全文获取类型
收费全文 | 280篇 |
免费 | 4篇 |
专业分类
林业 | 42篇 |
农学 | 4篇 |
基础科学 | 2篇 |
108篇 | |
综合类 | 35篇 |
农作物 | 7篇 |
水产渔业 | 24篇 |
畜牧兽医 | 36篇 |
园艺 | 12篇 |
植物保护 | 14篇 |
出版年
2023年 | 3篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 11篇 |
2016年 | 2篇 |
2015年 | 8篇 |
2014年 | 5篇 |
2013年 | 13篇 |
2012年 | 16篇 |
2011年 | 15篇 |
2010年 | 3篇 |
2009年 | 7篇 |
2008年 | 13篇 |
2007年 | 17篇 |
2006年 | 19篇 |
2005年 | 12篇 |
2004年 | 9篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1996年 | 2篇 |
1995年 | 14篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有284条查询结果,搜索用时 15 毫秒
231.
Can picnic influence floral diversity and vitality of trees in Bhawal National Park of Bangladesh? 总被引:1,自引:0,他引:1
We examined the impact of picnic activities on forest diversity, structure, regeneration and vitality of tree species in the
Bhawal National Park of Bangladesh. The study area was classified as a non-used, occasionally used and frequently used area
on the basis of the intensity of the picnic activities. A total of 43 plant species were enumerated in the whole study area.
The highest plant species richness (41 species) was observed in the non-used area whereas the lowest species richness (11
species) in the frequently used area. The diversity index decreased with the increase of picnic intensity whereas the concentration
of dominance increased. Density of all plant groups except mature trees, and the basal area of the mature trees showed a declining
trend from the non-used to frequently used area. The frequently used area exhibited very poor regeneration. Tree vitality
decreased with the increase of picnic intensity. The relevance of our study as a basis for further research to determine the
impact of tourism on biodiversity in Bangladesh is discussed. 相似文献
232.
Metrafenone: studies on the mode of action of a novel cereal powdery mildew fungicide 总被引:2,自引:0,他引:2
Opalski KS Tresch S Kogel KH Grossmann K Köhle H Hückelhoven R 《Pest management science》2006,62(5):393-401
Powdery mildew fungi are among the major pathogens causing diseases of cereals in the world. The mode of action of a novel systemic benzophenone fungicide, metrafenone, which is based on a precursor that is discussed in the preceding paper, has been analysed on the powdery mildew fungi of barley (Blumeria graminis Speer f. sp. hordei Marchal) and wheat (Blumeria graminis Speer f. sp. tritici Marchal). Preventive treatments reduced germination and blocked development beyond formation of appressoria, which penetrated less often. Moreover, metrafenone turned out to be an efficient curative fungicide, which rapidly affected fungal survival at low concentrations. The fungicide induced swelling, bursting and collapse of hyphal tips, resulting in the release of globules of cytoplasm. Bifurcation of hyphal tips, secondary appressoria and hyperbranching were also frequently observed. A histochemical analysis showed that metrafenone caused disruption of the apical actin cap and apical vesicle transport as well as weakening of the cell wall at hyphal tips. Finally, metrafenone strongly reduced sporulation. Reduced sporulation was associated with malformation of conidiophores that showed irregular septation, multinucleate cells and delocalisation of actin. Microtubules appeared to be only secondarily affected in metrafenone-treated B. graminis. The results suggest that the mode of action of metrafenone interferes with hyphal morphogenesis, polarised hyphal growth and the establishment and maintenance of cell polarity. Metrafenone likely disturbs a pathway regulating organisation of the actin cytoskeleton. 相似文献
233.
234.
235.
