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   87302篇
  免费   5188篇
  国内免费   42篇
林业   2978篇
农学   2711篇
基础科学   526篇
  9924篇
综合类   16188篇
农作物   3655篇
水产渔业   4302篇
畜牧兽医   45552篇
园艺   1082篇
植物保护   5614篇
  2019年   807篇
  2018年   1193篇
  2017年   1376篇
  2016年   1291篇
  2015年   1145篇
  2014年   1361篇
  2013年   3454篇
  2012年   2559篇
  2011年   3040篇
  2010年   1979篇
  2009年   1948篇
  2008年   2934篇
  2007年   2836篇
  2006年   2688篇
  2005年   2535篇
  2004年   2385篇
  2003年   2412篇
  2002年   2277篇
  2001年   2904篇
  2000年   2783篇
  1999年   2268篇
  1998年   975篇
  1997年   893篇
  1996年   790篇
  1995年   957篇
  1994年   863篇
  1993年   857篇
  1992年   1812篇
  1991年   1811篇
  1990年   1752篇
  1989年   1816篇
  1988年   1570篇
  1987年   1680篇
  1986年   1739篇
  1985年   1665篇
  1984年   1312篇
  1983年   1167篇
  1982年   842篇
  1981年   723篇
  1979年   1107篇
  1978年   900篇
  1977年   781篇
  1976年   734篇
  1975年   810篇
  1974年   999篇
  1973年   1041篇
  1972年   994篇
  1971年   946篇
  1970年   887篇
  1969年   811篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
The objective of this study was to assess the effect of dietary copper and/or vitamin E supplementation on composition and oxidation of M. longissimus in Iberian pigs and to compare it with meat samples from pigs produced extensively and fed with acorn and grass. Grass had the highest α-tocopherol content (> 150 mg/kg DM), while acorns had the highest copper concentration (78.1 mg/kg DM). Dietary treatment did not affect copper composition in muscle and no interactions were detected between copper and α-tocopherol. The α-tocopherol content in muscle from pigs fed diets supplemented with α-tocopheryl acetate (100 mg/kg feed) was 1.5 times greater (p < 0.0001) than those from pigs receiving a basel diet. M. longisssimus dorsi from pigs fed extensively had a higher concentration of α-tocopherol than those fed in confinement with the basel level of α-tocopheryl acetate, but lower values than pigs fed supplemented levels. Total n -3 fatty acids (p < 0.02) and hematin (p < 0.0001) concentrations were significantly higher in muscle from pigs fed extensively than when fed in confinement. Muscle homogenates from Iberian pigs fed in extensive conditions showed significantly (p < 0.02) higher susceptibility to oxidation than those from pigs fed mixed diets. Dietary α-tocopheryl acetate supplementation (100 mg/kg feed) significantly (p < 0.05) reduced lipid oxidation of muscle, while dietary copper concentration did not modify susceptibility to lipid oxidation.  相似文献   
132.
The clinical signs and laboratory changes of brodifacoum (BDF) intoxicated dogs and their response to vitamin K1 treatment were examined. Brodifacoum, a second-generation anticoagulant rodenticide, was fed to four dogs for 3 consecutive days producing a cumulative dose of 1.1 mg BDF/kg body weight. Clinical observations of the animals were made daily throughout the study. Monitored laboratory parameters included: one-stage prothrombin time (OSPT), activated partial thromboplastin time (APTT), activated coagulation time (ACT), complete blood counts, thrombocyte counts, and serum chemistry values. Response to vitamin K1 therapy was evaluated clinically and by laboratory tests. Serum BDF concentrations were monitored. Inappetence and hemorrhagic tendencies were exhibited by day 5 postrodenticide exposure. One-stage prothrombin time, APTT, and ACT were 25% greater than time zero values at 24, 24, and 72 hours postdosing, respectively. All laboratory parameters returned to normal within 48 hours of initiating vitamin K1 therapy (0.83 mg/kg orally, TID for 5 days). Serum brodifacoum concentrations were highest (1065-1215 ng/mL) during the 3 days after BDF dosing and were detectable (3.0-7.5 ng/mL) until day 24 postexposure. A mean BDF elimination half-life of 6 +/- 4 days was observed.  相似文献   
133.
Long‐term experiments are a classical case of repeated measurements. Traits are measured on the same experimental unit over many years so that correlations arise between the observations made on the same plot in consecutive years. This paper describes the analysis of a three‐crop‐rotation long‐term experiment. We analysed the yields of the crops and the organic carbon content in the topsoil over 30 consecutive years. Several variance–covariance approaches are discussed and the trait‐specific best fit is interpreted. Mixed models are used to describe the structure of the experiment. Both yields and soil organic carbon show a more or less pronounced variance heterogeneity. Especially for yields, the heterogeneity of cycles and years is dominant. The consideration of correlations results in a better model fit in all cases.  相似文献   
134.
Three different milk sampling techniques were evaluated during milk sampling: a direct aseptic collection from the udder through a sterile cannula was used as the reference technique, compared with either a manual or a mechanical sampling method. In this study 30 high-yielding Holstein-Friesian dairy cows at different stages of lactation and free of udder infection were used. For each milk sample, the influence of milk sampling techniques was determined for the following parameters: somatic cell count, milk composition, bacterial contamination, viability, in vitro phagocytosis and overall killing of Staphylococcus aureus Newbould 305, and cellular chemiluminescence. Because milk sampling occurred throughout lactation, the differences between early, mid- and late lactation were estimated. It was concluded that bacterial contamination was not significantly different in manual milking samples and the reference technique; bacterial contamination was, however, significantly (P < 0.001) higher in machine milking samples than in the reference technique. Among the different sampling techniques, no significant effects on SCC, milk composition, viability and functions of the cells isolated from milk were observed. It was found that viability, intracellular killing and cellular chemiluminescence of milk PMN were significantly lower (P < 0.05) in early lactation compared to mid-lactation. Phagocytosis was significantly (P < 0.05) higher in early lactation compared to mid- and late lactation, and no significant differences were observed between mid- and late lactation. From this study, it can be concluded that despite a higher bacterial contamination obtained with the mechanical sampling method, the 3 milk sampling techniques described in this study can be used for the evaluation of milk cell functions.  相似文献   
135.
136.
137.
138.
139.
140.
The fungal pathogen Verticillium dabliae was less likely to cause symptoms of verticillium wilt on cotton seedlings that had been previously exposed to spider mites than on unexposed cotton seedlings. Conversely, populations of the spider mite Tetranychus urticae grew less rapidly on seedlings that had been inoculated with V. dabliae than on uninoculated controls. Changes caused by pathogen or herbivore attack reduced the suitability of the host plant to a diversity of organisms. This result suggests that highly unrelated organisms that share a host plant may interact strongly.  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