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   5628篇
  免费   340篇
林业   1028篇
农学   165篇
基础科学   10篇
  1205篇
综合类   538篇
农作物   145篇
水产渔业   187篇
畜牧兽医   2177篇
园艺   119篇
植物保护   394篇
  2023年   35篇
  2022年   37篇
  2021年   81篇
  2020年   79篇
  2019年   44篇
  2018年   191篇
  2017年   174篇
  2016年   155篇
  2015年   137篇
  2014年   152篇
  2013年   367篇
  2012年   321篇
  2011年   348篇
  2010年   163篇
  2009年   147篇
  2008年   285篇
  2007年   312篇
  2006年   306篇
  2005年   259篇
  2004年   255篇
  2003年   274篇
  2002年   218篇
  2001年   183篇
  2000年   175篇
  1999年   105篇
  1998年   35篇
  1997年   35篇
  1996年   45篇
  1995年   74篇
  1994年   43篇
  1993年   22篇
  1992年   28篇
  1991年   24篇
  1990年   27篇
  1989年   17篇
  1988年   26篇
  1987年   16篇
  1986年   31篇
  1985年   28篇
  1984年   26篇
  1983年   19篇
  1982年   14篇
  1980年   27篇
  1978年   14篇
  1977年   22篇
  1966年   16篇
  1961年   13篇
  1955年   14篇
  1941年   14篇
  1857年   13篇
排序方式: 共有5968条查询结果,搜索用时 15 毫秒
1.
High occurrence of Fusarium poae (FP) and Fusarium langsethiae (FL) and their mycotoxins nivalenol (NIV) and T-2/HT-2 have been observed in Swiss oats. Early prediction of mycotoxin levels is important for farmers and the cereal industry to minimize the risk of contaminated food and feed. Therefore, climate chamber experiments were conducted to investigate the influence of different temperatures (10, 15, 20 °C) and durations (4, 8, 12 h) at 99% relative humidity (RH) on the infection of oats with FP and FL. In addition, to discover the most susceptible period of oats, artificial FL inoculations were conducted at different growth stages. Field experiments were performed to observe the dispersal of these fungal species within the field and to investigate the weather conditions that influence the dispersal. The climate chamber experiments revealed higher contamination with NIV and T-2/HT-2 in the 10 °C treatments and with a prolonged humidity duration of 12 h 99% RH. Inoculations of oat plants at early (DC 61) and mid (DC 65) anthesis, led to higher FL infection and T-2/HT-2 accumulation in the grains compared with treatments at earlier growth stages, which might be due to an increased susceptibility during anthesis. No indication for spore dispersal was observed in the field experiments. The results obtained, together with the cropping factors that influence infection and mycotoxin production, could be used as a first step in developing forecasting models to predict the contamination of oats with the mycotoxins NIV and T-2/HT-2.  相似文献   
2.
Vegetation indices are widely used as model inputs and for non‐destructive estimation of biomass and photosynthesis, but there have been few validation studies of the underlying relationships. To test their applicability on temperate fens and the impact of management intensity, we investigated the relationships between normalized difference vegetation index (NDVI), leaf area index (LAI), brown and green above‐ground biomass and photosynthesis potential (PP). Only the linear relationship between NDVI and PP was management independent (R2 = 0·53). LAI to PP was described by a site‐specific and negative logarithmic function (R2 = 0·07–0·68). The hyperbolic relationship of LAI versus NDVI showed a high residual standard error (s.e.) of 1·71–1·84 and differed between extensive and intensive meadows. Biomass and LAI correlated poorly (R2 = 0·30), with high species‐specific variability. Intensive meadows had a higher ratio of LAI to biomass than extensive grasslands. The fraction of green to total biomass versus NDVI showed considerable noise (s.e. = 0·13). These relationships were relatively weak compared with results from other ecosystems. A likely explanation could be the high amount of standing litter, which was unevenly distributed within the vegetation canopy depending on the season and on the timing of cutting events. Our results show there is high uncertainty in the application of the relationships on temperate fen meadows. For reliable estimations, management intensity needs to be taken into account and several direct measurements throughout the year are required for site‐specific correction of the relationships, especially under extensive management. Using NDVI instead of LAI could reduce uncertainty in photosynthesis models.  相似文献   
3.
Thymoma is a rare condition in horses. This case of a 24-year-old Warmblood gelding that was presented with oedema and signs of vascular congestion of the left forelimb caused by a thoracic mass is described. The diagnostic work-up included blood chemistry, cytology of pleural effusion, ultrasonography, radiography and the visualisation and collection of a tissue sample by thoracoscopy. Finally, post-mortem findings and histopathology revealed thymic epithelial neoplasia with histomorphologic features previously unreported in horses. The unique mixture of spindle-shaped and epithelioid tumour cells in combination with clear features of malignancy suggested the application of the Moran and Suster histological classification system for thymomas in humans (Moran and Suster, 2008, Curr. Treat. Options Oncol., 9, 288), which has not been reported in an equine case before and fits well to the present case.  相似文献   
4.
Landscape Ecology - Several case studies investigated the role of ecosystem services in participatory planning processes. However, no systematic study exists that cuts across a large number of...  相似文献   
5.
6.
7.
Ohne Zusammenfassung Bergleiche Auguftheft diefer Bl?tter, in melchem gleichfalls auf die Wichtigfeit diefes Qegenftandes hingemiefen murde. Die Red.  相似文献   
8.
The article considers the attractions and dangers of homeopathic therapy from the view of a pharmacologist. Homeopathic drugs may exert pharmacodynamic (but also toxic) effects at low dilutions (D0-D6), but there is no scientific proof for specific effects of higher dilutions except for substances with a high toxic potential. Most homeopathic drugs have no reasonable basis for clinical use but, in case of toxic compounds, especially those with carcinogenic or allergic potential, homeopathy may bear risks for the animal and, because of residues in food animals, also for humans. Thus, homeopathic treatment should not be used when effective conventional treatments are available, and the use of homeopathic drugs with toxic potential should be avoided.  相似文献   
9.
10.
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