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   389篇
  免费   51篇
林业   31篇
农学   20篇
基础科学   2篇
  53篇
综合类   21篇
农作物   15篇
水产渔业   47篇
畜牧兽医   193篇
园艺   4篇
植物保护   54篇
  2024年   1篇
  2023年   10篇
  2022年   11篇
  2021年   21篇
  2020年   28篇
  2019年   25篇
  2018年   18篇
  2017年   25篇
  2016年   19篇
  2015年   17篇
  2014年   23篇
  2013年   28篇
  2012年   35篇
  2011年   27篇
  2010年   14篇
  2009年   22篇
  2008年   15篇
  2007年   20篇
  2006年   9篇
  2005年   11篇
  2004年   6篇
  2003年   7篇
  2002年   8篇
  2001年   3篇
  2000年   3篇
  1999年   5篇
  1998年   1篇
  1997年   3篇
  1996年   1篇
  1995年   1篇
  1992年   3篇
  1991年   3篇
  1990年   2篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1986年   3篇
  1985年   3篇
  1984年   1篇
  1983年   2篇
  1972年   1篇
  1970年   1篇
排序方式: 共有440条查询结果,搜索用时 0 毫秒
61.
The digestive utilization of Fe and its nutritive interaction with Ca, P, and Mg were studied in rats with nutritional ferropenic anemia. The diet contained 80% ferric citrate and 20% heme iron (80/20 diet). The weight gain, digestive utilization of Fe, and regeneration efficiency of hemoglobin and seric Fe were higher in iron-deficient rats (ID) fed the 80/20 diet than in iron-deficient rats fed the 50/50 diet (Campos et al., 1996). The phospho-calcic metabolism, which is adversely affected in ferropenic anemia, returned to normal values when iron was added to the diet. The digestive utilization of Mg, which fell with the 50/50 diet (Campos et al., 1996), returned to normal values when the ferropenic anemia was reversed with the 80/20 diet. In a state of iron deficiency, certain parameters related to the glucose and lipid metabolism are affected; the glucose and triglycerides values return to a normal range with the 80/20 diet.  相似文献   
62.
63.
The in vitro production of proinflammatory cytokines after stimulation with Actinobacillus pleuropneumoniae and the relation of these cytokines in vivo with the disease caused by A. pleuropneumoniae were investigated. Within 24 h, in vitro stimulation by A. pleuropneumoniae (serotype 1) preparations, including killed bacteria, bacterial culture supernatant, lipopolysaccharide, and bacterial extracts, porcine pulmonary alveolar macrophages (PAM) produced significant (P < 0.05) amounts of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) as measured by bioassays. The supernatants containing interleukin-8 from PAM after stimulation by bacterial preparations showed significant neutrophil chemotaxis, while bacterial preparations alone did not. After in vivo infection with A. pleuropneumoniae, the mean levels of TNF-alpha and IL-1 in serum, as measured by bioassays, were elevated 37- to 27836-fold for TNF-alpha and 11- to 5941-fold higher for IL-1 within 4 d post-infection, depending on the treatments, and remained elevated up to Day 7. Both cytokines were also detected in porcine lungs by bioassays and immunocytochemistry. The results indicated that both secreted and surface components of A. pleuropneumoniae can stimulate PAM to produce proinflammatory mediators. Neutrophil chemoattractants rather than bacterial components are the major factor causing acute lung inflammation. The elevation of TNF-alpha and IL-1 in pigs occurred coincident with the onset of acute clinical disease.  相似文献   
64.
Biofouling, which occurs when certain marine species attach and accumulate in artificial submerged structures, represents a serious economic and environmental issue worldwide. The discovery of new non-toxic and eco-friendly antifouling systems to control or prevent biofouling is, therefore, a practical and urgent need. In this work, the antifouling activity of a series of 24 xanthones, with chemical similarities to natural products, was exploited. Nine (1, 2, 4, 6, 8, 16, 19, 21, and 23) of the tested xanthones presented highly significant anti-settlement responses at 50 μM against the settlement of mussel Mytilus galloprovincialis larvae and low toxicity to this macrofouling species. Xanthones 21 and 23 emerged as the most effective larval settlement inhibitors (EC50 = 7.28 and 3.57 µM, respectively). Additionally, xanthone 23 exhibited a therapeutic ratio (LC50/EC50) > 15, as required by the US Navy program attesting its suitability as natural antifouling agents. From the nine tested xanthones, none of the compounds were found to significantly inhibit the growth of the marine biofilm-forming bacterial strains tested. Xanthones 4, 6, 8, 16, 19, 21, and 23 were found to be non-toxic to the marine non-target species Artemia salina (<10% mortality at 50 μM). Insights on the antifouling mode of action of the hit xanthones 21 and 23 suggest that these two compounds affected similar molecular targets and cellular processes in mussel larvae, including that related to mussel adhesion capacity. This work exposes for the first time the relevance of C-1 aminated xanthones with a 3,4-dioxygenated pattern of substitution as new non-toxic products to prevent marine biofouling.  相似文献   
65.
  1. Crocodilians represent one of the oldest extant vertebrate lineages. They have co-existed with humans throughout the Amazon basin for thousands of years, often having a strong cultural and economic influence on people's lives. Shifts in the socio-economic and political reality of the Amazon basin during the last century have led crocodilian populations to face large variations in their numbers according to different levels of exploitation and strategies for their conservation.
