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   1034篇
  免费   101篇
林业   149篇
农学   36篇
基础科学   1篇
  285篇
综合类   11篇
农作物   66篇
水产渔业   98篇
畜牧兽医   395篇
园艺   20篇
植物保护   74篇
  2023年   10篇
  2022年   9篇
  2021年   32篇
  2020年   30篇
  2019年   38篇
  2018年   80篇
  2017年   71篇
  2016年   81篇
  2015年   52篇
  2014年   56篇
  2013年   68篇
  2012年   65篇
  2011年   91篇
  2010年   46篇
  2009年   26篇
  2008年   34篇
  2007年   37篇
  2006年   34篇
  2005年   41篇
  2004年   35篇
  2003年   29篇
  2002年   32篇
  2001年   13篇
  2000年   13篇
  1999年   14篇
  1998年   6篇
  1997年   6篇
  1996年   5篇
  1995年   4篇
  1994年   3篇
  1993年   7篇
  1992年   4篇
  1991年   6篇
  1990年   6篇
  1989年   5篇
  1988年   2篇
  1987年   3篇
  1986年   3篇
  1984年   6篇
  1983年   4篇
  1982年   4篇
  1981年   4篇
  1977年   2篇
  1976年   5篇
  1971年   3篇
  1970年   1篇
  1969年   1篇
  1968年   2篇
  1966年   1篇
  1938年   1篇
排序方式: 共有1135条查询结果,搜索用时 15 毫秒
991.
992.
The effects of feeding autoclaved commercial SSNIFF (SN) diet and diets containing soya bean (S) and casein (C) to growing conventional (CON) and specified pathogen‐free (SPF) rats were determined. Diets S, C and SN, autoclaved at 121 °C during 20 min (T1), at 134 °C during 10 min (T2) and non‐autoclaved (T0), were fed during four weeks, each to 8 CON males and 8 females of mean initial body weight 56 g, kept individually. Diets S, C and SN, autoclaved at T1, were fed during two months, each to 20 SPF males and 20 females of mean initial body weight 58 g, kept in group of 5 animals per cage. In CON rats, autoclaving did not affect feed intake and weight gain, decreased thyroid and stomach weight, increased caecal tissue and digesta weight, and concentrations of isobutyric, isovaleric and valeric acid in caecal digesta. Among biochemical blood parameters, autoclaving decreased only total protein concentration and aspartate aminotransferase activity. Feeding C diet resulted in lower feed intake and weight gain in CON and SPF males. Diet affected organ weights and the greatest differences were found in rats on SN diet for weights of stomach, caecum and female reproductive organs. Diet affected concentration of all short‐chain fatty acids, pH and weight of caecal digesta, the most important being the greatest butyric acid concentration on SN diet and isoacids on C diet. It is concluded that autoclaving of both soya‐containing and soya‐free diets does not affect negatively animal performance and physiology.  相似文献   
993.
The aim of this study was to investigate social behavior in preweaning lambs, especially their preferences in social interactions. A total of 30 lambs (16 Polish Milk Sheep 05 and 14 Polish Whiteheaded Mutton Sheep) were observed for 113 h 30 min during the first 2 months of their lives. Interbreed differences were insignificant both in agonistic and affiliative behavior. Males appeared to be more active both in agonistic and affiliative interactions. They also preferred other males in agonistic interactions. On the other hand, females fought more often with males, than with females. Lambs of both breeds preferred individuals of their own breed as partners in affliative behaviors. Twins preferred most their siblings in affliliative interactions and usually did not attack and fight with them. This study shows that sex and breed can influence social preferences in preweaning lambs.  相似文献   
994.
