全文获取类型
收费全文 | 176篇 |
免费 | 14篇 |
专业分类
林业 | 16篇 |
农学 | 10篇 |
58篇 | |
综合类 | 21篇 |
农作物 | 8篇 |
水产渔业 | 15篇 |
畜牧兽医 | 47篇 |
园艺 | 7篇 |
植物保护 | 8篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 7篇 |
2020年 | 3篇 |
2019年 | 11篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 13篇 |
2012年 | 11篇 |
2011年 | 20篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 17篇 |
2007年 | 14篇 |
2006年 | 4篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1992年 | 1篇 |
1986年 | 1篇 |
1981年 | 2篇 |
排序方式: 共有190条查询结果,搜索用时 15 毫秒
51.
There are only a few studies of land cover-land use changes which provide an integrated assessment of the biophysical and
societal causes and consequences of environmental degradation in Ethiopia. Our objectives were to determine the status of
the environmental degradation, analyse and evaluate the relationships among vegetation, geomorphological and socio-economic
factors contributing to environmental degradation, and propose opportunities for rehabilitation of these natural resources.
Field and other environmental data in northern Ethiopia and those acquired by remote sensing techniques were used to accomplish
these objectives. These were integrated with socio-economic data obtained from official sources using a Geographic Information
System (GIS).Spatial information such as the percent of land cover-land use types and geomorphological categories, and the
percent of each land cover-land use type in the geomorphological categories were calculated using Geographic Information System
(GIS). The three most dominant features of the geomorphological categories (93.0%) are scarps and denuded rock slopes, erosion
surfaces and badlands, while the three most dominant features in the land cover-land use types (71.3%) are croplands, open
woodlands and bushlands. Badlands account for 38.7% of the geomorphological units and 41.8% of the croplands currently occur
on badlands. Simple and partial correlation analyses were applied to explore the extent of the interaction between the anthropogenic
and the natural system. The anthropogenic system is influenced by elevation, which is positively correlated with human population
and livestock densities and area of croplands. The natural system finds its place only on steep slopes as shown by the positive
correlation between woodland,slope, high potential erosion, scarps and denudational rock slopes. The study indicates that
agriculture in the study area is in a critical environmental situation. A change of paradigm in land-use and development is
needed to encourage participation of the landowners and users in the efforts to conserve the vegetation and the soil. This
study provides sound options that could be used to rehabilitate the vegetation directly and to alleviate the current pressure
on the land and improve human welfare indirectly. Matching the human and livestock densities with the carrying capacity of
the land through recruitment of the surplus labour force for a modern economy, resettlement,off-farm employment and intensification
of agriculture are t he long and short-term actions that may contribute to the rehabilitation of the degraded areas.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
52.
Dinelli G Accinelli C Vicari A Catizone P 《Journal of agricultural and food chemistry》2000,48(7):3037-3043
A study was carried out in a loamy soil to evaluate the degradation of atrazine and metolachlor under laboratory-controlled and field-variable conditions as a function of temperature and soil moisture content. In laboratory trials, metolachlor showed fast degradation, with half-lives from 100 to 5.7 days in a temperature range from 5 to 35 degrees C at 100% of field capacity, whereas in the same conditions the degradation rate of atrazine was relatively slow, with half-lives from 407 to 23 days. Modeling of laboratory degradation data to predict field persistence was carried out. Field persistence of atrazine and metolachlor was measured in the same soil during the corn growing seasons in 1993, 1994, and 1996. In the three years the mean half-dissipation times for atrazine and metolachlor were 36 and 21 days, respectively. Calculations from model equations gave acceptable prediction of field dissipation of both herbicides. Limitations and perspectives of employed modelization procedure are discussed. 相似文献
53.
