全文获取类型
收费全文 | 2546篇 |
免费 | 171篇 |
专业分类
林业 | 216篇 |
农学 | 138篇 |
基础科学 | 13篇 |
569篇 | |
综合类 | 125篇 |
农作物 | 150篇 |
水产渔业 | 369篇 |
畜牧兽医 | 920篇 |
园艺 | 54篇 |
植物保护 | 163篇 |
出版年
2024年 | 2篇 |
2023年 | 34篇 |
2022年 | 44篇 |
2021年 | 108篇 |
2020年 | 89篇 |
2019年 | 129篇 |
2018年 | 99篇 |
2017年 | 110篇 |
2016年 | 95篇 |
2015年 | 73篇 |
2014年 | 114篇 |
2013年 | 140篇 |
2012年 | 204篇 |
2011年 | 217篇 |
2010年 | 124篇 |
2009年 | 128篇 |
2008年 | 149篇 |
2007年 | 135篇 |
2006年 | 133篇 |
2005年 | 127篇 |
2004年 | 110篇 |
2003年 | 106篇 |
2002年 | 74篇 |
2001年 | 24篇 |
2000年 | 22篇 |
1999年 | 13篇 |
1998年 | 17篇 |
1997年 | 13篇 |
1996年 | 4篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1983年 | 2篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1968年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有2717条查询结果,搜索用时 31 毫秒
991.
992.
Jesús Cerezo Valverde María D. Hernández Sandra García-Garrido Carmen Rodríguez Juán Estefanell Joan I. Gairín Carlos J. Rodríguez Ana Tomás Benjamín García García 《Aquaculture International》2012,20(1):71-89
In this study, HPTLC was used to make a quantitative analysis of the total lipid content (TL dry weight) and their classes
in 39 samples, including molluscs, crustaceans, fish and meals in an attempt to identify those most suitable for formulating
diets for cephalopods by reference to an index of nutritional quality (OILC: Oser’s index modified for lipid classes). All the crustaceans analysed (<10% TL), fish from artisanal fisheries such as
Boops boops, Gadus poutassou, Mugil sp. and Gadus minutus (<10% TL) and the plant meals (TL < 5%) would cause fewer digestive problems than the fish that were a by-catch from fish
farms (B. boops or Sparus aurata), pelagic species (Sardina pilchardus or Trachurus trachurus) or krill meal, which are characterised by their high lipid content (20–60% TL). These latter feeds were associated with
neutral lipids, mainly triglycerides during the summer. Mytilus galloprovincialis, Carcinus maenas, G. poutassou, Mugil sp., S. pilchardus and G. minutus had a more appropriate lipid content and profile during the winter, when they showed a higher OILC due to the greater variety of polar lipid classes they contained. Phospholipids like PS, PI and PE seem to be limiting nutrients
in cephalopods because of their high content (78–542, 41–309 and 152–2,114 mg/100 g, respectively) compared with the rest
of the samples. None of the meals analysed showed a good nutritional balance per se and should only be used in conjunction
with other foods. 相似文献
993.
Pedro Domingues Javier Alaminos Sandra García‐Garrido Ismael Hachero‐Cruzado Carlos Rosas 《Aquaculture Research》2012,43(2):167-177
The effects of diet freezing on the growth, survival and biochemical composition of the diets and juvenile spider crabs (Maja brachydactyla) were studied. Fresh and frozen (at ?20 °C for 21 days) mussels, Mytilus edulis, were used as food. Two experiments were conducted and in each, spider crabs were placed in individual trays. During experiment I, 40 juvenile spider crabs (2 months old) were used. Twenty animals (9 ± 2 mg) were fed fresh mussels, and 20 animals (8 ± 2 mg) were fed frozen mussels. Spider crabs fed fresh mussels grew larger than the ones fed frozen mussels (304.0 ± 118.0 and 70.0 ± 40.1 mg respectively). During experiment II, 16 juvenile spider crabs (5 months old) were used. Eight animals (3.4 ± 0.8 g) were fed fresh mussel and eight animals (4.1 ± 1.3 g) were fed frozen mussel. Spider crabs fed with fresh mussels were larger than the ones fed with frozen mussels (92.5 ± 41.7 and 41.5 ± 17.7 g respectively). There were no significant differences in the protein, amino acids and fatty acid composition between fresh and frozen mussels. The freezing procedure makes mussels less adequate for the culture of 2‐month‐old early juveniles of M. brachydactyla up to 5 months, although they promoted acceptable growth and good survival in older animals (>5 months old). 相似文献
994.
