全文获取类型
收费全文 | 2504篇 |
免费 | 187篇 |
国内免费 | 273篇 |
专业分类
林业 | 209篇 |
农学 | 298篇 |
基础科学 | 140篇 |
309篇 | |
综合类 | 1107篇 |
农作物 | 177篇 |
水产渔业 | 113篇 |
畜牧兽医 | 424篇 |
园艺 | 63篇 |
植物保护 | 124篇 |
出版年
2024年 | 11篇 |
2023年 | 68篇 |
2022年 | 81篇 |
2021年 | 116篇 |
2020年 | 124篇 |
2019年 | 111篇 |
2018年 | 96篇 |
2017年 | 119篇 |
2016年 | 151篇 |
2015年 | 134篇 |
2014年 | 141篇 |
2013年 | 176篇 |
2012年 | 175篇 |
2011年 | 186篇 |
2010年 | 159篇 |
2009年 | 149篇 |
2008年 | 134篇 |
2007年 | 165篇 |
2006年 | 116篇 |
2005年 | 87篇 |
2004年 | 64篇 |
2003年 | 62篇 |
2002年 | 47篇 |
2001年 | 53篇 |
2000年 | 28篇 |
1999年 | 36篇 |
1998年 | 26篇 |
1997年 | 23篇 |
1996年 | 17篇 |
1995年 | 18篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 19篇 |
1990年 | 11篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1979年 | 1篇 |
1956年 | 4篇 |
1955年 | 1篇 |
排序方式: 共有2964条查询结果,搜索用时 330 毫秒
1.
面向养殖水体,传统光谱法对化学需氧量(Chemical Oxygen Demand,COD)检测模型构建的基础:源域(现有样本库)与目标域(检测地水体)间光谱数据独立同分布。但是当源域与目标域分布间存在差异时,由源域得到的低误差模型常在目标域上表现下滑。针对该问题,提出面向UV Vis光谱的域对抗训练网络(DAUVwpNet),将分布不同的源域和目标域数据映射至相同分布的特征空间中,使其在该空间的分布距离尽可能接近,从而在特征空间中对源域训练的目标函数也可以迁移至目标域上,以降低模型在目标域的误差。试验表明:面向同一批测试数据,DAUVwpNet的预测误差为0.78,要低于传统模型的预测误差(0.85);DAUVwpNet预测值与实测值间相关系数为0.95,要高于传统模型的相关系数(0.89)。表明了该网络能够较好对齐两域特征空间数据分布,降低因分布差异带来的COD检测误差。 相似文献
2.
CIDR、PMSG、FSH联合使用对初产供体羊Borderdale(波德代)3♂15♀、Poll Dorset(无角陶赛特)5♂18♀和Ger-man Mutton Merino(德国肉毛兼用美利奴—德美)3♂15♀进行同期发情和超数排卵。同期化发情波德代、无角陶赛特和德美分别为100.00%、88.89%和93.33%,羊只同期化发情时间经历和各时间点分布3个品种各有特点。超数排卵效果品种间存在差异,波德代、无角陶赛特、德美分别为6.60±2.97(枚)、3.63±2.25(枚)、5.50±3.32(枚),波德代极显著地高于无角陶赛特(P<0.01)。超排有效率波德代、无角陶赛特、德美分别为100.00%、87.50%、92.86%。未受精卵波德代极显著地高于德美羊和无角陶赛特羊(P<0.01)。胚胎总数德美羊极显著地高于波德代(P<0.01)。有效胚胎波德代羊、无角陶赛特羊、德美羊分别为2.40±2.31、2.75±2.05、4.07±3.79,德美极显著地高于波德代(P<0.01)。同一方法进行同期化发情,羊只经历时间和各时间点均衡分布能否有效控制是同期发情的焦点问题,是有效胚胎数目差异的主导因素之一。 相似文献
3.
