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   414篇
  免费   44篇
林业   25篇
农学   20篇
基础科学   4篇
  97篇
综合类   14篇
农作物   36篇
水产渔业   70篇
畜牧兽医   151篇
园艺   3篇
植物保护   38篇
  2023年   10篇
  2022年   11篇
  2021年   15篇
  2020年   20篇
  2019年   19篇
  2018年   25篇
  2017年   31篇
  2016年   27篇
  2015年   16篇
  2014年   24篇
  2013年   15篇
  2012年   29篇
  2011年   28篇
  2010年   13篇
  2009年   15篇
  2008年   25篇
  2007年   21篇
  2006年   13篇
  2005年   11篇
  2004年   12篇
  2003年   10篇
  2002年   14篇
  2001年   8篇
  2000年   5篇
  1999年   12篇
  1998年   5篇
  1997年   2篇
  1996年   3篇
  1995年   5篇
  1994年   1篇
  1991年   1篇
  1990年   1篇
  1989年   4篇
  1986年   1篇
  1985年   1篇
  1982年   1篇
  1980年   1篇
  1973年   1篇
  1971年   1篇
  1945年   1篇
排序方式: 共有458条查询结果,搜索用时 31 毫秒
71.
The aim of this study was to evaluate the effect of the addition of Chaetoceros calcitrans, Navicula sp. and Phaeodactylum tricornutum (diatoms) on phytoplankton composition and the growth of Litopenaeus vannamei postlarvae reared in a biofloc system . Four treatments were used: BFT (biofloc system without feed and no addition of diatoms); BFT‐F (biofloc system with feed and no addition of diatoms); BFT‐D (biofloc system with the addition of diatoms and no feed); and BFT‐FD (biofloc system with the addition of feed and diatoms), all in triplicate. The shrimp (16 ± 0.02 mg) were stocked at 2500 postlarvae m?3 and fed a commercial feed. Diatoms were added on the 1st, 5th, 10th and 15th day at a density of 5 × 104 cells mL?1 for each species. No significant differences (> 0.05) between treatments were observed for gross primary production, net ecosystem production and water column respiration rate. However, significant differences (< 0.05) were observed for nitrite, orthophosphate, alkalinity, final weight, weight gain, yield, feed conversion ratio (FCR), phytoplankton and cyanobacteria composition. The BFT‐FD treatment had better performance parameters for final weight (270 mg), weight gain (254 mg), yield (0.67 Kg m?3) and FCR (0.61), indicating the benefits of the diatoms C. calcitrans, Navicula sp. and P. tricornutum for decreasing cyanobacteria and improving growth of L. vannamei postlarvae reared in biofloc systems.  相似文献   
72.
73.
Intensive fish farming has resulted in an increased concern for disease outbreaks. Probiotic use is one of the strategies being developed to improve fish health and productivity. Measures of probiotic colonization, growth performance, haematological characteristics and parasite load were used to evaluate the effect of diets supplemented with Enterococcus faecium on growth and health of Arapaima gigas juveniles. A completely randomized design with four treatments (diet with E. faecium at 1 × 106 CFU/g and 1 × 108 CFU/g, control diet and diet with the culture medium MRS) and three replicates was used. Ninety‐six Arapaima juveniles were distributed in 12 cages fed with the specified diet for 68 days. Colonization of the intestinal tract by lactic acid bacteria reduced the total number of heterotrophic bacteria in fish fed with probiotics compared to controls. Fish fed a supplemented diet containing 1 × 108 CFU/g presented higher values of weight gain, survival and fish growth uniformity, and lower values of feed conversion ratio. The prevalence of Trichodina sp. could have affected the survival of fish in the control group. Reduction in parasite load and an increase in haematocrit, the number of erythrocytes, thrombocytes, neutrophils and monocytes were also observed in fish fed the diet containing 1 × 108 CFU/g. Enterococcus faecium presented a probiotic effect in A. gigas juveniles and can be recommended for use at a concentration of 1 × 108 CFU/g to modify the gut microbiota, improve growth performance and haematology and reduce parasitic load.  相似文献   
74.
