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   376篇
  免费   31篇
林业   32篇
农学   12篇
  72篇
综合类   12篇
农作物   30篇
水产渔业   34篇
畜牧兽医   177篇
园艺   12篇
植物保护   26篇
  2023年   4篇
  2022年   12篇
  2021年   24篇
  2020年   18篇
  2019年   17篇
  2018年   27篇
  2017年   22篇
  2016年   24篇
  2015年   19篇
  2014年   22篇
  2013年   18篇
  2012年   33篇
  2011年   30篇
  2010年   18篇
  2009年   17篇
  2008年   13篇
  2007年   26篇
  2006年   12篇
  2005年   15篇
  2004年   10篇
  2003年   8篇
  2002年   6篇
  2001年   4篇
  1998年   1篇
  1997年   1篇
  1995年   1篇
  1993年   1篇
  1992年   1篇
  1980年   1篇
  1973年   1篇
  1971年   1篇
排序方式: 共有407条查询结果,搜索用时 5 毫秒
131.

The present study attempted to verify the prevalence of and risk factors for diarrhea-causing agents in dairy calves from Brazil. Additionally, ages with a higher risk of occurrence for each agent were verified by means of the receiver operating characteristic (ROC) curve. The collections were performed on 39 farms, belonging to 29 municipalities located in eight states of Brazil. It was possible to conclude that the prevalence of Coronavirus, Rotavirus, Cryptosporidium spp., Eimeria spp., and nematodes was 7.20% (95% CI 4.54–9.78), 6.37% (95% CI 3.85–8.89), 51.52% (95% CI 45.26–55.57), 3.46% (95% CI 2.24–4.67), and 3.46% (95% CI 2.24–4.67), respectively. Ages with higher probabilities of occurrence of these diseases in calves were <?10, >?8, >?6, >?37, and >?36 days, respectively. Diarrhea occurred more significantly (P?<?0.0001) in animals less than 21 days old and mainly on those receiving milk through automatic feeders (P?<?0.001). Cryptosporidium spp. were a risk factor for the occurrence of Rotavirus, and vice versa (P?=?0.0039) and presented a positive correlation with Coronavirus (P?=?0.0089). Calves that drink water from rivers, streams, and ponds had a higher chance of being infected by Eimeria spp. (P?<?0.0001), as well as developing infection by nematodes (P?<?0.0001). The results found in this study highlight the importance of studying the agents of diarrhea together, once they act as coinfection where the losses triggered for the owners will involve some of these agents simultaneously.

  相似文献   
132.

The objective of this study was to evaluate the effects of nutritional strategies on productive and nutritional performance, metabolic profile, and ovarian activity in heifers under grazing in the tropics in Brazil. Forty Nellore heifers averaging 8.5?±?0.06 months and 248.6?±?3.3 kg body weight (BW) were distributed in a completely randomized 2?×?2 factorial design with four treatments and ten replicates. The evaluated strategies consisted of different amounts of energetic-protein supplement: (1) 4 g/kg of BW of supplement in the pre-weaning and post-weaning; (2) 4 g/kg of BW of supplement pre-weaning and 6 g/kg in the post-weaning; (3) 6 g/kg of BW of supplement in the pre-weaning and 4 g/kg of BW in the post-weaning and; (4) 6 g/kg of BW of supplement in the pre-weaning and post-weaning. Crude protein (CP) and organic matter (OM) intake were increased (P?<?0.05) by increasing the amounts of supplement in the post-weaning. Additionally, increasing supplement amounts in the post-weaning increased the digestibility of OM and CP (P?<?0.05). Means insulin and glucose concentrations were greater (P?<?0.05) for heifers that received higher amounts of supplement in the post-weaning. Average daily gain and fat thickness in the rump were increased (P?<?0.05) by increasing supplement amounts in the post-weaning. Amounts of supplement did not influence the body growth of heifers. However, follicular number, diameter, and progesterone concentration were greater (P?<?0.05) for heifers that received higher amounts of supplement in the post-weaning. In summary, increasing supplement amounts in the post-weaning improve the performance, energy and metabolic status, and ovarian activity in beef heifers under grazing in the tropics. Due to higher intake of supplement, the heifers receiving 6 g/kg of BW post-weaning had greater responses, independently of the supplement amount received pre-weaning.

