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   284篇
  免费   12篇
林业   19篇
农学   6篇
基础科学   1篇
  56篇
综合类   22篇
农作物   12篇
水产渔业   39篇
畜牧兽医   91篇
园艺   5篇
植物保护   45篇
  2024年   1篇
  2023年   5篇
  2022年   8篇
  2021年   15篇
  2020年   10篇
  2019年   14篇
  2018年   15篇
  2017年   11篇
  2016年   13篇
  2015年   10篇
  2014年   6篇
  2013年   26篇
  2012年   19篇
  2011年   10篇
  2010年   10篇
  2009年   6篇
  2008年   22篇
  2007年   7篇
  2006年   10篇
  2005年   13篇
  2004年   8篇
  2003年   5篇
  2002年   8篇
  2001年   5篇
  2000年   4篇
  1999年   6篇
  1998年   2篇
  1997年   2篇
  1996年   2篇
  1993年   1篇
  1992年   1篇
  1991年   3篇
  1989年   2篇
  1987年   3篇
  1986年   1篇
  1984年   1篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1976年   1篇
  1970年   1篇
  1967年   1篇
  1966年   2篇
  1965年   1篇
  1962年   1篇
排序方式: 共有296条查询结果,搜索用时 890 毫秒
81.
An 84‐day feeding experiment was conducted to determine the effects of dietary ginseng extract (GE), tribulus extract (TE) and date palm pollen grains (DPPG) on growth, testosterone level and nutrient utilization of Nile tilapia, Oreochromis niloticus, fingerlings. Seven experimental treatments were conducted in three replicates: control fed basal diets without any supplementations, GE0.2 (supplemented with 0.2 g GE/kg diet), GE0.4 (supplemented with 0.4 g GE/kg diet), TE0.6 (supplemented with 0.6 g TE/kg diet), TE1.2 (supplemented with 1.2 g TE/kg diet), DPPG3 (supplemented with 3 g DPPG/kg diet) and DPPG6 (supplemented with 6 g DPPG/kg diet). The results indicated that all dietary phytochemicals significantly increased growth compared to the control. Plasma testosterone levels were improved by 86.27%, 64.58%, 57.35% and 24.58% with TE1.2, GE0.4, TE0.6 and DPPG6, respectively, more than the control. The relationship between testosterone and final body weight showed a significant simple linear regression with a positive correlation. The nutrient utilization imprxoved with higher doses of phytochemical supplementations. Moreover, protein content increased and ether extract decreased with phytochemical supplementation. The present results concluded that higher doses of GE, TE and DPPG could be used as growth promoters and testosterone boosters for Nile tilapia fingerlings.  相似文献   
82.
83.
The transfer of maternal antibodies to Friesian and buffalo calves born of dams vaccinated against rinderpest was through colostrum only. Colostral antibody titers at the time of parturition were higher than the serum titer. Two hours after suckling, a high level of rinderpest neutralizing antibodies was detected in the sera of newborn animals. The half-life of maternal antibodies in buffalo and Friesian calves was found to be approximately 33 and 29 days respectively. By the age of 7-8 months, 60 per cent of buffalo calves and 80 per cent of Friesian calves had no detectable levels of rinderpest neutralizing antibody.  相似文献   
84.
Newcastle disease (ND) is a highly contagious avian disease and one of the major causes of economic losses in the poultry industry. The emergence of virulent NDV genotypes and repeated outbreaks of NDV in vaccinated chickens have raised the need for fundamental studies on the virus–host interactions. In this study, the profiles of B and T lymphocytes and macrophages and differential expression of 26 immune-related genes in the spleen of specific-pathogen-free (SPF) chickens, infected with either the velogenic genotype VII NDV strain IBS002 or the genotype VIII NDV strain AF2240, were evaluated. A significant reduction in T lymphocyte population and an increase in the infiltration of IgM+ B cells and KUL01+ macrophages were detected in the infected spleens at 1, 3 and 4 days post-infection (dpi) (P < 0.05). The gene expression profiles showed an up-regulation of CCLi3, CXCLi1, CXCLi2 (IL-8), IFN-γ, IL-12α, IL-18, IL-1β, IL-6, iNOS, TLR7, MHCI, IL-17F and TNFSF13B (P < 0.05). However, these two genotypes showed different cytokine expression patterns and viral load. IBS002 showed higher viral load than AF2240 in spleen at 3 and 4 dpi and caused a more rapid up-regulation of CXCLi2, IFN-γ, IL-12α, IL-18, IL-1β, iNOS and IL-10 at 3 dpi. Meanwhile, the expression levels of CCLI3, CXCLi1, IFN-γ, IL-12α, IL-1β and iNOS genes were significantly higher in AF2240 at 4 dpi. In addition, the expression levels of IL-10 were significantly higher in the IBS002-infected chickens at 3 and 4 dpi. Hence, infection with velogenic genotype VII and VIII NDV induced different viral load and production of cytokines and chemokines associated with inflammatory reactions.  相似文献   
85.
Gas adsorption sites in a large-pore metal-organic framework   总被引:2,自引:0,他引:2  
The primary adsorption sites for Ar and N2 within metal-organic framework-5, a cubic structure composed of Zn4O(CO2)6 units and phenylene links defining large pores 12 and 15 angstroms in diameter, have been identified by single-crystal x-ray diffraction. Refinement of data collected between 293 and 30 kelvin revealed a total of eight symmetry-independent adsorption sites. Five of these are sites on the zinc oxide unit and the organic link; the remaining three sites form a second layer in the pores. The structural integrity and high symmetry of the framework are retained throughout, with negligible changes resulting from gas adsorption.  相似文献   
86.
