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   737篇
  免费   99篇
林业   49篇
农学   18篇
基础科学   4篇
  125篇
综合类   25篇
农作物   52篇
水产渔业   89篇
畜牧兽医   377篇
园艺   13篇
植物保护   84篇
  2023年   15篇
  2022年   22篇
  2021年   47篇
  2020年   50篇
  2019年   68篇
  2018年   43篇
  2017年   60篇
  2016年   54篇
  2015年   36篇
  2014年   34篇
  2013年   58篇
  2012年   40篇
  2011年   65篇
  2010年   25篇
  2009年   42篇
  2008年   35篇
  2007年   26篇
  2006年   29篇
  2005年   15篇
  2004年   14篇
  2003年   19篇
  2002年   7篇
  2001年   6篇
  2000年   4篇
  1999年   3篇
  1998年   3篇
  1997年   5篇
  1996年   2篇
  1994年   1篇
  1993年   1篇
  1991年   2篇
  1990年   2篇
  1988年   1篇
  1987年   1篇
  1984年   1篇
排序方式: 共有836条查询结果,搜索用时 15 毫秒
41.
Supercritical fluid extraction (SFE) from aniseed using carbon dioxide was performed at 30 degrees C and pressures of 80-180 bar. The chemical composition of the SFE extract was determined by GC-MS; the quantitative analysis was done by GC-FID and TLC. The total amount of extractable substances or global yield (mass of extract/mass of feed) for the SFE process varied from 3.13 to 10.67% (mass). The solubilities of the anise essential oil in CO(2) were 0.0110, 0.0277, 0.0143, and 0.0182 kg of solute/kg of CO(2) at 80, 100, 140, and 180 bar, respectively. The major compounds identified and quantified in the extracts were anethole ( approximately 90%), gamma-himachalene (2-4%), p-anisaldehyde (<1%), methylchavicol (0.9-1.5%), cis-pseudoisoeugenyl 2-methylbutyrate ( approximately 3%), and trans-pseudoisoeugenyl 2-methylbutyrate ( approximately 1.3%). The Sovová model described quite well the experimental overall extraction curves.  相似文献   
42.
Cancer and infectious diseases continue to be a major public health problem, and new drugs are necessary. As marine organisms are well known to provide a wide range of original compounds, the aim of this study was to investigate the bioactivity of the main constituents of the cosmopolitan red alga, Sphaerococcus coronopifolius. The structure of several bromoditerpenes was determined by extensive spectroscopic analysis and comparison with literature data. Five molecules were isolated and characterized which include a new brominated diterpene belonging to the rare dactylomelane family and named sphaerodactylomelol (1), along with four already known sphaerane bromoditerpenes (2–5). Antitumor activity was assessed by cytotoxicity and anti-proliferative assays on an in vitro model of human hepatocellular carcinoma (HepG-2 cells). Antimicrobial activity was evaluated against four pathogenic microorganisms: Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans. Compound 4 exhibited the highest antimicrobial activity against S. aureus (IC50 6.35 µM) and compound 5 the highest anti-proliferative activity on HepG-2 cells (IC50 42.9 µM). The new diterpene, sphaerodactylomelol (1), induced inhibition of cell proliferation (IC50 280 µM) and cytotoxicity (IC50 720 µM) on HepG-2 cells and showed antimicrobial activity against S. aureus (IC50 96.3 µM).  相似文献   
43.
ABSTRACT

This work aimed to evaluate the physicochemical and functional properties of proteins recovered from whitemouth croaker (Micropogonias furnieri) and Argentine anchovy (Engraulis anchoita) residues obtained by the process of acid solubilization using HCl at pH = 2 and alkaline solubilization using NaOH at pH = 12 and isoelectric precipitation (pH = 5.5). The proximate composition and functional properties were determined. The solubilization and water holding capacity (WHC) of the recovered protein were studied in the pH range of 3, 5, 7, 9, and 11. The high protein content and lowest lipid reduction presented by the protein recovered from the whitemouth croaker residue and obtained by the acid solubilizing process was 97.1 and 98.4%, respectively. The maximum solubilized protein was at pH 3 and 11, and the minimum solubilized protein was at pH 5 for both species. The greater ability to retain oil was observed for the alkaline solubilization process (8.3 and 7.3). The lower WHC was at pH 5. The acid and alkali residue concentrates of the whitemouth croaker presented higher WHC at pH 3 and 11. These proteins can be used in preparing edible films and have been used to produce bioactive compounds for supplements or functional ingredients.  相似文献   
44.
45.
