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   64864篇
  免费   3720篇
  国内免费   37篇
林业   2779篇
农学   2052篇
基础科学   343篇
  7700篇
综合类   10369篇
农作物   2325篇
水产渔业   3354篇
畜牧兽医   34755篇
园艺   825篇
植物保护   4119篇
  2019年   669篇
  2018年   1134篇
  2017年   1112篇
  2016年   1018篇
  2015年   935篇
  2014年   1055篇
  2013年   2860篇
  2012年   1988篇
  2011年   2355篇
  2010年   1448篇
  2009年   1455篇
  2008年   2132篇
  2007年   2089篇
  2006年   1936篇
  2005年   1763篇
  2004年   1688篇
  2003年   1684篇
  2002年   1609篇
  2001年   1889篇
  2000年   1859篇
  1999年   1524篇
  1998年   645篇
  1997年   625篇
  1995年   666篇
  1994年   610篇
  1993年   583篇
  1992年   1237篇
  1991年   1387篇
  1990年   1280篇
  1989年   1282篇
  1988年   1171篇
  1987年   1151篇
  1986年   1200篇
  1985年   1200篇
  1984年   965篇
  1983年   910篇
  1982年   587篇
  1979年   896篇
  1978年   707篇
  1977年   703篇
  1976年   716篇
  1975年   716篇
  1974年   869篇
  1973年   843篇
  1972年   815篇
  1971年   731篇
  1970年   772篇
  1969年   745篇
  1968年   653篇
  1967年   663篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Marketing to veterinarians is the process of synchronizing the business aspects of his or her goods and services so that they are understood and desired by animal owners. The basic components of a successful marketing program are in four categories: the individual, the situation, the needs, and the implementation. Each category is important and all are interrelated; however, the implementation of a program should not begin until a self-analysis has been done and the situation and its needs are thoroughly researched. Programs that have been used by successful practitioners can be copied. No program can be effective unless the economic status of the client's enterprise is known and understood.  相似文献   
42.
Taenia saginata cyst fluid was examined for host proteins; IgG1 and IgG2 as well as haemolytic complement activity were detected. Polyacrylamide gel electrophoresis revealed differences in proteinograms among the samples taken from 1-, 4-, and 10-month old cysts. Fluid from older cysts had fewer protein components and showed a weaker antigenic reaction with sera of bovines infected with T. saginata than that of younger cysts. The roles of antibody and complement in initiating degeneration of the parasite are discussed.  相似文献   
43.
Abstract –  Changes in the numbers and size-class structure of European silver eels, Anguilla anguilla , in the River Frémur (France) were examined over a 9-year period after installation of downstream eel passes. The number of silver eels migrating downstream peaked in 1999, then decreased strongly and steadily after 2000, reaching relatively low levels. At the same time, a gradual shift in the silver eel sex ratio from a dominance of males (size from 270 to 442 mm, age from 3 to 6 years) to females (size from 366 to 1112 mm, age from 4 to 9 years) was recorded. Possible explanations for the escapement patterns observed are environmental sex determination and the installation of eel passes on the main hydraulic engineering structures in 1992 and 1996.  相似文献   
44.
Fifty six dogs of mixed age and sex were acquired from farms in the Otago/Southland region, and maintained at the Hydatid Research Unit, Taieri, where 43 were each fed two Tueniu ovis cysts. All were bled fortnightly for six or 12 weeks. Coded sera were sent to Wallaceville Animal Research Centre for testing using ELISA, with antigen from T. ovis scoleces. Dog treatments were identified after all tests were complete. A discriminant level was derived from the mean absorbance value plus three standard deviations of 56 sera taken at time zero and 78 sera from serially bled uninfected dogs. None of these 134 sera registered as a false positive using this discriminant level. The data showed no significant deviation from normality, and the expected frequency of the occurrence of false positives is therefore less than 0.14%. Four weeks after infection 63% of dogs proved to be infected were serologically positive, rising to 78% after 6 weeks. When worms were removed by anthelmintic treatment, ELISA absorbance levels decreased. Four weeks after removal 70% of previously infected dogs remained positive, decreasing to 30% after 6 weeks. Six weeks after infection the sensitivity of the test was 78%, and the specificity 63%. However, if dogs with positive ELISA absorbance levels, but which did not purge worms, were regarded as having had worms, the respective figures would be 82% and 100%. The latter figures are similar to our previously published laboratory results. The test is of comparable efficiency to arecoline purgation for surveillance, and has the additional advantage of detecting infection in the majority of those dogs that have been infected for three weeks or more but fail to pass worms on purgation, and a substantial proportion of those infected dogs that were treated by their owners prior to presenting them for purgation in order to avoid detection of infection.  相似文献   
45.
46.
47.
48.
Correction     
  相似文献   
49.
50.
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