The aim of the study was to establish the optimal methods for hypothermic storage of equine isolated hepatocytes. Viability of equine isolated hepatocytes after hypothermic storage was dependent on the type of storage medium as well as on the cell density in the storage suspension and the preservation period. Hepatocytes stored at 4 degrees C in Hanks' Balanced Salt Solution (HBSS) and Williams' Medium E (WE) for 24 h showed very low viability, numerous cell membrane blebs, very low attachment rate (11.9 +/- 6.5% and 34.8 +/- 19.1%, respectively) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction rate (6.4 +/- 3.9% and 25.1 +/- 14.8%, respectively). In contrast, hepatocytes stored in University of Wisconsin Solution (UW) after 24 h of storage at a density of 12.5 x 10(6) cells/ml showed high viability (over 70%), typical and intact morphology, high cell attachment rates and MTT reduction. Our findings clearly demonstrate that UW is a good preservation solution for equine isolated hepatocytes. Hepatocytes harvested from slaughterhouse organs can be stored at 4 degrees C in UW at a density of 12.5 x 10(6) cells/ml for at least 24 h without significant decrease in functional integrity.  相似文献   
995.
996.
This paper is devoted to the assessment of the impact of the Upper Silesian Industrial Region on greenhouse gases emissions in Poland. Detailed analysis will cover emissions of methane and carbon dioxide which are characteristic for the mining and power engineering industry prevailing in this region. The industries of Silesia emit 16.2% of CO2, and about 30% of methane emissions in Poland come from coal seams. The leading strategy to counteract this situation, not only in Upper Silesia, should involve the improved efficiency of energy use and decreased use of primary energy carriers.  相似文献   
997.
The aim of the work was to determine the concentration of 234U and 238U and calculate the values of the 234U/238U activity ratio in samples of living organisms, bottom water, surface and interstitial water and also sediments from the various regions of southern Baltic Sea. The knowledge of 234U/238U activity ratio in ecosystem allows getting know about the mechanisms and processes of uranium transport and origin.The activities of the analyzed uranium radionuclides in samples were measured using alpha spectrometry. The results of researches revealed diversified concentrations of uranium in the sediments of the southern Baltic Sea (sea and coastal waters) and increase of uranium with sediment depth, suggesting the diffusion of uranium from sediments to water through interstitial water and diagenesis processes in sediment material. The nuclides of uranium 234U and 238U were radioactive state equilibrium in most of the sediments. The values of the 234U/238U activity ratio oscillate around one. In bottom, surface, interstitial water and living organisms mean values of the 234U/238U activity ratio are between 1.12 and 1.15. Higher uranium concentration was observed in samples of sediments and seawater after flood in 1997 and torrential rainfalls in 2000–2001. River waters are characterized by higher 234U/238U activity ratio. The values of the 234U/238U activity ratio equal 1.27 in sediments and 1.34–1.38 in seawater indicate the influence of fresh waters.  相似文献   
998.
In order to determine the concentrations of atmospheric selenium and divide it into size classes, aerosols were collected on nitro-cellulose filters, using the PIXE impactors, at three coastal stations in Preila (Lithuania), Hoburg (Gotland, Sweden) and Kap Arkona (Rugia Island, Germany). The determination of selenium and other elements in samples was made using the TXRF (total-reflection X-ray fluorescence) analysis. Air mass trajectories and the results of selenium studies indicate that the highest concentrations of selenium occur with air masses advecting from western and southwestern Europe, while the smallest concentrations were observed for air masses from north and northeastern Europe. It was confirmed that submicron particles of sizes smaller than 2 μm dominate the transport of suspended selenium. It was revealed that selenium in the air above the Baltic Sea is mainly of anthropogenic origin and originates in the same sources as the trace metals such as Cu, Pb and Zn.  相似文献   
999.
1000.
This paper describes the effect of the oxygen analog of ronnel (OAR) on the respiration of brain mitochondria from 4- and 16-day-old and 2- and 18-month-old rats. The oxygen analog of ronnel seems to be an uncoupler of oxidative phosphorylation in brain mitochondria derived from rats at all ages investigated. The results reported here suggest that the sensitivity of mitochondria to the uncoupling effect of OAR is an age-dependent phenomenon. Most sensitive were mitochondria isolated from brains of 18-month-old animals, while the most resistant were mitochondria derived from newborn rats (4 days old), as compared with young adult rats (2 months old). The relation between membrane structure and insecticide action is 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