Although reported as a slow growing species, to date information regarding nutritional dynamics of blackspot seabream, Pagellus bogaraveo, is limited, especially during ongrowing phase. This study determined the effects of different feeding levels on growth response, body composition, and energy expenditure of blackspot seabream juveniles (initial weight = 64 g). Fish were allocated in nine indoor tanks (15 fish per tank) and fed a basal diet twice daily at increasing levels (2.5, 3.3, and 4.1 g feed/kg0.8/d) for 138 d. Growth response decreased with decreasing feeding levels, but only at 2.5 g feed/kg0.8/d (P < 0.001). Differences in growth rates were positively correlated with body lipid content (r2 = 0.90). Net protein utilization decreased with each increase in feeding level. The energy requirement for zero growth (maintenance) and the estimated energy loss on starvation were calculated as 22.6 and 17.9 kJ/kg0.8/d, respectively. The energy cost for protein and lipid gain was calculated as 3.8 and 1.4 kJ/kJ energy deposited, respectively. This study suggested that blackspot seabream may grow slower than the other close‐related species because of its higher demand of dietary protein energy in favor of lipid deposition.  相似文献   
75.
Studies investigating improved protein:lipid ratios based on their effects on growth, nutrient utilization, digestive enzyme activities, blood metabolites and erythogram in tropical carnivorous fish are very scarce. This study evaluated the effect of different protein:lipid ratios on these parameters in the hybrid surubim Pseudoplatystoma corruscans × Leiarius marmoratus. Juvenile fish (8.90 ± 0.94 g initial weight) were fed 3% of total biomass for 60 days using four isoenergetic experimental diets with different protein:lipid ratios (9.00, 4.60, 3.54 and 1.78). Higher growth performance parameters were observed at higher protein:lipid ratios. The activities of intestine total alkaline protease, trypsin and lipase (U/mg protein) were not affected by dietary treatments. Chymotrypsin (U/mg protein) was higher in the 4.60 protein:lipid ratio group. Amylase (U/mg protein) was higher in intermediate groups. Blood glucose, total plasma protein, triglycerides, cholesterol and free amino acids decreased as the protein:lipid ratio decreased. Haematocrit was higher at the 9.00 and 4.60 protein:lipid ratios. Hybrid surubim showed metabolic adaptation to the different protein:lipid ratios tested. These results suggest that the 4.60 protein:lipid ratio showed the best protein‐sparing effect of lipids.  相似文献   
76.

The extraction of oil from baru almonds produces a waste that carries part of their nutritional qualities and antioxidants. It can be used to produce partially deffated baru flour (PDBF). We aimed to evaluate the applicability of PDBF and the effect of the addition of xanthan gum (XG) to produce gluten free cakes. Cakes were prepared with 100 % wheat flour (WF cake) and with 100 % PDBF and four different levels of XG (0 %-PDBF cake, 0.1 %-X1, 0.2 %-X2 and 0.3 %-X3 cakes), and evaluated for composition, antioxidants, moisture, specific volume, texture and sensory acceptance. PDBF cakes showed lower carbohydrate values, but higher protein, lipids, calories and antioxidant contents. They were rich in fiber, as well as iron, zinc and copper. The replacement of WF by PDBF resulted in an increased hardness and adhesiveness and a decreased cohesiveness, elasticity and moisture. Chewiness of X2 cake was similar to that of WF cake. X2 and X3 cakes showed specific volume closer to that of WF cake. No difference was found among the treatments for texture and appearance acceptances. Flavor of X2 and X3 cakes were more accepted than WF cake. Acceptance of all cakes were in the liking region of hedonic scale. PBDF associated to XG is a feasible option to substitute WF in gluten free cake, improving its nutritional quality.

