全文获取类型
收费全文 | 2919篇 |
免费 | 665篇 |
国内免费 | 29篇 |
专业分类
林业 | 1119篇 |
农学 | 160篇 |
基础科学 | 392篇 |
401篇 | |
综合类 | 1081篇 |
农作物 | 180篇 |
水产渔业 | 16篇 |
畜牧兽医 | 111篇 |
园艺 | 71篇 |
植物保护 | 82篇 |
出版年
2025年 | 40篇 |
2024年 | 69篇 |
2023年 | 67篇 |
2022年 | 107篇 |
2021年 | 124篇 |
2020年 | 108篇 |
2019年 | 164篇 |
2018年 | 56篇 |
2017年 | 118篇 |
2016年 | 185篇 |
2015年 | 111篇 |
2014年 | 160篇 |
2013年 | 143篇 |
2012年 | 269篇 |
2011年 | 182篇 |
2010年 | 182篇 |
2009年 | 193篇 |
2008年 | 163篇 |
2007年 | 169篇 |
2006年 | 177篇 |
2005年 | 134篇 |
2004年 | 123篇 |
2003年 | 99篇 |
2002年 | 67篇 |
2001年 | 79篇 |
2000年 | 62篇 |
1999年 | 43篇 |
1998年 | 30篇 |
1997年 | 31篇 |
1996年 | 34篇 |
1995年 | 26篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 15篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1976年 | 1篇 |
排序方式: 共有3613条查询结果,搜索用时 0 毫秒
1.
2.
Daljit Singh Virk 《Journal of Crop Improvement》2017,31(1):1-24
The analysis of residuals computes general adaptabilities (GAs) and specific adaptabilities (SAs) of genotypes similar to combining ability analysis. The residual analysis is simple and robust being based on the first-degree statistics, and is assumption-free. A unique statistic of ratio of variances (VR) of residuals for individual genotypes allows comparing their stability. The residuals analysis of genotype × environment (GE) interactions was performed for grain yield (t ha?1) of 25 rice (Oryza sativa L.) genotypes, including two developed by marker-assisted selection for root traits quantitative trait loci (QTL), tested across 16 sites. Results were compared with the linear regression analysis for (i) full set of 16 sites showing adequacy of linear model and (ii) subset of nine-poor sites showing inadequacy of linear model. There was agreement between the two analyses for situation (i) but not for situation (ii) when the regression analysis fails because of nonlinearity but the residual analysis retains its validity. 相似文献
3.
Anna Karina R. Schmidt 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2017,67(5):416-424
Seed crops of white clover (Trifolium repens L.) are usually established with a cover crop. Provided sufficient light, white clover may compensate for low plant density by stoloniferous growth. Our objectives were (1) to compare spring barley or spring wheat used as cover crops for white clover and (2) to find the optimal seeding rate/row distance for white clover. Seven field trials were conducted in Southeast Norway from 2000 to 2003. Barley was seeded at 360 and 240 seeds m?2 and wheat at 525 and 350 seeds m?2. White clover was seeded perpendicularly to the cover crop at 400 seeds m?2/13 cm row distance or 200 seeds m?2/26 cm. Results showed that light penetration in spring and early summer was better in wheat than in barley. On average for seven trials, this resulted in 11% higher seed yield after establishment in wheat than in barley. The 33% reduction in cover crop seeding rate had no effect on white clover seed yield for any of the cover crops. Reducing the seeding rate/doubling the row distance of white clover had no effect on seed yield but resulted in slightly earlier maturation of the seed crop. 相似文献
4.
5.
黄土高原降水资源特征与林木适宜度研究 总被引:2,自引:4,他引:2
黄土高原位于干旱半干旱地区,水资源匮乏,如何根据当地的降水条件来确定适宜的植被类型是生态建设中的一个关键问题.通过对黄土高原68个气象台站1961-2000年逐月降水量的统计,结果表明:黄土高原的降水特征总体表现为年平均降水量区域差异大,由东南部的大于600 mm逐渐递减到西北部的不足200 mm;植物生长期间的降水占全年80%以上,且季节分配不均,表现为春旱、夏多、秋少.依据黄土高原的降水资源特征,从林地水量平衡理论出发,以生长季期间林地的水分收支状况来确定林木的适生程度,并以县为单位对黄土高原的林木适宜性进行分区.结果表明,黄土高原适宜于乔木林和灌木林的区域各占1/4左右. 相似文献
6.
We analyzed indices of gap dynamics, i.e. gap formation and gap closure rates as well as turnover rates, in a montane conifer forest in the temperate zone and asked: (1) Are the characteristics of gap dynamics comparable with those of other temperate forests? (2) Do gap dynamics exhibit temporal trends, and (3) if so, are they related to recent climate change? We also addressed methodological issues concerning the differences observed at differing temporal and spatial scales of the used datasets. Thus, we asked further how the indices of gap dynamics are influenced (4) by differences in the length of observation periods and (5) by differences in gap size categories included in the study? 相似文献
7.
8.
为了提高造林成活率,作者从选择合适的造林时间和造林树种,选择良种壮苗,因地整地、因势整地,覆盖地膜保温保墒,覆盖油桶保温防风防鼠兔危害等措施入手,使困难立地造林成活率有了显著地提高。 相似文献
9.
10.
在福建省大田梅林国有林场连续4年调查火炬松×马尾松、湿地松×马尾松杂种F1代以及马尾松纯种苗木造林早期生长情况,结果表明:幼树存活率在造林4年后趋于稳定,且火炬松×马尾松杂种F1存活率高于湿地松×马尾松。火炬松×马尾松、湿地松×马尾松杂种F1代和马尾松纯种3个树种4年生以下(含4年生)幼树的平均地径(胸径)、抽梢、树高生长总体大小依次为:火炬松×马尾松〉湿地松×马尾松〉马尾松纯种,但3个树种间差异均不显著。4年生(48个月)幼树火炬松×马尾松杂种F1代和马尾松纯种平均树高差异显著;50个月生幼树火炬松×马尾松杂种F1代和马尾松纯种间、湿地松×马尾松杂种F1代与马尾松纯种间差异显著,但火炬松×马尾松与湿地松×马尾松间差异不显著。 相似文献