Caroline Pelegrina Teixeira Margarida Maria Barros Luiz Edivaldo Pezzato Ademir Calvo Fernandes Jr João Fernando Albers Koch Carlos Roberto Padovani 《Aquaculture Research》2012,43(8):1081-1088
In order to assess the effect of dietary pyridoxine supplementation on the growth performance of Nile tilapia and the haematological response under heat stress, 192 fingerlings (8.41 ± 0.22 g) were randomly distributed into eight tanks and fed practical diets supplemented with increasing levels of pyridoxine (0.0; 5.0; 10.0 and 20.0 mg of pyridoxal HCl kg?1 diet) for 91 days. The fish were then weighed and the diet was quantified to determine the growth performance [weight gain (WG), feed intake, feed conversion ratio, protein efficiency rate, protein retention (PR) and survival percentage]. Haematological analyses (red blood cell count, haematocrit, haemoglobin, total leucocyte and differentiation, mean corpuscular volume, mean corpuscular haemoglobin concentration, albumin, globulin and albumin/globulin ratio) were carried out and then 32 fish were transferred and subjected to heat stress (32 °C) for 3 days, after which the haematological parameters were analysed. The fish fed the unsupplemented diet showed the lowest WG and PR. For the normal growth and health of the Nile tilapia, the Pyridoxine requirement in a practical diet is 10.0 mg of pyridoxine HCl kg?1. 相似文献
995.
Alvarez González Carlos Enrique Gil E. Fernández-Falcón M. Hernández M. M. 《Water, air, and soil pollution》2009,196(1-4):273-285
Water, Air, & Soil Pollution - The paper summarizes results of chemical analyses of fog and rime water samples. The samples were collected at Milesovka, the Czech meteorological observatory.... 相似文献
996.
Carlos R. Fonseca Gislene Ganade Ronei Baldissera Carlos R. Boelter Lucas M. Campos Vanda S. Fonseca Fernando Joner Ana M. Leal-Zanchet Alex S. Mesquita Claudia P. Paz Fabio N. Piovensan Anamaria Stranz Emerson M. Vieira 《Biological conservation》2009,142(6):1209-31
Since pristine Atlantic Forest remnants are vanishing, and biological reserves are in short, conservation of biodiversity will largely depend on proper management of the anthropogenic matrix. Here, we test (1) the effectiveness of ecologically-managed tree monocultures in maintaining Araucaria Forest biodiversity, (2) how this effectiveness change among taxa, and (3) we discuss management principles that can be used by the forestry industry in order to contribute positively to biodiversity conservation. The study was conducted in the São Francisco de Paula National Forest, southern Brazil, an environmental mosaic composed mostly of patches of Araucaria Forest and ecologically-managed monocultures of Araucaria, Pinus and Eucalyptus. Using standardized sampling methods in these four main habitats, we have recorded the richness and species composition of small mammals, birds, leaf-litter frogs, butterflies, galling insects, spiders, opiliones, flatworms, woody plants, epiphytic angiosperms, epiphytic ferns, lichens, and fruit-body producing fungi. Overall, we recorded 506 species in Araucaria Forest, 181 (36%) of which were exclusive of this habitat while 325 (64%) could be found in at least one monoculture. Distribution patterns of species richness and number of records across taxonomic groups showed that a large biodiversity can be found inside ecologically-managed plantations of Araucaria, Pinus, and Eucalyptus. For all studied taxa, except for epiphytic angiosperms and fruit-body producing fungi, more than half of the Araucaria Forest species could be found living on monocultures. We discuss how the actual management practices of the forest industry can be improved to contribute positively to the conservation of the Atlantic Forest biodiversity. 相似文献
997.
