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   89篇
  免费   12篇
林业   14篇
农学   5篇
  17篇
综合类   6篇
农作物   2篇
畜牧兽医   55篇
植物保护   2篇
  2023年   2篇
  2021年   1篇
  2019年   1篇
  2018年   3篇
  2017年   1篇
  2016年   5篇
  2015年   4篇
  2014年   4篇
  2012年   4篇
  2011年   5篇
  2010年   2篇
  2009年   3篇
  2008年   5篇
  2007年   3篇
  2006年   5篇
  2005年   4篇
  2004年   5篇
  2003年   2篇
  2002年   1篇
  2001年   2篇
  2000年   2篇
  1999年   1篇
  1996年   5篇
  1994年   1篇
  1993年   1篇
  1992年   2篇
  1990年   5篇
  1989年   2篇
  1988年   2篇
  1985年   3篇
  1984年   1篇
  1983年   2篇
  1981年   1篇
  1980年   2篇
  1979年   4篇
  1978年   3篇
  1881年   1篇
  1880年   1篇
排序方式: 共有101条查询结果,搜索用时 15 毫秒
51.
OBJECTIVE: To determine the association between the 3-dimensional (3-D) motion pattern of the caudal lumbar and lumbosacral portions of the canine vertebral column and the morphology of vertebrae, facet joints, and intervertebral disks. SAMPLE POPULATION: Vertebral columns of 9 German Shepherd Dogs and 16 dogs of other breeds with similar body weights and body conditions. PROCEDURE: Different morphometric parameters of the vertebral column were assessed by computed tomography (CT) and magnetic resonance imaging. Anatomic conformation and the 3-D motion pattern were compared, and correlation coefficients were calculated. RESULTS: Total range of motion for flexion and extension was mainly associated with the facet joint angle, the facet joint angle difference between levels of the vertebral column in the transverse plane on CT images, disk height, and lever arm length. CONCLUSIONS AND CLINICAL RELEVANCE: Motion is a complex process that is influenced by the entire 3-D conformation of the lumbar portion of the vertebral column. In vivo dynamic measurements of the 3-D motion pattern of the lumbar and lumbosacral portions of the vertebral column will be necessary to further assess biomechanics that could lead to disk degeneration in dogs.  相似文献   
52.
The purpose of this research note is to provide an empirical indication of how China's increasing role in the South Pacific has been presented in their own and other nations' media over the last 20 years. What is the tone of coverage? Which issues are salient? How does this vary by nation? What changes are there over time? This research note reports information derived from over 1000 articles published in Australasian, Asian and Pacific newspapers in the last 20 years. The findings demonstrate that nations dealing with ‘China's rise’ in the South Pacific are faced with a range of complex issues, which can produce ambivalent and mixed reactions. For instance, although the tone of Australian and New Zealand newspaper coverage of China's entry into their ‘special patch’ is, overall, more negative than positive, negativity is largely driven by coverage of China's diplomatic efforts in the region and geopolitical considerations. Other aspects of China's expanding role (e.g. economic and cultural aspects) are treated much more positively. Similarly, although the major focus of Pacific newspapers is on Chinese aid and economic impact, which are treated very positively, coverage of other issues can be negative.  相似文献   
53.
Respiration is responsible for much of the sucrose loss that occurs during sugarbeet (Beta vulgans L.) storage. Genotypes with reduced storage respiration rates would provide an efficient method for reducing sucrose losses. However, the current techniques for measuring storage respiration are not adapted easily to breeding programs. Internal CO2 concentration has been recommended as an efficient method for measuring the respiration rate of individual sugar-beet roots in storage. This study examined the effectiveness of internal CO2 concentration as a selection criterion for reducing respiration rate of sugarbeet during storage. Lines resulting from four cycles of divergent selection for internal CO2 concentration were evaluated along with commercial hybrids and low internal CO2 germplasm lines. Selection was effective in shifting internal CO2 concentration. Relative differences in internal CO2 concentration were consistent throughout the 3-year study. Neither the fourth-cycle selections for low nor the fourth-cycle selections for high internal CO2 concentration were significantly different from the original population for evolved CO2. This lack of a close relationship between internal and evolved CO2 indicated that internal CO2 concentration is not an effective selection criterion in a breeding program.  相似文献   
54.