South-Westerm blot mapping是一种结合Western blotting和Southern blotting某些特点的方法.本文介绍用其成功地观察到锥虫核蛋白中DNA结合蛋白的情况,并对一个分子量在40000左右、于较严谨条件下与DNA结合的核蛋白进行了特性鉴定.该蛋白等量地存在于锥虫的前循环期和血液期,对双链DNA有较大的亲和力,并能与酵母菌复制起始片段结合.本文还介绍了锥虫细胞核的提取技术和核蛋白的制备技术. 相似文献
4.
荔枝生产相关的水分生理指标远程监测研究 总被引:2,自引:0,他引:2
利用植物远程监测系统对荔枝园中的大气温湿度、土壤湿度、光照强度、大气蒸汽压差(VPD)等环境因子和茎干直径微变化、果实生长、叶片温度等树体生理指标进行了监测,发现该系统能准确及时并无伤害地记录他们的实时和周期性变化。据获得的数据初步表明,当果实处于快速膨大期,主茎的加粗生长明显缓慢,一旦果实采收后,茎干加粗生长则有一个迅速上升的变化;当土壤湿度高于33%(v/v)时,主茎的生长受到明显的抑制;VPD白天上升,夜间下降,当夜间VPD始终高于0,就形成所谓的“夜间干燥”,VPD的这种变化对荔枝主茎和果实的生长以及叶气温差(LATD)都有较大的影响,如主茎和果实的日间收缩量随VPD的增大而增大,夜间空气干燥不但抑制了主茎生长,也使日最大LATD下降。据此认为,果实和茎干的生长之间存在竞争关系,土壤湿度过高或者夜间空气干燥对荔枝的生长不利。 相似文献
5.
Seasonal variation in pigmentation and anthocyanidin phenetics in commercial Eustoma flowers 总被引:2,自引:0,他引:2
A. F. M. Jamal Uddin Fumio Hashimoto Toshiki Miwa Katsuhiro Ohbo Yusuke Sakata 《Scientia Horticulturae》2004,100(1-4):103-115
The seasonal change in petal color and pigmentation of 29 commercial Eustoma cultivars was studied. The flowers are basically divided into four groups according to the major anthocyanidin phenotype in association with petal coloration, i.e., delphinidin (Dp)-based (purple flower), cyanidin (Cy)-based (reddish purple flower), pelargonidin (Pg)-based (pink flower), and none (white flower) groups. The constitution of petal anthocyanidins was not changed by forcing treatment in most of the flowers. Lightness (L*) and chroma (C*, color saturation) showed a change along with the increase/decrease of hue angle difference (ΔH*), thus simultaneously the chromatic tonalities tended to move to redder and bluer, respectively. Floral pigment clustering described two flower groups in a dendrogram, based on anthocyanidin constitutions as phenetic markers, which are apparently the Dp- and Pg-based phenotypes of anthocyanidin syntheses. The Cy-based flowers made a subcluster with the Pg-based flowers, indicating a close relationship in the biosynthesis of the two anthocyanidins, and suggesting the Dp- and Pg-syntheses complement one another. 相似文献
6.
7.
The impact of truncating data on the predictive ability for single‐step genomic best linear unbiased prediction
下载免费PDF全文
![点击此处可从《Zeitschrift für Tierzüchtung und Züchtungsbiologie》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jeremy T. Howard Tom A. Rathje Caitlyn E. Bruns Danielle F. Wilson‐Wells Stephen D. Kachman Matthew L. Spangler 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2018,135(4):251-262
Simulated and swine industry data sets were utilized to assess the impact of removing older data on the predictive ability of selection candidate estimated breeding values (EBV) when using single‐step genomic best linear unbiased prediction (ssGBLUP). Simulated data included thirty replicates designed to mimic the structure of swine data sets. For the simulated data, varying amounts of data were truncated based on the number of ancestral generations back from the selection candidates. The swine data sets consisted of phenotypic and genotypic records for three traits across two breeds on animals born from 2003 to 2017. Phenotypes and genotypes were iteratively removed 1 year at a time based on the year an animal was born. For the swine data sets, correlations between corrected phenotypes (Cp) and EBV were used to evaluate the predictive ability on young animals born in 2016–2017. In the simulated data set, keeping data two generations back or greater resulted in no statistical difference (p‐value > 0.05) in the reduction in the true breeding value at generation 15 compared to utilizing all available data. Across swine data sets, removing phenotypes from animals born prior to 2011 resulted in a negligible or a slight numerical increase in the correlation between Cp and EBV. Truncating data is a method to alleviate computational issues without negatively impacting the predictive ability of selection candidate EBV. 相似文献
8.
