全文获取类型
收费全文 | 583篇 |
免费 | 24篇 |
国内免费 | 23篇 |
专业分类
林业 | 127篇 |
农学 | 50篇 |
基础科学 | 9篇 |
157篇 | |
综合类 | 121篇 |
农作物 | 42篇 |
水产渔业 | 5篇 |
畜牧兽医 | 48篇 |
园艺 | 24篇 |
植物保护 | 47篇 |
出版年
2024年 | 6篇 |
2023年 | 9篇 |
2022年 | 10篇 |
2021年 | 17篇 |
2020年 | 15篇 |
2019年 | 22篇 |
2018年 | 13篇 |
2017年 | 20篇 |
2016年 | 25篇 |
2015年 | 29篇 |
2014年 | 22篇 |
2013年 | 42篇 |
2012年 | 45篇 |
2011年 | 35篇 |
2010年 | 37篇 |
2009年 | 42篇 |
2008年 | 40篇 |
2007年 | 34篇 |
2006年 | 36篇 |
2005年 | 24篇 |
2004年 | 12篇 |
2003年 | 16篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有630条查询结果,搜索用时 15 毫秒
51.
Total and active soil fungal communities in a native eucalypt forest and first rotation Pinus elliotti plantation were investigated by direct extraction of DNA and RNA from soil. Terminal restriction fragment length polymorphism (T-RFLP) analysis of internal transcribed spacer (ITS) and 18S rRNA profiles indicated that total and active fungal communities differed significantly in both forest types. This was supported by DGGE profile analysis on an individual plot basis for both forest types and when groups in the canonical analysis were redefined to allow comparison between forest types. Analyses of both ITS and 18S T-RFLP profiles indicated that conversion from native eucalypt forest to P. elliottii plantation may significantly alter total and active soil fungal communities. ITS DGGE (DNA) and 18S (RNA) profiles also suggested differences in fungal communities in the two forest types. No significant separation of the fungal communities in the two forest types was observed, however, when ITS DGGE (RNA) profiles were compared. Overall, the data suggest that conversion from native eucalypt forest to P. elliottii plantation at the Beerburrum State Forest in subtropical Australia has significantly altered soil fungal communities. 相似文献
52.
The influence of native vegetation clearing and different further soil managements on fungal propagule population diversity
was studied in the present work. In each of the 3 years (1998, 1999, and 2000), soil samples were collected at the depth of
0–7.5 cm from sites under native vegetation (V0); naturalized prairie, cleared in 1982 (P16); conventional tillage, cleared
in 1972 (T26); and direct drilling, cleared in 1958 (D40). Fungal population size and relative abundance of fungal genera
were studied by plate counts and further identification of isolates on potato dextrose agar. The undisturbed site and the
other sites with increasing time elapsed since native vegetation clearing and different management history showed a distinctive
distribution of fungal genera. There were significant differences (p<0.05) among the sites in the abundance of fungal genera analyzed in all the 3 years. Principal component analysis based on
relative fungal genus abundance differentiated the sites with 75% variance explained by the first and second components. Diversity
and abundance of isolated fungal genera were increased as density of Penicillium spp. decreased, suggesting a competitive effect of this fungal genus. The largest diversity was found in the site under no-till
management. The different distribution and relative abundance of the fungal genera studied seemed to be influenced strongly
by the management and the presence of surface residue in the no-tilled site. 相似文献
53.
Identification of ergosterol in vesicular-arbuscular mycorrhizae 总被引:1,自引:0,他引:1
Summary Ergosta-5,7,22-tri-3-enol (ergosterol) was identified by gas chromatography-mass spectrometry in roots of berseem (Trifolium alexandrinum L., cv. Landsorte) and sweet corn (Zea mays L., cv. Honeycomb-F1) infected with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus intraradices. The fungal-derived compound ergosterol was determined quantitatively in root extracts using reverse-phase high performance liquid chromatography. The concentrations of ergosterol in VAM-infected roots reached 72 g-1 dry material in berseem and 52 g-1 in sweet corn after 80 days of growth, whereas concentrations in non-infected roots remained below 8 g-1 dry weight. Additionally, phytosterols such as -sitosterol, campesterol, and stigmasterol were detected in both infected and non-infected roots. Ergosterol, as a characteristic fungal substance, is proposed as an indicator of fungal biomass in the early stages of VAM infection. 相似文献
54.
