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   268篇
  免费   5篇
林业   13篇
农学   17篇
基础科学   6篇
  69篇
综合类   17篇
农作物   22篇
水产渔业   29篇
畜牧兽医   75篇
园艺   4篇
植物保护   21篇
  2023年   4篇
  2022年   7篇
  2021年   13篇
  2020年   19篇
  2019年   22篇
  2018年   14篇
  2017年   10篇
  2016年   15篇
  2015年   8篇
  2014年   5篇
  2013年   8篇
  2012年   22篇
  2011年   26篇
  2010年   7篇
  2009年   8篇
  2008年   15篇
  2007年   12篇
  2006年   8篇
  2005年   8篇
  2004年   6篇
  2003年   7篇
  2002年   10篇
  2001年   1篇
  2000年   1篇
  1999年   1篇
  1998年   2篇
  1997年   1篇
  1996年   3篇
  1995年   1篇
  1994年   1篇
  1993年   1篇
  1992年   2篇
  1981年   1篇
  1980年   2篇
  1975年   2篇
排序方式: 共有273条查询结果,搜索用时 15 毫秒
91.
In this study, we captured 60 wild New World monkeys (Cebus spp.; Alouatta caraya) at the Paraná river basin, Paraná State, Brazil, and modified agglutination test (MAT) was performed to evaluate anti-Toxoplasma gondii antibodies. Prevalence was 30.2% (13/43) in Cebus spp. (capuchin monkeys) and 17.6% (3/17) for A. caraya (black and golden howler monkeys). MAT showed antibody titers of 16 (15/16) and 64 (1/16). Herein, we have observed an odds ratio (OR)=4.67 (1.060.05). The present work is the first report on serum occurrence of anti-T. gondii antibodies in wild capuchin monkeys and in wild black and golden howler monkeys.  相似文献   
92.
93.
The action of safener benoxacor on the detoxification of terbuthylazine (TBA) in Zea mays and Festuca arundinacea was ascertained by the investigation of the effects of benoxacor on the activity of glutathione-S-transferases (GSTs) in the shoots of the two plant species. TBA treatment generally reduced GST activity toward 1-chloro-2,4-dinitrobenzene (CDNB) in corn and did not affect the enzyme activity in festuca. When applied alone, benoxacor stimulated GST activity in both plants; however, when it was applied in mixture with TBA, generally, an enhancement of the enzyme activity was found in corn but not in festuca in comparison with the respective TBA-treated samples. The enhancement of GST activity in response to the benoxacor treatment in both corn and festuca resulted to be concomitant with decreases in apparent K(M) in both the plant species, with V(max) unaffected, and with an increased expression of proteins having molecular masses in the characteristic range of plant GSTs. After the benoxacor treatment, increased GST activity toward TBA as a substrate was observed in both corn and festuca. As a consequence, lesser amounts and persistence of TBA residues were found in shoots of corn and festuca treated with the TBA and benoxacor mixture compared to TBA-only-treated samples. Therefore, benoxacor enhances TBA detoxification in both corn and festuca; the induction of detoxifying activity in a nondomesticated grass is discussed in view of its use in vegetating buffer strips around crops to prevent TBA pollution.  相似文献   
94.
The present study was designed to assess the balance between antioxidant and prooxidant components and the oxidative stability of beef from cattle fed exclusively grazed pasture (PAS) or a barley-based concentrate offered indoors (CONC) for 11 mo, or fed grass silage indoors for a 5-mo winter period, followed for the remaining 6-mo summer period by grazed pasture (SiP) or by grazed pasture plus concentrate at 50% of the dietary DM (SiPC). Muscle prooxidant and antioxidant components were determined by measuring fatty acids and α-tocopherol concentration of LM, respectively. Lipid oxidation and color stability were monitored in ground LM, packaged in a high-oxygen modified atmosphere, over 11 d of refrigerated storage. Vitamin E concentration decreased (P < 0.0005) with an increasing proportion of concentrate in the diet (2.59, 2.45, 1.76, and 1.15 μg/g for PAS, SiP, SiPC, and CONC, respectively). A greater proportion of PUFA was found in LM from cattle in the PAS, SiP, and SiPC groups compared with animals in the CONC group (9.62, 11.04, 8.96, and 6.94%, respectively; P < 0.0005). A greater concentration of highly peroxidizable PUFA was found in LM from heifers in the PAS, SiP, and SiPC groups compared with those in the CONC group (0.84, 0.85, 0.87, and 0.65 mg/g of muscle, respectively; P = 0.02). Dietary treatment affected lipid oxidation (P < 0.0005), with greater 2-thiobarbituric acid reactive substance values in beef from heifers in the SiPC group than in beef from those in the PAS, SiP, and CONC groups. Dietary treatment affected myoglobin oxidation (P = 0.002) during storage, with greater metmyoglobin accumulation in beef from animals receiving concentrate (CONC and SiPC treatments) than in beef from cattle in the PAS and SiP groups. Consequently, feeding concentrate impaired meat color stability over the storage duration, with greater H* (hue angle) values (P < 0.0005) in meat from heifers in the SiPC and CONC groups compared with meat from those in the PAS and SiP groups. The results of the present study confirm a positive effect of grass-based feeding systems on meat color stability compared with concentrate-based dietary strategies. It appears that vitamin E in muscle alone does not explain the resistance of meat to oxidative deterioration because a clear interaction with highly peroxidizable PUFA exists.  相似文献   
95.
96.
The present study was conducted to evaluate the effects of high and low supplementation levels pre- and post-weaning on performance, endocrine, metabolic, and reproductive responses of Nellore heifers. Fifty Nellore heifers with 132?±?9.9 kg average body weight (BW) and 138?±?19 days of age were supplemented from 4 to 14 months. The heifers were distributed into five supplementation plans: HH—6 g/kg of BW of supplement pre- and post-weaning, HL—6 g/kg of BW of supplement pre-weaning and 3 g/kg post-weaning, LH—3 g/kg of BW pre-weaning and 6 g/kg of BW post-weaning, LL—3 g/kg of BW pre- and post-weaning, and CC—control, no supplementation. Interactions were not significant (P?>?0.10). The level of supplement fed pre-weaning did not affect any of the performance variables evaluated at the end of the experiment (P?>?0.10). There was a significant effect of supplementation and level of supplementation fed post-weaning on average daily gain (ADG) and final BW (P?<?0.05). Overall ADG was also affected only by supplementation and level of supplement fed post-weaning (P?<?0.05) with animals receiving 6 g/kg of BW post-weaning gaining more weight. Follicular diameter was greater in animals that received 6 g/kg of BW post-weaning (P?<?0.05). In summary, performance, endocrine, metabolic, and reproductive variables evaluated in the current study were improved by the level of supplement fed post-weaning. Heifers receiving supplementation of 6 g/kg of BW post-weaning had greater responses, independent of the level received during the pre-weaning phase.  相似文献   
97.

