全文获取类型
收费全文 | 678篇 |
免费 | 76篇 |
专业分类
林业 | 45篇 |
农学 | 33篇 |
基础科学 | 1篇 |
144篇 | |
综合类 | 15篇 |
农作物 | 47篇 |
水产渔业 | 87篇 |
畜牧兽医 | 315篇 |
园艺 | 17篇 |
植物保护 | 50篇 |
出版年
2023年 | 7篇 |
2022年 | 16篇 |
2021年 | 31篇 |
2020年 | 40篇 |
2019年 | 46篇 |
2018年 | 52篇 |
2017年 | 45篇 |
2016年 | 46篇 |
2015年 | 28篇 |
2014年 | 52篇 |
2013年 | 40篇 |
2012年 | 66篇 |
2011年 | 55篇 |
2010年 | 30篇 |
2009年 | 27篇 |
2008年 | 23篇 |
2007年 | 23篇 |
2006年 | 18篇 |
2005年 | 22篇 |
2004年 | 22篇 |
2003年 | 15篇 |
2002年 | 8篇 |
2001年 | 13篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有754条查询结果,搜索用时 234 毫秒
41.
C.S. Carvalho 《Aquaculture (Amsterdam, Netherlands)》2006,251(1):109-117
Copper sulfate has been widely used to control algae and pathogens in fish culture ponds. However, its toxic effects on fish depend not only on its concentration in water but also on water quality. The susceptibility of the neotropical freshwater fish Prochilodus scrofa to copper was evaluated at two temperatures with low and high water pH. Juvenile fish were acclimated at 20 and 30 °C and exposed to copper (static bioassay system) in water with pH 4.5 and 8.0. The 96 h-LC50 were determined at each temperature and pH, as were the hematological parameters. The 96 h-LC50 for copper (98 and 88 μg Cu L− 1 in water with pH 4.5 and 16 and 14 μg Cu L− 1 in water with pH 8.0 for fish kept at 20 and 30 °C, respectively) was significantly dissimilar in pH 4.5 and 8.0, but no difference was found between 20 and 30 °C in the same water pH. At 20 °C, regardless of the water pH, the hematocrit (Hct) increased while the red blood cells (RBC) and hemoglobin (Hb) concentration decreased compared to control pH 7.0. Copper exposure in water pH 4.5 and 8.0 causes an increase on the Hct, RBC and Hb concentrations in relation to the controls pH 4.5 and 8.0. At 30 °C, the changes on the blood parameters depended on the water pH and, after copper exposure at low and high pH, the blood changes indicated more complex responses. The changes in hematological parameters of the fish, regardless of the pH and water temperature, indicate ionoregulatory or respiratory disturbances that imply an increase in energy consumption to restore homeostasis instead of other physiological functions such as weight gain and growth. 相似文献
42.
Carvalho Thayslan Brosinsky Arlena Foerster Saskia Teixeira Adunias Medeiros Pedro 《Journal of Soils and Sediments》2022,22(9):2557-2577
Journal of Soils and Sediments - Soil erosion by water yields sediment to surface reservoirs, reducing their storage capacities, changing their geometry, and degrading water quality. Sediment... 相似文献
43.
