全文获取类型
收费全文 | 1823篇 |
免费 | 121篇 |
专业分类
林业 | 197篇 |
农学 | 90篇 |
基础科学 | 9篇 |
619篇 | |
综合类 | 34篇 |
农作物 | 120篇 |
水产渔业 | 187篇 |
畜牧兽医 | 467篇 |
园艺 | 26篇 |
植物保护 | 195篇 |
出版年
2024年 | 4篇 |
2023年 | 16篇 |
2022年 | 22篇 |
2021年 | 46篇 |
2020年 | 50篇 |
2019年 | 35篇 |
2018年 | 87篇 |
2017年 | 95篇 |
2016年 | 85篇 |
2015年 | 71篇 |
2014年 | 88篇 |
2013年 | 120篇 |
2012年 | 171篇 |
2011年 | 156篇 |
2010年 | 88篇 |
2009年 | 65篇 |
2008年 | 124篇 |
2007年 | 127篇 |
2006年 | 98篇 |
2005年 | 82篇 |
2004年 | 76篇 |
2003年 | 67篇 |
2002年 | 47篇 |
2001年 | 14篇 |
2000年 | 11篇 |
1999年 | 13篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1983年 | 2篇 |
1977年 | 2篇 |
1974年 | 4篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1966年 | 4篇 |
1939年 | 2篇 |
1937年 | 8篇 |
1933年 | 2篇 |
1926年 | 4篇 |
1925年 | 2篇 |
1924年 | 2篇 |
1922年 | 4篇 |
1914年 | 2篇 |
1911年 | 2篇 |
1898年 | 1篇 |
排序方式: 共有1944条查询结果,搜索用时 234 毫秒
61.
62.
Javier Puntieri Javier Grosfeld Marina Stecconi Cecilia Brion María Marta Azpilicueta Leonardo Gallo Daniel Barthélémy 《Annals of Forest Science》2007,64(8):839-844
Shoot growth and dieback were compared among progenies of nursery-grown seedlings of Nothofagus obliqua belonging to seven progenies of the same provenance (Quila-Quina, Argentina). First-year shoots consisted of one growth unit (GU) and second-year shoots of one or two GUs. The probability of development of two GU was similar for all progenies. Progenies were different in terms of shoot size, terminal bud abscission, the extent of shoot dieback after shoot extension and the node of origin of the relay shoot on the first shoot. Plants with a second-year shoot consisting of two GUs had a thicker stem and more nodes than those with single-GU shoots. The selection of N. obliqua seed trees based on architectural traits suitable for forestry development at specific sites must contemplate variability among progenies and their probabilities of successful development under different conditions. 相似文献
63.
Pastur Guillermo Martínez Peri Pablo Luis Fernández María Cecilia Staffieri Gabriela Lencinas Mará Vanessa 《Journal of Forest Research》2002,7(3):165-174
Human commercial activities must be compatible with sustainable management to achieve species conservation in the natural
environment. After harvesting, diversity and abundance of understory species differ substantially from the pre-harvest situation.
Have knowledge of the changes that logging produces in all components of the system allows us to develop management alternatives
with reduced impacts. The objective of this work was to evaluate changes in density, biomass and diversity of understory species
along a forest shelterwood cut system management cycle in aNothofagus pumilio forest. Six forest management situations (postharvesting stands and different phases of forest development) were sampled
in a pureN. pumilio forest of Tierra del Fuego (Argentina) of middle-high site class (fromclass I toIII). Species number, density and biomass were modified substantially after a shelterwood cut. These were being greatest after
cutting and falling substantially when the forest canopy closes during theinitial growth phase, returning to values similar to this virgin forest when themature phase was reached. The impact of the forest management on understory species diversity is analyzed and discussed. The silvicultural
practices applied toN. pumilio forest in Tierra del Fuego permit the introduction of alien flora to the system, and produce great changes during the forest
management cycle.
To Celina Matteri, Itatí Ferraro, and Rosa Kofalt for their aid in taxonomical identification. To Juan Manuel Cellini, Ricardo
Vukasovic and Gregorio Martínez Pastur for their participation in the field work; and to the sawmillLos Castores, Universidad Nacional de la Patagonia Austral, Centro Austral de Investigaciones Científicas and Instituto Nacional de Tecnología
Agropecuaria for the institutional and financial support. 相似文献
64.
The density of Armillaria gallica epiphytic rhizomorphs on tree collar was mapped in a young stand of pedunculate oaks (Quercus robur). A quick method to estimate the rhizomorph density was developed, investigating 19 trees, and was used in the subsequent study. The method consists of measuring the frequency of rhizomorphs present on a grid applied to an exposed small area of the tree collar. The pattern in tree collar rhizomorph density was closely related to the pattern of stump colonization by Armillaria and stumps were therefore important as inoculum sources. Rhizomorph density on tree collar showed a strong aggregated spatial pattern which could not be explained by variability in the soil characteristics, in particular waterlogging, or by a spatial pattern in tree vigour. Moreover, rhizomorph density on tree collar did not depend on their dominance status. 相似文献
65.
The study developed management instructions for even-aged Pinus sylvestris stands in Galicia (north-western Spain). Although these stands are highly productive, no silvicultural management schedules have been proposed so far for them on the basis of systematic analyses. This study used data from 2160 optimisation runs to develop the management instructions. Land expectation value was used as the objective function. Different prices of timber assortments were considered and the discounting rate was varied from 0.5 to 5%. The method employed to find the optimal management schedules of stands was the combination of a stand simulator and an optimisation algorithm. The simulator uses an earlier growth and yield model for Pinus sylvestris in Galicia to predict the future development of the stand with a given management schedule while the optimisation algorithm seeks the best management schedule among all the possible alternatives. The results show that optimal rotation lengths vary widely between 42 and 170 years, high discounting rates and good site quality resulting in the shortest rotations. Four thinnings were found to be suitable for all sites and discounting rates. With discounting rates higher than 1% the commercial thinnings should gradually decrease the stand basal area towards the end of the rotation. 相似文献
66.
67.
68.
Plasma N‐terminal pro‐B‐type natriuretic peptide concentration in healthy retired racing Greyhounds 下载免费PDF全文
69.
Biochemical variables from Holstein‐Friesian calves older than one week are comparable to those obtained from adult animals of stable metabolic status on the same farm 下载免费PDF全文
70.