Lassnig H Much P Schliessnig H Osterreicher E Kostenzer K Kornschober C Köfer J 《Berliner und Münchener tier?rztliche Wochenschrift》2012,125(3-4):129-137
In Austria an EU-wide baseline survey on the prevalence of Salmonella spp. in broilers organized by the EU commission was conducted from October 2005 to September 2006. The aim of this study was to produce comparable data on the prevalence of Salmonella in broiler flocks and holdings for all member states and for the EU-Commission to set EU-wide targets for the control of Salmonella in the broiler populations. A randomised sampling plan was designed according to EU-commission parameters (p = 50%; CI = 95%, a = 5%). Sampling was carried out regularly throughout the whole year. On every farm one flock was sampled with five pairs of boot swabs and analysed in the lab according to appendix D of ISO 6579 (2002). In Austria, 363 flocks on farms consisting of at least 5000 broilers each were tested. 28 flocks (7.7%) showed infections with Salmonella spp., eight flocks (2.2%) had either S. Enteritidis (six flocks) or S. Typhimurium (two flocks). In detail, S. Enteritidis (1.7%), S. Typhimurium (0.6%), S. Montevideo (4.1%), S. Infantis 0.6%, S. Senftenberg, S. Tennessee and S. Virchow (0.3% each) have been found. Data indicated that the risk of vertical transmission of Salmonella spp. to broiler flocks has almost been kept at bay; however, the risk of horizontal transmission still needs attention. Contamination of feeding stuff, possible persistence, spreading between barns of a farm as well as introduction of Salmonella spp. through individuals or materials are important factors for future control strategies. 相似文献
236.
Process-based forest landscape models are valuable tools for testing basic ecological theory and for projecting how forest
landscapes may respond to climate change and other environmental shifts. However, the ability of these models to accurately
predict environmentally-induced shifts in species distributions as well as changes in forest composition and structure is
often contingent on the phenomenological representation of individual-level processes accurately scaling-up to landscape-level
community dynamics. We use a spatially explicit landscape forest model (LandClim) to examine how three alternative formulations
of individual tree growth (logistic, Gompertz, and von Bertalanffy) influence model results. Interactions between growth models
and landscape characteristics (landscape heterogeneity and disturbance intensity) were tested to determine in what type of
landscape simulation results were most sensitive to growth model structure. We found that simulation results were robust to
growth function formulation when the results were assessed at a large spatial extent (landscape) and when coarse response
variables, such as total forest biomass, were examined. However, results diverged when more detailed response variables, such
as species composition within elevation bands, were considered. These differences were particularly prevalent in regions that
included environmental transition zones where forest composition is strongly driven by growth-dependent competition. We found
that neither landscape heterogeneity nor the intensity of landscape disturbances accentuated simulation sensitivity to growth
model formulation. Our results indicate that at the landscape extent, simulation results are robust, but the reliability of
model results at a finer resolution depends critically on accurate tree growth functions. 相似文献
237.
Berisha B Welter H Shimizu T Miyamoto A Meyer HH Schams D 《The Journal of reproduction and development》2006,52(2):307-313
The aim of this study was to evaluate the expression pattern of mRNA for fibroblast growth factor 1 (FGF1), FGF7, and their receptor variants (FGFR2IIIb) in time-defined follicle classes before LH surge, between LH surge and ovulation, and in the early corpus luteum (CL) in the cow. The ovaries were collected by transvaginal ovariectomy (n=5 cows/group), and the follicles (n=5, one follicle/cow) were classified into the following groups: before GnRH administration (before LH surge); 3-5 h after GnRH (during LH surge); 10 h after GnRH; 20 h after GnRH; 25 h after GnRH (periovulation), and early CL (Days 2-3). The mRNA expression was analyzed by quantitative real-time PCR (RotorGene 3000). The mRNA expression of FGF1 showed no significant differences in the follicle groups examined, but increased significantly at the early CL phase. A transient increase in FGF7 mRNA expression was observed 3-5 h after GnRH and again in the early CL phase. In contrast, the expression of FGFR2IIIb was constant throughout the period from the final growth of the follicle to early CL formation. The results of this study suggest that FGF1 and FGF7 may be involved differently in the process of follicle maturation and CL formation, which is strongly dependent on angiogenesis. 相似文献
238.
