from shrimp sourced from one hatchery (40.5%) compared to the other two hatcheries (61.0%–69.8%). Results demonstrated acceptable growth performance and survival from all hatchery sources.  相似文献   
18.
Fish-derived antimicrobial peptides are an important part of the innate immune system due to their potent antimicrobial properties. Piscidins are a class of antimicrobial peptides first described in hybrid striped bass (Morone chrysops x Morone saxatilis) but have also been identified in many other fish species. Previous work demonstrated the broad antimicrobial activity of piscidins against Gram-negative and Gram-positive bacterial species. This study sought to determine the extent to which class I (striped bass piscidin 1, white bass piscidin 1 and striped bass/white bass piscidin 3) and class II (striped bass piscidin 4 and white bass piscidin 5) piscidins inhibit biofilm formation of different Gram-negative bacteria. In general, the class I and II piscidins demonstrate potent activity against Escherichia coli and Flavobacterium columnare biofilms. The class II piscidins showed more activity against E. coli and F. columnare isolates than did the class I piscidins. The piscidins in general were much less effective against inhibiting Aeromonas hydrophila and A. veronii biofilm growth. Only the class I piscidins showed significant growth inhibition among the Aeromonas spp. examined.  相似文献   
19.
  1. Bottlenose dolphins encountered around the Irish coast are considered part of a wide‐ranging coastal community; however, knowledge on the significance of the north of Ireland for this species is limited by a lack of dedicated effort.
  2. Through social media, the opportunity now exists to gather large volumes of citizen science data in the form of high‐quality images, potentially extending the spatial and temporal scope of photo‐identification studies.
  3. The purpose of this study was to investigate social media as a data resource for photo‐identification studies and to provide a preliminary assessment of bottlenose dolphins in the north of Ireland. Specifically, the study sought to examine the photo‐identification data for spatial clustering.
  4. The study identified 54 well‐marked individuals and provided evidence of potential year‐round occurrence, with successful re‐sightings throughout the study period (2007–2016). There was a geographic concentration of re‐sightings along the north of Ireland, suggestive of interannual site fidelity. These results provide scientific rationale for strategically targeting the north of Ireland in future research on the Irish coastal community.
  5. For effective conservation of the bottlenose dolphin it is imperative that scientific research, and resultant management objectives, consider wide‐ranging communities such as the Irish coastal community. Our research highlights data collection via social media as a cost‐effective and scientifically valuable tool in the photo‐identification of coastal cetaceans. We recommend that this method is used in research on low‐density and wide‐ranging coastal cetaceans.
  相似文献   
20.
Dinitrogen fixation and legume productivity are greatly influenced through the interactions of legume host, Rhizobium, and the above- and below-ground environment. The benefits of improving legume N2 fixation include reduced reliance on soil N, leading to more sustainable agricultural systems and reduced requirements for fertilizer N, enhanced residual benefits to subsequent crops, and increased legume crop yields. Most of the gains in N2 fixation to date have been derived from management of legume cropping systems and through inoculation of legume seed with competitive and symbiotically effective rhizobia. Further gains are possible by developing plant cultivars with tolerance to soil abiotic factors, increased plant yield, and a broader and more effective matching of plant host and rhizobia. Techniques for screening material for superior N2 fixation and examples of programs to increase fixed N, with attention to the major abiotic stresses, are discussed.  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