首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   526篇
  免费   29篇
林业   49篇
农学   15篇
基础科学   6篇
  167篇
综合类   46篇
农作物   36篇
水产渔业   26篇
畜牧兽医   143篇
园艺   18篇
植物保护   49篇
  2023年   6篇
  2022年   5篇
  2021年   19篇
  2020年   15篇
  2019年   16篇
  2018年   19篇
  2017年   17篇
  2016年   16篇
  2015年   13篇
  2014年   18篇
  2013年   26篇
  2012年   45篇
  2011年   50篇
  2010年   20篇
  2009年   24篇
  2008年   26篇
  2007年   34篇
  2006年   26篇
  2005年   26篇
  2004年   16篇
  2003年   16篇
  2002年   16篇
  2001年   5篇
  2000年   3篇
  1999年   6篇
  1998年   4篇
  1997年   2篇
  1996年   4篇
  1995年   3篇
  1994年   2篇
  1993年   3篇
  1990年   2篇
  1988年   3篇
  1986年   4篇
  1985年   6篇
  1984年   4篇
  1982年   2篇
  1981年   2篇
  1972年   2篇
  1966年   2篇
  1963年   3篇
  1959年   1篇
  1956年   2篇
  1955年   2篇
  1954年   1篇
  1936年   2篇
  1934年   1篇
  1932年   1篇
  1931年   1篇
  1925年   1篇
排序方式: 共有555条查询结果,搜索用时 15 毫秒
11.

Background

Root-knot nematodes (RKN) are major pest of olive tree (Olea europaea ssp. europaea), especially in nurseries and high-density orchards. Soil samples were collected from main olive growing areas of Morocco, to characterize Meloidogyne species and to discuss the contribution of biotic and abiotic factors in their spatial distribution.

Results

RKN were found in 159 soil samples out of 305 from nurseries (52.1% occurrence) and in 11 out of 49 soil samples from orchards (23.2% occurrence). Biochemical and molecular characterisation (PAGE esterase and SCAR) revealed the dominance of M. javanica both in nurseries and orchards with minor presence of M. incognita only in nurseries, and M. arenaria in only one nursery. RKN were distributed on aggregated basis. Frequent presence of M. javanica in orchards might have come from nurseries. In contrast, the detection of M. incognita in nurseries alone suggests that this species could not reproduce in orchards because of either the competition with other plant-parasitic nematodes or unfit local habitats. The impact of environmental variables (climate, habitat origin and physicochemical characteristics of the substrates) on the distribution of Meloidogyne species is also discussed.

