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   363篇
  免费   54篇
  国内免费   1篇
林业   21篇
农学   8篇
  39篇
综合类   31篇
农作物   30篇
水产渔业   39篇
畜牧兽医   220篇
园艺   6篇
植物保护   24篇
  2023年   9篇
  2022年   14篇
  2021年   18篇
  2020年   17篇
  2019年   21篇
  2018年   19篇
  2017年   23篇
  2016年   26篇
  2015年   18篇
  2014年   19篇
  2013年   24篇
  2012年   25篇
  2011年   21篇
  2010年   7篇
  2009年   17篇
  2008年   15篇
  2007年   16篇
  2006年   17篇
  2005年   8篇
  2004年   10篇
  2003年   11篇
  2002年   12篇
  2001年   3篇
  2000年   5篇
  1999年   5篇
  1998年   7篇
  1997年   4篇
  1996年   4篇
  1995年   3篇
  1994年   3篇
  1993年   1篇
  1991年   3篇
  1989年   3篇
  1988年   1篇
  1987年   1篇
  1985年   1篇
  1983年   1篇
  1982年   2篇
  1978年   1篇
  1971年   1篇
  1970年   1篇
  1967年   1篇
排序方式: 共有418条查询结果,搜索用时 15 毫秒
61.
Clownfish, Amphiprion ocellaris Cuvier, produced and grown in an experimental indoor aquaculture facility, presented with lipomatous tumours. A total of 14 affected fish were examined. Based on the total number of fish at the aquaculture facility at the time of outbreak of this pathology, the scope of the incident is estimated to be 1 of 300 fish. The tumours were characterized by the presence of mature adipocytes of variable sizes, lipoblasts and by an invasive behaviour, which affected internal organs, muscle, central nervous system and, in one case, an eye. Detailed macroscopic and histopathological features are presented. The suggested diagnosis is that of a well‐differentiated liposarcoma, a diagnosis so far never applied to fish. The limited outbreak of the neoplasm lasted a few months in 2011 and did not recur. Possible factors leading to this phenomenon, notably the metastasis, are discussed.  相似文献   
62.
While much is known about the metabolism of exogenous nutrients such as glucose, lactate, pyruvate, amino acids by oocytes and pre-implantation mammalian embryos, the role of endogenous stores, particularly lipid, has been largely overlooked. The presence of lipid within oocytes and early embryos has been long known, and comparisons between species indicate that the amounts and types of lipid present vary considerably. Large amounts of intracellular lipid can compromise the success of cryopreservation and the removal of such lipid has been the subject of considerable effort. In this review, we present evidence that strongly suggests a metabolic role for lipid, specifically with regard to energy provision, in the late-stage oocyte and the pre-implantation embryo. We focus initially on oxygen consumption as a global indicator of metabolic activity, before reviewing different approaches that either have been designed to investigate directly, or have revealed indirectly the role of endogenous lipid in energy generation. These fall under five headings: (i) fatty acid oxidation; (ii) inhibition of triglyceride oxidation; (iii) culture in the absence of exogenous substrates; (iv) cytoplasmic organization; and (v) delipidation. On the basis of the data derived from these studies, we conclude that there is strong evidence for the utilization of endogenous lipid as an energy substrate by oocytes and early embryos.  相似文献   
63.
Surface wettability and topography are recognized as critical factors influencing cell behavior on biomaterials. So far only few works have reported cell responses on surfaces exhibiting extreme wettability in combination with surface topography. The goal of this work is to study whether cell behavior on superhydrophobic surfaces is influenced by surface topography and polymer type. Biomimetic superhydrophobic rough surfaces of polystyrene and poly(L-lactic acid) with different micro/nanotopographies were obtained from smooth surfaces using a simple phase-separation based method. Total protein was quantified and showed a less adsorption of bovine serum albumin onto rough surfaces as compared to smooth surfaces of the same material. The mouse osteoblastic MC3T3-E1 cell line and primary bovine articular chondrocytes were used to study cell attachment and proliferation. Cells attached and proliferate better in the smooth surfaces. The superhydrophobic surfaces allowed cells to adhere but inhibited their proliferation. This study indicates that surface wettability, rather than polymer type or the topography of the superhydrophobic surfaces, is a critical factor in determining cell behavior.  相似文献   
64.
Water deficit is among the main environmental factors limiting agricultural productivity of sugarcane in Northeast Brazil by affecting virtually every aspect of plant growth, with consequent reduction of the agro-industrial productivity of this crop. This study aimed to use path analysis to evaluate the physiological components of sugarcane under two water conditions, with photosynthesis as the basic variable, in order to obtain subsidies that can help the genetic breeding of this crop by selection of superior clones with drought tolerance. The experiment was carried out in a greenhouse with a completely randomized experimental design, 4 × 2 factorial arrangements (four sugarcane genotypes × two soil moisture regimes: control, with 80-100% available water and stressed, with 0-20% water available) and with four replications. Each plot consisted of one pot with 12 kg of substrate containing one plant. Treatments were maintained at a humidity close to field capacity with daily replacement of the evapotranspired water with a water supply for 66 days of cultivation for treatments under stress. Evaluations were conducted on the fourth day after severe water stress at 70 days of cultivation. Data from nine physiological variables were considered, with six of these being used in the model after exclusion of those that were contributing to multicollinearity. Variables used in path analysis were enough to explain the variation found in photosynthesis under both water conditions. Stomatal conductance, transpiration and the SPAD index should be considered as a priority in breeding programs for sugarcane aiming to get more productive and tolerant genotypes to water stress, and selection indexes should be used with due consideration of these variables to promote gains in photosynthesis.  相似文献   
65.
