全文获取类型
收费全文 | 1333篇 |
免费 | 92篇 |
国内免费 | 121篇 |
专业分类
林业 | 102篇 |
农学 | 53篇 |
基础科学 | 25篇 |
123篇 | |
综合类 | 662篇 |
农作物 | 98篇 |
水产渔业 | 120篇 |
畜牧兽医 | 158篇 |
园艺 | 167篇 |
植物保护 | 38篇 |
出版年
2024年 | 13篇 |
2023年 | 28篇 |
2022年 | 61篇 |
2021年 | 74篇 |
2020年 | 63篇 |
2019年 | 54篇 |
2018年 | 47篇 |
2017年 | 66篇 |
2016年 | 42篇 |
2015年 | 64篇 |
2014年 | 81篇 |
2013年 | 103篇 |
2012年 | 91篇 |
2011年 | 98篇 |
2010年 | 105篇 |
2009年 | 106篇 |
2008年 | 84篇 |
2007年 | 110篇 |
2006年 | 61篇 |
2005年 | 50篇 |
2004年 | 25篇 |
2003年 | 8篇 |
2002年 | 25篇 |
2001年 | 24篇 |
2000年 | 29篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 6篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1969年 | 1篇 |
1962年 | 1篇 |
1955年 | 2篇 |
1931年 | 1篇 |
排序方式: 共有1546条查询结果,搜索用时 62 毫秒
991.
992.
AIM: The aim of this study was to evaluate, under farm conditions, the use of a teat sealant in addition to whole herd dry cow antibiotic therapy on the risk of clinical mastitis in dairy cattle at pasture, and to evaluate the impact of dry period length on that risk and the impact of the teat sealant on that risk.METHODS: Dairy cows in three herds which used routine whole herd antibiotic therapy were randomly assigned to receive either treatment with an internal teat sealant (n=322) or no additional treatment (n=313) at drying-off between March and May 2010. All clinical mastitis cases during the dry period and to the end of the subsequent lactation were recorded by farm staff; factors affecting risk of clinical mastitis were then analysed using a Cox proportional hazards model.RESULTS: Median duration of the dry period was 112 days with >25% of cows having a dry period >130 days. The incidence risk of mastitis during lactation for cows treated with teat sealant was 9.9 (95% CI=6.9–13.7) cases per 100 cows compared with 17.9 (95% CI=13.8–22.6) cases per 100 cows for cows treated with antibiotic alone. The addition of a teat sealant to dry cow antibiotic therapy decreased the risk of clinical mastitis only in the first 33 days after calving (Hazard risk 0.24 (95% CI=0.12–0.48)). Length of dry period did not significantly affect the risk of clinical mastitis, or the effect of adding teat sealant to dry cow antibiotic therapy on the risk of clinical mastitis.CONCLUSIONS: In these herds where, based on the mastitis history, whole herd antibiotic therapy had been recommended, the use of a teat sealant significantly reduced the risk of clinical mastitis. This effect was limited to the first 33 days after calving; subsequently there was no significant effect of treatment. There was no effect of dry period length on risk of clinical mastitis, nor any significant interaction with treatment.CLINICAL RELEVANCE: Combination therapy with teat sealant and antibiotic was effective under New Zealand conditions in herds using whole herd antibiotic treatment at drying off. Teat sealant reduced risk of clinical mastitis in cattle with dry periods substantially longer than 100 days, and there was no evidence that this effect changed as dry period length increased. 相似文献
993.
Abstract AIM: To determine whether there is a seasonal variation in the phenotypic hip score of dogs born in New Zealand as assessed by the New Zealand Veterinary Association (NZVA) canine hip dysplasia (CHD) scheme. METHODS: Data from dogs born in New Zealand between 1988 and 2009 that have been scored for CHD were retrospectively evaluated for the effect of month of birth on radiographic phenotype. Data included both the total score and the subtotal score, comprising Norberg's angle, the subluxation score and changes to the cranial acetabular edge, for each dog. Datasets were created for all breeds combined and for the four most populous breeds using the scheme (German Shepherd dog, Labrador Retriever, Golden Retriever and Rottweiler) and stratified according to month of birth and season. Due to the skewed nature of the data, a Kruskal–Wallis Rank Sum test was used to test for statistical significance. Additionally, χ2 analysis was performed using the median of each dataset (proportion above/below the median). The null hypothesis was that there would be no effect of month of birth, and hence seasonality, on hip phenotype for dogs born and scored in New Zealand by the NZVA. RESULTS: For all breeds combined, month of birth had an effect on total and subtotal NZVA CHD scores (p<0.001) with a lower total hip score in the autumn months of March and April than other months. When individual large breed data were analysed, there was an effect of month of birth on total and subtotal scores for the Labrador Retriever and the Rottweiler (p≤0.05), but not the German Shepherd dog or Golden Retriever breeds. CONCLUSIONS: Being born in the autumn was associated with a protective effect on hip phenotype in some breeds. These results suggest that weather and/or another seasonal factor may have a significant environmental effect on the phenotype of the coxofemoral joint. CLINICAL RELEVANCE: The protective effect of being born in autumn suggests that a decreased level of exercise during subsequent development over winter may positively impact on final coxofemoral joint conformation. Whilst statistically significant, the magnitude of the sparing effect is not likely to be clinically relevant. However, this study, in concert with other studies, may suggest that the effects of exercise can be manipulated to improve hip phenotype. 相似文献
994.