Many dogs are relinquished worldwide, so it is important to enhance adoptions’ success. We aimed at investigating factors associated with owners’ satisfaction with adopted dogs, both in general and focusing on galgos. Data on 392 dogs (191 galgos) were gathered using an online survey, investigating dogs’ and owners’ demographics, satisfaction with the adopted dog and post-adoption behavior. Satisfaction was affected by different variables in galgos’ owners as compared to non-sighthound non-podenco dogs’ ones, with only the presence of disobedience on walks negatively affecting satisfaction in both samples. Depending on dogs’ type, the presence of some behavioral problems was associated with decreased satisfaction with the dog (e.g., destructiveness for galgos, or separation problems for non-sighthound non-podenco dogs), whereas that of others increased it (e.g., not being interested in social interactions with dogs for galgos, and shadowing for non-sighthound non-podenco dogs). The variables most often being predictors of the behaviors influencing satisfaction were dog type, with being a galgo as a negative predictor, and dog’s age, with being older as a negative predictor. Further studies on dog adopters’ satisfaction are needed.  相似文献   
87.
Levels of trace metals and chlorinated hydrocarbons were determined in sludge produced at the three main wastewater treatment plants in Kuwait (Ardhiya, Jahra, and Reqqa). Over the 6 mo study period (October 1984 to March 1985) levels at the three plants showed the following ranges (μg g?1 dry weight); Cd, 0.5 to 5.0; Cu, 90 to 270; Zn, 1100 to 3000; Pb, 80 to 300; Ni, 25 to 60; Hg, 1.8 to 3.6; Ag, 1 to 35; PCBs, 0.1 to 3.6; lindane, 0.4 to 7.4; EDDT (i.e., DDT + DDD + DDE), 0.07 to 0.20; aldrin, below detection to 0.07; endrin, below detection to 0.27; dieldrin, 0.005 to 0.04). Mean levels were generally close or lower than mean concentrations reported in the United Kingdom and the United States. They were also lower than suggested concentration limits for application of sludge on agricultural land, which is one of the most cost-effective and attractive techniques for sludge disposal. For Kuwait to adopt this application, however, the characteristics of the local soil and prevailing environmental conditions, notably the frequent occurrence of severe dust storms, should be considered.  相似文献   
88.
89.
The objective of this study was to determine the energy balance in early lactating local goats when supplemented with conjugated linoleic acid. Fifteen local goats from the north‐east of Mexico were used. Three treatments were evaluated: (a) Control (Base diet); (b) CLA 50 g; and (c) CLA 90 g. The CLA was a mixture of micro‐encapsulated FA, which supplied c9, t11 and t10, c12. Goats had an adaptation period of 2 weeks and 7 experimental weeks. The variables evaluated were body weight, DMI, milk yield, and fat, protein, and lactose yield, FA milk profile, and energy balance. The analysis of the data was analyzed as repeated measures using the PROC MIXED procedure and Tukey test (p < .05). In milk of goats from the treatment 90 g of the isomer t10, c12 CLA (p < .05) the milk fat content and milk fat yield with respect to the control treatment were reduced and the energy balance was improved. In goats treated with 11 g of t10, c12 CLA increased (p < .05) milk yield and milk lactose content. These results suggest that energy not used to synthesize dairy fat was used to increase milk yield and improve energy balance.  相似文献   
90.
  1. Fish aggregating devices (FADs) are floating objects that facilitate the aggregation of fish; those that aggregate pelagic species such as tunas are of particular interest for artisanal and industrial fisheries.
  2. Due to the increasing use of these devices worldwide, bodies responsible for the administration and management of fishery resources have proposed control and surveillance activities focused on the use of such devices. To achieve this, it is essential to have access to quality information, which is usually obtained through on-board observer programmes such as the Colombian Fisheries Observer Program.
  3. Based on the historical records of this programme, and for the first time, the spatial–temporal distribution of the FADs in the eastern tropical sector of the Eastern Pacific Ocean is presented, analysing 166 records of tuna fishing operations carried out between 2009 and 2015. Of the 2,328 sets identified in the records, 957 corresponded to sets on FADs, of which 80.56% were effective and caught 12,246 tons of tuna.
  4. The number of sets of FADs increased over time, representing approximately 86.9% of the sets recorded in 2015, compared to 4.8% of this type of set recorded in 2009, with the Eastern Tropical Pacific Marine Corridor being the area of greatest concentration of sets.
  5. Considering that the Eastern Tropical Pacific Marine Corridor was designed to promote the conservation and sustainable use of biological diversity in the Eastern Tropical Pacific, this study highlights the need to include as a research priority, the potential effect that aggregation devices may have on the biological connectivity processes present in the corridor, as well as on the dynamics of large pelagic fish populations of commercial interest.
  6. In terms of management of FADs, it is recommended that a precautionary approach be adopted and that regulations related to the maximum number of FADs per vessel be adjusted according to their Inter-American Tropical Tuna Commission class, in addition to assigning a maximum number of sets per vessel.
  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