Goal, Scope and Background  Situated in the transboundary belt between Montenegro and Albania, Lake Skadar is the largest freshwater reservoir in Southeastern Europe. Because of the wide range of endemic, rare or endangered plant and animal species it supports, Lake Skadar and its extensive adjacent wetlands are internationally recognised as a site of significance and importance (Ramsar site). Within the last 10 to 20 years, Lake Skadar was exposed to intensive pollution. For the assessment of the ecotoxic load of the sediments sampled in Lake Skadar, a triad approach was recently applied. Overall, a complex spectrum of ecotoxic loads was elucidated. The aim of the present study was to use plant-based bioassays for assessing the sediment quality of Lake Skadar in order to facilitate and complement the triad test battery. The newly developed sediment contact test with Myriophyllum aquaticum and the aquatic growth inhibition test with Lemna minor were applied to native sediments and pore water, respectively, allowing the investigation of different toxicity-effects caused by particle-bound pollutants as well as pollutants in the interstitial water. This investigation is the first application of the novel sediment contact test with Myriophyllum aquaticum to lake sediments. Methods  Sediment samples were taken from nine selected sites at Lake Skadar and investigated by the sediment contact assay with Myriophyllum aquaticum. The pore water was extracted from these sediment samples to be analysed in the aquatic growth inhibition test with Lemna minor. The results of the sediment contact tests were compared with each other and with those of the aquatic growth inhibition test. Results and Discussion  Both applied macrophyte biotests revealed distinct changes in the growth behaviour of the two macrophytes subsequent to the exposure to the investigated natural sediments of Lake Skadar. The Myriophyllum sediment contact test revealed significant toxicity in the sediment samples from Radus and Kamenik, whereas the aquatic Lemna test showed inhibition effects for the samples from Sterbeq, Plavnica and Kamice. Data obtained with the newly developed Danio rerio contact test and the Arthrobacter globiformis contact test confirmed the Myriophyllum results. Analyses of the heavy metal content in the sediments revealed low or moderate contamination levels. Correlation analyses between the content of heavy metals in the sediments and growth inhibition of Myriophyllum aquaticum showed a significant correlation between Cr concentrations and growth inhibition. Comparable findings are available for a German river system. In contrast, no significant correlation between inhibition rates and concentration of metals could be observed with Lemna minor. Conclusions  It was shown that the newly developed sediment contact test with Myriophyllum aquaticum is applicable to lake sediments. In both the sediment contact test with Myriophyllum aquaticum on whole sediments and the aquatic growth inhibition test with Lemna minor on pore water, plant growth was influenced by the natural sediments and its components. Therefore, both test systems were found to be suitable for the detection of phytotoxic effects upon exposure to sediments. Myriophyllum aquaticum as test organism of the contact test grows directly in the sediment without an additional water-layer. Thus, it is able to detect toxicity caused by particle-bound phytotoxic substances as well as pore water-related contamination, while the floating Lemna minor can only detect effects emanating from pore water. Significant differences of the results were observed between these two test systems and, accordingly, the two different exposure scenarios. Hence, none of the tests can replace the other one and, as a consequence, both should be included into a test battery for the assessment of sediment toxicity. Recommendations and Perspectives  Both plant assays were shown to be reliable tools for the evaluation of the eco-toxicological risk potentials of pore water and solid-phase sediment. They should become a complement to the standardised test battery generally used for comprehensive hazard assessment. ESS-Submission Editor: Dr. Ulrike Kammann (ulrike.kammann@ifo.bfa-fisch.de)  相似文献   
55.
Insoluble fiber fractions from 11 fruits and vegetables were investigated for their lignin composition using the derivatization followed by reductive cleavage (DFRC) methodology. To enrich lignin contents and to minimize polysaccharide excess that led to nonanalyzable DFRC chromatograms, the insoluble fibers were degraded by a carbohydrolases mixture. The residues that were found to be representative for the insoluble fiber lignins were analyzed. The investigated fibers differ considerably in their lignin contents and also in their lignin compositions. With the exception of radish fiber, only trace amounts (or none) of the products resulting from p-hydroxyphenyl units were detected. Lignins noticeably differed in the ratio of the DFRC products resulting from syringyl units (S) and guaiacyl (G) units (G/S ratios ranged from approximately 39 to 0.2). The insoluble fiber lignins were classified as G-rich lignins (G/S ratio > 3; carrot, spinach, kiwi, curly kale, radish, and asparagus), S-rich lignins (S/G ratio > 3; rhubarb), or balanced lignins (0.3 < G/S ratio < 3; pear, apple, small radish, and kohlrabi). Information about further structural characteristics, for example, cinnamyl endgroups, was obtained from the analysis of DFRC minor products.  相似文献   
56.
