全文获取类型
收费全文 | 223196篇 |
免费 | 13940篇 |
国内免费 | 911篇 |
专业分类
林业 | 23058篇 |
农学 | 13939篇 |
基础科学 | 2992篇 |
41280篇 | |
综合类 | 14746篇 |
农作物 | 17195篇 |
水产渔业 | 15963篇 |
畜牧兽医 | 79785篇 |
园艺 | 6183篇 |
植物保护 | 22906篇 |
出版年
2021年 | 2496篇 |
2020年 | 2882篇 |
2019年 | 3683篇 |
2018年 | 3920篇 |
2017年 | 4280篇 |
2016年 | 4712篇 |
2015年 | 4265篇 |
2014年 | 5626篇 |
2013年 | 16149篇 |
2012年 | 5474篇 |
2011年 | 7174篇 |
2010年 | 7101篇 |
2009年 | 7743篇 |
2008年 | 6645篇 |
2007年 | 5512篇 |
2006年 | 6252篇 |
2005年 | 5449篇 |
2004年 | 5337篇 |
2003年 | 5103篇 |
2002年 | 4413篇 |
2001年 | 4825篇 |
2000年 | 4471篇 |
1999年 | 4424篇 |
1998年 | 4006篇 |
1997年 | 4071篇 |
1996年 | 3810篇 |
1995年 | 4334篇 |
1994年 | 3714篇 |
1993年 | 3398篇 |
1992年 | 3495篇 |
1991年 | 3706篇 |
1990年 | 3346篇 |
1989年 | 3339篇 |
1988年 | 2936篇 |
1987年 | 2955篇 |
1986年 | 2863篇 |
1985年 | 3186篇 |
1984年 | 3089篇 |
1983年 | 2992篇 |
1982年 | 2594篇 |
1981年 | 2587篇 |
1980年 | 2560篇 |
1979年 | 2753篇 |
1978年 | 2544篇 |
1977年 | 2393篇 |
1976年 | 2264篇 |
1975年 | 2055篇 |
1974年 | 2126篇 |
1973年 | 2041篇 |
1972年 | 1773篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
A system dynamic model for epidemics of Blumeria graminis (powdery mildew) on wheat was elaborated, based on the interaction between stages of the disease cycle, weather conditions and host characteristics. The model simulates the progress of disease severity, expressed as a percentage of powdered leaf area, on individual leaves, with a time step of one day, as a result of two processes: the growth of fungal colonies already present on the leaves and the appearance of new colonies. By means of mathematical equations, air temperature, vapour pressure deficit, rainfall and wind are used to calculate incubation, latency and sporulation periods, the growth of pathogen colonies, infection and spore survival. Effects of host susceptibility to infection, and of leaf position within the plant canopy, are also included. Model validation was carried out by comparing model outputs with the dynamics of epidemics observed on winter wheat grown at several locations in northern Italy (1991–98). Simulations were performed using meteorological data measured in standard meteorological stations. As there was good agreement between model outputs and actual disease severity, the model can be considered a satisfactory simulator of the effect of environmental conditions on the progress of powdery mildew epidemics. 相似文献
952.
For more than 10 years, a forecasting model for Cydia pomonella in apple orchards, worked out by the French NPPO, has described the development of emergence cohorts in spring, and followed their development and descent, through the whole agricultural season. In homogeneous areas, this tool, still under development, can be used to define periods for effective treatment (ovicides, larvicides, mating disruption) and the tolerance for codling moth levels in various situations. Alternation of insecticides is provided for, so as to manage resistance phenomena. The reliability of the model is based on rigorous continuous biological checks on the forecasts made by the algorithm, on scientific surveillance by INRA and on regular collaboration between the advisers involved and the agrometeorological services. The model forms part of a wider decisional scheme, or expert system, in which the fruit grower and his adviser provide observations on the changes which cannot be provided by the model: installation of hail protection nets, night lights, fruit spreading. More parameters will be incorporated in future and the geographical validity of the model will be extended, particularly to more northerly areas. 相似文献
953.
A mechanistic model called PLASMO was developed earlier to simulate grapevine downy mildew (Plasmopara viticola) and has been applied in several viticultural areas of Italy since 1988 by the collaboration of several research institutions of Firenze. In this study, a new simulation model based on fuzzy logic has been developed for the same structure (biological cycle of P. viticola). This approach allows classical quantitative information to be used together with qualitative information. Vague concepts can also be handled. Agrometeorological data is used, with an hourly time step, starting from budbreak to the end of the growing season. Air temperature, relative humidity, rainfall and leaf wetness are required. The simulated processes are the growth of grapevine leaf area and the main phases of the biological cycle of the pathogen: incubation, sporulation, germination, spore survival and inoculation. The main epidemiological outputs are timing of infection events and disease intensity. The performance of the model is evaluated and the mechanistic and fuzzy logic approaches are compared. 相似文献
954.
