全文获取类型
收费全文 | 8151篇 |
免费 | 541篇 |
国内免费 | 602篇 |
专业分类
林业 | 362篇 |
农学 | 587篇 |
基础科学 | 124篇 |
987篇 | |
综合类 | 3309篇 |
农作物 | 651篇 |
水产渔业 | 576篇 |
畜牧兽医 | 1305篇 |
园艺 | 252篇 |
植物保护 | 1141篇 |
出版年
2024年 | 68篇 |
2023年 | 201篇 |
2022年 | 359篇 |
2021年 | 336篇 |
2020年 | 348篇 |
2019年 | 354篇 |
2018年 | 282篇 |
2017年 | 378篇 |
2016年 | 395篇 |
2015年 | 367篇 |
2014年 | 418篇 |
2013年 | 495篇 |
2012年 | 600篇 |
2011年 | 591篇 |
2010年 | 489篇 |
2009年 | 445篇 |
2008年 | 379篇 |
2007年 | 414篇 |
2006年 | 329篇 |
2005年 | 290篇 |
2004年 | 210篇 |
2003年 | 183篇 |
2002年 | 187篇 |
2001年 | 158篇 |
2000年 | 151篇 |
1999年 | 140篇 |
1998年 | 82篇 |
1997年 | 97篇 |
1996年 | 71篇 |
1995年 | 76篇 |
1994年 | 65篇 |
1993年 | 49篇 |
1992年 | 72篇 |
1991年 | 47篇 |
1990年 | 36篇 |
1989年 | 40篇 |
1988年 | 14篇 |
1987年 | 18篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1962年 | 3篇 |
1955年 | 6篇 |
排序方式: 共有9294条查询结果,搜索用时 865 毫秒
881.
Zahid R. Shah MD Jeffrey R. Crass MD Dubravka C. Oravec MD Errol M. Bellon MD 《Veterinary radiology & ultrasound》1992,33(2):94-100
Foreign bodies in the soft tissues are frequent problems in both veterinary and human medical practice. Radiography has been the principle tool for diagnosis, but is unable to define many foreign bodies. This study was undertaken to compare the sonographic and radiographic visualization for a variety of foreign bodies. Fresh turkey muscle (pectoral and thigh) with skin was used as the soft tissue model. Assorted foreign bodies were introduced 1 cm into the muscle. Materials examined were small wood fragments, steel wire, glass, nails, graphite, rock, BB pellets, and polystyrene plastic. Following introduction of the foreign bodies radiographs were obtained and the specimens were studied sonographically at 5.0 mHz and 7.5 mHz. All foreign bodies were visible with sonography. A bright echo with either acoustic shadowing or reverberations was present for all specimens. Radiographically metallic foreign bodies were visible but wood, some graphite, and plastic were not seen. We conclude that radiography should remain the primary imaging modality for foreign body detection because of its general availability and low cost. If radiography is negative ultrasound can detect and guide the removal of radiolucent foreign bodies. 相似文献
882.
小麦根腐病的流行强度受气象因子的影响很大,小麦扬花期旬平均气温10℃以上,相对湿度80%以上,病害流行起点值高。在小麦生育后期出现高温高湿的气候环境,当年根腐叶枯发生严重。小麦扬花期病情指数5%左右,当年病害流行强度1级;叶部病情指数20%左右,当年病害流行强度可达4级。据病害发生程度与小麦扬花期叶部病情以及与气象因子的相关研究结果,研制出两种予测根腐叶枯流行强度的方法,置信度90%以上,可用于指导根腐叶枯的药剂防治。 相似文献
883.
The inhibition of mycelial growth of Rhizoctonia solani in vitro was strongest with pencycuron, followed by tolclofos-methyl, carboxin and thiabendazole. Against cowpea seedling rot in soil infested with R. solani, tolclofos-methyl was most effective, followed by pencycuron, thiabendazole and carboxin. Of nine insecticides tested, only parathion-methyl and quinalphos suppressed mycelial growth of R. solani in vitro, although their activity was much lower than that of the four tested fungicides. The inhibition of mycelial growth by fungicide-insecticide mixtures was antagonistic in only two out of 36 combinations; it was additive in most cases or synergistic, e.g. for most mixtures of pencycuron and insecticides. Quinalphos, applied to the soil, was the only insecticide which reduced cowpea seedling rot in soil infested with R. solani. Soil application of parathion-methyl, phorate, aldicarb or carbofuran and seed treatment with phosphamidon, monocrotophos, endosulfan or dimethoate had little or no effect on seedling rot. Carboxin gave better disease control when applied to the seed already coated with phosphamidon, monocrotophos, endosulfan or dimethoate and when carboxin-treated seeds were sown in soil treated with quinalphos, parathion-methyl, aldicarb or carbofuran. Efficacy of thiabendazole seed treatment was slightly higher in the presence of insecticides, particularly dimethoate. Pencycuron and tolclofos-methyl as seed treatment gave nearly 100% disease control both in the presence and absence of insecticides. The synergistic interactions detected between fungicides and insecticides represent interesting opportunities for the control of R. solani. 相似文献
884.
885.