Sea anemones of the genus Aiptasia are used as biological models for research and as a prey for the culture of the highly priced ornamental nudibranch Aeolidiella stephanieae. Symbiotic Aiptasia display a remarkable trophic plasticity, being able to fulfil their energetic demands heterotrophically and autotrophically. Consequently, they display a highly variable fatty acid (FA) profile. The objective of the present study was to analyse how light regime (12 h light : 12 h dark versus 24 h darkness), water temperature (22 versus 26 °C) and diet (Artemia nauplii versus enriched Artemia metanauplii) affect the FA composition of A. pallida. The FA profile of wild specimens was also analysed. The dominant FAs of cultured A. pallida were 16:0, 18:1n‐9 and 22:6n‐3. Higher FA levels were recorded when anemones were exposed to light, with this factor explaining the largest amount of variation in the composition of FA profiles. Cultured A. pallida that best mimicked wild anemones were obtained when using a regular light regime, Artemia metanauplii and 22 °C water temperature. Higher FA levels were obtained at a higher temperature and by providing nauplii to cultured anemones. The present study also indicated that A. pallida has the potential to recycle nutrients in marine aquacultures.  相似文献   
66.
67.
Sludge-derived activated carbons (ACs) were prepared by conventional heating and microwave pyrolysis. The ACs were characterized using several analytical and functional techniques and used for removal of six phenolic compounds from aqueous solutions. The adsorbents exhibited similar features and possessed hydrophobic surfaces. The ACs were assigned mesoporous materials, with specific surface areas of up to 641 and 540 m2 g?1 for CAC-500 and MAC-980, respectively. The preliminary results indicated that phenol removal onto the ACs increased in the order: m-cresol?<?phenol?<?o-cresol?<?2-chrorophenol?<?2-nitrophenol?<?hydroquinone. Hydroquinone exhibited the highest adsorption capacity and was chosen to continue the remaining part of the experimental work—kinetic and isothermal studies. The adsorption kinetic and isotherm data were well described by the Avrami fractionary order and Redlich–Peterson models, respectively. The maximum amounts (Q max) of hydroquinone adsorbed at 25 °C were too high, reaching 1218.3 and 1202.1 mg g?1 for CAC-500 and MAC-980, respectively. The mechanism of adsorption was proposed in this work, and it was suggested that donor–acceptor complex and ππ interactions play major roles in the adsorption process. The adsorbents were also tested on simulated effluents. The two ACs displayed good efficiency for the treatment of industrial simulated effluents.  相似文献   
68.
Amazonian Dark Earth (ADE) is a highly fertile soil of anthropogenic origin characterized by high levels of charred black carbon (BC).It is considered a model of fertility;however,knowledge on the fungal community structure and diversity inhabiting ADE and its BC particles is scarce.Fungal community structure and diversity of ADE and its BC from four sites under different land uses (three agricultural systems and a secondary pristine forest) in the Brazilian Central Amazon were evaluated by 18S rRNA gene pyrosequencing.Fungal communities in ADE and BC were dissimilar and showed differential abundances of fungal operational taxonomic units (OTUs).Estimated fungal species richness (abundance-based coverage estimate and Chao-1 index) and diversity estimators (Shannon and Simpson's reciprocal indices) were higher in ADE than in BC in all agricultural areas.No differences were observed in those parameters in ADE and BC samples from the secondary forest.Pezizomycotina fungi and OTUs assigned to Cordyceps confragosa,Acremonium vitellinum,Camarops microspora,and Hirsutella rhossiliensis were more abundant in BC particles than in ADE.These findings represent a breakthrough in our understanding of fungal communities in BC particles from ADE,and will be valuable in future studies considering biochar application in soil.  相似文献   
69.
Tropical Animal Health and Production - Porcine circovirus type 2 (PCV2) has been identified in pig population in Brazil since 2000, but scarce studies involving wild boars with PCV2 infection are...  相似文献   
70.
This study was aimed at investigating the anti-osteoporotic effects of the extract of Ginkgo biloba (EGb) in glucocorticoid-induced-osteoporosis. A significant reduction was observed in the percentage of the bone of the osteoporosis group in both the mandible and femur. The EGb group treated with 28 and 56 mg/Kg showed a significant increase in the percentage of trabecular bone (PTB) of the femur. The percentage of the alveolar bone of the mandible (PAB) had a significant increase with all doses of EGb. The treatment with EGb significantly reversed the loss of the PAB of the mandible and of the PTB of the femur.  相似文献   
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