全文获取类型
收费全文 | 1120篇 |
免费 | 39篇 |
国内免费 | 3篇 |
专业分类
林业 | 112篇 |
农学 | 18篇 |
基础科学 | 12篇 |
259篇 | |
综合类 | 125篇 |
农作物 | 110篇 |
水产渔业 | 34篇 |
畜牧兽医 | 361篇 |
园艺 | 28篇 |
植物保护 | 103篇 |
出版年
2022年 | 13篇 |
2021年 | 11篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 26篇 |
2017年 | 18篇 |
2016年 | 29篇 |
2015年 | 17篇 |
2014年 | 28篇 |
2013年 | 52篇 |
2012年 | 48篇 |
2011年 | 56篇 |
2010年 | 29篇 |
2009年 | 38篇 |
2008年 | 44篇 |
2007年 | 49篇 |
2006年 | 59篇 |
2005年 | 70篇 |
2004年 | 43篇 |
2003年 | 53篇 |
2002年 | 47篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 13篇 |
1997年 | 16篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 18篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 11篇 |
1972年 | 7篇 |
1971年 | 8篇 |
1952年 | 6篇 |
1926年 | 11篇 |
1925年 | 10篇 |
1924年 | 7篇 |
排序方式: 共有1162条查询结果,搜索用时 15 毫秒
11.
12.
Land use and mineral characteristics affect the ability of surface as well as subsurface soils to sequester organic carbon and their contribution to mitigation of the greenhouse effect. There is less information about the effects of land use and soil properties on the amount and composition of organic matter (OM) for subsurface soils as compared with surface soils. Here we aimed to analyse the long‐term (≥ 100 years) impact of arable and forest land use and soil mineral characteristics on subsurface soil organic carbon (SOC) contents, as well as on amount and composition of OM sequentially separated by Na pyrophosphate solution (OM(PY)) from subsurface soil samples. Seven soils with different mineral characteristics (Albic and Haplic Luvisol, Colluvic and Haplic Regosol, Haplic and Vertic Cambisol, Haplic Stagnosol) were selected from within Germany. Soil samples were taken from subsurface horizons of forest and adjacent arable sites continuously used for >100 years. The OM(PY) fractions were analysed for their OC content (OCPY) and characterized by Fourier transform infrared spectroscopy. Multiple regression analyses for the arable subsurface soils indicated significant positive relationships between the SOC contents and combined effects of the (i) exchangeable Ca (Caex) and oxalate‐soluble Fe (Feox) and (ii) the Caex and Alox contents. For these soils the increase in OC (OCPY multiplied by the relative C=O content of OM(PY)) and increasing contents of Caex indicated that OM(PY) mainly interacts with Ca2+. For the forest subsurface soils (pH < 5), the OCPY contents were related to the contents of Na‐pyrophosphate‐soluble Fe and Al. The long‐term arable and forest land use seems to result in different OM(PY)‐mineral interactions in subsurface soils. On the basis of this, we hypothesize that a long‐term land‐use change from arable to forest may lead to a shift from mainly OM(PY)‐Ca2+ to mainly OM(PY)‐Fe3+ and ‐Al3+ interactions if the pH of subsurface soils significantly decreases to <5. 相似文献
13.
Radial stem growth in response to microclimate and soil moisture in a drought-prone mixed coniferous forest at an inner Alpine site 总被引:1,自引:0,他引:1
Walter Oberhuber Andreas Gruber Werner Kofler Irene Swidrak 《European Journal of Forest Research》2014,133(3):467-479
Dendroclimatological studies in a dry inner Alpine environment (750 m a.s.l.) revealed different growth response of co-occurring coniferous species to climate, which is assumed to be caused by a temporal shift in wood formation among species. The main focus of this study therefore was to monitor intra-annual dynamics of radial increment growth of mature deciduous and evergreen coniferous species (Pinus sylvestris, Larix decidua and Picea abies) during two consecutive years with contrasting climatic conditions. Radial stem growth was continuously followed by band dendrometers and modelled using Gompertz functions to determine time of maximum growth. Histological analyses of tree ring formation allowed determination of temporal dynamics of cambial activity and xylem cell development. Daily fluctuations in stem radius and radial stem increments were extracted from dendrometer traces, and correlations with environmental variables were performed. While a shift in temporal dynamics of radial growth onset and cessation was detected among co-occurring species, intra-annual radial growth peaked synchronously in late May 2011 and early June 2012. Moist atmospheric conditions, i.e. high relative air humidity, low vapour pressure deficit and low air temperature during the main growing period, favoured radial stem increment of all species. Soil water content and soil temperature were not significantly related to radial growth. Although a temporal shift in onset and cessation of wood formation was detected among species, synchronous culmination of radial growth indicates homogenous exogenous and/or endogenous control. The close coupling of radial growth to atmospheric conditions points to the importance of stem water status for intra-annual growth of drought-prone conifers. 相似文献
14.
