全文获取类型
收费全文 | 16430篇 |
免费 | 3篇 |
专业分类
林业 | 3624篇 |
农学 | 1295篇 |
基础科学 | 137篇 |
2732篇 | |
综合类 | 708篇 |
农作物 | 2097篇 |
水产渔业 | 1789篇 |
畜牧兽医 | 1079篇 |
园艺 | 1110篇 |
植物保护 | 1862篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2019年 | 1篇 |
2018年 | 2744篇 |
2017年 | 2702篇 |
2016年 | 1183篇 |
2015年 | 72篇 |
2014年 | 16篇 |
2013年 | 11篇 |
2012年 | 793篇 |
2011年 | 2122篇 |
2010年 | 2102篇 |
2009年 | 1257篇 |
2008年 | 1313篇 |
2007年 | 1575篇 |
2006年 | 31篇 |
2005年 | 96篇 |
2004年 | 103篇 |
2003年 | 152篇 |
2002年 | 59篇 |
2001年 | 5篇 |
2000年 | 40篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1995年 | 1篇 |
1993年 | 12篇 |
1992年 | 7篇 |
1990年 | 1篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 1篇 |
1977年 | 4篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1968年 | 4篇 |
1967年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
Mikko Mönkkönen Pasi Reunanen Janne S. Kotiaho Artti Juutinen Olli-Pekka Tikkanen Jari Kouki 《European Journal of Forest Research》2011,130(5):717-727
Setting aside parcels of land is the main conservation strategy to reduce the rate of biodiversity loss worldwide. Because
funding for biological conservation is limited, it is important to distinguish the most efficient ways to use it. Here, we
assess implications of alternative measures to conserve biodiversity in managed boreal forest landscapes. We calculated four
alternative spatio-temporal scenarios and compared these to the current management regime over 100-year time period. In the
alternative scenarios, a fixed amount of funding was invested in (1) permanent large reserves (each tens of ha in size), (2)
permanent small reserves (each a few ha in size), (3) temporary small reserves (based on 10-year contracts with private land
owners), and (4) green-tree retention (small groups of trees retained on clear-cuts). To assess biodiversity implications,
we used habitat suitability indices to calculate overall habitat availability for five groups of red-listed and habitat-specific
species associated with decaying spruce logs. The possibilities for timber harvests did not differ among the scenarios, but
biodiversity performance was different. The scenarios with permanent reserves tended to outperform other scenarios, suggesting
that conservation policies based on permanent reserves are the most cost-efficient in the long term. Results, however, varied
among time scales and species groups. In the short term, a strategy of investment in temporary small reserves was the most
efficient. Habitat for species associated with old spruce dead-wood and preferring shade was rare throughout all simulations,
and therefore, it is likely that these species cannot be sustained in managed forests. Species that live on fresh dead-wood
and are associated with forest edges coped well in all scenarios suggesting that such species will persist in managed landscapes
without additional conservation efforts. Explicit definition of conservation objectives and time frames for conservation action
are thus prerequisites for successful conservation planning. 相似文献
912.
913.
Background
There is an increasing demand for renewable resources to replace fossil fuels. However, different applications such as the production of secondary biofuels or combustion for energy production require different wood properties. Therefore, high-throughput methods are needed for rapid screening of wood in large scale samples, e.g., to evaluate the outcome of tree breeding or genetic engineering. In this study, we investigated the intra-specific variability of lignin and energy contents in extractive-free wood of hybrid poplar progenies (Populus trichocarpa × deltoides) and tested if the range was sufficient for the development of quantitative prediction models based on Fourier transform infrared spectroscopy (FTIR). Since lignin is a major energy-bearing compound, we expected that the energy content of wood would be positively correlated with the lignin content. 相似文献914.
FlordeFátima Rosas-Cárdenas Noé Durán-Figueroa Jean-Philippe Vielle-Calzada Andrés Cruz-Hernández Nayelli Marsch-Martínez Stefan de Folter 《Plant methods》2011,7(1):4
Background
Small RNAs emerged over the last decade as key regulators in diverse biological processes in eukaryotic organisms. To identify and study small RNAs, good and efficient protocols are necessary to isolate them, which sometimes may be challenging due to the composition of specific tissues of certain plant species. Here we describe a simple and efficient method to isolate small RNAs from different plant species. 相似文献915.