Objective

To evaluate the use of an experimental colloid model for teaching veterinary anesthesia residents ultrasound-guided technique for nerve blockade.

Study design

Prospective, blinded and randomized.

Methods

Colloid models were constructed for practice in ultrasound-guided needle location. Nine veterinary anesthesia residents with no prior experience of ultrasound-guided technique for nerve blocks were randomly divided into three groups. Each group received theoretical orientation. Two groups were assigned to practical training using the experimental model: group 1 (G1) received 2 hours of training and group 2 (G2) received 1 hour of training prior to testing with specific tasks. Group 3 (G3) received no practical training. During testing, the time required for task completion (e.g., display of structures and positioning a needle) and the number of failures were recorded.

Results

The average times to completion of the tasks and the number of technical failures were: G1, 47 seconds and 1 failure; G2, 68 seconds and 2 failures; G3, 187 seconds and 7 failures.

Conclusions and clinical relevance

In residents with no prior experience of ultrasound-guided needle placement, using an experimental colloid model and a longer training period was associated with increased accuracy and decreased time to task completion. Based on the results of this study, training with an experimental model can be recommended to improve the speed and accuracy of needle manipulation using ultrasound in clinicians with no prior experience of ultrasound-guided technique.  相似文献   
98.
Compost (CP) made from 70% ligno-cellulosic compounds and 30% sewage sludge was studied as a component of growing media in a 6-month Philodendron cultivation. CP's agronomic viability was evaluated via four plant-growth media containing 25–50–75–100% CP and white sphagnum peat (WP) in comparison to a commercial substrate with white and black peat. Plant nutrition conditions were investigated by determining macro- (TKN, P, K, Ca, Mg and micronutrients (Mn, Fe, Cu, Zn, Na) and heavy metals (Ni, Cd, Cr, Pb) in roots and shoot tissues. Data were compared by vector analysis against control. Even if no leaf injuries were visible after 6-months’ growth, a CP ratio of up to 50% caused growth depression of canopy tissues, as attested by the 37 and 36% reduction in total leaf dry weight and leaf area, respectively. Root growth decline was also notable at 25% CP, where 38% root dry weight reduction implied a significant increase (46%) in shoot–root dry weight ratio. The investigation on nutrient tissue content showed high accumulation of Ni, Fe, Cr, Zn, Cd, Mn, Mg and P in roots; Mg appeared related to K deficiency. Above-ground nutritional status showed a severe lack of P, Mg and Mn. Vector analysis suggests the sewage sludge CP in Philodendron pot cultivation produces many such effects like direct toxic action and antagonistic action, resulting in a general nutrient imbalance in plants.  相似文献   
99.
Ethyl acetate and chloroform extracts from aerial parts of Portulaca werdermannii and P. hirsutissima were tested in lymphoproliferation assays and axenic cultures of Leishmania amazonensis and Trypanosoma cruzi. Both extracts of P. werdermannii and P. hirsutissima had a potent inhibitory activity on lymphocyte proliferation. On the contrary, only the chloroformic extract of both plants inhibited L. amazonensis growth, without effect on T. cruzi cultures. These results indicate these Portulaca species as potential sources of new active molecules for the treatment of leishmaniasis and immune-mediated pathologies.  相似文献   
100.
Terrestrial ecosystems represent a major sink for atmospheric carbon (C) and temperate forests play an important role in global C cycling, contributing to lower atmospheric carbon dioxide (CO2) concentration through photosynthesis. The Intergovernmental Panel of Climate Change highlights that the forestry sector has great potential to decrease atmospheric CO2 concentration compared to other sectoral mitigation activities. The aim of this study was to evaluate CO2 sequestration (CO2S) capability of Fagus sylvatica (beech) growing in the Orfento Valley within Majella National Park (Abruzzo, Italy). We compared F. sylvatica areas subjected to thinning (one high-forest and one coppice) and no-management areas (two high-forests and two coppices). The results show a mean CO2S of 44.3 ± 2.6 Mg CO2 ha?1 a?1, corresponding to 12.1 ± 0.7 Mg C ha?1 a?1 the no-managed areas having a 28% higher value than the managed areas. The results highlight that thinning that allows seed regeneration can support traditional management practices such as civic use in some areas while no management should be carried out in the reserve in order to give priority to the objective of conservation and naturalistic improvement of the forest heritage.  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