We studied the defense reactions of 33-year-old susceptible and resistant clones of Norway spruce (Picea abies (L.) Karst.) to the major root-rot fungus Heterobasidion annosum (Fr.) Bref. and determined if tissue cultures can be used as a model system for studying defense responses of mature trees at the molecular level. Quantitative PCR analysis of genomic DNA obtained from samples taken at different times along the lesion length in living bark indicated that the fungus was present in higher amounts and extended further into the host tissue in the susceptible clone than in the resistant clone. In protein extracts from the same lesion samples, there were differences in temporal and spatial changes in host chitinase isoform profiles between the resistant and susceptible clones. Host chitinase isoforms with pI values approximately 4.8, 4.4 and 3.7 increased more during the first 7 days after wounding and inoculation and extended further along the lesion length in the resistant clone than in the susceptible clone. These results suggest that the time from wounding and infection to induction of defense-related expression is shorter in the resistant clone indicating a more efficient host defense response than in the susceptible clone. Tissue cultures from the same clones were not resistant to H. annosum and showed no difference in the timing of the increase in chitinase isoforms in response to the pathogen. However, tissue cultures from both clones showed an increase in chitinase isoforms within 6 to 24 h past inoculation, indicating that increased chitinase expression in response to the pathogen is part of a general defense response common to both mature clones and tissue cultures. 相似文献
239.
Stéphanie Schmid Andreas Zingg Peter Biber Harald Bugmann 《European Journal of Forest Research》2006,125(1):43-55
The semi-empirical single-tree model SILVA 2.2 has been developed and parameterised using forest research and inventory data
from Germany that range from the colline to the montane zone. The focus of the model evaluation presented in this study was
to test the applicability of the model for the main Swiss forest types and at elevations ranging from the colline to the upper
subalpine zone. To this end, SILVA was initialized using data from long-term forest yield research plots. The results at the
end of the 30-year simulation were compared with observed data. The analysis of the results at each test site showed that
there were no significant differences in model performance between forest types. However, the deviation between simulated
and observed growth depended strongly on the elevational zone, i.e., on climate. As expected, the best results were found
in the colline zone, for which the model had been calibrated, whereas the upper subalpine sites revealed the strongest differences.
The quality of the data regarding forest structure that were available for model initialization had a strong impact on the
simulation results, mainly at high-elevation zones (i.e., supalpine and upper subalpine). We conclude that SILVA 2.2 is a
suitable tool to estimate the development of single trees and standing volume for a large fraction of the forests in Switzerland.
However, extreme climate conditions should be avoided with the model, and the availability of detailed stand structure information
is a key priority that has a strong effect on the quality of the simulation results.
相似文献
Harald BugmannEmail: |
240.
Pedersen ME Takle H Ytteborg E Veiseth-Kent E Enersen G Færgestad E Baeverfjord G Hannesson KO 《Fish physiology and biochemistry》2011,37(4):821-831
We have previously characterized the development of vertebral fusions induced by elevated water temperature in Atlantic salmon.
Molecular markers of bone and cartilage development together with histology were used to understand the complex pathology
and mechanism in the development of this spinal malformation. In this study, we wanted to use proteomics, a non-hypothetical
approach to screen for possible new markers involved in the fusion process. Proteins extracted from non-deformed and fused
vertebrae of Atlantic salmon were therefore compared by two-dimensional electrophoresis (2DE) and MALDI-TOF analysis. Data
analysis of protein spots in the 2DE gels demonstrated matrilin-1, also named cartilage matrix protein, to be the most highly
up-regulated protein in fused compared with non-deformed vertebrae. Furthermore, real-time PCR analysis showed strong up-regulation
of matrilin-1 mRNA in fused vertebrae. Immunohistochemistry demonstrated induced matrilin-1 expression in trans-differentiating
cells undergoing a metaplastic shift toward chondrocytes in fusing vertebrae, whereas abundant expression was demonstrated
in cartilaginous tissue and chordocytes of both non-deformed and fused vertebrae. These results identifies matrilin-1 as a
new interesting candidate in the fusion process, and ratify the use of proteomic as a valuable technique to screen for markers
involved in vertebral pathogenesis. 相似文献