全文获取类型
收费全文 | 7928篇 |
免费 | 499篇 |
国内免费 | 581篇 |
专业分类
林业 | 665篇 |
农学 | 578篇 |
基础科学 | 351篇 |
1290篇 | |
综合类 | 3708篇 |
农作物 | 305篇 |
水产渔业 | 479篇 |
畜牧兽医 | 1007篇 |
园艺 | 261篇 |
植物保护 | 364篇 |
出版年
2024年 | 55篇 |
2023年 | 200篇 |
2022年 | 324篇 |
2021年 | 304篇 |
2020年 | 355篇 |
2019年 | 379篇 |
2018年 | 229篇 |
2017年 | 339篇 |
2016年 | 442篇 |
2015年 | 461篇 |
2014年 | 523篇 |
2013年 | 496篇 |
2012年 | 631篇 |
2011年 | 637篇 |
2010年 | 470篇 |
2009年 | 459篇 |
2008年 | 403篇 |
2007年 | 448篇 |
2006年 | 332篇 |
2005年 | 288篇 |
2004年 | 214篇 |
2003年 | 176篇 |
2002年 | 131篇 |
2001年 | 107篇 |
2000年 | 85篇 |
1999年 | 81篇 |
1998年 | 59篇 |
1997年 | 65篇 |
1996年 | 51篇 |
1995年 | 55篇 |
1994年 | 43篇 |
1993年 | 39篇 |
1992年 | 20篇 |
1991年 | 31篇 |
1990年 | 18篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1956年 | 2篇 |
排序方式: 共有9008条查询结果,搜索用时 15 毫秒
931.
932.
民勤沙拐枣克隆种群构件结构及与环境因子的灰色关联分析 总被引:3,自引:0,他引:3
引入"构件"一词来表述植物体的不同组分,并在此基础上将其进一步发展为种群构件理论,极大地推动了植物种群生态学的发展(Bazzaz et al.,1978;Halle et al.,1978;Harper,1977;1980;钟章成,1992)。对木本植物而言,其地上部分枝或茎的顶端分生组织和侧生分生组织通过不断重复的、持续的活动产生新的分枝,构成了复杂的枝系构件和多样的外部形态特征。克隆种群对环境因子的反应首先表现在种群个体的构件结构上,对克隆植物构件的统计研究可涉及个体(基株)、分株和枝系3个水平(董鸣,1997),从构件间及其与环境因子的相 相似文献
933.
Maddox TW Pinchbeck GL Clegg PD Wedley AL Dawson S Williams NJ 《Equine veterinary journal》2012,44(3):297-303
Reasons for performing study: The increasing prevalence of antimicrobial resistant bacteria such as antimicrobial‐resistant and extended spectrum β‐lactamase (ESBL)‐producing Escherichia coli represents a significant problem for human and veterinary medicine. Despite this, the risk factors for faecal carriage of such bacteria by horses in the UK, particularly those in the wider community, have not been well described. Objectives: To characterise the risk factors for faecal carriage of antimicrobial‐resistant E. coli amongst horses in the mainland UK. Methods: A cross‐sectional study of horses recruited by 65 randomly selected equine veterinary practices was conducted, with a faecal sample collected and self‐administered questionnaire completed by the horse owner. Faecal samples were cultured for antimicrobial‐resistant E. coli, with isolates confirmed as E. coli having their antimicrobial resistance profile determined. Multilevel, multivariable logistic regression models were used to investigate risk factors for the carriage of antimicrobial‐resistant E. coli in the sample population. Results: Faecal samples and completed questionnaires were obtained for 627 horses located on 475 premises. Recent hospitalisation, contact with specific types of nonequid animals, the type of premises, the surrounding land use, the reason for veterinary treatment received in the last 6 months and antimicrobial treatment in the previous 10 days were identified as risk factors for many of the antimicrobial‐resistance outcomes considered. Being stabled on the same yard as a recently hospitalised horse was identified as a risk factor for increased risk of carriage of ESBL‐producing E. coli. Conclusions and potential relevance: Increasing antimicrobial resistance may have significant health implications for the horse population of Great Britain. This form of epidemiological investigation highlights potential risk factors that may be controlled to limit the extent of the problem. 相似文献
934.
935.