  相似文献   
77.
Microalgae are well known for their biotechnological potential, namely with regard to bioactive lipidic components—especially carotenoids and polyunsaturated fatty acids (PUFA), well-known for therapeutic applications based on their antioxidant capacity. The aim of this work was to evaluate the influence of four distinct food-grade solvents upon extractability of specific lipidic components, and on the antioxidant capacity exhibited against both synthetic (2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTS+•)) and biological reactive species (O2 and NO). A eukaryotic microalga (Scenedesmus obliquus (M2-1)) and a prokaryotic one (Gloeothece sp.) were used as case studies. Concerning total antioxidant capacity, the hexane:isopropanol (3:2) and acetone extracts of Sc. obliquus (M2-1) were the most effective against DPPH and ABTS+•, respectively. Gloeothece sp. ethanol extracts were the most interesting scavengers of O2, probably due the high content of linolenic acid. On the other hand, acetone and hexane:isopropanol (3:2) extracts were the most interesting ones in NO assay. Acetone extract exhibited the best results for the ABTS assay, likely associated to its content of carotenoids, in both microalgae. Otherwise, ethanol stood out in PUFA extraction. Therefore, profiles of lipidic components extracted are critical for evaluating the antioxidant performance—which appears to hinge, in particular, on the balance between carotenoids and PUFAs.  相似文献   
78.
Purified phlorotannin extracts from four brown seaweeds (Cystoseira nodicaulis (Withering) M. Roberts, Cystoseira tamariscifolia (Hudson) Papenfuss, Cystoseira usneoides (Linnaeus) M. Roberts and Fucus spiralis Linnaeus), were characterized by HPLC-DAD-ESI-MSn. Fucophloroethol, fucodiphloroethol, fucotriphloroethol, 7-phloroeckol, phlorofucofuroeckol and bieckol/dieckol were identified. The antioxidant activity and the hyaluronidase (HAase) inhibitory capacity exhibited by the extracts were also assessed. A correlation between the extracts activity and their chemical composition was established. F. spiralis, the species presenting higher molecular weight phlorotannins, generally displayed the strongest lipid peroxidation inhibitory activity (IC50 = 2.32 mg/mL dry weight) and the strongest HAase inhibitory capacity (IC50 = 0.73 mg/mL dry weight). As for superoxide radical scavenging, C. nodicaulis was the most efficient species (IC50 = 0.93 mg/mL dry weight), followed by F. spiralis (IC50 = 1.30 mg/mL dry weight). These results show that purified phlorotannin extracts have potent capabilities for preventing and slowing down the skin aging process, which is mainly associated with free radical damage and with the reduction of hyaluronic acid concentration, characteristic of the process.  相似文献   
79.
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   
80.
Dry-milling performance of maize (Zea mays, L.) kernels primarily depends on their hardness. The flint type is harder than the dent and semi-dent maize, yielding a higher proportion of big endosperm pieces in the mill. Nevertheless, crop growing conditions could modify milling properties. The objective of this work was to analyze the effect of different crop environments and management practices on dry-milling quality of flint maize kernels. Two orange-flint hybrids from different eras of breeding differing in flint type expression and grain yield potential were evaluated. They were grown at three different locations of the Argentina's main maize-production area under different sowing dates, plant densities, and fertilization rates during two growing seasons. Crop post-silking growth, grain yield and its components (kernel number and weight), kernel size and hardness-associated properties (test weight, percent floaters and milling ratio), and flaking-grit yield were analyzed. Most of observed differences in physical properties of kernels, particularly for the high-yielding new hybrid with unstable flint expression, were associated with the source-sink ratio established during the post-silking period (explored range from 154 to 617 mg kernel−1). This variable mainly results from changes in crop growth during that period. Increases in weight per kernel improved hardness-associated properties. High crop grain yields together with top dry-milling quality were achieved when the new high-yielding hybrid was cropped with an appropriated crop management.  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