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   103275篇
  免费   5697篇
  国内免费   69篇
林业   5418篇
农学   3555篇
基础科学   549篇
  12604篇
综合类   15990篇
农作物   3854篇
水产渔业   5211篇
畜牧兽医   54528篇
园艺   1233篇
植物保护   6099篇
  2019年   886篇
  2018年   1570篇
  2017年   1699篇
  2016年   1593篇
  2015年   1409篇
  2014年   1685篇
  2013年   3891篇
  2012年   3080篇
  2011年   3608篇
  2010年   2358篇
  2009年   2382篇
  2008年   3421篇
  2007年   3451篇
  2006年   3243篇
  2005年   3049篇
  2004年   2858篇
  2003年   2833篇
  2002年   2647篇
  2001年   3594篇
  2000年   3422篇
  1999年   2759篇
  1998年   1077篇
  1997年   1038篇
  1996年   1020篇
  1995年   1130篇
  1994年   976篇
  1993年   981篇
  1992年   2044篇
  1991年   2173篇
  1990年   2222篇
  1989年   2090篇
  1988年   1983篇
  1987年   1995篇
  1986年   1950篇
  1985年   1891篇
  1984年   1559篇
  1983年   1301篇
  1982年   917篇
  1979年   1372篇
  1978年   1082篇
  1977年   881篇
  1976年   927篇
  1975年   950篇
  1974年   1244篇
  1973年   1156篇
  1972年   1242篇
  1971年   1206篇
  1970年   1121篇
  1969年   1070篇
  1967年   960篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Inclusion of high-ionic strength buffers helped us to develop a sandwich ELISA to detect hemorrhagic septicemia virus (HSV) in cell culture and infected trout tissue extracts. For maximal sensitivity of 0.1 to 0.2 ng/well/100 microliters or about 10 to 50 TCID50/well/100 microliters, trout extracts were diluted 1:1 and assayed for the earliest synthesized nucleoprotein N. Simultaneous binding of the N protein from HSV in the sample to the wells coated with monoclonal antibody (2D5 against the N protein) and to the peroxidase-labeled monoclonal antibody (2C9 against the N protein) proceeded during a 2-hour incubation at 20 to 22 C (room temperature). The response was linear between 6 to 60 ng/well of purified virus. Monoclonal antibodies used were noncompetitive with each other and reacted with F1, F2, 23.75, and 5 Spanish isolates of HSV, but not with infectious hematopoietic necrosis or infectious pancreatic necrosis viruses. Tissue specimens with low content of HSV virus may now be assayed directly without use of cell culture, rapidly, and with high precision, during the acute phase of the disease in salmonid fishes.  相似文献   
102.
103.
Abstract –  Foraging juvenile fish with relatively high food demands are usually vulnerable to various aquatic and avian predators. To compromise between foraging and antipredator activity, they need exact and reliable information about current predation risk. Among direct predator-induced cues, visual and olfactory signals are considered to be most important. Food intake rates and prey-size selectivity of laboratory-reared, naive young-of-the-year (YOY) perch, Perca fluviatilis , were studied in experiments with Daphnia magna of two size classes: 2.8 and 1.3 mm as prey and northern pike, Esox lucius , as predator. Neither total intake rate nor prey-size selectivity was modified by predator kairomones alone (water from an aquarium with a pike was pumped into the test aquaria) under daylight conditions. Visual presentation of pike reduced total food intake by perch. This effect was significantly more pronounced (synergistic) when visual and olfactory cues were presented simultaneously to foraging perch. Moreover, the combination of cues caused a significant shift in prey-size selection, expressed as a reduced proportion of large prey in the diet. Our observations demonstrate that predator-induced olfactory cues alone are less important modifiers of the feeding behaviour of naive YOY perch than visual cues under daylight conditions. However, pike odour acts as a modulatory stimulus enhancing the effects of visual cues, which trigger an innate response in perch.  相似文献   
104.
To evaluate the transplacental transfer of Theileria sergenti infection in cattle, we used DNA probes to detect T. sergenti in 6 pregnant cows and their calves. All the animals were monitored by parasitologic, serologic, and polymerase chain reaction (PCR) assays for a predicted 875-base-pair (bp) DNA product and a 684-bp amplicon detected by nested PCR in the blood and spleens of aborted fetuses. An open reading frame (ORF) starting at nucleotide 170 and terminating at position 1021 was shown to code for a polypeptide of 283 amino acid residues. All 6 dams and 5 calves were positive for T. sergenti in all tests. One calf was positive only with nested PCR. We conclude that transplacental transmission of T. sergenti is a significant problem. The relevance of the data in the programmed introduction of new (especially pregnant) animals into established clean herds needs serious consideration with regard to control of theileriosis and other tickborne diseases.  相似文献   
105.
Dogs (n = 13), which had failed to be cured of giardiosis following chemotherapeutic measures, were treated with a Giardia vaccine (2-3 injections). Clinical signs resolved between 16 and 42 days postvaccination and cessation of fecal cyst shedding was between 21 and 70 days. Vaccination is a potential method of treating giardiosis in dogs.  相似文献   
106.
107.
108.
Canine distal renal tubular acidosis and urolithiasis   总被引:1,自引:0,他引:1  
Distal RTA is characterized by decreased distal renal tubular hydrogen ion secretion, decreased ability to acidify urine, hypercalciuria, hyperphosphaturia, hypocitraturia, and metabolic acidosis. Because of the resulting alterations in urine composition and pH, patients with distal RTA are predisposed to urolithiasis and renal calcification. Diagnosis of distal RTA is important because it is a potentially reversible disorder that, left untreated, may cause nephrocalcinosis, recurrent urolith formation, moderate to severe metabolic acidosis, and renal failure.  相似文献   
109.
110.
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