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   10146篇
  免费   525篇
  国内免费   14篇
林业   684篇
农学   267篇
基础科学   98篇
  1837篇
综合类   1629篇
农作物   406篇
水产渔业   896篇
畜牧兽医   3737篇
园艺   291篇
植物保护   840篇
  2024年   20篇
  2023年   61篇
  2022年   97篇
  2021年   163篇
  2020年   227篇
  2019年   217篇
  2018年   245篇
  2017年   256篇
  2016年   242篇
  2015年   220篇
  2014年   291篇
  2013年   523篇
  2012年   626篇
  2011年   772篇
  2010年   416篇
  2009年   389篇
  2008年   699篇
  2007年   668篇
  2006年   643篇
  2005年   623篇
  2004年   652篇
  2003年   611篇
  2002年   531篇
  2001年   127篇
  2000年   116篇
  1999年   123篇
  1998年   84篇
  1997年   74篇
  1996年   68篇
  1995年   64篇
  1994年   61篇
  1993年   51篇
  1992年   63篇
  1991年   50篇
  1990年   62篇
  1989年   54篇
  1988年   42篇
  1987年   46篇
  1986年   37篇
  1985年   34篇
  1984年   36篇
  1983年   41篇
  1982年   26篇
  1981年   25篇
  1980年   28篇
  1979年   23篇
  1978年   20篇
  1976年   20篇
  1975年   23篇
  1974年   15篇
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
991.
992.
Traditional methods of teaching intracellular biological processes and pathways use figures or flowcharts with the names of molecules linked with arrows. Many veterinary students, presented with such material, simply memorize the names or chemical structures of the molecules and are then likely to forget the material once the examination is completed. To address this problem, the authors designed, created, and field-tested new teaching media that incorporate realistic three-dimensional (3D) animations depicting the dynamic changes that occur in intracellular molecules during cellular activation. Testing found that veterinary students taught using traditional teaching media (e.g., lectures, handouts, textbooks) are proficient in memorizing the names and order of intracellular molecules but unable to appreciate the interactions between these elements or their spatial relationships within cells. In contrast, more than 90% of veterinary students taught using 3D animations not only recall the facts about the intracellular elements but also develop accurate mental images of the interactions among these molecules and their spatial relationships. These findings strongly suggest that the comprehension of complex biological processes by veterinary students can be enhanced by the use of dynamic 3D depictions of these processes in the classroom.  相似文献   
993.
The process of obtaining a veterinary medical education creates a number of potential cognitive, emotional, physical, interpersonal, and developmental stressors for veterinary students. Although most universities offer stress management interventions for their students, these programs are often directed toward undergraduate students or non-veterinary graduate students, whose educational programs differ significantly from those of veterinary students. There is a need for specific stress management programs tailored to the needs of veterinary students. This article summarizes research drawn from the psychology, medical, and veterinary medical literature about the causes of stress that veterinary students experience. Interventions are discussed, and several Oregon State University (OSU) programs and liaisons are described. Stress management resources are suggested.  相似文献   
994.
995.
The activins and inhibins are members of the transforming growth factor-beta (TGF-beta) superfamily and, along with follistatin, a high affinity binding protein of activin, form a group of interrelated factors originally isolated for their role in regulating the release of follicle-stimulating hormone (FSH). Knowledge of their function, particularly that of activin, has expanded since being originally isolated, such that they are now regarded as important paracrine regulators in many cellular systems. This review summarizes the biology of these proteins as has been established in the large domestic animals. While the majority of data relate to the pituitary, ovary, uterus/placenta and testis, consideration is also given to emerging roles in inflammatory processes and in non-reproductive tissues or systems.  相似文献   
996.
