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   1137篇
  免费   87篇
林业   68篇
农学   34篇
基础科学   2篇
  231篇
综合类   54篇
农作物   51篇
水产渔业   124篇
畜牧兽医   533篇
园艺   18篇
植物保护   109篇
  2024年   2篇
  2023年   22篇
  2022年   23篇
  2021年   43篇
  2020年   48篇
  2019年   29篇
  2018年   33篇
  2017年   37篇
  2016年   45篇
  2015年   41篇
  2014年   61篇
  2013年   69篇
  2012年   78篇
  2011年   102篇
  2010年   45篇
  2009年   57篇
  2008年   97篇
  2007年   58篇
  2006年   34篇
  2005年   45篇
  2004年   39篇
  2003年   43篇
  2002年   30篇
  2001年   20篇
  2000年   19篇
  1999年   3篇
  1998年   4篇
  1997年   7篇
  1995年   5篇
  1993年   3篇
  1992年   6篇
  1991年   5篇
  1990年   3篇
  1989年   5篇
  1988年   2篇
  1987年   8篇
  1986年   7篇
  1985年   9篇
  1984年   4篇
  1982年   3篇
  1980年   3篇
  1978年   3篇
  1977年   3篇
  1975年   2篇
  1972年   4篇
  1971年   1篇
  1970年   1篇
  1969年   3篇
  1968年   2篇
  1949年   1篇
排序方式: 共有1224条查询结果,搜索用时 15 毫秒
131.
In order to investigate the occurrence of Campylobacter, Helicobacter and Arcobacter species in caecal contents of rabbits reared in intensive and rural farms, a total of 87 samples from animals belonging to 29 farms were analysed by both cultural and PCR analyses.  相似文献   
132.
The aim of this study was to measure the levels of inflammatory mediators in serum from horses naturally infected with Trypanosoma vivax. Banked serum samples collected during a previously reported T. vivax natural infection were used to analyze proinflammatory cytokines such as interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), interleukin 1 (IL-1), interleukin 6 (IL-6), and nitrite/nitrate (NOx) levels. We evaluated 12 serum samples from horses from a farm in southern Brazil, four of which had parasitological and molecular diagnoses for T. vivax and presented with clinical signs of disease. Cytokines were assessed by quantitative sandwich enzyme-linked immunosorbent assay, and NOx was measured using the modified Griess method. Levels of IFN-γ, TNF-α, IL-1, IL-6, and NOx were increased in serum of infected animals compared to that in noninfected animals. Therefore, infection with T. vivax caused an increase in proinflammatory cytokines and nitric oxide content.  相似文献   
133.

Background

Salmonella species (spp.) are zoonotic enteric bacteria able to infect humans, livestock and wildlife.However, little is known about the prevalence and the presence of the different serovars in wildlife. Considering the wide distribution of wild boars and the feeding behaviour (omnivorous scavengers), wild boars may be a good indicator for environmental presence of Salmonella spp. The aims of this study were to determine the presence of Salmonella spp. in hunted wild boars and to determine the serotype the isolated strains.

Findings

Over three hunting seasons, the intestinal contents of 1,313 boars hunted in northern Italy were sampled and cultured. Salmonella spp. were isolated from 326 boars (24.82%). Thirty different serovars belonging to three different S. enterica spp. were found. Twenty-one serovars of S. enterica subsp. Enterica were found including the human pathogens S. Typhimurium and S. Enteritidis. In addition, nine serovars belonging to S.enterica subsp. diarizonae and S. enterica subsp. houtenae were detected.