P. Battilani V. Rossi B. Girometta M. Delos J. Rouzet N. Andr S. Esposito 《EPPO Bulletin》2003,33(3):427-431
Diaporthe helianthi is the causal agent of a severe sunflower disease but, in Italy, disease outbreaks are sporadic with no significant losses. The present work investigates the role of meteorological conditions on the potential development of D. helianthi epidemics in Italy, using the French model Asphodel, which simulates the effect of air temperature, relative humidity and rainfall on ascospore maturation and dispersal, infection establishment, disease onset and severity during the period of host susceptibility. Meteorological data measured in eight stations distributed from north to south Italy, over a 5‐year period (1995–99), was used as model input. Results showed that meteorological conditions in Italy are frequently favourable for D. helianthi infections on sunflower, and severe epidemics are possible. Therefore, climatic conditions are not a limiting factor for disease development in the Italian sunflower‐growing areas. The lack of disease epidemics in Italy may be related to differences in the pathogen populations compared with the French ones. 相似文献
955.
Journal of Plant Diseases and Protection - Effect of GCSC-BtA (Germany-China Scientific Cooperation — Bacillus thuringiensis — Abamectin) biocide on abundance and diversity of some... 相似文献
956.
957.
958.
D. Boscia H. Zeramdini M. Cambra O. Potere M.T. Gorris A. Myrta B. Di Terlizzi V. Savino 《European journal of plant pathology / European Foundation for Plant Pathology》1997,103(5):477-480
A monoclonal antibody to an Albanian isolate of plum pox potyvirus (PPV) was obtained (MAbAL), that specifically recognized strain M of this virus. The specificity of MAbAL, assessed by comparative ELISA on 130 PPV isolates of different geographical origin, 22 of which were also tested by comparative IC-PCR, gave consistent and highly reproducible results. MAbAL seems to be elicited by a stable surface determinant that makes it particularly suitable for successful use under a wide range of conditions. MAbAL is an useful addition to the panel of PPV-specific MAbs available to date. 相似文献
959.
R.B. Mabagala 《European journal of plant pathology / European Foundation for Plant Pathology》1997,103(2):175-181
Surface and internal populations of Xanthomonas campestris pv. phaseoli, causal agent of common bacterial blight of bean, on and in flower buds, blossoms and pods of seven bean (Phaseolus vulgaris) genotypes were studied. Bean plants were grown in the field and artificially inoculated at the seedling stage (18 days old). The pathogen was recovered in high numbers from flower buds, blossoms, pods and seed of both resistant and susceptible bean genotypes. Significant differences (P = 0.05) in population levels of X. c. pv. phaseoli between stages of reproductive tissue development were observed. Infected seed from resistant bean genotypes had no visible symptoms. Such seed may play an important role in the epidemiology of common bacterial blight because they are difficult to detect and may occur at low frequency in seed lots, as was the case in the current study. 相似文献
960.
P. Larignon B. Dubos 《European journal of plant pathology / European Foundation for Plant Pathology》1997,103(2):147-157
Cross sections of woody stems of 309 diseased grapevines collected in France showed two kinds of necrosis typical of esca: a) A central light-colored necrosis of soft consistency, consisting of three zones, preceded by a centrally discolored wood, and b) a sectorial light-colored necrosis composed of two zones preceded by a sectorial brown necrosis. Isolations showed that different microflora was associated with each necrosis. Phaeoacremonium aleophilum and Phaeoacremonium chlamydosporum occurred in the discolored wood and the zones bordering the central decayed wood. Eutypa lata was the main fungus isolated from sectorial brown necrosis and the zones adjoining the decay wood. Phellinus punctatus was isolated from the sectorial and central decayed wood. Stereum hirsutum was present in decayed wood of 15 grapevines with esca symptoms not inhabited by P. punctatus. Wood decay tests and pathogenicity tests showed that S. hirsutum and P. punctatus were responsible for the decayed wood. Phaeoacremonium chlamydosporum and S. hirsutum produced a centrally discolored wood similar to that found in esca-affected vines. Phaeoacremonium aleophilum caused a sectorial brown necrosis of soft texture. From these studies, it was found that esca is a complex disease involving several microorganisms whose role in the process leading to wood degradation is discussed. 相似文献