The objective of this study was to describe a standardised and non-invasive method for exhaled breath condensate (EBC) collection in cats and to test whether determination of hydrogen peroxide (H(2)O(2)) in EBC might be used as marker of lower airway inflammation. The technique of barometric whole body plethysmography for cats was combined with a system to condense the effluent air from the plethysmograph, allowing simultaneous EBC collection and respiratory pattern measurement. H(2)O(2) was determined spectrophotometrically. Eighteen experimental cats were used to investigate the impact on EBC volume and EBC H(2)O(2) of plethysmograph ventilation rate, collection duration, sample stability, within-day and day-to-day variability. After determination of a standardised EBC collection procedure, correlation analyses between EBC H(2)O(2) and bronchoalveolar lavage (BAL) cytology of healthy and allergen-challenged Ascaris suum (AS)-sensitised cats were performed. A significant and positive correlation between EBC H(2)O(2) and bronchoalveolar lavage (BAL) neutrophil% was found in healthy cats (P < 0.001, r = 0.55), whereas in AS-sensitised cats, correlation with BAL eosinophil% was significant (P < 0.005, r = 0.61). H(2)O(2) was increased after an allergen challenge in AS-sensitised cats (n = 6, 0.56+/-0.12 versus 1.08+/-0.35 micromol/L, P < 0.05). This study proposes a non-invasive, well tolerated and repeatable method of EBC collection for cats and suggests that EBC H(2)O(2) might be used as non-invasive biomarker for monitoring lower airway inflammation.  相似文献   
997.
Results of this study confirm that dietary supplementation in dogs with a natural source of omega-3 fatty acids (salmon oil), with a docosahexaenoic acid:eicosapentaenoic acid (DHA:EPA) ratio of 1.5:1, increases plasma and red blood cell levels of these fatty acids. Supplementation with this DHA-enriched oil improves the long-chain polyunsaturated fatty acid omega-6:omega-3 (n-6:n-3) ratio, which may benefit dogs of all ages. Studies describing some of the neurologic, renal, cardiovascular, immune, and musculoskeletal effects of elevated blood levels of n-3 fatty acids, especially DHA, are reviewed. The importance of providing an enriched source of DHA, instead of its shorter precursors, is emphasized.  相似文献   
998.
A raised concentration of serum cardiac troponin I (cTnI) is a sensitive marker of cardiac myocyte injury in the cat and assays developed for its measurement in human patients have been validated in the cat. Raised levels have been associated with a number of cardiac insults including hypertrophic cardiomyopathy and trauma. Hyperthyroidism is a common disease of older cats and excess thyroid hormone is known to produce significant cardiovascular effects in this species. This study evaluated the effect of treatment for hyperthyroidism with radioactive iodine on cTnI concentration, assessed the association between thyroxin levels and glomerular filtration rate (GFR) and cTnI concentration in cats treated for hyperthyroidism and described changes in echocardiographic parameters following treatment. Prior to the treatment serum cTnI was measured and echocardiography performed, thyroxin, cTnI, and echocardiography were then repeated at various time points following radioisotope therapy. The results show that higher thyroxin levels were significantly (P=0.002) associated with a higher likelihood of the cat presenting with detectable levels of cTnI. No significant association was found between GFR and presence of detectable levels of cTnI. Furthermore the results indicate that the effects of hyperthyroidism on echocardiographic parameters appear considerably less in this study than in previous studies and that the main outcome of treatment on these parameters is a significant reduction in fractional shortening (P=0.006). These results suggest that chronic exposure to excess thyroid hormone may induce myocyte damage of sufficient severity to raise serum cTnI concentration in a proportion of cats that resolves following establishment of a euthyroid state.  相似文献   
999.
1000.
Two hundred years of landscape changes were studied on a 3,760 ha area of central Corsica (France) representing a typical Mediterranean environment. Different historical sources, including an accurate land-cover map from 1774 and statistics on land cover from 1848 and 1913, were used. Three additional maps (1960, 1975 and 1990) were drawn, and a complete fire history from 1957 to 1997 was created. Forests expanded slowly by a border effect. Forest expansion was more rapid in unburnt sites (0.59% per year) than in burnt sites (0.23% per year), mostly because the initial amount of forests was greater. Because of the border effect, the combination of past landscape pattern and short distance colonization abilities of forest species may have allowed the shrublands to persist in some places after land abandonment. This persistence may explain the pattern of fire in the landscape, since shrubland burn more readily than forests.  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