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   321323篇
  免费   17443篇
  国内免费   685篇
林业   24508篇
农学   14207篇
基础科学   2996篇
  46530篇
综合类   45313篇
农作物   17457篇
水产渔业   18306篇
畜牧兽医   137834篇
园艺   6537篇
植物保护   25763篇
  2019年   3729篇
  2018年   4305篇
  2017年   4664篇
  2016年   5023篇
  2015年   4500篇
  2014年   5885篇
  2013年   16578篇
  2012年   7823篇
  2011年   10135篇
  2010年   7938篇
  2009年   8366篇
  2008年   9461篇
  2007年   8660篇
  2006年   9178篇
  2005年   8355篇
  2004年   8187篇
  2003年   7949篇
  2002年   7379篇
  2001年   8480篇
  2000年   8150篇
  1999年   7215篇
  1998年   4403篇
  1997年   4451篇
  1996年   4138篇
  1995年   4807篇
  1994年   4273篇
  1993年   3952篇
  1992年   5912篇
  1991年   6203篇
  1990年   6040篇
  1989年   6010篇
  1988年   5482篇
  1987年   5554篇
  1986年   5585篇
  1985年   5657篇
  1984年   5025篇
  1983年   4620篇
  1982年   3569篇
  1981年   3381篇
  1980年   3316篇
  1979年   4512篇
  1978年   3878篇
  1977年   3502篇
  1976年   3193篇
  1975年   3199篇
  1974年   3905篇
  1973年   3941篇
  1972年   3718篇
  1971年   3518篇
  1970年   3342篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
941.
In this study, the effects of nitrogen (N) rate (60, 120, 180 and 240 kg N ha?1 applied in three equal dressings at seeding and after the first and second cuttings) and stubble height (7, 14 and 21 cm) on the dry matter (DM) yield, crude protein (CP) content, and CP yield of a sorghum–sudangrass hybrid [Sorghum bicolor (L.) Moench × Sorghum sudanense (Piper) Stapf., cv. Pioneer 988] in the three‐cut system was investigated. The N rate had no significant effect in the first and third cuttings, but in the second cutting DM yields increased significantly with increase in N rate. The highest yield of 9.1 t ha?1 was obtained with 80 kg N ha?1 for the average of 2 years at the second cutting, but no significant difference was found among the 40, 60 and 80 kg N ha?1 rates. CP content and yield were not significantly affected by N rate at the first and third cuttings, but CP content and yield were significantly affected by application of N at the second cutting. Stubble height had a significant effect on CP content at the third cutting. However, it had no significant effect on CP content at the first and second cuttings. Stubble height had a significant effect on the CP yield at the first cutting, but no significant effect on CP yield at the second and third cuttings.  相似文献   
942.
The clinical documentation of enteropathogenic bacteria causing diarrhea in dogs is clouded by the presence of many of these organisms existing as normal constituents of the indigenous intestinal flora. The diagnosis of a putative bacterial enteropathogen(s) in dogs should be made based on a combination of parameters, including signalment and predisposing factors, clinical signs, serologic assays for toxins, fecal culture, and PCR. Relying on results of fecal culture alone is problematic, because C perfringens, C difficile, Campylobacter spp, and pathogenic and non-pathogenic E coli are commonly isolated from apparently healthy dogs [10,13,33]. Nevertheless, culture may be useful in procuring isolates for the application of molecular techniques, such as PCR, for detection of specific toxin genes or molecular typing of isolated strains to establish clonality in suspected outbreaks. The oversimplistic attempt to characterize bacterially associated diarrhea by anatomic localization of clinical signs should be discouraged, because most of the previously mentioned bacteria have been associated with small and large intestinal diarrhea. Accurate diagnosis of infections may require diagnostic laboratories to incorporate PCR-based assays using genus- and species-specific primers to facilitate detection of toxin genes and differentiation of species that appear phenotypically and biochemically similar. There has been tremendous interest in the application of microarray technology for the simultaneous detection of thousands of genes or target DNA sequences on one glass slide. This powerful tool could be used for detection of specific pathogenic bacterial strains in fecal specimens obtained from dogs in the future.  相似文献   
943.
944.
945.
946.
    
Ohne Zusammenfassung  相似文献   
947.
948.
949.
Ohne Zusammenfassung  相似文献   
950.
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