Prusinkiewicz P Erasmus Y Lane B Harder LD Coen E 《Science (New York, N.Y.)》2007,316(5830):1452-1456
To understand the constraints on biological diversity, we analyzed how selection and development interact to control the evolution of inflorescences, the branching structures that bear flowers. We show that a single developmental model accounts for the restricted range of inflorescence types observed in nature and that this model is supported by molecular genetic studies. The model predicts associations between inflorescence architecture, climate, and life history, which we validated empirically. Paths, or evolutionary wormholes, link different architectures in a multidimensional fitness space, but the rate of evolution along these paths is constrained by genetic and environmental factors, which explains why some evolutionary transitions are rare between closely related plant taxa. 相似文献
54.
Gratton E 《Science (New York, N.Y.)》2011,331(6020):1016-1017
55.
Enrico Bottero Emanuele Mussi Fabiano Raponi Davide De Lorenzi Pietro Ruggiero 《The Canadian veterinary journal. La revue veterinaire canadienne》2021,62(7):736
This study describes the clinical, diagnostic, and pathological characteristics of canine nasal polyps and how they responded to medical, endoscopic, and surgical treatments. The database of a multi-center veterinary endoscopy group was searched from 2010 to 2018. All dogs with a histological diagnosis of nasal polyposis that were undergoing endoscopic investigation (N = 23), were included. Clinical signs at presentation were sneezing (91%), nasal discharge (83%), stertor (74%), and frontonasal deformation (17%). Skull radiography on 13 dogs had alterations in 77% of cases, including turbinate lysis (6/13), increased radiopacity of one (4/13) or both (6/13) nasal cavities, and lysis of the nasal vomer bone (3/13). Nasal polyposis had a characteristic endoscopic appearance. There were clinical and diagnostic similarities between this cohort of dogs and dogs with nasal neoplasia, although dogs with nasal polyps were often younger and polypoid tissue was external to the nose. Steroid therapy alone was not effective in treating polyposis in dogs; however, endoscopic debulking with a laser and forceps was more effective. 相似文献
56.
Alessandro Vetere Mara Bertocchi Igor Pelizzone Giuseppe F. La Cauza Laura Denti Enrico Bigliardi Francesco Di Ianni 《Journal of veterinary diagnostic investigation》2021,33(1):116
Forty-five Horsfield’s tortoises (Testudo horsfieldii; syn. Agrionemys horfieldii, Russian tortoise) belonging to different owners had decreased appetite and respiratory issues. Twenty-nine tortoises had epiphora, dyspnea, and white necrotic diphtheroid oral plaques (group G1). Ten of the remaining 16 tortoises had serious dehydration, appetite disorder, and depression (G2). The last 6 tortoises had only decreased appetite and moderate conjunctival discharge (G3). During the physical examination of all 45 tortoises, a cytologic sample and an oral swab for herpesvirus and Mycoplasma agassizii PCR testing were taken. In 20 of 29 specimens from G1, in 8 of 16 from G2, and 0 of 6 from G3, the cytologic exam revealed intranuclear acidophilic inclusion bodies, multinucleate cellular syncytia, and further abnormalities caused by herpesviral infection. Moreover, all 45 tested subjects were found to be positive for testudinid herpesvirus 1; 2 were positive for M. agassizii. This prospective study suggests that Horsfield’s tortoises with such signs would benefit from this screening procedure, given that it was effective in a significant proportion of infected and symptomatic animals, and no negative effects were seen. 相似文献
57.