Ariadna Valentina Lopes Luciana Coe Girão Carlos A. Peres 《Biological conservation》2009,142(6):1154-1997
Habitat loss and fragmentation promote relatively predicable shifts in the functional signature of tropical forest tree assemblages, but the full extent of cascading effects to biodiversity persistence remains poorly understood. Here we test the hypotheses that habitat fragmentation (a) alters the relative contribution of tree species exhibiting different reproductive traits; (b) reduces the diversity of pollination systems; and (c) facilitates the functional convergence of reproductive traits between edge-affected and early-secondary forest habitats (5-32 years old). This study was carried out in a severely fragmented 670-km2 forest landscape of the Atlantic forest of northeastern Brazil. We assigned 35 categories of reproductive traits to 3552 trees (DBH ? 10 cm) belonging to 179 species, which described their pollination system, floral biology, and sexual system. Trait abundance was calculated for 55 plots of 0.1 ha across four habitats: forest edges, small forest fragments (3.4-83.6 ha), second-growth patches, and core tracts of forest interior within the largest available primary forest fragment (3500 ha) in the region. Edge-affected and secondary habitats showed a species-poor assemblage of trees exhibiting particular pollination systems, a reduced diversity of pollination systems, a higher abundance of reproductive traits associated with pollination by generalist diurnal vectors, and an elevated abundance of hermaphroditic trees. As expected, the reproductive signature of tree assemblages in forest edges and small fragments (edge-affected habitats), which was very similar to that of early second-growth patches, was greatly affected by both habitat type and plot distance to the nearest forest edge. In hyper-fragmented Atlantic forest landscapes, we predict that narrow forest corridors and small fragments will become increasingly dominated by edge-affected habitats that can no longer retain the full complement of tree life-history diversity and its attendant mutualists. 相似文献
998.
Mauro Galetti Henrique C. Giacomini Christine S.S. Bernardo Ricardo S. Bovendorp Paulo Rubim Camila I. Donatti Rodrigo A. Begotti Rodrigo de A. Nobre Carlos A. Peres 《Biological conservation》2009,142(6):1229-1241
Large mammal faunas in tropical forest landscapes are widely affected by habitat fragmentation and hunting, yet the environmental determinants of their patterns of abundance remain poorly understood at large spatial scales. We analysed population abundance and biomass of 31 species of medium to large-bodied mammal species at 38 Atlantic forest sites (including three islands, 26 forest fragments and six continuous forest sites) as related to forest type, level of hunting pressure and forest fragment size using ANCOVAs. We also derived a novel measure of mammal conservation importance for each site based on a “Mammalian Conservation Priority index” (MPi) which incorporates information on species richness, population abundance, body size distribution, conservation status, and forest patch area. Mammal abundance was affected by hunting pressure, whereas mammalian biomass of which was largely driven by ungulates, was significantly influenced by both forest type and hunting pressure. The MPi index, when separated into its two main components (i.e. site forest area and species-based conservation index Ci), ordered sites along a gradient of management priorities that balances species-focused and habitat-focused conservation actions. Areas with the highest conservation priority were located in semi-deciduous forest fragments, followed by lowland forests. Many of these fragments, which are often embedded within large private landholdings including biofuel and citrus or coffee crops, cattle ranches and pulpwood plantations, could be used not only to comply with environmental legislation, but also enhance the prospects for biodiversity conservation, and reduce edge effects and hunting. 相似文献
999.
Carlos E. Hernandez Ho-Hsien Chen Chi-I. Chang Tzou-Chi Huang 《Industrial Crops and Products》2009,30(3):359-365
The direct esterification of chlorogenic acid (5-CGA) by immobilized Candida antarctica lipase B (Novozym 435) in supercritical CO2/t-butanol has been studied. The Taguchi approach was applied to evaluate the effects of temperature (35–55 °C), pressure (150–250 bar), t-butanol (2–10%, v/v), and the enzyme amount (10–30 mg/ml), on the ester concentration and overall conversion. Optimum reaction conditions were established at: 150 bar, 55 °C, 10% t-butanol (v/v), 20 mg/ml of lipase. Addition of 20 mg/ml of molecular sieves (3 Å) was also necessary to minimize the inhibiting effect of the increasing water concentration. Maximum conversions reached 77, 82 and 85% in 25 h using geraniol, pentanol and heptanol as aliphatic chain donors, respectively. HPLC analysis demonstrated the selective esterification of 5-CGA from a coffee pulp aqueous-methanolic extract, which reached a conversion to heptyl ester of 65% at the optimal condition. The supercritical CO2 selectivity towards the esterified product was the working principle of this study, by which minimized interphase transport limitations and enhanced mass-transfer phenomena substantially improved the reaction kinetics. 相似文献
1000.
Manuela Branco Conceição Boavida Nicolas Durand José Carlos Franco Zvi Mendel 《Phytoparasitica》2009,37(1):51-54
The Eucalyptus gall wasp Ophelimus maskelli (Hymenoptera: Eulophidae) and its parasitoid Closterocerus chamaeleon (Hymenoptera: Eulophidae) were observed for the first time in Portugal, in 2006 and 2007, respectively. Data on the distribution
of O. maskelli in Portugal, differences in the susceptibility of two host species, Eucalyptus globulus and Eucalyptus camaldulensis, and parasitism by C. chamaeleon are given. 相似文献