全文获取类型
收费全文 | 1095篇 |
免费 | 102篇 |
国内免费 | 4篇 |
专业分类
林业 | 32篇 |
农学 | 29篇 |
基础科学 | 12篇 |
130篇 | |
综合类 | 166篇 |
农作物 | 38篇 |
水产渔业 | 111篇 |
畜牧兽医 | 519篇 |
园艺 | 25篇 |
植物保护 | 139篇 |
出版年
2021年 | 14篇 |
2020年 | 23篇 |
2019年 | 15篇 |
2018年 | 20篇 |
2017年 | 24篇 |
2016年 | 20篇 |
2015年 | 20篇 |
2014年 | 25篇 |
2013年 | 55篇 |
2012年 | 61篇 |
2011年 | 62篇 |
2010年 | 40篇 |
2009年 | 28篇 |
2008年 | 66篇 |
2007年 | 58篇 |
2006年 | 54篇 |
2005年 | 52篇 |
2004年 | 44篇 |
2003年 | 56篇 |
2002年 | 46篇 |
2001年 | 29篇 |
2000年 | 22篇 |
1999年 | 31篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1974年 | 8篇 |
1973年 | 10篇 |
1972年 | 7篇 |
1968年 | 6篇 |
1966年 | 11篇 |
1963年 | 6篇 |
1961年 | 6篇 |
排序方式: 共有1201条查询结果,搜索用时 31 毫秒
1.
2.
3.
4.
Landscape Ecology - Maintaining biodiversity in multifunction landscapes is a significant challenge. Planning for the impacts of change requires knowledge of how species respond to landscape... 相似文献
5.
6.
7.
8.
The performance (survival and growth) of Douglas-fir (Pseudotsuga menziesii Mirb. Franco.) seedlings planted in minimally disturbed, scalped, and bedded soils, both with and without herbicidal control of weeds, were compared. Douglas-fir growing for 3 years in bedded soils treated with herbicide were heavier, taller, and had deeper root systems than trees growing in other preparations. Scalping did not improve seedling performance when compared to minimally disturbed soils. Soils rich in organic matter benefited tree growth. Competing vegetation in raised beds was detrimental to seedling performance. 相似文献
9.
Lloyd J Bird MI Vellen L Miranda AC Veenendaal EM Djagbletey G Miranda HS Cook G Farquhar GD 《Tree physiology》2008,28(3):451-468
To estimate the relative contributions of woody and herbaceous vegetation to savanna productivity, we measured the 13C/12C isotopic ratios of leaves from trees, shrubs, grasses and the surface soil carbon pool for 22 savannas in Australia, Brazil and Ghana covering the full savanna spectrum ranging from almost pure grassland to closed woodlands on all three continents. All trees and shrubs sampled were of the C3 pathway and all grasses of the C4 pathway with the exception of Echinolaena inflexa (Poir.) Chase, a common C3 grass of the Brazilian cerrado. By comparing the carbon isotopic compositions of the plant and carbon pools, a simple model relating soil delta 13C to the relative abundances of trees + shrubs (woody plants) and grasses was developed. The model suggests that the relative proportions of a savanna ecosystem's total foliar projected cover attributable to grasses versus woody plants is a simple and reliable index of the relative contributions of grasses and woody plants to savanna net productivity. Model calibrations against woody tree canopy cover made it possible to estimate the proportion of savanna productivity in the major regions of the world attributable to trees + shrubs and grasses from ground-based observational maps of savanna woodiness. Overall, it was estimated that 59% of the net primary productivity (Np) of tropical savannas is attributable to C4 grasses, but that this proportion varies significantly within and between regions. The C4 grasses make their greatest relative contribution to savanna Np in the Neotropics, whereas in African regions, a greater proportion of savanna Np is attributable to woody plants. The relative contribution of C4 grasses in Australian savannas is intermediate between those in the Neotropics and Africa. These differences can be broadly ascribed to large scale differences in soil fertility and rainfall. 相似文献
10.
Sonia Graham Heather M. McGinness Deborah A. O’Connell A. O. Nicholls 《Small-Scale Forestry》2008,7(2):183-203
Investment in small and large-scale revegetation in Australia is growing in response to concerns regarding the sustainability
and productivity of agricultural landscapes. Site preparation and management––such as soil cultivation, weed control, fertilising,
mulching, use of treeguards and watering––are major costs associated with small-scale revegetation. The aim of this study
has been to investigate local revegetation knowledge and practices to determine the usefulness of each management practice
for achieving success and to determine whether some practices are more suited to particular climatic zones. A national online
revegetation survey was conducted to ascertain current small-scale revegetation practices and the factors that drive these
choices. Management practices were found to be strongly associated with climate. Mulch, fertiliser, weed control and watering
were applied more frequently in higher rainfall and higher temperature zones. Soil cultivation and treeguards were used more
frequently in lower rainfall and lower temperature zones. These findings suggest that there may be some benefit in modifying
existing revegetation guidelines to reflect climatic zones and management flexibility.
相似文献
Sonia GrahamEmail: |