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   73300篇
  免费   4133篇
  国内免费   32篇
林业   3173篇
农学   2397篇
基础科学   469篇
  8672篇
综合类   12016篇
农作物   2818篇
水产渔业   3522篇
畜牧兽医   38594篇
园艺   835篇
植物保护   4969篇
  2018年   967篇
  2017年   1073篇
  2016年   1000篇
  2015年   845篇
  2014年   1046篇
  2013年   2746篇
  2012年   1943篇
  2011年   2268篇
  2010年   1533篇
  2009年   1558篇
  2008年   2321篇
  2007年   2221篇
  2006年   2035篇
  2005年   1969篇
  2004年   1846篇
  2003年   1990篇
  2002年   1806篇
  2001年   2239篇
  2000年   2190篇
  1999年   1748篇
  1998年   714篇
  1997年   776篇
  1996年   685篇
  1995年   865篇
  1994年   735篇
  1993年   734篇
  1992年   1494篇
  1991年   1636篇
  1990年   1602篇
  1989年   1611篇
  1988年   1494篇
  1987年   1457篇
  1986年   1536篇
  1985年   1450篇
  1984年   1270篇
  1983年   1063篇
  1982年   748篇
  1979年   1171篇
  1978年   887篇
  1977年   841篇
  1976年   799篇
  1975年   829篇
  1974年   1030篇
  1973年   1070篇
  1972年   1018篇
  1971年   951篇
  1970年   927篇
  1969年   899篇
  1968年   754篇
  1967年   844篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Serosurvey of five viruses in chickens on smallholdings in Bangladesh   总被引:1,自引:0,他引:1  
A serologic survey was undertaken in chickens in smallholdings in Bangladesh for avian influenza A virus (AIV), egg drop syndrome '76 virus (EDS'76V), infectious bronchitis virus (IBV), Newcastle disease virus (NDV) and reovirus (RV) in three phases: January 2002-May 2003, September 2003-August 2004, and August 2005-March 2006. Four hundred thirty-six sera collected in the 2nd phase, 295 in the first phase, 755 in the 1st plus 2nd phases and 295 in the 1st phase were investigated for AIV, EDS'76V, IBV and RV, respectively, using enzyme linked immunosorbent assays. All 854 sera collected in the three phases were screened for NDV using hemagglutination inhibition test. In chickens 20% were seropositive to AIV, 3% to EDS'76V, 74% to IBV, 88% to NDV, and 47% to RV. The seroprevalence in flocks was 23% to AIV, 6% to EDS'76V, 79% to IBV, 89% to NDV and 56% to RV. Twenty-five percent chickens had > or = 10log(2)HI titers to NDV.  相似文献   
992.
993.
994.
995.
A nonhealing wound associated with a laceration in a 12-year-old llama was evaluated. Initial attempts at closure were unsuccessful and biopsy revealed scar tissue. Subsequent biopsies, 18 mo later, revealed squamous cell carcinoma with regional metastasis. This report describes squamous cell carcinoma, secondary to a traumatic wound in a llama.  相似文献   
996.
Summary

This mini‐review highlights new information on various research aspects presented by specialists from all over the world at the 4th Pestivirus meeting held in Giessen (Germany) from March 15–19, 1999. Especial attention is paid towards differences in humeral and cellular immune response of naive and persistently infected calves with BVDV, and towards BVD eradication programmes m the Scandinavian countries.

The development of techniques for an early diagnosis of CSF in live pigs and the progress on both sub‐unit and MLV marker vaccines against this disease are reported.  相似文献   
997.
998.
The genomic region spanning the two ribosomal RNA internal transcribed spacers (ITS1 and ITS2) and the 5.8S rRNA gene was cloned and sequenced from sixteen Theileria isolates. Each Theileria species possessed ITS1 and ITS2 of unique size(s) and species specific nucleotide sequences. Varying degrees of ITS1 and ITS2 intra- and inter-species sequence polymorphism were found among ruminant Theileria species. The spacers were most polymorphic in the agent of tropical theileriosis, Theileria annulata, and were more conserved in two benign species, Theileria buffeli and Theileria sergenti Chitose. Phylogenetic analysis of the rDNA ITS1-5.8S rRNA gene-ITS2 region clearly separated each taxon, placing them in three clusters. One held T. annulata, Theileria parva, and Theileria mutans, with the latter two most closely related. The second held T. sergenti Ikeda, T. sergenti Chitose, and T. buffeli, with the latter two most closely related. The third cluster held the Theileria ovis isolates.  相似文献   
999.
A crossbred cat developed a subcutaneous fibrosarcoma on the left side of the thorax at the site of previous administration of a feline parvo-, herpes- and calicivirus vaccine. A few months later the cat developed a second mass on the right side of the thorax after a booster vaccine had been administered at this site. This unique case of bilateral fibrosarcomas in a cat shortly after vaccination with parvo-, herpes- and caliciviruses suggests an individual disposition for the development of vaccine-associated sarcomas and a possible triggering of this type of pathological response which could have precipitated the development of the second tumour. To the authors' knowledge, this is the first case of vaccine-induced fibrosarcomas occurring bilaterally after injection of a feline parvo-, herpes- and calicivirus containing vaccine at different sides of the thorax.  相似文献   
1000.
Although conjugated linoleic acid (CLA) shows inhibitory effects on histamine release, eicosanoid production and pruritus in laboratory rodents, its use in canine atopic dermatitis (AD) has not been reported. The aims of this study were to assess the efficacy of CLA, black currant seed oil (BSO) or a combination of both, compared to placebo, in dogs with AD and to evaluate any changes in fatty acid metabolism with these treatments. Twenty-four dogs with AD were randomly allocated to four groups, and were treated orally each day for two months with either 1 mL/10 kg CLA (80% purity), 1 mL/10 kg pure BSO, 1 mL/10 kg CLA+1 mL/10 kg BSO, or 1 mL/10 kg sugar syrup (placebo). Serum was obtained on days 0, 30 and 60 for analysis of CLA metabolites, linoleic acid (LA), gamma-linolenic acid (GLA), dihomo-gamma-linolenic acid (DGLA) and arachidonic acid (AA). At the same time point, the owners were asked to assess pruritus and the veterinarians evaluated any skin lesions present. Although the best clinical results occurred with BSO treatment alone, improvement of clinical signs and pruritus was not significant with any of the treatments. Serum levels of GLA and DGLA significantly increased in BSO-treated dogs, but not in the CLA+BSO group. CLA at the dosage used in this study was not efficacious in treating canine AD, whereas BSO may help some dogs with AD, although further studies are necessary before this can be recommended as a treatment.  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