全文获取类型
收费全文 | 4078篇 |
免费 | 383篇 |
国内免费 | 12篇 |
专业分类
林业 | 376篇 |
农学 | 173篇 |
基础科学 | 22篇 |
735篇 | |
综合类 | 214篇 |
农作物 | 222篇 |
水产渔业 | 540篇 |
畜牧兽医 | 1723篇 |
园艺 | 97篇 |
植物保护 | 371篇 |
出版年
2024年 | 7篇 |
2023年 | 41篇 |
2022年 | 105篇 |
2021年 | 204篇 |
2020年 | 216篇 |
2019年 | 246篇 |
2018年 | 254篇 |
2017年 | 254篇 |
2016年 | 220篇 |
2015年 | 153篇 |
2014年 | 204篇 |
2013年 | 270篇 |
2012年 | 307篇 |
2011年 | 329篇 |
2010年 | 152篇 |
2009年 | 164篇 |
2008年 | 188篇 |
2007年 | 196篇 |
2006年 | 151篇 |
2005年 | 101篇 |
2004年 | 107篇 |
2003年 | 111篇 |
2002年 | 116篇 |
2001年 | 69篇 |
2000年 | 65篇 |
1999年 | 33篇 |
1998年 | 19篇 |
1997年 | 14篇 |
1996年 | 18篇 |
1995年 | 14篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1973年 | 3篇 |
1969年 | 5篇 |
1968年 | 4篇 |
1948年 | 2篇 |
排序方式: 共有4473条查询结果,搜索用时 31 毫秒
101.
Measurements were carried out to survey the quantity of above- and below-ground biomass and its distribution of five Japanese
black pines (Pinus thunbergii Parl.) growing on a sandy soil. The roots, divided into diameter groups, were surveyed using two methods—soil coring and
excavation. Average dry weight of total biomass of the trees was 176,185 g. Roots represented 13.2%, below-ground stump 6.5%,
stem 70.4% and branches with needles 9.9% of total biomass. Roots made up about two thirds and stump one third of below-ground
biomass. Total length of below-ground biomass (except roots with diameter < 0.1 cm) was 479.1 m/tree. Roots with diameter
of 0.1–0.2 cm represented only 0.7% of below-ground biomass, however as much as 49.9% of their total length. Roots with diameter
over 10.0 cm constituted as much as 21.6% of below-ground biomass, however were only 0.3% of its total length. Root systems
had well developed tap roots to maximal depth of 231 cm. The results indicated that mass and length of roots with diameter
0.5–2.0 cm had a close correlation with branch mass. Mass and length of roots with diameter 2.0–10.0 cm closely correlated
to stem mass. Stem mass, root mass and root length closely correlated to DBH. A rather low correlation was found between DBH
and mass of branches and below-ground stump. DBH was a suitable variable for predicting total biomass. 相似文献
102.
Peterman William E. Winiarski Kristopher J. Moore Chloe E. Carvalho Carolina da Silva Gilbert Anthony L. Spear Stephen F. 《Landscape Ecology》2019,34(9):2197-2208
Landscape Ecology - Landscape resistance surfaces are often used to address questions related to movement, dispersal, or population connectivity. However, modeling landscape resistance is... 相似文献
103.
104.
105.
106.
107.
108.
Chung Yong Suk Silva Renato Rodrigues Park Minwoo Lee Sanghyeob 《Journal of Crop Science and Biotechnology》2019,22(1):17-20
Journal of Crop Science and Biotechnology - The ionizing radiation methods, including X-rays, gamma rays, and neutrons to create variation is well established and used in major crops. Many... 相似文献
109.
紫花苜蓿耗水规律及灌溉制度优化研究 总被引:1,自引:0,他引:1
为研究河套灌区紫花苜蓿的耗水规律,同时对现有灌溉制度进行优化,在田间试验的基础上,设置不同灌水水平对前两茬苜蓿进行了研究。结果表明:现蕾期和开花期是紫花苜蓿耗水的旺盛阶段,该阶段土壤水分亏缺会直接影响苜蓿产量的形成。通过多元线性回归的方法求解得到了两茬紫花苜蓿各生育期的敏感性系数,分别在0.103~0.731和0.041~0.375之间,且以现蕾期和开花期为最大,说明这两个生育阶段为苜蓿生长的关键阶段。以Jensen模型为基础,采用最小二乘法初步优化了两茬紫花苜蓿生育期内的灌溉制度,第1茬灌溉定额以1 400 m3/hm~2为宜,第2茬以2 300 m3/hm~2为宜,两茬灌水次数分别以4次和5次为最优。 相似文献
110.
Plant breeders have been trying to predict the performance of hybrids based on their parental performance. One application of molecular markers is its use in selection. The objectives were to map quantitative trait loci (QTL) and verify its congruence in maize lines and in their testcrosses and verify the possibility to select testcrosses from the predicted means of the lines by using information from markers. Two-hundred and fifty six lines and the testcrosses of these lines with two testers were evaluated in six environments, considering grain yield, plant lodging, days to anthesis and silking, anthesis-silking interval, plant and ear height and ear placement. QTL were mapped in the lines and in testcrosses and the predicted means of the lines were computed based on QTL effects and in all markers of the genome. The congruence of QTL detected in the lines and testcrosses were small for all traits. The correlations between the predicted means of the lines and the phenotypic means of the testcrosses ranged from low for grain yield to moderate for cycle and stature traits. The highest coincidences of the lines and selected testcrosses were observed for cycle and stature traits and the lowest for grain yield. Even by using molecular markers information, it is only possible to predict the testcrosses performance from the lines information to less complex traits and with reduced dominance effect. For complex traits and with pronounced dominance effect, information of markers must be obtained directly in the testcrosses, so they can be used for selection. 相似文献