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   25330篇
  免费   1342篇
  国内免费   10篇
林业   906篇
农学   772篇
基础科学   155篇
  3694篇
综合类   3553篇
农作物   949篇
水产渔业   1443篇
畜牧兽医   13327篇
园艺   276篇
植物保护   1607篇
  2019年   272篇
  2018年   439篇
  2017年   533篇
  2016年   489篇
  2015年   356篇
  2014年   479篇
  2013年   999篇
  2012年   820篇
  2011年   985篇
  2010年   701篇
  2009年   684篇
  2008年   992篇
  2007年   936篇
  2006年   830篇
  2005年   751篇
  2004年   654篇
  2003年   716篇
  2002年   617篇
  2001年   820篇
  2000年   808篇
  1999年   639篇
  1998年   278篇
  1997年   287篇
  1996年   230篇
  1995年   261篇
  1993年   233篇
  1992年   426篇
  1991年   517篇
  1990年   436篇
  1989年   414篇
  1988年   403篇
  1987年   410篇
  1986年   363篇
  1985年   391篇
  1984年   339篇
  1983年   290篇
  1982年   244篇
  1979年   384篇
  1978年   290篇
  1977年   290篇
  1976年   299篇
  1975年   318篇
  1974年   332篇
  1973年   304篇
  1972年   290篇
  1971年   246篇
  1969年   289篇
  1968年   269篇
  1967年   326篇
  1966年   304篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
    
Ohne Zusammenfassung  相似文献   
32.
33.
34.
35.
The survival period of 22 S. gallinarum strains in chicken feces was examined. The suspension of the bacterium was homogenized with a certain feces quantity. The initial ratio was 10(7) to 10(9) colony forming units per gram of feces. The results show that the growth of 5 strains was completely inhibited within 24 hours post homogenization, 7 strains were still positive to S. gallinarum for 24 hours, 5 strains were positive for 48 hours and the last 5 strains were positive for 4 days. Additionally, the effect of tryptose soy (TSB) and Rappaport-Vassiliadis (RV) nutrient broths on the isolation rate of S. gallinarum from feces was examined at 37 degrees C and 43 degrees C. It was shown that the TSB medium was the best at 37 degrees C, in this experiment. The S. gallinarum concentration in RV medium was decreased at 37 degrees C from 9.1 x 10(8) to 1.6 x 10(6) and at 43 degrees C from 9.1 x 10(8) to 4.1 x 10(2).  相似文献   
36.
Thirty-five Pasteurella haemolytica strains were isolated in Hungary from goat carcasses sent for postmortem examination from two farms with large goat flocks. All strains belonged to biotype A and with the exception of one strain of serotype A8 they belonged to serotype A2. No untypable strains were found by the indirect haemagglutination test.  相似文献   
37.
The effect of a novel lairage environment on the ability of sheep to recover from 16 h of transport was investigated. Sheep were transported from grass paddocks to either novel outside paddocks or inside pens, and housed groups were transported to either familiar or novel inside pens. During transport, sheep from outside paddocks lay down less than those from inside pens. In sheep transported to inside pens, those from outside paddocks spent more time lying and spent less time eating; hay and water intakes during the first 12 h post-transport were lower than those previously kept inside. There was no obvious effect of a novel environment post-transport on blood biochemistry, suggesting that the lower post-transport feed and water intakes in a novel environment did not have a significant effect on the ability of the sheep to recover from the feed and water deprivation associated with transport.  相似文献   
38.
Hydraulic retention time (HRT) influence improving sludge flocculation with adding the polyelectrolytes (non-ionic, anionic, and cationic) was studied on an activated sludge (AS) system fed with synthetic domestic wastewater (SDW), dairy industry wastewater (DIW), and caramel industry wastewater (CIW). The sludge volumetric index, food/microorganism ratio (F/M), and mixed liquor volatile suspended solids at different HRTs (6, 8 and 10 h) were monitored on an experimental model. Results showed that both SDW and IW had the best sludge flocculation conditions at 8 h and 100 mL of non-ionic polyelectrolyte (0.2 mg L?1). In addition, this phenomenon reached the organic matter removal efficiencies of 95.9, 95.7, and 94.2% for SDW, DIW, and CIW, respectively. Therefore, optimum HRT increased the organic matter removal efficiencies by 10%, sludge concentration by 37% (22–55%), and F/M ratio by 70%. Moreover, the polyelectrolytes used in AS improved the sludge flocculation by 2.9 times.  相似文献   
39.
40.
Abstract The main question which must be raised when planning to enhance natural populations through sea ranching is whether reared organisms are fit for a life in the wild, or more specifically, whether there are differences between reared and naturally resident individuals. The causes and effects of these differences are reviewed, and results from the Norwegian enhancement programme, which compared reared and wild individuals of Atlantic salmon, Salmo salar L., Atlantic cod, Gadus morhua L., and European lobster, Homarus gammarus L., are discussed with emphasis on morphological and behavioural differences. It was concluded that exposure to an artificial rearing environment during ontogeny can affect both the phenotype and the behaviour of the reared individuals, and thereby, their potential for survival after release into the wild as well. Suggestions are made as to how to diminish observed differences, and thereby, improve the survival potential.  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