Inhibition of polyphenol oxidases activity by various dipeptides 总被引:1,自引:0,他引:1
Girelli AM Mattei E Messina A Tarola AM 《Journal of agricultural and food chemistry》2004,52(10):2741-2745
In an effort to develop natural and nontoxic inhibitors on the activity of mushroom polyphenol oxidase (PPO) the effect of various glycyl-dipeptides (GlyAsp, GlyGly, GlyHis, GlyLeu, GlyLys, GlyPhe, GlyPro, GlyTyr) was investigated. The inhibition study with dihydroxyphenylalanine (DOPA) as substrate is based on separation of the enzymatic reaction components by reversed phase HPLC and the UV detection of the dopachrome formed. The results have evidenced that several of tested dipeptides inhibited PPO activity in the range of 20-40% while GlyPro and GlyLeu had no effect. The study has also permitted the characterization of the following kinetic pattern: a linear-mixed-type mechanism for GlyAsp, GlyGly, GlyLys, and GlyPhe and a hyperbolic-mixed-type for GlyTyr. It was not possible to identify the inhibition mechanism for GlyHis, although it affects PPO activity. In addition the effects of GlyAsp, GlyLys and GlyHis were evaluated for lessening the browning of fresh Golden Delicious apple and Irish White Skinned potato. The effectiveness of such inhibitors was determined by the difference between the colors observed in the dipeptide-treated sample and the controls using the color space CIE-Lab system. The % browning inhibition on potato (20-50%) was greater than of apple (20-30%) by the all tested dipeptides. Only GlyLys presented the significant value of 50%. 相似文献
58.
59.
The origin of rhizomania resistance in sugar beet 总被引:9,自引:0,他引:9
Enrico Biancardi Robert T. Lewellen Marco De Biaggi Alvin W. Erichsen Piergiorgio Stevanato 《Euphytica》2002,127(3):383-397
In the last 35 years, breeding has greatly reduced the damages caused by rhizomania in sugar beet crops. After the first encouraging
results using the Alba genotypes, the cultivar Rizor represented a substantial step forward and has given good yield improvement
in diseased fields in many parts of the world. The original variety and subsequent improved versions continued to offer good
performances for about a decade, after which it was surpassed by other hybrids derived in part from the Rizor itself. Further
progress in terms of sugar production became possible in 1986, when the Holly monogerm lines were released in USA and Europe.
In spite of the incomplete information about the genealogy of the first resistant materials,many evidences and the molecular
analyses on the different genotypes suggest a possible common progenitor and lineage. The resistant cultivars have kept the
yield at an adequate level, allowing cultivation to continue in countries where the disease has reached epidemic proportions.
The case of rhizomania resistance in sugar beet can therefore be considered as one of the most important achievements in plant
breeding.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
60.
Ilaria Marotti Alessandra Bonetti Maurizio Minelli Pietro Catizone Giovenni Dinelli 《Genetic Resources and Crop Evolution》2007,54(1):175-188
Randomly amplified polymorphic DNA (RAPD), inter-simple sequence repeat (ISSR) and a semi-random PCR system were used to analyze
the genetic diversity of 16 Italian common bean landraces and their relationship to four commercial cultivars. Of the primers
tested, 8 ISSR, 6 RAPD and 7 semi-random primers produced polymorphic and reproducible DNA fragments. A higher proportion
of polymorphic bands were observed using ISSR (85%) and semi-random (90%) primers than RAPD (69%) method. The combination
of any two semi-random markers allowed the identification of all 20 bean genotypes. In contrast ISSR (except for primer (CAC)3GC) and RAPD markers appeared to be less informative as more than two markers were necessary to achieve the same diagnostic
level. Moreover, 7 ISSR, 2 RAPD and 8 semi-random exclusive bands were identified as putative population-specific markers.
Semi-random and ISSR derived dendrograms showed similar tendencies in terms of genetic relatedness, whereas clustering of
genotypes within groups was not similar when compared with the RAPD technique. Despite the different ability to resolve genetic
variation among the investigated landraces, two major clusters with less than 60% (ISSR) and 40% (RAPD and semi-random) genetic
similarity were formed with all three marker systems. The two groups were correlated with the phaseolin patterns and seed
size of the landraces. The analysis showed that the cultivar ȁ8Lingua di Fuocoȁ9 and most of the landraces (13 out of 16)
collected in Italy belong to the Andean gene pool, whereas only the three populations from Pratomagno belong to the Middle
American gene pool. 相似文献