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   1315篇
  免费   81篇
  国内免费   13篇
林业   113篇
农学   58篇
基础科学   11篇
  343篇
综合类   92篇
农作物   103篇
水产渔业   117篇
畜牧兽医   443篇
园艺   26篇
植物保护   103篇
  2024年   1篇
  2023年   15篇
  2022年   13篇
  2021年   58篇
  2020年   60篇
  2019年   55篇
  2018年   51篇
  2017年   59篇
  2016年   64篇
  2015年   43篇
  2014年   61篇
  2013年   70篇
  2012年   118篇
  2011年   110篇
  2010年   65篇
  2009年   54篇
  2008年   80篇
  2007年   77篇
  2006年   60篇
  2005年   52篇
  2004年   37篇
  2003年   41篇
  2002年   40篇
  2001年   16篇
  2000年   9篇
  1999年   16篇
  1998年   13篇
  1997年   12篇
  1996年   9篇
  1995年   6篇
  1994年   6篇
  1993年   5篇
  1992年   4篇
  1991年   4篇
  1990年   5篇
  1989年   6篇
  1988年   4篇
  1987年   3篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1979年   1篇
  1967年   1篇
  1966年   1篇
排序方式: 共有1409条查询结果,搜索用时 62 毫秒
991.
The influence of 2 different levels of the inspired oxygen fraction (FiO2) on blood gas variables was evaluated in dogs with high intracranial pressure (ICP) during propofol anesthesia (induction followed by a continuous rate infusion [CRI] of 0.6 mg/kg/min) and intermittent positive pressure ventilation (IPPV). Eight adult mongrel dogs were anesthetized on 2 occasions, 21 d apart, and received oxygen at an FiO2 of 1.0 (G100) or 0.6 (G60) in a randomized crossover fashion. A fiberoptic catheter was implanted on the surface of the right cerebral cortex for assessment of the ICP. An increase in the ICP was induced by temporary ligation of the jugular vein 50 min after induction of anesthesia and immediately after baseline measurement of the ICP. Blood gas measurements were taken 20 min later and then at 15-min intervals for 1 h. Numerical data were submitted to Morrison’s multivariate statistical methods. The ICP, the cerebral perfusion pressure and the mean arterial pressure did not differ significantly between FiO2 levels or measurement times after jugular ligation. The only blood gas values that differed significantly (P < 0.05) were the arterial oxygen partial pressure, which was greater with G100 than with G60 throughout the procedure, and the venous haemoglobin saturation, that was greater with G100 than with G60 at M0. There were no significant differences between FiO2 levels or measurement times in the following blood gas variables: arterial carbon dioxide partial pressure, arterial hemoglobin saturation, base deficit, bicarbonate concentration, pH, venous oxygen partial pressure, venous carbon dioxide partial pressure and the arterial-to-end-tidal carbon dioxide difference.  相似文献   
992.
The objective of this study was to develop and evaluate new baits for the oral delivery of vaccine preparations to 2–4 month-old wild boar piglets. Baits were prepared using a matrix composed of wild boar feed, wheat flour, paraffin, sacarose and cinnamon-truffle powder attractant with polyethylene capsules dipped into the matrix to introduce vaccine formulation. Physical stability studies demonstrated that baits were stable for at least three days at temperatures as high as 42 °C. Recombinant Escherichia coli expressing the membrane-displayed BM95-MSP1a fusion protein were used to test bacterial viability in the baits and the antibody response in orally immunized wild boar. The E. coli viability was not significantly affected after bait incubation at 25 and 37 °C for 96 h. Bait acceptance studies using artificial feeders in the field showed that baits were accepted by 2–3 month-old animals, the preferred age for vaccination. Orally immunized wild boar piglets excreted recombinant E. coli in the feces and developed antibody titers to recombinant BM95-MSP1a protein, thus confirming that vaccine composition was released and reached the wild boar gastrointestinal track. The results of these experiments support the use of these baits for oral delivery of vaccine formulations to 2–4 month-old wild boar piglets.  相似文献   
993.
An in vitro study was carried out to examine the influence of two fish-oil-derived long chain ω-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), on goat polymorphonuclear leukocytes (PMN). Twelve Saanen healthy goats were used as blood donors. Neutrophils were isolated from blood and incubated with increasing concentration of EPA and DHA (25, 50, 100, 200 μM). Control samples were incubated in the absence of ω-3 PUFAs. Phagocytosis was evaluated by fluorescein-labeled Escherichia coli incorporation, while extracellular Reactive Oxygen Species (ROS) production was determined by cytochrome c reduction assay, which was selected among the others due to its specificity for extracellular superoxide anion release. Phagocytic activity was significantly increased by EPA (P < 0.05) and DHA (P < 0.01). Treating PMN with EPA does not affect extracellular ROS production which is, on the contrary, down-regulated by DHA. This effect was increased in experimental conditions which mimic pro-inflammatory challenges (stimulation with PMA).This study demonstrates that EPA and DHA may have beneficial effect on neutrophil function by increasing their phagocytosis activity and, in the meanwhile, decreasing the tissue damages due to extracellular release of ROS.  相似文献   
994.