土壤铜形态与环境因素的关系及其对黑麦草生长的影响 总被引:1,自引:0,他引:1
采用盆栽试验研究酸度与氮素水平对土壤易溶态铜形态的影响,以及土壤铜含量与形态对黑麦草生长的影响。结果表明,土壤水溶态铜、有机碳结合态铜、离子态铜与铜处理水平呈极显著正相关关系,相关系数分别达到0.70、0.96、0.61。土壤酸度影响土壤中各形态铜的含量,随pH值降低土壤水溶态铜、离子态铜均显著增加,在pH4.7土壤上二者的含量随铜处理浓度的不同分别为pH6.0土壤上的1.6~6.3倍和39~148倍,两种土壤上水溶态铜、离子态铜含量差异达显著水平。铜处理水平、水溶态铜、有机碳结合态铜、离子态铜含量均强烈影响黑麦草的生长和其对铜的吸收,牧草鲜重与各形态铜呈极显著负相关,相关系数分别为-0.73、-0.76、-0.71、-0.72,而植株铜含量则与各形态铜间呈极显著正相关关系,相关系数分别为0.61、0.87、0.56、0.87。土壤氮素水平影响土壤溶解有机碳的含量,但对土壤各种铜的形态及牧草对铜的吸收并无显著影响。 相似文献
936.
Fuller W Bazer Gwonhwa Song Jinyoung Kim Kathrin A Dunlap Michael Carey Satterfield Gregory A Johnson Robert C Burghardt 《畜牧与生物技术杂志(英文版)》2012,3(3):109-129
There is a dialogue between the developing conceptus (embryo-fetus and associated placental membranes) and maternal uterus which must be established during the peri-implantation period for pregnancy recognition signaling, implantation, regulation of gene expression by uterine epithelial and stromal cells, placentation and exchange of nutrients and gases. The uterus provide a microenvironment in which molecules secreted by uterine epithelia or transported into the uterine lumen represent histotroph required for growth and development of the conceptus and receptivity of the uterus to implantation. Pregnancy recognition signaling mechanisms sustain the functional lifespan of the corpora lutea (CL) which produce progesterone, the hormone of pregnancy essential for uterine functions that support implantation and placentation required for a successful outcome of pregnancy. It is within the peri-implantation period that most embryonic deaths occur due to deficiencies attributed to uterine functions or failure of the conceptus to develop appropriately, signal pregnancy recognition and/or undergo implantation and placentation. With proper placentation, the fetal fluids and fetal membranes each have unique functions to ensure hematotrophic and histotrophic nutrition in support of growth and development of the fetus. The endocrine status of the pregnant female and her nutritional status are critical for successful establishment and maintenance of pregnancy. This review addresses the complexity of key mechanisms that are characteristic of successful reproduction in sheep and pigs and gaps in knowledge that must be the subject of research in order to enhance fertility and reproductive health of livestock species. 相似文献
937.
938.
939.
为了研究钦州市猪链球菌2型(SS2)的毒力因子分布特征,采用多重PCR方法对从我市健康猪扁桃体分离的11株SS2相关毒力基因——荚膜多糖(Cps2J),溶菌酶释放蛋白(Mrp),胞外蛋白因子(EF),溶血素(Sly),进行毒力基因检测。检测结果显示:毒力基因型为Mrp+epf+Sly+共有8株,毒力基因型为Mrp+epf+Sly-共有1株,这两种毒力基因型可归为强毒力基因型,占此次健康猪源毒株的81.8%;另外Mrp-epf-Sly-共有2株,属于弱毒和无毒基因型,占健康猪源毒株的18.2%。通过结果分析,预示我市目前SS2的主要流行菌株是同时具有4种毒力因子的高致病性菌株。 相似文献
940.
《Scandinavian Journal of Forest Research》2012,27(1-4):313-325
A simulation model was used to predict the spatial distribution of direct and diffuse photosynthetically active radiation below a heterogenous canopy of a Pinus sylvestris stand in eastern Finland. Seedling growth was related to both measured and predicted radiation. The model predicted rather well the overall pattern of radiation distribution beneath the canopy. All the growth parameters of Pinus sylvestris seedlings (height, current height increment and mean height increment) correlated positively with the amount of both measured and predicted radiation. The correlation between seedling growth and irradiance was better for predicted diffuse radiation than for total radiation. This was probably because diffuse radiation, being symmetrically distributed around trees, correlates more strongly than direct radiation with other factors affecting seedling growth. 相似文献