Walmir Ribeiro de Carvalho Steel Silva Vasconcelos Osvaldo Ryohei Kato Carlos José Bispo Capela Débora Cristina Castellani 《Agroforestry Systems》2014,88(2):357-368
The current expansion of the oil palm (Elaeis guineensis Jacq.) in the Brazilian Amazon has mainly occurred within smallholder agricultural and degraded areas. Under the social and environmental scenarios associated with these areas, oil palm-based agroforestry systems represent a potentially sustainable method of expanding the crop. The capacity of such systems to store carbon (C) in the soil is an important ecosystem service that is currently not well understood. Here, we quantified the spatial variation of soil C stocks in young (2.5-year-old) oil palm-based agroforestry systems with contrasting species diversity (high vs. low); both systems were compared with a ~10-year-old forest regrowth site and a 9-year-old traditional agroforestry system. The oil palm-based agroforestry system consisted of series of double rows of oil palm and strips of various herbaceous, shrub, and tree species. The mean (±standard error) soil C stocks at 0–50 cm depth were significantly higher in the low (91.8 ± 3.1 Mg C ha?1) and high (87.6 ± 3.3 Mg C ha?1) species diversity oil palm-based agroforestry systems than in the forest regrowth (71.0 ± 2.4 Mg C ha?1) and traditional agroforestry (68.4 ± 4.9 Mg C ha?1) sites. In general, no clear spatial pattern of soil C stocks could be identified in the oil palm-based agroforestry systems. The significant difference in soil carbon between the oil palm area (under oil palm: 12.7 ± 2.3 Mg C ha?1 and between oil palm: 10.6 ± 0.5 Mg C ha?1) and the strip area (17.0 ± 1.4 Mg C ha?1) at 0–5 cm depth very likely reflects the high input of organic fertilizer in the strip area of the high species diversity oil palm-based agroforestry system treatment. Overall, our results indicate a high level of early net accumulation of soil C in the oil palm-based agroforestry systems (6.6–8.3 Mg C ha?1 year?1) that likely reflects the combination of fire-free land preparation, organic fertilization, and the input of plant residues from pruning and weeding. 相似文献
44.
Marisa Naia Virgilio Hermoso Sílvia B. Carvalho José Carlos Brito 《水产资源保护:海洋与淡水生态系统》2021,31(7):1886-1900
- Systematic conservation planning in freshwater ecosystems faces multiple challenges because of the dynamic nature of rivers and their multiple dimensions of connectivity. In intermittent hydrological systems connectivity is functional when water is available, allowing the exchange of aquatic individuals between isolated freshwater ecosystems. Integrating these isolated systems in their hydrological context is essential when identifying priority areas for conservation, in order to try to minimize the propagation of threats into target water bodies (management units) from the surrounding landscape.
- Here, the use of a systematic planning approach is demonstrated to identify a set of priority management units to preserve freshwater biodiversity in an arid system of fragmented water bodies immersed in a landscape subject to a range of impacts.
- Twenty-six water-dependent taxa from 59 mountain rock pools (gueltas) of three southern Mauritanian mountains were used as a case study. A conservation planning tool (marxan ) was used to find priority conservation areas to integrate intermittent hydrological systems in their hydrological context, promote connectivity, and minimize the downstream propagation of threats. Three types of connectivity were analysed: (i) no connectivity, (ii) connectivity between gueltas, and (iii) connectivity between gueltas and sub-catchments.
- Considering different types of longitudinal connectivity affects the number and spatial allocation of the priority gueltas selected, and the conservation status of the gueltas and their upstream areas. Incorporating connections between gueltas and upstream locations in the modelling resulted in the selection of gueltas in areas with a low human footprint and in the increased connectivity of the solutions.
- The results obtained revealed important locations for local biodiversity conservation, and the method presented can be used when assessing the propagation of potential waterborne threats into isolated management units. The framework developed allows connectivity to be addressed in conservation planning. It can be replicated in regions with similar isolated habitats that connect through intermittent hydrological systems and can also be applied to lateral and vertical hydrological connectivity.
45.
Tillage and weed control are critical components of cropping systems that need to be combined such that crops benefit from reduced competition. However, weeds may also contribute to the biological diversity within the agro‐environment. This greenhouse study investigated whether common weeds of arable cropping systems were suitable host plants for arbuscular mycorrhizal fungi (AMF), allowing the development of extraradical mycelium (ERM) that can contribute to the early colonization of a following wheat crop, especially in the absence of soil disturbance. Weeds were allowed to grow for up to 2 months before being controlled by soil disturbance or herbicide application (glyphosate or paraquat). Pregerminated wheat seeds were then planted. Chemical control of the weeds prior to sowing enhanced the early arbuscular mycorrhiza (AM) colonization rate of wheat roots, whereas mechanical disturbance was less acceptable as a method of weed control for rapid AM colonization. The type of herbicide (contact or systemic) had no impact on colonization of the wheat crop. Enhanced AM colonization promoted early P acquisition and growth of the crop. Appropriate management of weeds emerging between two consecutive cropping seasons coupled with no‐till soil management could ensure a quick and efficient AM colonization of the following wheat plants. 相似文献
46.