Thomas Eglin Christian Walter Claude Nys Stéphane Follain Françoise Forgeard Arnaud Legout Hervé Squividant 《Annals of Forest Science》2008,65(2):202-202
The Kyoto protocol [39] directs the signatory countries including France to establish an inventory of carbon stocks in forests. Precise estimates of carbon stocks are hampered by local spatial variability, in particular in wetland areas [25]. The aims of this work are: (i) to estimate the spatial variability of carbon stocks on two hillslopes presenting respectively, a transition between a well-drained zone and a wetland area over a short-distance, and a very progressive transition; (ii) to correlate this variability with soil waterlogging and topographic variations and (iii) to evaluate carbon stock prediction by modelling waterlogging intensity as soil organic carbon (SOC) stocks increase significantly with waterlogging. However, SOC stocks in redoximorphic soils are highly variable, particularly in zones where carbon is redistributed due to erosion and sedimentation. In the litter and the vegetation, the age and density of the stand are the main explanatory factors of C variability. Topographic modelling of the waterlogging intensity could improve the spatial estimation of SOC stocks but not of the C stocks in the humus and vegetation. 相似文献
15.
Walter Thalenhorst 《Journal of pest science》1938,14(9):105-109
Ohne Zusammenfassung
Mit 2 Abbildungen. 相似文献
16.
17.
Background
Red foxes (Vulpes vulpes L.) have become successful inhabitants of urban areas in recent years. However, our knowledge about the occurrence, distribution and association with land uses of these urban foxes is poor, partly because many favoured habitats are on private properties and therefore hardly accessible to scientists. We assumed that citizen science, i.e. the involvement of the public, could enable researchers to bridge this information gap. We analysed 1179 fox sightings in the city of Vienna, Austria reported via citizen science projects to examine relationships between foxes and the surrounding land use classes as well as sociodemographic parameters.Results
Conditional probabilities of encountering foxes were substantially higher in gardens, areas with a low building density, parks or squares as compared to agricultural areas, industrial areas or forests. Generalized linear model analyses showed that sociodemographic parameters such as education levels, district area, population density and average household income additionally improved the predictability of fox sightings.Conclusions
Reports of fox sightings by citizen scientists might help to support the establishment of wildlife management in cities. Additionally, these data could be used to address public health issues in relation with red foxes as they can carry zoonoses that are also dangerous to humans.18.
Freeman RG Grabar KC Allison KJ Bright RM Davis JA Guthrie AP Hommer MB Jackson MA Smith PC Walter DG Natan MJ 《Science (New York, N.Y.)》1995,267(5204):1629-1632
The self-assembly of monodisperse gold and silver colloid particles into monolayers on polymer-coated substrates yields macroscopic surfaces that are highly active for surface-enhanced Raman scattering (SERS). Particles are bound to the substrate through multiple bonds between the colloidal metal and functional groups on the polymer such as cyanide (CN), amine (NH(2)), and thiol (SH). Surface evolution, which can be followed in real time by ultraviolet-visible spectroscopy and SERS, can be controlled to yield high reproducibility on both the nanometer and the centimeter scales. On conducting substrates, colloid monolayers are electrochemically addressable and behave like a collection of closely spaced microelectrodes. These favorable properties and the ease of monolayer construction suggest a widespread use for metal colloid-based substrates. 相似文献
19.
20.
Morphological and Immunohistochemical Characterization of Canine Osteosarcoma Spheroid Cell Cultures 下载免费PDF全文
Spheroid cell culture emerges as powerful in vitro tool for experimental tumour research. In this study, we established a scaffold‐free three‐dimensional spheroid system built from canine osteosarcoma (OS) cells (D17). Spheroids (7, 14 and 19 days of cultivation) and monolayer cultures (2 and 7 days of cultivation) were evaluated and compared on light and electron microscopy. Monolayer and spheroid cultures were tested for vimentin, cytokeratin, alkaline phosphatase, osteocalcin and collagen I by means of immunohistochemistry. The spheroid cell culture exhibited a distinct network of collagen I in particular after 19‐day cultivation, whereas in monolayer cultures, collagen I was arranged as a lamellar basal structure. Necrotic centres of large spheroids, as observed in 14‐ and 19‐day cultures, were characterized by significant amounts of osteocalcin. Proliferative activity as determined by Ki‐67 immunoreactivity showed an even distribution in two‐dimensional cultures. In spheroids, proliferation was predominating in the peripheral areas. Metastasis‐associated markers ezrin and S100A4 were shown to be continuously expressed in monolayer and spheroid cultures. We conclude that the scaffold‐free spheroid system from canine OS cells has the ability to mimic the architecture of the in vivo tumour, in particular cell–cell and cell–matrix interactions. 相似文献