Penultimate and last instar larvae of the common citrus swallowtail butterfly, Papilio demoleus L. (Papilionidae: Lepidoptera), were treated with different doses of a novel juvenoid, diofenolan. Several deformities were
observed as a result of topical administration of diofenolan which include delay in larval–larval and larval–pupal ecdysis,
ecdysial failure, mortality, severe reduction in pupation, deformed pupae and complete inhibition of adult emergence. The
juvenoid diofenolan severely hampers the normal growth, development and metamorphosis of P. demoleus and can be incorporated into integrated pest management programs for successful control of this important pest of citrus
all over the world. 相似文献
916.
Alate viviparous females of Wahlgreniella nervata (Gillette) were found on a Damask rose (Rosa damascena Mill.) plantation in Isparta Province, Turkey. The aphid is recorded for the first time from Turkey. Besides, Damask rose
is a new host for this species. Brief information about this aphid including a key to the alate females of aphid species known
to infest Damask rose in Turkey is provided. 相似文献
917.
Chao Zhou Yongqiang Liu Weili Yu Zhaorong Deng Ming Gao Feng Liu Wei Mu 《Phytoparasitica》2011,39(4):315-324
Spodoptera exigua (Hübner) collected from three regions (two scallion-producing regions and one ginger-producing region) in Shandong, China
and a laboratory colony of Wuhan (WHLC) were evaluated for their susceptibilities to ten insecticides (emamectin benzoate,
chlorfenapyr, indoxacarb, spinosyn, tebufenozide, methoxyfenozide, chlorfluazuron, beta-cypermethrin, chlorpyrifos and methomyl)
in 2008, 2009 and 2010 using a leaf-dip bioassay method. The results indicate that the resistance ratios of S. exigua to newer insecticides such as emamectin benzoate, chlorfenapyr and indoxacarb were all below 20-fold, with no obvious change
in all 3 years. S. exigua exhibits moderate resistance to spinosyn, and its resistance ratios increased from 1.98–5.31-fold in 2008 to 14.31–64.20-fold
in 2010 from three regions as compared with WHLC. S. exigua showed moderate to high resistance to insect growth regulators such as tebufenozide, methoxyfenozide, chlorfluazuron in 2008,
2009 and 2010, in which resistance to chlorfluazuron was rapidly increased from 31.49–88.19-fold in 2008 to 1184.39–2789.67-fold
in 2010. Resistance of S. exigua to beta-cypermethrin and chlorpyrifos varied greatly among the three regions, ranging from 95.31–437.97-fold and 25.05–40.64-fold
in 2008, 951.81–1304.40-fold and 44.91–186.33-fold in 2009, to 27.27–1095.31-fold and 19.12–267.98-fold in 2010. In contrast,
S. exigua showed low resistance to methomyl, and the resistance ratio was below 5-fold in 3 years. There are several reasons accounting
for varying degrees of resistance, including selection pressure, cropping structure and migration, in which the migration
of S. exigua may play an important role. 相似文献
918.
919.
920.
Yong Zhang Yu Chen Xiaofeng Zhu Ying Xu Yiping Hou Tongchun Gao Mingguo Zhou 《Phytoparasitica》2011,39(4):393-401
Xanthomonas oryzae pv. oryzicola, the causal agent of rice leaf streak disease, was found to be sensitive to streptomycin (an aminocyclitol glycoside antibiotic),
by inhibition of protein synthesis resulting from interference with translational proofreading. This study aimed to determine
the molecular resistance mechanism of X. oryzae pv. oryzicola to streptomycin. Seven streptomycin-resistant mutants were obtained by UV induction or streptomycin selection. These mutants
can grow at 100 μg ml−1 of streptomycin while the wild-type strain (RS105) cannot grow at 5 μg ml−1. Sequencing indicated that the rpsL gene encoding ribosomal protein S12 has 375 bp encoding 125 amino acid residues. In all resistant strains, a mutation in
which AAG was substituted for AGG (Lys→Arg) occurred either at codon 43 or 88. Two plasmids, pUFRRS and pUFRRX, were constructed
by ligating the rpsL gene into the cosmid pUFR034. The plasmids pUFRRS and pUFRRX containing the Lys→Arg mutation of the rpsL gene conferred streptomycin resistance to the sensitive wild-type strain by electroporation. Both transformants, RS1 and
RS2, could grow in the medium containing 50 μg ml−1 of streptomycin. A mutation at codon 43 or 88 in rpsL can result in resistance of Xanthomonas oryzae pv. oryzicola to streptomycin. 相似文献