Robert McDonald Meghan McKnight Elizabeth Selig Christy Violin 《Biological conservation》2005,126(1):24-40
The concept of an ecoregion, a discrete spatial area where species composition is presumed to be relatively homogeneous compared to that between areas, has become an increasingly common conservation tool. We test the effectiveness of one ecoregion delineation (World Wildlife Fund) in capturing patterns of change in species composition of birds, mammals, and trees across the United States (excluding Hawaii) and Canada, and describe the extent to which each ecoregion boundary is concurrent with relatively large changes in species composition. Digitized range maps were used to record presence/absence in 50 × 50 km equal-area grid cells covering the study area. Jaccard’s index of similarity was calculated for all pairs of cells in the same or adjacent ecoregions. The average rate at which similarity declined with geographic distance was calculated using pairs of cells within the same ecoregion (intra-ecoregion turnover) or using pairs of cells in adjacent ecoregions (inter-ecoregion turnover). The intra-ecoregion rate varies widely among ecoregions and between taxa, with trees having a faster rate of similarity decline than mammals or birds. For all three species groups, most ecoregion boundaries have similar rates across them (inter-ecoregion) than that within each adjacent ecoregion (intra-ecoregion), with the exception of zones of transition between biomes and major geographical features. Although the ecoregion concept is useful for many other conservation applications, the lack of systematic, high turnover rates along ecoregion boundaries suggests that ecoregions should not be used as a quantitative basis for delineating geographic areas of a particular taxonomic group. 相似文献
55.
Characterization of fungal melanins and soil humic acids by chemical analysis and infrared spectroscopy 总被引:5,自引:0,他引:5
Summary Humic acids from two Brazilian topsoils under savanna grassland and five soil fungal melanins were characterized by elemental, functional group and infrared analysis. C, N, total acidity, COOH, and phenolic OH contents were within the ranges reported for several other fungal melanins and soil humic acids. Compared with the soil humic acids, the infrared spectra of the fungal melanins showed greater detail, indicative of higher aliphaticity. They were similar to the type III infrared spectra of humic acids, which are characteristically high in proteinaceous material and polysaccharides. The infrared spectra of the humic acids from the two Brazilian soils studied were classified as type I, which includes most soil humic acids. Notwithstanding the greater detail, in some areas the fungal melanin spectra were similar to those reported for other fungal melanins and humic acids of different origins. The probable contribution of the melanic fungi to the formation of soil humic polymers is discussed. 相似文献
56.
中国自实施退耕还林生态补偿政策以来,执行分长江南北两种不同的补偿政策,生态补偿并未考虑退耕还林微观地理区位及造林质量的差异。"一刀切"虽具有统一简化的优点,却忽视了实际存在的造林质量及林地地形、土壤、气候等诸多因素,补偿标准不尽合理。该文为了探讨退耕还林补偿金的合理标准,以张家口地区为研究区,应用遥感(RS)、地理信息系统(GIS)等数据,建立了退耕还林生态补偿体系。结果表明:张家口地区各区县中,单位面积退耕还林补偿系数最高的是尚义县(0.082),退耕还林补偿系数最低是怀来县(0.036),各县单位面积退耕还林补偿系数的差距较大。该文结果为生态补偿金的科学、合理分配提供参考。 相似文献
57.
The biodegradability of chars derived from pyrolysis and
hydrothermal carbonisation (HTC) was studied in short-term
dynamic incubation experiments under controlled conditions.
Carbon dioxide C (CO$_{2}$) emissions from soil-char mixtures in combination
with solid digestate or mineral nitrogen (N) fertiliser were measured
in dynamic chambers for 10 d.~Compared to the original
material (maize straw), pyrolysis and HTC chars showed
significantly lower CO$_{2}$ emissions and slower decay
dynamics; and compared to the soil control, HTC char
increased soil respiration to a significant extent, while
pyrolysis char did not. The addition of mineral N resulted
in a delayed respiration dynamics for HTC char, while the
addition of digestate resulted in an increase in the
respired CO$_{2}$ for pyrolysis char and a decrease for HTC
char. For the first time, a peculiar two-stage decay
kinetics was observed for HTC char, indicating a highly
inhomogeneous substrate consisting at least of two C pools. 相似文献
58.