A comparative slaughter trial was conducted to assess the net requirements for gain of Ca, P, Na, K and Mg of bulls, steers and heifers of Nellore and Red Angus crossbreds. Twenty seven F1 Nellore and Red Angus crossbred calves (9 steers, 9 bulls, and 9 heifers), averaging 274 kg BW, were used. At the beginning of the trial, three animals from each gender were slaughtered to determine the initial body composition. The remaining 18 animals (3 animals of each gender) were randomly assigned to two treatments: fed 0.75 or 1.5% of BW of concentrate. The diets were based on corn silage and were isonitrogenous (2% N, DM). After three growing periods of 28 d, all animals were slaughtered. The cleaned gastrointestinal tract, organs, carcass, head, hide, tail, feet, and tissues were weighed to determine the empty BW (EBW). These parts were ground separately and subsampled for chemical analyses. The log of the contents of each mineral in the empty body was regressed on the log of the EBW to estimate the net requirement for each mineral per kg of empty body gain (EBG). There were no differences (P > 0.05) in the net requirements for growth of all macrominerals among genders. The equations of the pooled data of the net requirements for growth (g/kg EBG) were: 332.6 × EBW − 0.6367 for Ca, 112.1 × EBW − 0.5615 for P, 10.85 × EBW − 0.3992 for Na, 4.01 × EBW − 0.153 for K, and 3.589 × EBW − 0.462 for Mg. Our findings indicated that retained Ca and retained P were poorly related to the retained protein.  相似文献   
46.
由于霉菌毒素是一类无色无臭无味的物质,所以测定饲料原料和饲料成品以监测霉菌毒素的污染是非常重要的. 霉菌毒素这一术语源自希腊语单词"mycos"和"toxikon",是指在各种各样环境条件下由真菌产生的次生有毒代谢产物.  相似文献   
47.
The amount of photosynthetic radiation intercepted by a crop is a function of the incident solar radiation on the plants, the leaf area index (L AI), and the light extinction coefficient (k). We quantified L AI and k in stands of black wattle (Acacia mearnsii De Wild.) over a 7-year growth cycle at two locations in the state of Rio Grande do Sul, Brazil. Our study was conducted in commercial stands in agroecological regions with high densities of black wattle plantations. L AI was calculated as the ratio between the leaf area of a tree and its planting space, and k was derived from Beer’s law. L AI depends on the planting site and stand age. Between the two sites, the L AI was similar over time, the amount of variation differed. Values of k depended only on stand age, with the highest average observed for stands up to 5 years old. The trend of k during the plantation cycle was inversely proportional to L AI and was correlated with L AI, leaf area, leaf dry mass, canopy volume, height, branches dry mass, total dry mass, and crown diameter.  相似文献   
48.
49.
This study evaluated the effect of short-term baths with the essential oils (EOs) of Lippia sidoides, Ocimum gratissimum and Zingiber officinale on the survival, haematological, biochemical and histopathological parameters of native fish tambaqui (Colossoma macropomum), challenged with Aeromonas hydrophila. After challenge, the fish infected with A. hydrophila received therapeutic baths of 60 min, for five consecutive days. Treatments were as follows: challenged and not treated; challenged and treated with 10 mg L?1 of gentamicin; challenged and treated with EO of L. sidoides (2.5 and 5.0 mg L?1); challenged and treated with EO of O. gratissimum (5.0 and 10.0 mg L?1); challenged and treated with Z. officinale EO (5.0 and 10.0 mg L?1). The highest survival rates were 89.5% (fish treated with 5.0 mg L?1 of O. gratissimum EO) and 75.0% (fish treated with 5.0 mg L?1 of L. sidoides EO). Reductions in the haematocrit percentage, haemoglobin and erythrocyte number were observed in fish treated with L. sidoides and Z. officinale EOs compared with control fish. Mild to moderate damage to the liver tissue of fish after challenge and EO treatments were observed. It is suggested that baths containing O. gratissimum and L. sidoides EOs consist in a viable treatment to increase survival rates of C. macropomum infected with A. hydrophila.  相似文献   
50.
The digestive capacity of the Portuguese native breed of Barrosão cattle and the Holstein–Friesian breed was measured when fed meadow hay (72–74 g CP and 641–671 g NDF/kg dry matter), offered either alone or supplemented with soya bean meal (150 g/kg dry matter), at maintenance level. Four mature cows of each breed were used. Average initial live weight (LW) was 457 and 635 kg for the Barrosão and the Holstein–Friesian cows respectively. The organic matter digestibility (OMD) of the meadow hay was higher in Holstein–Friesian than in Barrosão cows (p < 0.08) whether supplemented or not. The neutral detergent fibre digestibility of the hay was also higher in Holstein–Frisian when the hay was fed alone (p < 0.08). The soya bean meal supplementation increased the OMD and the NDFD digestibility of the total diet (p < 0.05), but not the OMD digestibility of the hay (p > 0.05). The results obtained in this study suggest a higher ability to digest fibre in the large dairy breed than in the small native breed. This suggestion is also supported by previous findings with sheep breeds largely differing in mature live weight.  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