  2. This article reviews the scientific knowledge obtained between 1945 and 2019 on the biology, conservation and management for the four Amazonian crocodilian (caiman) species (Caiman crocodilus, Melanosuchus niger, Paleosuchus palpebrosus and Paleosuchus trigonatus). It provides a general overview on past and current population status and research efforts involving caimans in the Amazon basin and discusses perspectives for the future.
  3. The most significant studies on the ecology, genetics and management strategies are examined in more detail and this information is contextualized to provide an overview of the most relevant findings that might explain caiman population trends over the last 75 years.
  4. Systems for sustainable management in the Amazon basin have been discussed for the past 20 years, but remain rarely applicable. It is necessary to develop new ways to maintain healthy caiman populations through innovative management programmes. Sustainable harvesting of wildlife has been shown to promote conservation targets, especially those initiatives based on community co-management. In this article, we propose some general guidelines for future management schemes, in the expectation that the information provided by the scientific community will be considered fully without political agendas determining the priorities.
  相似文献   
66.
Apparent digestibility coefficients (ADCs) of processed agro‐food by‐products were assessed in European seabass (Dicentrarchus labrax). Each experimental diet was obtained by replacing 300 g/kg of a commercial‐based diet used as reference (REF) with a test ingredient: wheat germ (GERM), okara meal (OKA), poultry by‐product meal (POULT), steam hydrolysed (FeHY) and enzyme‐treated feather meal (FeENZ), beta‐lactoglobulin (β‐Lg) and peptide fractions >3,000 Da obtained from brewer's yeast (YeastP) and fish by‐products (FishP). Dry matter ADC was highest in β‐Lg (95%) and lowest in OKA (40%). Protein ADCs were high in β‐Lg, FishP, GERM and POULT (>93%); intermediate in FeHY and FeENZ (85%–88%); and moderate in OKA and YeastP (70%–78%). The essential amino acids' ADC mean was above 91% in POULT, β‐Lg, GERM and FishP, 84%–89% in FeHY and FeENZ and 73%–76% in YeastP and OKA. Energy ADC was highest in POULT and β‐Lg (89%–95%) and lowest in YeastP and OKA (61%–64%). Lipid ADC was highest for POULT and GERM (100%). Phosphorus ADC was lowest in GERM (19%) and highest in β‐Lg (88%). FeHY, FeENZ, POULT, GERM, FishP and β‐Lg are highlighted as protein sources for European seabass.  相似文献   
67.
In several laboratory and production species, the establishment of a proteome reference map of a specific tissue has been accomplished. The rabbit is widely used as both a production and experimental animal. A lot of physiology research involving the gastrocnemius muscle of rabbit is described, although no reference proteome map is available. In this work, the first reference map of the rabbit’s gastrocnemius muscle using 2D gel electrophoresis and the identification of proteins through peptide mass fingerprinting (PMF) was established. A total of 45 proteins were localized and identified with three major roles: cell structure and contractile apparatus; metabolic and cell defense proteins. A reference map of major proteins expressed is described enabling possible comparisons with other physiological studies.  相似文献   
68.
Factors associated with parasitism by helminths and protozoans in 500 dogs presented to three veterinary clinics in the municipality of Rio de Janeiro from November 2003 to September 2004 were evaluated. Dogs were submitted to physical examination and owners were interviewed about the animal's management. One fecal sample from each dog was examined by centrifugal flotation and sedimentation methods followed by the safranin–methylene blue staining technique. Positive results for gastrointestinal parasites were detected in 46.4% of the examined samples. Infection with protozoans (29.6%) was more frequent than with helminths (23.2%). Cryptosporidium sp. (26.2%) and Ancylostoma sp. (15.2%) were the most frequent parasites. Logistic regression analysis showed that age (p < 0.001), access to soil (p < 0.001), hygiene of the environment (p = 0.001), illness (p = 0.007), owner's level of education (p < 0.006) and veterinary clinic (p = 0.043) were associated with gastrointestinal parasite infections in dogs. Treatment and control are especially important for puppies. Adult dogs should be submitted to fecal examination before treatment, placing special emphasis on those that present one or more factors associated with infection.  相似文献   
69.
Lentil is cultivated in Chilean Mediterranean drylands, in areas with soils that are nutrient depleted and eroded. Inoculation of lentil with rhizobia in co-inoculation with growth promoting rhizobacteria would allow higher biomass and an opportunity for early nodulation and increased nitrogen fixation. The objective of this research was to select rhizosferic bacteria (PGPR) from lentils and to evaluate their effect on lentil nodulation in co-inoculation with rhizobia. Sixty three lentil rhizobacteria isolates where obtained from nine soils in the mediterranean area. These were fingerprinted through BOX-PCR reducing the number to 57 distinct strains. The strains were evaluated for ACCdeaminase activity, IAA production and compatibility with rhizobia. Seventeen strains showed ACC-deaminase activity, all of them synthesized IAA and 38 were compatible with the rhizobia. Ten selected strains were identified as Pseudomonas spp. through 16S rRNA sequencing. The strains were inoculated in lentil seedlings growing on seed germination pouches, to evaluate nodule formation. The strain LY50a increased early nodulation in 85% in comparison to the control inoculated with rhizobia (AG-84) only. In conclusion, bacteria from the rhizosphere from Mediterranean soils of Chile can be used as nodulation promoters in lentils.  相似文献   
70.
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