研究不同光质、光照条件下,红平菇(Pleurotus djamor)菌丝体、子实体生长发育情况.结果表明,黑暗条件有利于红平菇菌丝体生长;白光和自然光照条件下,红平菇子实体生长发育最好、子实体数目多、成菇率高、外观整齐一致、颜色鲜艳,具有较好的商业应用价值;红平菇子实体生长发育最优光照条件为40W散射白光、每天光照8h,光照强度为1 020 lx. 相似文献
995.
996.
从已发表论文和相关数据库中收集到与ABA代谢有关数据,构建脱落酸代谢网络图;根据信号传递网络性质,获得ABA信号传递中所需要的信号分子、受体、第二信使和激酶等信息.应用CellNetAnalyzer软件分析ABA信号传递网络,获得了信号传递路径与网络冗余性,为研究植物ABA代谢调控机理提供依据. 相似文献
997.
耕种方式对小麦产量的影响 总被引:1,自引:0,他引:1
以矮抗58为试材,采取旋耕后直接播种( CK)、旋耕+耙实后播种、深耕(25 cm 左右)+旋耕后播种、深耕(25 cm左右)+耙实后播种4种耕种方式处理,研究了不同耕种方式对小麦生育进程、干物质积累动态、群体茎蘖数量动态以及小麦穗粒数、千粒重和产量的影响。结果表明:不同耕种方式对小麦生长发育进程、干物质积累动态、茎蘖数量变化动态以及穗粒数和千粒重均无显著影响,但对籽粒产量的影响达到了极显著水平。深耕(25 cm 左右)和耙实后播种均对小麦增产作用非常明显。采取深耕(25 cm左右)+耙实后播种方式小麦产量最高,在生产上具有很好的推广应用价值。 相似文献
998.
敏捷厚结猛蚁Pachycondyla astuta Smith、聚纹双刺猛蚁Diacamma rugosum(Le Guillou)、横纹齿猛蚁Odonto-ponera transversa(Smith)和猎镰猛蚁Harpegnathos venator(Smith)是我国东部和南部地区比较常见的猛蚁,可捕食林木白蚁,是一类潜在的天敌昆虫.通过挖巢的方法对这4种猛蚁的筑巢环境、巢穴结构和巢内生物进行了研究.结果表明,4种猛蚁的巢穴均为地下巢,多建在橡胶林、荔枝林等林间空地;结构比较简单,深度一般不超过0.6 m,巢室仅有几个至数十个,在土壤中分布无规则至分层排列.巢穴内部或周围常可见到膜翅目、等翅目昆虫以及土壤小型多足类和等足类动物. 相似文献
999.
依据2010年4月、7月和11月对浙江中部近海上升流海域进行的海洋调查资料,运用定量、定性方法,探讨了上升流对该海域浮游动物生态类群分布的影响.结果表明:3个季节共鉴定浮游动物64种,桡足类占主要优势,包括5个生态类群,分别是暖温带近海种、暖温带外海种、亚热带近海种、亚热带外海种和热带大洋种.在种类数组成上,春季以暖温带近海种为主,夏季则是亚热带近海种和亚热带外海种居多,秋季也是亚热带种居多,其中夏季暖温带种种类数要高于春季和秋季,这一现象与同时期东黄海沿海有所不同,主要是由于上升流将一些在海洋底部度夏的暖温种带至海洋表面造成的.此外,3个季节生态类群都是以近海种为主,表明沿岸流是影响这一海域的最主要的水团.在丰度组成上,4月暖温带近海种占总丰度的98.79%,7月暖温带近海种也是组成丰度的重要部分,10月则是亚热带近海种丰度最高.丰度组成所反映的规律与种类数组成规律一致.上升流的存在导致夏季近海暖温带种大量出现,是影响这一海域浮游动物生态类群组成的重要因素;受长江径流和椒江径流的影响,近海种成为主要生态类群,是这一海域浮游动物的一个重要的生态特征. 相似文献
1000.