Abstract

Compost tea has been used throughout the world to control diseases and promote the growth of plants. The microbial community is the main factor involved both in the antagonistic effect against relevant phytopathogens and as a stimulator of plant growth. The objective of this research is to determine the bacterial diversity present in four types of compost as well as some of the mechanisms that may be involved in the positive effects of compost tea on crops. Aerated (ACT) and non-aerated (NCT) compost teas were obtained from four different composts: spent mushroom substrate compost (SMC), grape marc compost (GMC), greenhouse horticultural crop residues compost (CRC), and vermicompost (CRV). 16S rDNA-based DGGE profiles were obtained for each compost tea and their respective bacterial communities were analyzed. Of the 100 clones obtained, those typical for being dominant for all profiles were chosen. In total, 20 different clones were sequenced. The results showed that the bacterial communities of most compost teas had high richness, diversity, and evenness values, with relative abundance of species belonging to Bacteroidetes and Proteobacteria. The NCTs obtained from all the composts, especially CRC and CRV, showed high levels of siderophore production, while teas from GMC manifested high and consistent cellulase activity. The ACTs from all the composts, especially SMC, had high protease activity.  相似文献   
995.
ABSTRACT

The present study was performed to characterize the interaction between nitrogen (N) form and availability with respect to growth, water relations, and mineral nutrition of wild swiss chard (Beta macrocarpa Guss). Plants were cultured hydroponically with two levels of N concentrations, high-N (2.5 mM) or low-N (0.5 mM), added as nitrate (NO? 3) or ammonium (NH+ 4). At high N, growth was affected significantly by N form. If the NO? 3 medium was considered as control, the use of NH+ 4 decreased dry matter production and leaf area by ca. 35%. Use of NH+ 4 led to water economy and did not affect the nutrient content of the plant tissues. Compared to growth with high N, plants growth fell in either low- NO? 3 or low- NH+ 4 medium. In this case, the difference between the two N sources was not significant. Our results showed that the replacement of NO? 3 by NH+ 4 as the N source decreased the NO? 3 concentration in consumable leaves and increased the water use efficiency.  相似文献   
996.
997.
Pharmacokinetic and pharmacodynamic of IV enalapril at 0.50 mg/kg, PO placebo and PO enalapril at three different doses (0.50, 1.00 and 2.00 mg/kg) were analyzed in 7 healthy horses. Serum concentrations of enalapril and enalaprilat were determined for pharmacokinetic analysis. Angiotensin-converting enzyme (ACE) activity, serum ureic nitrogen (SUN), creatinine and electrolytes were measured, and blood pressure was monitored for pharmacodynamic analysis.  相似文献   
998.
Melanoma is a malignant neoplasm occurring in several animal species, and is the most frequently found tumor in the oral cavity in dogs. Melanomas are classified into two types: melanotic and amelanotic. Prior research suggests that human amelanotic melanomas are more aggressive than their melanotic counterparts. This study evaluates the behavior of canine melanotic and amelanotic oral cavity melanomas and quantifies cell proliferation and the expression of connexins. Twenty-five melanomas (16 melanotic and 9 amelanotic) were collected from dogs during clinical procedures at the Veterinary Hospital of the School of Veterinary Medicine and Animal Science of the University of São Paulo, Brazil. After diagnosis, dogs were followed until death or euthanasia. Histopathology confirmed the gross melanotic or amelanotic characteristics and tumors were classified according to the WHO. HMB45 or Melan A immunostainings were performed to confirm the diagnosis of amelanotic melanomas. Cell proliferation was quantified both by counting mitotic figures and PCNA positive nuclei. Expressions of connexins 26 and 43 were evaluated by immunohistochemistry, qRT-PCR and Western blot. Dogs bearing amelanotic melanomas presented a shorter lifespan in comparison to those with melanotic melanomas. Cell proliferation was significantly higher in amelanotic melanomas. Expressions of Connexins 26 and 43 were significantly reduced in amelanotic melanomas. The results presented here suggest that oral cavity melanotic and amelanotic melanomas differ regarding their behavior, cell proliferation and connexin expression in dogs, indicating a higher aggressiveness of amelanotic variants.  相似文献   
999.
Extremadura has been one of the regions in Spain most severely affected by Bluetongue (BT) epidemics. The first incursion of BTV, which was successfully eradicated one year later, occurred in 2004, involving the BTV-serotype 4. However, a second incursion occurred in September 2007, this time involving serotype 1. Since then, the implementation of intensive vaccination programs have significantly reduced BTV-1 occurrence, but the disease has not been completely eradicated yet.  相似文献   
1000.
  1. Marine ecosystems are highly affected by several human stressors. In this context, beyond passive restoration measures such as the creation of marine protected areas, it is urgent that we explore active restoration measures to enhance and accelerate the recovery of sessile marine species.
  2. Bryozoans are among the most common sessile invertebrates in rocky bottom ecosystems and are considered habitat‐forming species that are highly vulnerable to physical disturbances, such as recreational diving, ghost fishing nets, and global warming, which makes them highly vulnerable to other impacts. Despite their ecological importance and vulnerability, to date restoration actions for bryozoans have rarely been explored.
  3. In this study, different restoration techniques were developed and tested, with a focus on two types of effective methodologies previously applied to other marine invertebrates: recruitment enhancement and the transplantation of adult colonies, in both cases using the Mediterranean bryozoan Pentapora fascialis as a model species.
  4. First, different types of artificial surfaces were installed in different coralligenous habitats to test the enhancement of recruitment, concluding that plastic grids are the best substrate in terms of facilitating the recruitment of new bryozoan colonies.
  5. Second, different methodologies were tested for adult transplantation. The most successful was to fix colonies to a suitable substrate with a nylon thread attached to the colony ex situ (i.e. on the boat).
  6. Using this technique a trial restoration programme was undertaken, involving transplanting adult colonies collected from a ghost fishing net trapped on the bottom, which showed a high survival rate of ~50% after 6 months.
  7. The low economic cost of the implementation of the proposed techniques as well as the successful results obtained highlight the viability of restoring bryozoan populations over long temporal and spatial scales.
  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