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   52139篇
  免费   4215篇
  国内免费   6篇
  2023年   246篇
  2021年   412篇
  2020年   350篇
  2019年   350篇
  2018年   1009篇
  2017年   1025篇
  2016年   1149篇
  2015年   1109篇
  2014年   1338篇
  2013年   2259篇
  2012年   3558篇
  2011年   3922篇
  2010年   2053篇
  2009年   1400篇
  2008年   3219篇
  2007年   3315篇
  2006年   3102篇
  2005年   2797篇
  2004年   2641篇
  2003年   2489篇
  2002年   2466篇
  2001年   1629篇
  2000年   1868篇
  1999年   1064篇
  1998年   531篇
  1997年   434篇
  1996年   474篇
  1995年   418篇
  1994年   445篇
  1993年   409篇
  1992年   454篇
  1991年   381篇
  1990年   344篇
  1989年   344篇
  1988年   307篇
  1987年   311篇
  1986年   275篇
  1985年   369篇
  1984年   430篇
  1983年   371篇
  1982年   379篇
  1981年   341篇
  1980年   305篇
  1979年   304篇
  1978年   307篇
  1977年   288篇
  1976年   274篇
  1975年   324篇
  1974年   244篇
  1973年   225篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
A comparison was made between a hay fed group, consisting of 23 ewes, and a grass silage fed group of 22 ewes, all pregnant. Excretion of Listeria monocytogenes (Lm) in the faeces and milk, antibody titres in sera and whey and delayed hypersensitivity against Lm, and several blood components were determined. The animals had previously been exposed to Lm, and Lm was isolated from the faeces from several animals when the experiment started. No significant difference in number of excretors between the 2 groups was found during the experimental period. The haemagglutination titres in both sera and whey were low and on the same level in both groups. The titres were higher in animals with 1 foetus than in animals with more than 1 foetus. In the first part of the experimental period the silage group had a reduced number of lymphocytes, lower total serum protein values and higher serum iron values, compared with the hay group. The silage group also had a stronger delayed hypersensitivity reaction against Lm than the hay group, and in the silage group the reaction was significantly stronger in ewes with 3 or more foetuses than in ewes with 1 foetus. In conclusion, the combined effect of some of the changes found in animals fed grass silage may leave them more susceptible to infections.  相似文献   
3.
4.
5.
6.
In a section of the Liassic southwest of the village of Préjano (Prov. Logroño) Sinemurian Dasyclad algae were found for the first time in the “Bankkalk-Series” of the “Carniolas-Formation” which is not dated up to that time. Six species,Dissocladella lucasi (Cros & Lemoine),Dissocladella iberica nov. sp.,Dissocladella ebroensis nov. sp.,Sestrosphaera liasina Pia,Gyroporella retica (Zanin) andMacroporella nov. sp. aff. sturi Bystricky are described.  相似文献   
7.
8.
9.
Georg Söderbom 《Ethnos》2013,78(1-2):95-100
Current debates over the concept of culture are examined, especially with regard to the relationship of culture to bounded collectivities, human nature, and individuality; present‐day views are seen against the background of back‐and‐forth swings in the history of anthropological thought. Recent theorizing about cultural acquisition is also considered.  相似文献   
10.
As nutritional status and inflammation are strongly connected, feeding and nutritional strategies could be effective to improve the ability of pigs to cope with disease. The aims of this study were to investigate the impact of a feed restriction on the ability of pigs to resist and be tolerant to a coinfection with Mycoplasma hyopneumoniae (Mhp) and the European H1N1 swine influenza virus, and the consequences for nutrient metabolism, with a focus on amino acids. Two groups of specific pathogen-free pigs were inoculated with Mhp and H1N1 21 days apart. One group was fed ad libitum, the other group was subjected to a two-week 40% feed restriction starting one week before H1N1 infection. The two respective mock control groups were included. Three days post-H1N1 infection, 200 g of feed was given to pigs previously fasted overnight and serial blood samples were taken over 4 hours to measure plasma nutrient concentrations. Throughout the study, clinical signs were observed and pathogens were detected in nasal swabs and lung tissues. Feed-restricted pigs presented shorter hyperthermia and a positive mean weight gain over the 3 days post-H1N1 infection whereas animals fed ad libitum lost weight. Both infection and feed restriction reduced postprandial glucose concentrations, indicating changes in glucose metabolism. Post-prandial plasma concentrations of the essential amino acids histidine, arginine and threonine were lower in co-infected pigs suggesting a greater use of those amino acids for metabolic purposes associated with the immune response. Altogether, these results indicate that modifying feeding practices could help to prepare animals to overcome an influenza infection. Connections with metabolism changes are 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