Conclusions

Considering the widespread occurrence of wild boars in Europe, the epidemiological role of this species in relation to salmonellosis might be relevant and should be further investigated. Wild boars may act as healthy carriers of a wide range of Salmonella serotypes.  相似文献   
134.
Genomic analysis of a metronidazole resistant H. bizzozeronii strain revealed a frame length extension of the oxygen-insensitive NAD(P)H-nitroreductase HBZC1_00960 (RdxA), associated with the disruption of the C-terminal cysteine-containing conserved region (IACLXALGK). This was the result of the extension (from C8 to C9) of a simple sequence cytosine repeat (SSCR) located in the 3’ of the gene. A 3'' SSCR is also present in the rdxA homolog of H. heilmannii sensu stricto, but not in H. pylori. We showed that in the majority of in vitro spontaneous H. bizzozeronii metronidazole resistant mutants, the extension of the 3′ SSCR of rdxA was the only mutation observed. In addition, we observed that H. bizzozeronii ΔrdxA mutant strain showed the same MIC value of metronidazole observed in the spontaneous mutants. These data indicate that loss of function mutations in rdxA and in particular the disruption of the conserved region IACLXALGK is associated with reduced susceptibility to metronidazole in H. bizzozeronii. Slipped-strand mispairing of the SSCR located in the 3′ of the H. bizzozeronii rdxA appears to be the main mechanism. We also observed that H. bizzozeronii acquires resistance to metronidazole at high mutation rate, and that serial passages in vitro without selection induced an increased level of susceptibility. In conclusion, contrary to what was previously described in H. pylori, the H. bizzozeronii rdxA appears to be a contingency gene which undergoes phase variation. The contingency nature of rdxA should be carefully considered when metronidazole is used in the treatment of H. heilmannii-associated gastritis.  相似文献   
135.
136.
The effect of tillage on soil properties varies within field due to spatial variability of soils. Mapping changes of soil penetration resistance (PR) would be useful to understand and assess tillage practices to alleviate soil compaction. The objectives were to model the short-term effect of tillage on PR and its spatial structure, and to delineate homogeneous zones based on soil response in a Typic Argiudoll previously managed under no-till. A grid sampling for PR and soil water content (SWC) were performed before and after chiselling. Spatial analysis was performed on the effect of tillage on PR data by 10 cm layers and homogeneous zones were delineated by k-means cluster analysis. The effect of tillage was ?0.33 MPa in 10–20 and 20–30 cm layer. No differences of PR were found at 0–10 cm. Short range (5–7 m) spatial structure on the horizontal plane was observed in all layers. Only 45% of the field showed a marked effect of tillage on PR. Mapping the effect of tillage on PR would be a useful approach for evaluating the global and local response of soil to tillage, as well as for delineating of areas within field for site-specific tillage practices.  相似文献   
137.
Plant Foods for Human Nutrition - Jabuticaba has a high concentration of phenolic compounds, which have a significant antioxidant capacity. Methodologies have been developed to evaluate the ability...  相似文献   
138.
OBJECTIVE: To evaluate the impact and appropriateness of programmes for the management and treatment of severe malnutrition in emergency situations. DESIGN: A central unified database was set up with all data and statistics provided by nutritional centres (NC) active in Burundi. SETTING: The paper describes the case of Burundi as an example of the response of the humanitarian community to nutritional crisis. SUBJECTS: Since 1999, more than one million (1,054,210) severely malnourished patients were treated in NC established in Burundi. RESULTS: Peaks of beneficiaries were registered in 2000 and 2001; the admission rate started to decrease in 2002. In 2004, twenty therapeutic feeding centres (TFC) and 224 supplementary feeding centres (SFC) were active for the treatment of 127,420 beneficiaries. Nutritional programmes were present in every province with a coverage rate of 55%. The most convincing impact of the nutritional programme in Burundi was the reduction of mortality rate in children under 5 years of age; an impact on the prevalence of acute malnutrition could not be demonstrated. Children under 5 years old accounted for 62% of beneficiaries in TFC and 76% in SFC. TFC performance indicators fulfilled the minimum standards in disaster response; the performance of SFC was not so optimal with a low recovery rate (69% v. >80%) and a high non-respondent rate (16% v. <5%). With the combination of coverage and cure rate, the programme met 44% of the assessed needs in 2004. CONCLUSIONS: In Burundi the stabilisation of security conditions permitted a combination of humanitarian responses ranging from emergency activities to strengthening of community-based initiatives that could correct the coverage and impact limitations.  相似文献   
139.
Agricultural herbicides are among the most commonly used pesticides worldwide, posing serious concerns for both humans, exposed to these chemicals through many routes, and the environment. To clarify the effects of three herbicides as commercial formulations (namely, Pointer, Silglif, and Proper Energy), parameters related to oxidative issues were investigated on an autochthonous wine yeast strain. It was demonstrated that herbicides were able to affect the enzymatic activities of catalase and superoxide dismutase, as well as to induce carbonylation and thiol oxidation as post-translational modifications of proteins. Saccharomyces cerevisiae is an optimal model system to study responses to xenobiotics and oxidative stress. Thus, the results obtained could further the understanding of mechanisms underlying the toxicity of herbicides.  相似文献   
140.
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