We evaluate the use of signature fatty acids and direct hyphal counts as tools to detect and quantify arbuscular mycorrhizal (AM) and saprotrophic fungal (SF) biomass in three Hawaiian soils along a natural soil fertility gradient. Phospholipids16:1ω5c and 18:2ω6,9c were used as an index of AM and saprotrophic fungal biomass, respectively. Both phospholipid analysis and hyphal length indicated that the biomass of AMF was greatest at the highest fertility site, and lowest where phosphorus limits plant growth. Saprotrophic fungal biomass did not vary. Hyphal length counts appeared to under-estimate SF abundance, while the phospholipid AMF:SF ratio was in line with expectations. This study indicates that phospholipids may be a valuable and reliable tool for studying the abundance, distribution, and interactions between AM and saprotrophic fungi in soil. 相似文献
59.
Effects of fungal inocula on the decomposition of lignin and structural polysaccharides in Pinus sylvestris litter 总被引:2,自引:0,他引:2
Litter bags containing sterile Scots pine (Pinus sylvestris) needles (19.8% lignin, 26.5% cellulose and 0.34% N) were inoculated with two species of fungi in the laboratory and then
placed in the litter layer of a pine plantation. Marasmius androsaceus, which can degrade lignocellulose, was initially displaced by other fungal colonisers and was not detected in the litter
after 2–3 months; but was re-isolated from the needles after 12 months. Trichoderma viride, which is a cellulolytic species and also antagonistic to other fungi, dominated the litter throughout the experiment. The
control litter was naturally colonised by litter fungi. After 12 months, mass losses were similar at 52% for M. androsaceus and 48% for T. viride, compared with 36% for the control litter colonised by a more complex fungal community. Lignin concentrations increased with
time in control litter and with T. viride because mass losses of carbohydrates were greater than those of lignin. Litter inoculated with M. androsaceus showed significant lignin decomposition throughout the experiment but cellulose concentrations showed a proportional increase
in the first 6 months, suggesting that the fungus was preferentially exploiting hemicellulose and non-structural carbohydrates.
Analysis of TFA-extractable sugars (mainly from hemicellulose) and CuO-derived phenylpropanoid moieties from lignin confirmed
the differential patterns of resource decomposition which were not evident from total mass losses. During the initial stages
of decomposition, T. viride was as effective in utilising structural polysaccharides as the complex fungal community in the control litter. Furthermore,
M. androsaceus not only exhibited unexpectedly low cellulolytic activity but also facilitated lignin depolymerisation after the fungus was
no longer detectable in the litter. The pre-inoculation of litter with these two fungal species therefore affected the overall
dynamics of decomposition at a biochemical level. This study illustrates the importance of understanding the effects and interactions
of specific fungi, rather than assumptions about the functional competence of diverse communities, on the processes of litter
decomposition.
Received: 5 July 2000 相似文献
60.
[目的]拟利用内桂精油的挥发性、天然安全性和广谱抑菌特性,对玉米颗粒进行防霉研究.[方法]采用精油熏蒸的方法,将玉米颗粒置于自制的密闭容器中,人工模拟高温高湿条件对其进行肉桂精油熏蒸.[结果]研究表明,玉米颗粒的含水量对其霉变的影响很大.空气湿度为75%时,空间浓度分别为175和100 μl/L的肉桂精油对玉米颗粒霉菌的熏杀抑制效果随着熏蒸时间的延长而逐渐提高,熏蒸时间为8d时达到了最高的抑菌率.高湿高温条件下,肉桂精油空间浓度为1 000~2000 μl/L是最适抑菌浓度区间,其中精油浓度2000 μl/L为最佳抑菌浓度.[结论]研究可为玉米储藏的防霉工作提供理论依据. 相似文献