47.
48.
D. M. Moreira J. C. Carvalho A. G. Goulart T. Tirabassi 《Water, air, and soil pollution》2005,161(1-4):285-297
An Eulerian model and a Lagrangian particle model are used to study the dispersion of a contaminant released from a low source in the Stable Boundary Layer (SBL) using two different turbulence parameterisations. The Eulerian model is based on the solution of the advection–diffusion equation by the Laplace transform technique. The Lagrangian model is based on a generalized form of the Langevin equation. The first parameterisation, Degrazia et al. (2000), is based on Taylor’s statistical diffusion theory and the observed spectral properties, supposes a linear combination between shear and buoyancy turbulence. The second, Hanna (1982), is based on observed spectral properties from Minnesota Planetary Boundary Layer (PBL) observations and is widely used in pollutant dispersion models. Considering that these simulations are in the SBL, the analysis of the results shows a reasonably good agreement between the values computed by the models against the experimental ones for the two turbulence parameterisations. 相似文献
49.
Fernando Shintate Galindo Marcelo Carvalho Minhoto Teixeira Filho Salatiér Buzetti José Mateus Kondo Santini Eduardo Henrique Marcandalli Boleta Willian Lima Rodrigues 《Journal of plant nutrition》2020,43(8):1057-1069
AbstractNew studies are needed to optimize the nitrogen (N) amount that can be applied to utilize the Azospirillum brasilense benefits. In addition, information regarding the interaction between the urease inhibitor and biological nitrogen fixation (BNF) and how they affect the macronutrients accumulation are also needed. We evaluate the effect of N sources and doses associated with A. brasilense regarding the macronutrients accumulation in straw and grains and wheat grain yield in tropical conditions. A randomized block experimental design was used with four replications in a 2?×?5?×?2 factorial arrangement as follows: two N sources (urea and urea with urease enzyme inhibitor NBPT; five N doses (0, 50, 100, 150, and 200?kg ha?1) applied in topdressing; with and without A. brasilense inoculation. We found that an increase in N doses positively influenced the accumulation of macronutrients in straw and grains and the wheat grain yield. N sources have similar effects. Inoculation with A. brasilense increased accumulation of Mg and S in straw and P, Ca, and Mg in grains, regardless of the N dose. The inoculation with A. brasilense associated with 140?kg ha?1 of N increased wheat grain yield. The inoculation can contribute in a more sustainable way to wheat nutrition and optimizing N fertilization. 相似文献
50.
Duarte RT Carvalho Simões MC Sgarbieri VC 《Journal of agricultural and food chemistry》1999,47(1):231-236
The objective of this research work was to fractionate bovine blood, collected hygienically in a slaughterhouse, into blood plasma protein concentrate, red blood cell concentrate, globin isolate, and a carboxymethylcellulose-heme iron (CMC-heme) complex. All four fractions were studied for proximate composition and amino acid and mineral contents. The nutritive value of plasma protein concentrate and globin isolate was comparatively studied using rat bioassays. The amino acid content in plasma protein concentrate is well balanced and produced net protein utilization and net protein ratio equivalent to 95% those of casein. Globin isolate ( approximately 91% protein) is deficient in isoleucine and S-containing amino acids and was unable to support rat growth at 10% concentration in the diet. Red blood cell concentrate and the isolated CMC-heme complex were good sources of bioavailable iron. Iron availabilities for CMC-heme and whole blood cell concentrate, related to ferrous sulfate as 100%, were 64 and 70%, respectively. 相似文献