全文获取类型
收费全文 | 1574篇 |
免费 | 170篇 |
国内免费 | 3篇 |
专业分类
林业 | 123篇 |
农学 | 82篇 |
基础科学 | 14篇 |
266篇 | |
综合类 | 79篇 |
农作物 | 108篇 |
水产渔业 | 202篇 |
畜牧兽医 | 694篇 |
园艺 | 39篇 |
植物保护 | 140篇 |
出版年
2024年 | 1篇 |
2023年 | 26篇 |
2022年 | 39篇 |
2021年 | 83篇 |
2020年 | 97篇 |
2019年 | 119篇 |
2018年 | 120篇 |
2017年 | 108篇 |
2016年 | 123篇 |
2015年 | 61篇 |
2014年 | 87篇 |
2013年 | 89篇 |
2012年 | 124篇 |
2011年 | 110篇 |
2010年 | 65篇 |
2009年 | 62篇 |
2008年 | 66篇 |
2007年 | 65篇 |
2006年 | 56篇 |
2005年 | 32篇 |
2004年 | 37篇 |
2003年 | 29篇 |
2002年 | 24篇 |
2001年 | 21篇 |
2000年 | 22篇 |
1999年 | 14篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 2篇 |
排序方式: 共有1747条查询结果,搜索用时 203 毫秒
101.
In late 2003, a new disease appeared in protected bean crops in southeastern Spain, causing a decrease of over 50% in production.
Several samples of affected plants were collected and analyzed and the agent of this disease was identified as the bacterium
Erwinia aphidicola, which had never been described as a pathogen previously. We attempted to determine the possible bacterium transmission through
seeds, using 120 commercial bean seeds from the same batch as that used in an affected farm, and 120 seeds from the fruiting
plants of the same farm. Seed coats, cotyledons and leaves of plants originating from them, were taken and analyzed. Several
of the developed symptoms on plants from commercial and fruiting plant seeds were internervial chlorosis, necrotic pits and
rough roots and they coincided with those observed on affected crops. Bacteria present in commercial seed cotyledons were
isolated and analyzed by biochemical and molecular tests. Results confirmed the presence of Erwinia aphidicola in four analyzed seeds; moreover, Bacillus simplex/Bacillus muralis, Pseudomonas mendocina, Pseudomonas putida and Paenibacillus polymyxa were also identified. 相似文献
102.
Progressive adoption of no-tillage (NT) agriculture in the tropics is finally reversing physical, chemical, and biological erosion of soil and in Brazil, an estimated 19 Mha are now devoted to NT. Common bean (Phaseolus vulgaris L.) is a main component of Brazilian agriculture, and enhancement of yields has been achieved under NT as a result of mitigation of environmental stresses, resulting in higher N2 fixation. However, the effects of NT on rhizobial diversity are poorly understood. This study evaluated rhizobial diversity in soils planted to common bean under NT or conventional tillage (CT) systems that were compared with natural grassland used for grazing, in the State of Santa Catarina, southern Brazil. Genetic diversity was assessed by the amplification of the DNA by PCR with specific primers (BOX-PCR) and by RFLP-PCR analyses of the 16S rDNA region. A high level of diversity was observed among strains from all three systems, such that the similarity in the clustering analysis of BOX-PCR products ranged from 36% under natural grassland to only 23% for CT strains. High polymorphism was confirmed in the RFLP-PCR analysis; forty-seven different profiles were obtained, none sharing high similarity with the profiles of reference species of common bean rhizobia. These results indicate that other tropical rhizobial species remain to be described. Genetic diversity was higher among the NT than the CT rhizobial strains, especially when the RFLP-PCR profiles were considered. Genetic diversity in the natural grassland was lower than in the cropped systems, possibly due to absence of the host plant and stubble burning in winter. Average yields in the area under NT (e.g. common bean, approximately 1500 kg ha−1) have been about 30% higher than under CT, therefore high rhizobial diversity may be a parameter indicative of superior soil quality. 相似文献
103.