57.
Micromachining technology was used to prepare chemical analysis systems on glass chips (1 centimeter by 2 centimeters or larger) that utilize electroosmotic pumping to drive fluid flow and electrophoretic separation to distinguish sample components. Capillaries 1 to 10 centimeters long etched in the glass (cross section, 10 micrometers by 30 micrometers) allow for capillary electrophoresis-based separations of amino acids with up to 75,000 theoretical plates in about 15 seconds, and separations of about 600 plates can be effected within 4 seconds. Sample treatment steps within a manifold of intersecting capillaries were demonstrated for a simple sample dilution process. Manipulation of the applied voltages controlled the directions of fluid flow within the manifold. The principles demonstrated in this study can be used to develop a miniaturized system for sample handling and separation with no moving parts.  相似文献   
58.
Tendon and ligament injuries are common causes of impaired performance in equine athletes. Gray‐scale ultrasonography is the current standard method for diagnosing and monitoring these injuries, however this modality only provides morphologic information. Elastography is an ultrasound technique that allows detection and measurement of tissue strain, and may provide valuable mechanical information about equine tendon and ligament injuries. The purpose of this study was to determine the feasibility, reproducibility, and repeatability of elastography; and to describe elastographic characteristics of metacarpal tendons in sound horses. Nineteen legs for 17 clinically sound horses without evidence of musculoskeletal pathology were included. Elastographic images of the superficial and deep digital flexor tendons and the branches of the suspensory ligament (tendon of the interosseous muscle) were described quantitatively and qualitatively. There was no statistically significant difference between operators (P = 0.86) nor within operators (P = 0.93). For qualitative assessments, reproducibility (0.46) was moderate and repeatability (0.78) was good. Similar to human Achilles tendons, equine tendons were classified as predominantly hard using elastography. There was no statistically significant difference in stiffness of the flexor tendons (P = 0.96). No significant difference in stiffness was found with altered leg position during standing (P = 0.84) and while nonweight bearing (P = 0.61). The flexor tendons were softer when imaged in longitudinal versus transverse planes (P < 0.01) however, the suspensory branches were not (P = 0.67). Findings supported future clinical application of elastography as a noninvasive “stall‐side” imaging modality for evaluation of the tendons and ligaments of the distal forelimb in horses.  相似文献   
59.
The purpose of this study was to evaluate the variability of cystosonographic bladder tumor measurements with both operator and bladder volume changes. Ten dogs with bladder tumors were included. In each dog, three operators determined tumor dimensions for three different bladder volumes. Intraclass correlation coefficient was used to assess operator reliability. Response Evaluation Criteria in Solid Tumors (RECIST) and greater than or equal to 50% differences in tumor measurements were used as guidelines. Poor to fair correlations between operators were found for the different tumor dimensions (rI = 0.4 – 0.7). The percent differences in tumor dimensions with operator and bladder volume changes were significant enough to misclassify the tumors into the categories of partial response (PR) or progressive disease (PD). These results suggest that cystosonographic measurements of bladder tumors are affected by both changes in operator and bladder volume, and the discrepancies are significant enough to change response classification.  相似文献   
60.
Sunflower (Helianthus annuus L.) productions reliance on a single source of cytoplasmic male sterility, PET1, derived from H. petiolaris Nutt., makes the crop genetically vulnerable. Twenty diverse cytoplasmic substitution lines from annual and perennial wild species were compared with the inbred line HA89 over four environments. Pairwise comparisons of alloplasmic male fertile (MF) with euplasmic MF lines suggested that cytoplasm of perennial H. angustifolius increased lodging while perennial cytoplasms of H. mollis, H. grosseserratus, and H. divaricatus reduced head size and consequently reduced yield and will need to be used with caution. Lines having annual species, cytoplasms had no effects on agronomic traits. Comparisons of CMS HA 89 with 10 CMS lines suggested yield‐reducing cytoplasmic effects of perennial H. maximiliani and annual H. annuus PI 413178 and PI 413024. Cytoplasmic effects on oil percentage and fatty acid composition were minimal and should not be of concern for sunflower breeders. In general, most cytoplasms of wild annual Helianthus species accommodate cultivated nuclear genes without drastic adverse interactions, and are potential sources of cytoplasmic diversity for sunflower breeding.  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