Kaarina Matilainen Ismo Strandén Gert Pedersen Aamand Esa A. Mäntysaari 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2018,135(5):337-348
Joint Nordic (Denmark, Finland, Sweden) genetic evaluation of female fertility is currently based on the multiple trait multilactation animal model (BLUP). Here, single step genomic model (ssGBLUP) was applied for the Nordic Red dairy cattle fertility evaluation. The 11 traits comprised of nonreturn rate and days from first to last insemination in heifers and first three parities, and days from calving to first insemination in the first three parities. Traits had low heritabilities (0.015–0.04), but moderately high genetic correlations between the parities (0.60–0.88). Phenotypic data included 4,226,715 animals with records and pedigree 5,445,392 animals. Unknown parents were assigned into 332 phantom parent groups (PPG). In mixed model equations animals were associated with PPG effects through the pedigree or both the pedigree and genomic information. Genotype information of 46,914 SNPs was available for 33,969 animals in the pedigree. When PPG used pedigree information only, BLUP converged after 2,420 iterations whereas the ssGBLUP evaluation needed over ten thousand iterations. When the PPG effects were solved accounting both the pedigree and the genomic information, the ssGBLUP model converged after 2,406 iterations. Also, with the latter model breeding values by ssGBLUP and BLUP became more consistent and genetic trends followed each other well. Models were validated using forward prediction of the young bulls. Reliabilities and variance inflation of predicted genomic breeding values (values for parent averages in brackets) for the 11 traits ranged 0.22–0.31 (0.10–0.27) and 0.81–0.95 (0.83–1.06), respectively. The ssGBLUP model gave always higher validation reliabilities than BLUP, but largest increases were for the cow fertility traits. 相似文献
9.
为了从根本上了解区域内部生态系统的网络运行效率和发展潜力的空间差异,采用EMA(能值分析)方法,以福建省县域单位农业生态系统为研究对象,建立反映农业生态经济系统4大层面的13项能值指标,并运用主成分分析法筛选出主要能值评价指标,结合G IS(地理信息系统)技术,对该省67个县(市)样本的农业各层面综合发展水平进行等级划分和空间差异分析。结果表明:沿海与内陆县(市)在农业发展各层面上都存在着明显的空间差异;沿海低地县(市)在农业经济发展水平上和农民生活水平上有绝对优势,但这种优势可持续力很弱;山区贫困县(市)在农业自然环境条件与可持续发展性能上有明显的区域比较优势。分析结果为区域农业生态规划管理与决策提供客观的数据依据,对区域产业布局与可持续发展战略有一定的实际意义。 相似文献
10.
不同基因型小麦NDVI值与产量的关系 总被引:4,自引:0,他引:4
在旱地保护性耕作条件下,以11个不同基因型小麦(Triticum aestivumL.)品种为材料,研究了植被归一化指数(NDVI,Normalized difference vegetation index)与产量构成和抗旱性的关系。结果表明,不同基因型小麦各生育期的归一化植被指数(NDVI)存在显著性差异;小麦抽穗期NDVI值与其干旱产量指数呈正相关,抽穗期NDVI值较高的小麦品种其干旱产量指数也较高;本试验条件下,石麦15、石家庄8号和烟Blu6439三个小麦品种的干旱产量指数较高。 相似文献