Patrícia Valent?o Paula B Andrade Eurico Silva Ana Vicente Henrique Santos M Lourdes Bastos Rosa M Seabra 《Journal of agricultural and food chemistry》2002,50(3):460-463
In the course of a phytochemical study of the bitter tonic plant, small centaury (Centaurium erythraea), six methoxylated xanthones (1,5-hydroxy-3-methoxyxanthone, 1-hydroxy-3,5,6-trimethoxyxanthone, 1-hydroxy-3,5,6,7-tetramethoxyxanthone, 1-hydroxy-3,5,6,7,8-pentamethoxyxanthone, 1-hydroxy-3,7,8-trimethoxyxanthone and 1,8-dihydroxy-3,5,6,7-tetramethoxyxanthone) were isolated and identified by spectroscopic means (nuclear magnetic resonance, mass spectroscopy, and UV). Subsequently, a high-performance liquid chromatography/diode array detection method was developed for the determination of these and other methoxylated xanthones occurring in the chloroform extract of small centaury aerial parts. The methodology developed was applied to twelve samples, and in all of them, nine xanthones were identified and quantified. This methodology can be considered complimentary to the one proposed by the European Pharmacopoeia. 相似文献
104.
Bastos De Maria CA Moreira Santos MC José De Lima Dias U Marana M 《Journal of agricultural and food chemistry》2000,48(9):3935-3938
The effect of heated quercetin (400 mg/kg of oil) or 5-caffeoylquinic acid (5-CQA) and the presence of ferric ion (2.2 mg/kg of oil) on the stability of soya oil oxidized in an oxidative stability index (OSI) instrument was investigated. After heating the phenolic at 100 degrees C or 150 degrees C, the OSI values of treated oils were not significantly (p < 0.001) different, whereas, at 200 degrees C, the values decreased significantly with addition of quercetin, but not with 5-CQA. However, the antioxidative activity of quercetin remained significantly greater than that of 5-CQA. The antioxidative potency of quercetin was reduced significantly by addition of ferric palmitate (FP), but that of 5-CQA was not. Reaction between the ortho-dihydroxy groups of the quercetin and ferric ion may reduce the number of hydroxyls available to react with free radicals. Chelating action of 5-CQA might be provided by ortho-dihydroxy grouping of the quinic acid moiety. 相似文献
105.
Post-mortem examination of 658 goats showed that 17 (2.5%) exhibited hepatic abscesses. The following bacteria were isolated: Corynebacterium pseudotuberculosis (58.9%), Escherichia coli (11.8%), Corynebacterium sp. (11.8%), Pasteurella haemolytica (5.9%), Proteus sp. (5.9%) and Staphylococcus aureus (5.9%). Hepatic abscesses occurred more frequently in adult animals. Eleven of the 17 goats (64.7%) were older than 12 months of age. Four goats (23.5%) were 12 months of age and only two (11.8%) were less than 1 year of age. All of the goats with hepatic abscesses were in poor nutritional condition and the abscesses were invariably associated with accompanying pathological disorders at other body sites. 相似文献
106.
Santos M López-Sanromán J García-Iturralde P Fuente M Tendillo FJ 《Veterinary anaesthesia and analgesia》2005,32(6):355-359
OBJECTIVE: To determine the cardiopulmonary effects of desflurane (DES) in horses. ANIMALS: Six healthy adult horses, three males and three females, aged 9 +/- 4 (mean +/- SD) years and weighing 370 +/- 36 kg. MATERIALS AND METHODS: Anaesthesia was induced with an O2 (10 L minute(-1)) and DES mixture (vaporizer setting 18%). After oro-tracheal intubation, horses were positioned in right lateral recumbency. Anaesthesia was maintained with DES in O2 (20 mL kg(-1) minute(-1)) delivered through a large animal circle breathing system. The minimum alveolar concentration of DES (MAC(DES)) that prevented purposeful movement in response to 60 seconds of electrical stimulation of the oral mucous membranes was determined for each horse. The delivered concentration of DES was then increased to achieve end-tidal concentrations corresponding to 1.5 x MAC(DES), 1.75 x MAC(DES), and 2.0 x MAC(DES). Heart rate (HR), mean arterial blood pressure (MAP), respiratory rate (fr), tidal volume (VT), minute volume (VM) and core temperature were determined, and blood samples for arterial blood gas analysis taken at each DES concentration. All data were analysed by two-way anova for repeated measures and Fisher's test for multiple comparisons. A probability level of p < 0.05 was applied. RESULTS: Desflurane concentrations of 2.0 x MAC(DES) increased HR whereas lower concentrations did not. Mean arterial pressure was not affected by 1.0 x MAC(DES) 1.5 x MAC(DES) or 1.75 x MAC(DES), whereas it decreased at 2.0 x MAC(DES). All concentrations of DES examined significantly depressed fr, VT and VM. CONCLUSIONS AND CLINICAL RELEVANCE: Desflurane concentrations between 1.0 and 1.75 x MAC(DES) reduces fr and VM but does not affect HR or MAP in horses. 相似文献
107.
