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排序方式: 共有986条查询结果,搜索用时 265 毫秒
881.
882.
Retrospective evaluation of thoracic computed tomography findings in dogs naturally infected by Angiostrongylus vasorum 下载免费PDF全文
883.
Retrospective Evaluation of Whole Body Computed Tomography for Tumor Staging in Dogs with Primary Appendicular Osteosarcoma 下载免费PDF全文
884.
885.
Irvine NM Yerkes CN Graupner PR Roberts RE Hahn DR Pearce C Gerwick BC 《Pest management science》2008,64(9):891-899
BACKGROUND: The novel natural product cinnacidin was isolated from a fungal fermentation extract of Nectria sp. DA060097. The compound was found to contain a cyclopentalenone ring system with an isoleucine subunit linked through an amide bond. Initial biological characterization of cinnacidin suggested promising herbicidal activity. RESULTS: Two synthetic analogs, (2S,3S)-2-[(3RS,3aSR,6aRS)-3-methoxy-4-oxo-3,3a,4,5,6,6a-hexahydropentalen-1-ylcarbamoyl]-3-methylvaleric acid and benzyl (2S,3S)-2-[(3RS,3aSR,6aRS)-3-methoxy-4-oxo-3,3a,4, 5,6,6a-hexahydropentalen-1-ylcarbamoyl]-3-methylvalerate, were prepared for further characterization, and their herbicidal activities were compared with that of cinnacidin. CONCLUSIONS: The synthetic compounds were highly phytotoxic on a range of weeds. Based on the symptoms in treated plants, the mode of action of these compounds is suggested to be similar to that of coronatine and jasmonic acid. Coronatine was more active against warm-season grasses, while the cinnacidin benzyl ester analog was more effective on cool-season grasses. In a seedling growth bioassay conducted on bentgrass, the cinnacidin analog was equivalent in activity to coronatine. 相似文献
886.
Nicholas L. Crookston Gerald E. Rehfeldt Gary E. Dixon Aaron R. Weiskittel 《Forest Ecology and Management》2010
To simulate stand-level impacts of climate change, predictors in the widely used Forest Vegetation Simulator (FVS) were adjusted to account for expected climate effects. This was accomplished by: (1) adding functions that link mortality and regeneration of species to climate variables expressing climatic suitability, (2) constructing a function linking site index to climate and using it to modify growth rates, and (3) adding functions accounting for changing growth rates due to climate-induced genetic responses. For three climatically diverse landscapes, simulations were used to explore the change in species composition and tree growth that should accompany climate change during the 21st century. The simulations illustrated the changes in forest composition that could accompany climate change. Projections were the most sensitive to mortality, as the loss of trees of a dominant species heavily influenced stand dynamics. While additional work is needed on fundamental plant–climate relationships, this work incorporates climatic effects into FVS to produce a new model called Climate–FVS. This model provides for managers a tool that allows climate change impacts to be incorporated in forest plans. 相似文献
887.
Hollie Hall Yuncong Li Nicholas Comerford Enrique Arévalo Gardini Luis Zuniga Cernades Virupax Baligar Hugh Popenoe 《Agroforestry Systems》2010,80(3):447-455
In many tropical soils, excessive weathering of primary minerals confounded by intense agricultural production has resulted
in the depletion of organic matter and plant available forms of phosphorus (P). Long-term growth of cover crops in tropical
agroforestry systems have been shown to influence nutrient cycling, and soil organic matter pools. The objective of this experiment
was to assess the affect of 2 years of cover-crop cultivation on organic matter accumulation and P bioavailability using Mehlich
I and sequential fractionation methods. The experiment included six treatments in the understory of a cacao-plantain agroforestry
system adjacent to lower montane tropical forests of the San Martin district of Eastern Peru. Cacao and plantain formed the
primary canopy on otherwise abandoned agricultural land. The treatments consisted of four perennial leguminous cover crops
(Arachis pintoi, Calopogonium mucunoides, Canavalia
ensiformis, and Centrosema macrocarpum), a non-legume cover crop (Callisia repens), and a control treatment (no cover crop). After only 2 years of cultivation, results suggest that all cover crop species
accessed residual P pools in 0–5 cm soil depths as indicated by a decrease in the 0.5 M HCl extractable P pools when compared
to control. Additional use of residual P pools by A. pintoi and C. macrocarpum were indicated by significant reduction in the 6.0 M HCl extractable P pool. Relative to control, there was no treatment
effect on soil organic matter content; however significant differences occurred between treatments. The C. ensiformis, C. mucunoides and C. repens treatments in 5–15 cm soil depths contained significantly more organic matter than the A. pintoi treatment. In 15–30 cm soil depths the C. ensiformis treatment contains significantly more organic matter than the A. pintoi treatment. Continued research should focus on monitoring the long-term effects of cover crop cultivation on the bioavailability
of soil P pools in surface soil horizons, development of organic matter pools and the productivity of the agroforestry species. 相似文献
888.
Coastal Douglas-fir (Pseudotsuga menziesii spp. menziesii (Mirb.) Franco) occurs over a wide range of environmental conditions on Vancouver Island, British Columbia. Although ecological zones have been drawn, no formal spatial analysis of environmental limitations on tree growth has been carried out. Such an exercise is desirable to identify areas that may warrant intensive management and to evaluate the impacts of predicted climate change this century. We applied a physiologically based forest growth model, 3-PG (Physiological Principles Predicting Growth), to interpret and map current limitations to Douglas-fir growth across Vancouver Island at 100-m cell resolution. We first calibrated the model to reproduce the regional productivity estimates reported in yield table growth curves. Further analyses indicated that slope exposure is important; southwest slopes of 30 degrees receive 40% more incident radiation than similarly inclined northeast slopes. When combined with other environmental differences associated with aspect, the model predicted 60% more growth on southwest exposures than on northeast exposures. The model simulations support field observations that drought is rare in the wetter zones, but common on the eastern side of Vancouver Island at lower elevations and on more exposed slopes. We illustrate the current limitations on growth caused by suboptimal temperature, high vapor pressure deficits and other factors. The modeling approach complements ecological classifications and offers the potential to identify the most favorable sites for management of other native tree species under current and future climatic conditions. 相似文献
889.
Blackburn GM Williams NH Gamblin SJ Smerdon SJ 《Science (New York, N.Y.)》2003,301(5637):1184; author reply 1184
890.
Harberd NP 《Science (New York, N.Y.)》2003,299(5614):1853-1854