全文获取类型
收费全文 | 88825篇 |
免费 | 7652篇 |
国内免费 | 3027篇 |
专业分类
林业 | 5716篇 |
农学 | 5345篇 |
基础科学 | 2114篇 |
10901篇 | |
综合类 | 22665篇 |
农作物 | 4050篇 |
水产渔业 | 5915篇 |
畜牧兽医 | 34423篇 |
园艺 | 2442篇 |
植物保护 | 5933篇 |
出版年
2023年 | 607篇 |
2022年 | 1293篇 |
2021年 | 1759篇 |
2020年 | 1964篇 |
2019年 | 2709篇 |
2018年 | 2459篇 |
2017年 | 2923篇 |
2016年 | 2627篇 |
2015年 | 2903篇 |
2014年 | 3092篇 |
2013年 | 4493篇 |
2012年 | 4439篇 |
2011年 | 4727篇 |
2010年 | 4204篇 |
2009年 | 3698篇 |
2008年 | 3971篇 |
2007年 | 3664篇 |
2006年 | 3308篇 |
2005年 | 2843篇 |
2004年 | 2191篇 |
2003年 | 2076篇 |
2002年 | 2047篇 |
2001年 | 2251篇 |
2000年 | 2163篇 |
1999年 | 1698篇 |
1998年 | 767篇 |
1997年 | 772篇 |
1996年 | 700篇 |
1995年 | 724篇 |
1994年 | 646篇 |
1993年 | 632篇 |
1992年 | 1059篇 |
1991年 | 1061篇 |
1990年 | 1004篇 |
1989年 | 994篇 |
1988年 | 935篇 |
1987年 | 940篇 |
1986年 | 924篇 |
1985年 | 912篇 |
1984年 | 739篇 |
1983年 | 663篇 |
1979年 | 653篇 |
1978年 | 549篇 |
1974年 | 693篇 |
1973年 | 608篇 |
1972年 | 676篇 |
1971年 | 674篇 |
1970年 | 602篇 |
1969年 | 591篇 |
1967年 | 511篇 |
排序方式: 共有10000条查询结果,搜索用时 380 毫秒
91.
This study presents the estimates of heritability for spondylosis deformans in the boxer based on 353 offspring from 24 randomly selected sires, each with at least three radiographically investigated offspring. The estimated heritability (h2) for maximum degree of osteophyte development was high, both when estimated by paternal half-sib correlation (0·42) and by the regression of offspring based on the parents (0·62). The heritability for the number of affected discs estimated by paternal half-sib correlation was also high (0·47). The estimate of heritability for the number of affected discs based on regression of offspring on the parents was lower at 0·13. All heritabilities had large standard errors. A positive phenotypic correlation between spondylosis deformans and hip dysplasia was observed. Assuming a significant portion of the correlation is genetic, this fact may permit selection against spondylosis deformans without negatively influencing the incidence of hip dysplasia. Since the incidence of spondylosis deformans is high even in young dogs, it should be possible to detect a large proportion of genetically predisposed animals by radiographic examination of the spine at one year of age; at the same time that dogs are presented for a routine test for hip dysplasia. 相似文献
92.
The anthelmintic efficacy of abamectin (avermectin B1) was evaluated against gastrointestinal nematodes, including Ostertagia ostertagi inhibited larvae and lungworm, in yearling crossbred beef heifers during late spring. The calves were grazed on contaminated pasture for 10 weeks and then held under conditions free of nematode infection for 3 weeks prior to allotment and treatment on 5 June. Thirteen calves were randomly assigned to two groups of six by restricted randomization on body weights; the extra lightest calf was assigned to the non-treated control group. Group 1 calves were treated with abamectin at 200 micrograms kg-1 body weight by s.c. injection and Group 2 calves were not treated; all were killed at 14 days after treatment. Ostertagia ostertagi was present in all controls; arithmetic mean numbers of adults, developing fourth stage larvae (L4) and inhibited EL4 were 7683, 605 and 36,102, respectively. Other nematode genera present in controls in sufficient numbers for the experiment were Haemonchus placei adults, Trichostrongylus axei adults, Cooperia spp. adults, Oesophagostomum radiatum adults, Bunostomum phlebotomum adults, Dictyocaulus viviparus adults and E5 (immature adults). Abamectin was highly effective (consistently greater than 99% efficacy and P less than 0.05) in removing all nematodes present in treated calves as represented in non-treated controls, including the primary target of Ostertagia ostertagi inhibited EL4. The lowest efficacy was 93.8%, against D. viviparus E5. 相似文献
93.
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
94.
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
95.
96.
97.
试验采用单因素随机区组设计,叶面喷施肥料的施肥方法,应用方差分析和多重比较分析试验数据,从而筛选出小菊最佳的营养元素配方。试验从不同叶面肥料在小菊上的筛选与应用研究的试验结果得到:小菊对肥料具有较强的选择性:三高灵的施用能够增加小菊的开花数量和鲜叶片叶绿素的含量;宝力丰的施用能提高小菊单株的干物重;OPAL的施用能延长小菊开花的花期。 相似文献
98.
M E Olson C J Hannigan P F Gaviller L A Fulton 《The Canadian veterinary journal. La revue veterinaire canadienne》2001,42(11):865-868
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
99.
100.
上虞市海涂实验农场中心试验区的排水系统,能满足十年一遇的年最大24h降雨,两天内排出的要求。滨海盐土的地下水位高,农田基本建设除用浅、密的排水沟布置外,还应结合平整土地、发展灌溉以及适用的农、林技术等综合措施,才能达到治盐改土的效果。 相似文献