N.?VovlasEmail author N.?J.?O.?Sim?es N.?Sasanelli M.?C.?V.?dos?Santos I.?M.?de?O.?Abrantes 《Phytoparasitica》2004,32(2):167-173
During a nematode survey, severe infections of tobacco feeder roots and heavy soil infestations byMeloidogyne incognita race 1 were found in S. Miguel (Azores islands, Portugal). This is the first record ofM. incognita infection of tobacco in Azores. Morphology of various life stages, analysis of the esterase electrophoretic pattern and differential
host tests were used for nematode characterization and identification. Nematode-induced mature galls were spherical and/or
ellipsoidal and usually contained more than one female, males and egg masses with eggs. Feeding sites were characterized by
the development of giant cells that contained granular cytoplasm and many hypertrophied nuclei. Giant cell cytoplasm was aggregated
along a thickened cell wall. Vascular tissues within galls appeared disorganized. The relationship between the initial nematode
population density and growth of tobacco plants was tested in a glasshouse experiment in which inoculum levels varied from
0 to 512 eggs and juveniles (J2) cm−3 of soil. Seinhorst’s model was fitted to height and top fresh weight data of the inoculated and control plants. Tolerance
limits with respect to plant height and fresh top weight of tobacco cv. ‘Erzegovina’ plants toM. incognita race 1 were estimated as 1.25 eggs and J2 cm−3 of soil. The maximum nematode reproduction rate was 404.7 at an initial population density of 4 eggs and J2 cm−3 of soil.
http://www.phytoparasitica.org posting March 2, 2004. 相似文献
108.
Gennari SM Canón-Franco WA Yai LE de Souza SL Santos LC Farias NA Ruas J Rossi FW Gomes AA 《Veterinary parasitology》2004,121(3-4):337-340
The prevalence of anti-Toxoplasma gondii antibodies was evaluated by the indirect immunofluorescent-antibody test in serum of 57 wild canids from three different species: Lycalopex gymnocercus, Cerdocyon thous and Dusicyon vetulus from the northeast, southeast and southern regions of Brazil. The prevalence was 35.1%, with 20 of the 57 canids demonstrating antibodies anti-T. gondii at dilutions of 1:16 in 2, 1:32 in 4, 1:64 in 2, 1:128 in 2, 1:256 in 6, 1:512 in 2 and 1:2048 in 2 animals. None of the D. vetulus were positive. Among the L. gymnocercus 11 (91.7%) of the 12 samples were positive and among C. thous 9 (60%) of the 15 had antibodies anti-T. gondii. 相似文献
109.
Pigatto JA Andrade MC Laus JL Santos JM Brooks DE Guedes PM Barros PS 《Veterinary ophthalmology》2004,7(3):205-208
The objective of this study was to examine the endothelial surface morphology and to perform morphometric analysis of the corneal endothelial cells of Yacare caiman (Caiman yacare) using scanning electron microscopy. Morphometric analysis with regard to polygonality, mean cell area, cell density and coefficient of variation of mean cell area was performed. Cell areas were measured using image analysis software. The normal corneal endothelium of Yacare caiman consisted of polygonal cells of uniform size and shape with interdigitations of the cell borders. Microvilli appeared as protrusions on the cellular surface. The average cell area was 270 +/- 24 microm(2) and the endothelial cell density was 3704 +/- 324 cells/mm(2). The coefficient of variation of cell area was 0.22. This study demonstrates that the Yacare caiman corneal endothelium is similar to those described in other vertebrates. 相似文献
110.