全文获取类型
收费全文 | 1026篇 |
免费 | 45篇 |
专业分类
林业 | 120篇 |
农学 | 39篇 |
基础科学 | 6篇 |
218篇 | |
综合类 | 153篇 |
农作物 | 49篇 |
水产渔业 | 88篇 |
畜牧兽医 | 308篇 |
园艺 | 33篇 |
植物保护 | 57篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 16篇 |
2021年 | 31篇 |
2020年 | 33篇 |
2019年 | 27篇 |
2018年 | 24篇 |
2017年 | 26篇 |
2016年 | 28篇 |
2015年 | 27篇 |
2014年 | 26篇 |
2013年 | 38篇 |
2012年 | 89篇 |
2011年 | 85篇 |
2010年 | 35篇 |
2009年 | 39篇 |
2008年 | 94篇 |
2007年 | 73篇 |
2006年 | 68篇 |
2005年 | 71篇 |
2004年 | 64篇 |
2003年 | 50篇 |
2002年 | 40篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1955年 | 1篇 |
1940年 | 1篇 |
排序方式: 共有1071条查询结果,搜索用时 15 毫秒
51.
52.
A greenhouse experiment was conducted by growing oats (Avenasativa L.) in a continuously 13CO2 labeled atmosphere. The allocation of 13C-labeled photosynthates in plants, microbial biomass in rhizosphere and root-free soil, pools of soil organic C, and CO2 emissions were examined over the plant's life cycle. To isolate rhizosphere from root-free soil, plant seedlings were placed into bags made of nylon monofilament screen tissue (16 μm mesh) filled with soil. Two peaks of 13C in rhizosphere pools of microbial biomass and dissolved organic carbon (DOC), as well as in CO2 emissions at the earing and ripeness stages were revealed. These 13C maxima corresponded to: (i) the end of rapid root growth and (ii) beginning of root decomposition, respectively. The δ13C values of microbial biomass were higher than those of DOC and of soil organic matter (SOM). The microbial biomass C accounted for up to 56 and 39% of 13C recovered in the rhizosphere and root-free soil, respectively. Between 4 and 28% of 13C assimilated was recovered in the root-free soil. Depending on the phenological stage, the contribution of root-derived C to total CO2 emission from soil varied from 61 to 92% of total CO2 evolved, including 4-23% attributed to rhizomicrobial respiration. While 81-91% of C substrates used for microbial growth in the root-free soil and rhizosphere came from SOM, the remaining 9-19% of C substrates utilized by the microbial biomass was attributable to rhizodeposition. The use of continuous isotopic labelling and physical separation of root-free and rhizosphere soil, combined with natural 13C abundance were effective in gaining new insight on soil and rhizosphere C-cycling. 相似文献
53.
Van der Plancken I Van Loey A Hendrickx M 《Journal of agricultural and food chemistry》2007,55(1):127-135
This article addresses the effect of moisture content (0.8-9.9%) during dry-heating (80 degrees C) on selected physicochemical (solubility, turbidity, residual denaturation enthalpy, aggregation, surface hydrophobicity, and sulfhydryl content) and functional (foaming ability, foam density, and stability) properties of freeze-dried egg white (FDEW). Moisture content during dry-heating proved to be a parameter determining the functionality of the resulting egg white powder. The degree of conformational changes induced in the egg white proteins by dry-heating was strongly dependent on the amount of water present. Preferentially, dry-heating at 80 degrees C should be performed on egg white powder with a moisture content below 6.8%, as the loss of protein solubility above this value is extensive. In addition to insoluble aggregates, soluble, strongly stabilized aggregates were also formed, especially at higher moisture contents. The decrease in denaturation enthalpy, increase in surface hydrophobicity, and exposure of SH groups previously hidden in the protein core and their subsequent oxidation were more pronounced at prolonged dry-heating times and at higher moisture contents. These conformational changes resulted in improved foaming ability and foams with lower density. No effect of dry-heating on the foam stability was observed. 相似文献
54.
José Ramón González Antoni Trasobares Marc Palahí Timo Pukkala 《Annals of Forest Science》2007,64(7):733-742
The study developed models for predicting the post-fire tree survival in Catalonia. The models are appropriate for forest planning purposes. Two types of models were developed: a stand-level model to predict the degree of damage caused by a forest fire, and tree-level models to predict the probability of a tree to survive a forest fire. The models were based on forest inventory and fire data. The inventory data on forest stands were obtained from the second (1989–1990) and third (2000–2001) Spanish national forest inventories, and the fire data consisted of the perimeters of forest fires larger than 20 ha that occurred in Catalonia between the 2nd and 3rd measurement of the inventory plots. The models were based on easily measurable forest characteristics, and they permit the forest manager to predict the effect of stand structure and species composition on the expected damage. According to the stand level fire damage model, the relative damage decreases when the stand basal area or mean tree diameter increases. Conversely, the relative stand damage increases when there is a large variation in tree size, when the stand is located on a steep slope, and when it is dominated by pine. According to the tree level survival models, trees in stands with a high basal area, a large mean tree size and a small variability in tree diameters have a high survival probability. Large trees in dominant positions have the highest probability of surviving a fire. Another result of the study is the exceptionally good post-fire survival ability of Pinus pinea and Quercus suber. 相似文献
55.