Conclusion

Olive nurseries in Morocco are not able to guarantee the safety of rooted plants. As a result, olive production systems are exposed to strong RKN invasion risks. Consequently, the use of healthy substrates in nurseries may prevent plant-parasitic nematode induction in orchards.
  相似文献   
12.
Cereals contaminated by Aspergillus spp., Penicillium spp., and Fusarium spp. and their mycotoxins, for example, ochratoxin A (OTA) and deoxynivalenol (DON), are not only a risk to human and animal health but can also show poor technological properties and baking quality. The influence of these genera on the sulfur speciation of low molecular weight (LMW) subunits of glutenin was characterized by investigating suboptimally stored wheat samples in situ by X-ray absorption near edge structure (XANES) spectroscopy and baking tests. Field fungi of the genus Fusarium have hardly any influence on both the sulfur speciation of wheat gluten proteins and the baking properties, whereas storage fungi of the genera Aspergillus and Penicillium have a direct influence. An increased amount of sulfur in sulfonic acid state was found, which is not available for thiol/disulfide exchange reactions in the gluten network, and thus leads to a considerably reduced baking volume. From changes of the composition of the mould flora during suboptimal storage of wheat and from the mycotoxin contents, it can be concluded that microbial competitive interactions play an important role in the development of the mould flora and the mycotoxin concentrations during (suboptimal) storage of wheat.  相似文献   
13.
In low-intensity grazing systems, patch grazing leads to a mosaic structure of short (frequently defoliated) and tall (rarely defoliated) patches, with the stocking rate determining the proportion of these patch types on the pasture. Little is known about the long-term effects of patch grazing on the productivity of contrasting sward height patches developed under varying stocking rates. On a 12-year low-intensity cattle pasture we investigated aboveground net primary productivity (ANPP) and its seasonal variation in different patch types (‘short’, ‘medium’ and ‘tall’) under three stocking rates (‘moderate’, ‘lenient’ and ‘very lenient’) over two years. Additionally, we determined stocks of soil phosphorus, potassium and magnesium as well as soil pH. ANPP was affected by an interaction of patch type and stocking rate and ranged from less than 300 g/m2 in short patches under very lenient stocking to more than 1,000 g/m2 in medium patches under moderate stocking. In contrast with observations at the start of the experiment, ANPP in short patches was similar to or less than that in medium and tall patches. As topsoil phosphorus and potassium stocks were lowest in short patches, this indicates a long-term redistribution of nutrients by grazing animals, which limits short-patch productivity. Productivity of medium patches increased with stocking rate, and soil potassium concentration showed a similar trend, pointing towards enhanced nutrient cycling under more intensive stocking. We conclude that nutrient redistribution may lead to increasing trade-offs between ecological and agronomic aims in long-term low-intensity grazing systems.  相似文献   
14.
Accurate hybrid prediction and knowledge about the relative contribution of general (GCA) and specific combining ability (SCA) are of utmost importance for efficient hybrid breeding. We therefore evaluated 91 triticale single-cross hybrids in field trials at seven environments for plant height, heading time, fresh biomass, dry matter content and dry biomass. Fresh and dry biomass showed the highest proportion (23%) of variance due to SCA. Prediction accuracies based on GCA were slightly higher than based on mid-parent values. Utilizing parental kinship information yielded the highest prediction accuracies when both parental lines have been tested in other hybrid combinations, but still moderate-to-low prediction accuracies for two untested parents. Thus, hybrid prediction for biomass traits in triticale is currently promising based on mid-parent values as emphasized by our simulation study, but can be expected to shift to GCA-based prediction with an increasing importance of GCA due to selection in hybrid breeding. Moreover, the performance of potential hybrids between newly developed lines can be predicted with moderate accuracy using genomic relationship information.  相似文献   
15.
In the 1970s unexpected forest damages, called “new type of forest damage” or “forest decline”, were observed in Germany and other European countries. The Federal Republic of Germany and the German Federal States implemented a forest monitoring system in the early 1980s, in order to monitor and assess the forest condition. Due to the growing public awareness of possible adverse effects of air pollution on forests, in 1985 the ICP Forests was launched under the convention on long-range transboundary air pollution (CLRTAP) of the United Nations Economic Commission for Europe (UN-ECE). The German experience in forest monitoring was a base for the implementation of the European monitoring system. In 2001 the interdisciplinary case study “concept and feasibility study for the integrated evaluation of environmental monitoring data in forests”, funded by the German Federal Ministry of Education and Research, concentrated on in-depths evaluations of the German data of forest monitoring. The objectives of the study were: (a) a reliable assessment of the vitality and functioning of forest ecosystems, (b) the identification and quantification of factors influencing forest vitality, and (c) the clarification of cause-effect-relationships leading to leaf/needle loss. For these purposes additional data from external sources were acquired: climate and deposition, for selected level I plots tree growth data, as well as data on groundwater quality. The results show that in particular time series analysis (crown condition, tree growth, and tree ring analysis), in combination with climate and deposition are valuable and informative, as well as integrated evaluation of soil, tree nutrition and crown condition data. Methods to combine information from the extensive and the intensive monitoring, and to transfer process information to the large scale should be elaborated in future.
Sabine AugustinEmail:
  相似文献   
16.
Ohne ZusammenfassungHerr Professor Fabricius hat mir das Versuchsgelände, Herr Professor Schmausz, als Vorstand des Forstmeteorologischen Institutes, die Meszgeräte in liebenswürdiger Weise zur Verfügung gestellt. Herr Professor Geiger und Herr Regierungsforstrat Woelfle haben mich miederholt mit Rat und Hilfe unterstübt. Jhnen allen spreche ich zum Schlusz meinen besten Dank aus.  相似文献   
17.
18.
This study describes the experience with hypofractionated radiation therapy of squamous cell carcinoma and melanoma in dogs and cats. A total dose of 32-48 Gray (Gy) was delivered once a week in 8 Gy fractions. 34 animals in which a complete surgical excision was impossible were treated. There was no tumor detectable macroscopically in 14 patients at the beginning of radiation therapy. In 20 animals the median volume of the tumor was 9.9 cm3. The median survival times and the local tumor control of squamous cell carcinoma of the oral and nasal cavities and of the body are comparable to results which were reached with a Monday-Wednesday-Friday scheme. For the treatment of Melanoma the hypofractionated radiation therapy is first choice. There are no significant side effects. Late side effects did not occur. 88% of the owners are satisfied with this kind of treatment and would choose it again.  相似文献   
19.
Bacterial whole-cell biosensors were used to measure the concentration of chlortetracycline (CTC) in the feces of pigs. In this study, the Escherichia coli biosensor used has a detection limit of 0.03 mg/kg CTC in pig feces. The tetracycline concentration was correlated with the appearance and maintenance of fecal coliform bacteria resistant to tetracycline. Initially, large quantities of water-extractable CTC were excreted from the pigs and measurable amounts were detected even at 30 days after treatment cessation. This led to a sharp rise in the number of tetracycline resistant coliform bacteria in the feces, to within the same order of magnitude as the total coliform count. The high level of tetracycline resistance was maintained in spite of the declining concentration of tetracycline.  相似文献   
20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号