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   51647篇
  免费   2450篇
  国内免费   18篇
林业   1889篇
农学   1572篇
基础科学   318篇
  7361篇
综合类   6960篇
农作物   1956篇
水产渔业   2392篇
畜牧兽医   27905篇
园艺   583篇
植物保护   3179篇
  2019年   521篇
  2018年   901篇
  2017年   1039篇
  2016年   912篇
  2015年   661篇
  2014年   910篇
  2013年   2438篇
  2012年   1520篇
  2011年   1909篇
  2010年   1359篇
  2009年   1309篇
  2008年   1899篇
  2007年   1826篇
  2006年   1596篇
  2005年   1386篇
  2004年   1306篇
  2003年   1317篇
  2002年   1137篇
  2001年   1474篇
  2000年   1474篇
  1999年   1131篇
  1998年   495篇
  1997年   495篇
  1995年   505篇
  1993年   433篇
  1992年   780篇
  1991年   903篇
  1990年   834篇
  1989年   814篇
  1988年   722篇
  1987年   735篇
  1986年   720篇
  1985年   717篇
  1984年   655篇
  1983年   575篇
  1982年   439篇
  1979年   802篇
  1978年   574篇
  1977年   591篇
  1976年   687篇
  1975年   707篇
  1974年   790篇
  1973年   728篇
  1972年   703篇
  1971年   580篇
  1970年   567篇
  1969年   659篇
  1968年   639篇
  1967年   683篇
  1966年   674篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
An enzyme-linked immunosorbent assay has been shown to detect antibodies in the circulation of sheep infected with Psoroptes ovis. Strong positive reactions were obtained from 19 sheep with four-month-old infections. No cross reaction was observed with sera obtained from sheep infected with either Fasciola hepatica, Nematodirus battus, Ostertagia circumcincta or Damalinia ovis.  相似文献   
932.
Five monoclonal antibodies were obtained after immunising mice with superficial antigens of three strains representing serovars 1 to 3 of Actinobacillus (Haemophilus) pleuro-pneumoniae. When tested in ELISA against the standard strains representing serovars 1 to 10, the monoclonal antibody raised against the standard strain of serovar 1 reacted only with that strain. Of the three monoclonal antibodies raised against the standard strain of serovar 3, one reacted with serovars 3 and 8 only, another with serovar 7 only and the third with the strains representing serovars 7, 9 and 10. The monoclonal antibodies produced with the serovar 2 strain also reacted with a wide spectrum of strains, representing serovars 7 to 10.  相似文献   
933.
934.
935.
A serogroup-specific polymerase chain reaction (PCR) assay and isolate identification strategies (restriction endonuclease analysis (REA) and nucleotide sequencing) were developed for the detection of North American isolates of epizootic haemorrhagic disease virus (EHDV). PCR primers (EHDV-pr4, EHDV-pr5) were designed to hybridize to the L3 gene of a North American isolate of EHDV serotype 1. Total nucleic acid was extracted from preparations of infected tissue culture and PCR was performed using a cDNA-PCR kit, according to the manufacturer's specifications. The PCR assay generated a 459 base pair product from North American isolates of EHDV serotypes 1 and 2, while bluetongue virus (BTV) serotypes 10, 11, 13, and 17, and cell controls, failed to demonstrate PCR products. Slight modifications allowed for the PCR detection of EHDV-1 and -2 in white-tailed deer blood (Odocoileus virginiatus); PCR fragments were not amplified from uninfected deer blood. A number of restriction endonucleases and sequencing primers were evaluated for their utility in isolate identification experiments. Specifically, REA employing HincII and cycle sequencing with an internal primer (EHDV-1-pr3) proved most successful for identifying isolate-specific genome markers. The techniques presented are expected to prove valuable for rapid and specific detection of possible future EHDV incursions in wild and domestic animal species.  相似文献   
936.
Horses were examined for the behaviour of various blood constituents prior to and following infusions of solutions of glucose, fructose, invertose, and sorbitol. Infusion of 0.5 g/kg live weight glucose to six horses was followed by half-life variation between eleven and 23 minutes. Subsequent infusion of invertose to the same animals usually caused prolongation of glucose half-life. Half-life values were between 17 and 33 minutes for fructose and between 21 and 80 minutes for glucose. Infusion of 0.5 g/kg live weight fructose to two horses was followed by half-life values between 17 and 18 minutes, while the half-life values of sugar alcohol were 16, 16, 27, and 29 minutes in four horses who had received sorbitol. Sugar or sorbitol infusion was not followed by substantive change of lactate and pyruvate concentrations in the blood or free fatty acids in the blood plasma or GOT activity. The rise of insulin in the blood plasma was differentiated. Invertose and sorbitol solutions, consequently, can be recommended for application to horses.  相似文献   
937.
938.
939.
Contrary to expectation, immunoconglutinin levels failed to rise significantly in calves infected with Trypanosoma congolense. In addition, it was shown that trypanosome infection appeared to inhibit the immunoconglutinin response to Brucella abortus strain 19. The possible reasons for these findings are discussed.  相似文献   
940.
Teratogenic effects of methylparathion / Wofatox 50 EC/ and Parathion 20 WP as positive control material were tested in pheasant embryos. On the 12th day of incubation 0.1 ml of the emulsions or suspensions of the insecticides at different concentrations was inoculated into the air space of embryonated eggs. The following dose levels were employed: 27 and 270 mg/kg egg of Wofatox 50 EC, and 10 mg/kg of Parathion 20 WP. Morphological changes were evaluated by macroscopic, skeletal staining and light microscopic examinations of the embryos. Primary hypoplasia or atrophy developed in the cervical musculature /m. longus colli/ accompanied by lordosis and scoliosis of the cervical spine. In most cases we also found cyllosis .  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