CHEN Lin XIN Xiuli ZHANG Jiabao Marc REDMILE-GORDON NIE Guangsen WANG Qingyun 《土壤圈》2019,29(3):360-373
Modern breeding primarily targets crop yield traits and is likely to influence root-associated microbiomes, which play significant roles in plant growth and health. The relative importance of soil and cultivar factors in shaping root-associated microbiomes of modern maize (Zea mays L.) remains uncertain. We conducted a pot experiment in a controlled environment using three soils (Mollisol, Inceptisol, and Ultisol) and four contrasting cultivars, Denghai 605, Nonghua 816, Qiaoyu 8, and Zhengdan 958, which are widely planted in China. We used 16S rRNA gene amplicon sequencing to characterize the bacterial communities in the bulk soil, rhizosphere, and endosphere. Our results showed that the four cultivars had different shoot biomass and root exudate total organic carbon and organic acid contents. The microbiomes in the bulk soil, rhizosphere, and endosphere were different. We observed apparent community divergence between soils rather than cultivars, within which edaphic factors substantially contributed to microbiome variation. Moreover, permutational multivariate analysis of variance corroborated significant contributions of soil type but not cultivar on the root-associated microbiome structure. Differential abundance analysis confirmed that each soil presented a distinct root microbiome, while network analysis indicated different co-occurrence patterns of the root microbiome among the three soils. The core root microbiome members are implicated in plant growth promotion and nutrient acquisition in the roots. In conclusion, root-associated microbiomes of modern maize are much more controlled by soil characteristics than by cultivar root exudation. Our study is anticipated to help improve breeding strategies through integrative interactions of soils, cultivars, and their associated microbiomes. 相似文献
56.
The search for indicators to monitor management impact on biodiversity is a crucial question because management practices promote changes in community structure and composition of different animal groups. This study explores the effect of widely conducted management practices (forest logging and livestock) in Pinus uncinata forests in the Pyrenees range (NE Spain) on the structure and composition of ground ant communities compared to those of old-growth stands. Forest structure clearly differed in stands with different forest managements. These stands managed for different uses also showed marked differences in structure and composition of ground ant communities. There was a great dominance of a single species, Formica lugubris, which accounted for 99% of ants collected in pitfall traps. Rarefaction curves indicated that species richness was highest in old-growth stands and lowest in even-aged ones, with woodland pasture stands showing an intermediate value. Classification methods allowed us to identify two groups of species: six species related to old-growth plots and three species (including F. lugubris) associated to managed stands. Habitat structure played an important role in determining the structure of ant communities: forests with high tree density but low basal area were the most favourable forest type for F. lugubris, while the abundance of the remaining ant species was negatively affected by the abundance of F. lugubris and by tree cover. 相似文献
57.
Henrik Harms Barbora Orlikova Seungwon Ji Damun Nesaei-Mosaferan Gabriele M. K?nig Marc Diederich 《Marine drugs》2015,13(8):4949-4966
The Ascomycota Dichotomomyces cejpii was isolated from the marine sponge Callyspongia cf. C. flammea. A new gliotoxin derivative, 6-acetylmonodethiogliotoxin (1) was obtained from fungal extracts. Compounds 2 and 3, methylthio-gliotoxin derivatives were formerly only known as semi-synthetic compounds and are here described as natural products. Additionally the polyketide heveadride (4) was isolated. Compounds 1, 2 and 4 dose-dependently down-regulated TNFα-induced NF-κB activity in human chronic myeloid leukemia cells with IC50s of 38.5 ± 1.2 µM, 65.7 ± 2.0 µM and 82.7 ± 11.3 µM, respectively. The molecular mechanism was studied with the most potent compound 1 and results indicate downstream inhibitory effects targeting binding of NF-κB to DNA. Compound 1 thus demonstrates potential of epimonothiodiketopiperazine-derived compounds for the development of NF-κB inhibitors. 相似文献
58.
Carlos A. Guerra Marc J. Metzger Joachim Maes Teresa Pinto-Correia 《Landscape Ecology》2016,31(2):271-290
Context
Policy decisions form a major driver of land use change, with important implications for socially and environmentally susceptible regions. It is well known that there can be major unintended consequences, especially where policies are not tailored to regionally specific contexts.Objectives
In this paper we assess the implications of 60 years of agricultural policies on soil erosion prevention (SEP) by vegetation, an essential regulating ecosystem service in Mediterranean Europe.Methods
To assess these implications we produced and analysed a time series of land cover/use and environmental conditions datasets (from 1951 to 2012) in relation to changing agricultural policies for a specific region in the southern Portugal. A set of indicators related to SEP allowed us to identify that land use intensification as increased soil erosion in the last 60 years.Results
Particularly in the last 35 years, as a consequence of headage payments for cattle, the agricultural policy had a significant effect in the density and renewal of the tree cover, resulting in drastic effects for the provision of the SEP service. These are more significant after 1986, coinciding with the implementation of several Common Agricultural Policy instruments focused on increasing the modernization and productivity capacity of farm systems.Conclusions
The results show some unintended effects of agricultural policy mechanisms on ecosystem service provision and highlight the need for context-based policies, tailored to the environmental constrains and potentials of each region.59.
60.
在人工接种和自然感虫情况下美洲黑杨后代对桑天牛抗性的研究 总被引:5,自引:0,他引:5
杨树 (Populusspp .)是我国主要造林和工业用材树种之一 ,据统计我国杨树人工林面积达 666×1 0 4hm2 (王世绩 ,1 995 )。但杨树天牛危害十分猖獗 ,其中光肩星天牛 (Anoplophoraglabripennis)和黄斑星天牛 (Anoplophoranobi 相似文献