In a study of 4 sheep herds, 1 apparently healthy and 3 having respiratory problems, lesions typical of subacute or chronic pneumonia were found in 3–36 % of slaughtered lambs. Occurrence appeared to be related to certain environmental factors such as pasture, whereas moderate lungworm invasion was not found to contribute to subacute or chronic pneumonia. Relation between pneumonia and low carcass weight was established only in 1 herd.Lungs were subjected to microbiological examination. Mycoplasma ovipneumoniae was isolated from both normal and pneumonic lungs from all 4 herds. The prevalence was far higher in pneumonic (98 %) than in normal ones (28 %). Bacteria, mostly Pasteurella haemolytica, were also found in both pneumonic (49 %) and normal (18 %) lungs from all 4 herds. These results confirm the conclusions of a previous study that M. ovipneumoniae is of etiological significance in subacute or chronic pneumonia, whereas bacteria mainly occur as secondary invaders. M. ovipneumoniae appears, however, only to be a potential pathogen. Examinations for Mycoplasma arginini and virus were negative and these agents are considered to be of less significance in subacute or chronic pneumonia under Norwegian conditions. 相似文献
886.
对不发酵的革兰氏阴性杆菌群疑似摩拉克氏菌属的禽病流行病学,临床症状,病理剖检,病原分离,病原的初步鉴定及致病性试验进行了有系统的调查。对病学和诊断进行了研讨。 相似文献
887.
H2-oxidizing activities were assayed in slurries of four soils by measuring the consumption of H2 and the exchange of 3H2 with H2O at increasing mixing ratios of H2 or 3H2. Both H2 consumption and 3H2 exchange were abolished by autoclaving or the addition of formaldehyde. The rates of H2 consumption and 3H2 exchange were proportional to the quantity of soil used. Both activities increased with increasing concentrations of H2 or 3H2 and displayed biphasic kinetics, demonstrating the existence of two different H2-oxidizing activities, one with a relatively low K
m and V
max, and a second with a relatively high K
m und V
max. The first type of activity was characteristic of abiontic soil hydrogenases, and the second of aerobic H2-oxidizing bacteria. In contrast to H2 consumption, which required the presence of either O2 or ferricyanide, 3H2 exchange operated equally well without an external electron acceptor. The 3H2 exchange assay may thus be particularly useful for enrichment of soil hydrogenases which have not yet been isolated and for which no natural electron acceptor is known. 相似文献
888.
猪、禽安全生产中主要病原菌耐药性检测及控制技术研究进展 总被引:1,自引:0,他引:1
国内外研究及本课题组的调查表明,猪、禽养殖中主要病原菌的耐药性日趋严重,细菌产生耐药性的机理复杂多样.而药性的检测技术在常规药敏试验的基础上,国内外学者及本课题组已将质粒指纹图谱,PCR,SSCP,核酯探针等分子生物学技术用于耐药性检测.本文还综述和提出了加强兽药管理、制定用药规范、研究质粒消除技术、开发出针对性疫苗、益生素、噬菌体制剂等一系列耐药性的控制技术. 相似文献
889.
Solke H. De Boer 《European journal of plant pathology / European Foundation for Plant Pathology》2003,109(9):893-899
Erwinia carotovora and Erwinia chrysanthemi are the two most important soft rotting bacteria of commercially-grown plants. They are genetically diverse as is evident from polymorphisms in the pel and recA genes as well as in rrn, the ribsomal gene cluster. Subpopulations grouped into biovars, pathovars, or subspecies associated with various hosts and in different geographic regions suggest specialization in host preference and/or survival in diverse environments. Previous characterization of the pectolytic erwinias as opportunistic pathogens is being replaced by a realization that this group of bacteria exhibits a sophisticated repertoire of pathogenicity and virulence genes and regulators. The presence of an entire hrp gene cluster and associated type III secretion system, and global regulators which regulate virulence determinants such as exoenzyme production and motility, attest to a highly specialized pathogen. The fact that production of extracellular plant cell wall-degrading enzymes are coordinately activated by the diffusible signal molecule N-acyl-homoserine lactone in a population density-dependent manner may explain the occurrence of pectolytic erwinia in asymptomatic plant tissues. Transgenic plants expressing bacterial quorum-sensing signal molecules modulate this sensory system and exhibit resistance to soft rot infection. The pectolytic erwinias, being significant plant pathogens that are neither of quarantine concern nor a human health hazard while readily isolated from field sources, make an ideal model for investigating the genetic basis of plant pathogenesis and environmental fitness. 相似文献
890.
用传统的方法进行细菌的鉴定分类,工作量大,而且完全靠人的记忆和查阅资料,大大影响了工作效率及鉴定的准确性。 本研究的基本设想在于将汉化微型计算机应用于兽医细菌鉴定。文章将与兽医有关的28属,4亚属中的119种细菌的68种特性搜集归纳后,输入微机,贮存于磁盘内,鉴定时计算机可根据要求自动进行比较。实验室中的具有一定文化程度的非计算机专业工作人员只须稍加训练既可使用本程序。如果输入数据足够,此程序的鉴定符合率达100%。 相似文献