  相似文献   
133.
134.
We tested FSHp, eCG and FSHp + eCG to establish ovum pick-up (OPU) and in vitro maturation method in spotted paca. Eight healthy adult females were subjected to each of four treatments to stimulate ovarian follicular growth. All females were subjected to a hormonal protocol using a single dose of 45 mg of injectable progesterone and single intramuscular injection of 0.075 mg d-cloprostenol on day 6. Ovarian stimulation was carried out as follows: in Group TFE (FSHp and eCG), animals were treated with a single dose of 80 mg of FSHp and 200 IU of eCG intramuscularly on day 6 after the application of progesterone; in Group TF (FSHp), they were treated with a single dose of 80 mg of FSHp intramuscularly on day 6 after application of progesterone; in Group treatment eCG, they were treated with 200 IU of eCG intramuscularly on day 6 after application of progesterone; and in Group TC (saline solution), 1 ml of saline solution was administered to control does. The OPU was performed between 22 and 26 hr after gonadotropin treatments. All recovered oocytes were placed into maturation media and incubated for 24 hr. There were no differences among the mean number of observed follicles, aspirated follicles and oocytes recovered per treatment. Oocyte maturation rates did not differ among groups, except, TF and treatment eCG oocytes had greater maturation rates than TC oocytes. In this study, gonadotropin administration failed to superovulate treated does and increase oocyte retrieval efficiency. Despite the feasibility of the procedure, further studies are needed to develop and refine hormonal protocols for oocyte recovery and in vitro maturation in this species.  相似文献   
135.
136.
In several regions of Italy as well as other parts of southern Europe, the heterogeneity of the land, the climate and the soil favour the survival in cultivation of a large number of landraces specifically adapted to local conditions. Knowledge on the level and distribution of their genetic variation can help to develop appropriate strategies, in order to suistainably manage in situ these germplasm resources at risk of genetic erosion. C. annuum is an herbaceous diploid species and is considered to be self-pollinating, although different rates of out-crossing have been recorded. We used random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers to assess genetic diversity within and between five populations of a landrace of Capsicum annuum L., grown in a limited area in north-west Italy and locally known as Cuneo pepper. Partitioning the genetic variation with Shannon's diversity index revealed that 41.6% occurred between and 58.4% within populations. Analogous results were obtained when the analysis was based only on RAPD or AFLP markers. However, AFLP was more reliable, since a lower range of variation was observed among primer combinations in detecting the two components of genetic variation. Notwithstanding the rather high level of within genetic variation detected, the five populations were clearly differentiated and differed in the frequency of alleles exclusive and/or present at very low frequencies. Our results show the need for accurate estimation of allele frequencies, in order to identify populations to which priority should be given for dynamic conservation of landraces.  相似文献   
137.
Invasion, cell proliferation and apoptosis are important biological features of neoplasia, bearing prognostic importance. Histological stage, mitotic index, and apoptotic index have been assessed in 33 feline malignant mammary tumors. Histological stage (P < 0.01) and mitotic index (P < 0.001) had a significant association with prognosis in univariate analysis. Apoptotic index did not correlate with survival (P = 0.44), and histological stage (P = 0.48) did not correlate with mitotic index (P = 0.39). In feline malignant mammary tumors the apoptotic index seems unable to predict survival and lacks any correlation with proliferation assessed as mitotic index. A possible explanation for the lack of correlation between apoptotic index and survival may be due to the rapid acquisition of pathways of apoptosis resistance in feline mammary tumors or to rapid hormone receptors loss.  相似文献   
138.
ABSTRACT:   This study was carried out to investigate the genetic variability and the population genetics of Sparus auratus. In fact, despite its importance in Mediterranean fisheries and aquaculture, very little it is known concerning its population structure. Samples of wild gilthead sea bream were collected in seven different localities along the Mediterranean and Atlantic coasts and were genetically characterized by means of microsatellite markers. Genotyping at four microsatellite loci revealed high polymorphism (7–38 alleles/locus) and expected heterozygosities, which ranged from 0.80 to 0.85. A slight but significant population structure was found ( F ST = 0.010). In fact, at least three populations of gilthead sea bream within the Western Mediterranean Sea were identified (Sardinian Sea, Sardinian Channel and Central Tyrrhenian Sea), which are also genetically differentiated from those of the Atlantic Ocean and the Adriatic Sea.  相似文献   
139.
BACKGROUND: Qualitative and quantitative electroencephalography (EEG) parameters of healthy and Finnish Spitz dogs with epilepsy have not been determined. OBJECTIVE: To determine if EEG can provide specific characteristics to distinguish between healthy dogs and dogs with epilepsy. ANIMALS: Sixteen healthy and 15 Finnish Spitz dogs with epilepsy. METHODS: A prospective clinical EEG study performed under medetomidine sedation. Blinded visual and quantitative EEG analyses were performed and results were compared between study groups. RESULTS: Benign epileptiform transients of sleep and sleep spindles were a frequent finding in a majority of animals from both groups. The EEG analysis detected epileptiform activity in 3 Finnish Spitz dogs with epilepsy and in 1 healthy Finnish Spitz dog. Epileptiform activity was characterized by spikes, polyspikes, and spike slow wave complexes in posterior-occipital derivation in dogs with epilepsy and with midline spikes in control dog. The healthy dogs showed significantly less theta and beta activity than did the dogs with epilepsy (P < .01), but the only significant difference between healthy dogs and dogs with untreated epilepsy was in the alpha band (P < .001). Phenobarbital treatment increased alpha, beta (P < .001), and theta (P < .01), and decreased delta (P < .001) frequency bands compared with dogs with untreated epilepsy. CONCLUSIONS AND CLINICAL IMPORTANCE: Benign epileptiform transients of sleep could be easily misinterpreted as epileptiform activity. Epileptiform activity in Finnish Spitz dogs with epilepsy seems to originate from a posterior-occipital location. The EEG of dogs with epilepsy exhibited a significant difference in background frequency bands compared with the control dogs. Phenobarbital treatment markedly influenced all background activity bands. Quantitative EEG analysis, in addition to visual analysis, seems to be a useful tool in the examination of patients with epilepsy.  相似文献   
140.
OBJECTIVE: To evaluate the correlation between the bispectral index (BIS) and end-tidal isoflurane (ET(ISO)) concentration and compare the use of 3 BIS sensor positions in dogs. ANIMALS: 6 adult dogs. PROCEDURES: Mechanically ventilated dogs received pancuronium, and depth of anesthesia was altered by increasing ET(ISO) concentration from 1.5% to 2.3% and 3.0%. The BIS, suppression ratio (relative percentage of isoelectric electroencephalographic waveforms), and signal quality index (SQI) were recorded at each ET(ISO) concentration for each of 3 BIS sensor positions (frontal-occipital, bifrontal, and frontal-temporal positions). RESULTS: The BIS and ET(ISO) concentration were poorly correlated; regardless of sensor positioning, mean BIS values did not change significantly as ET(ISO) was increased. At 3% isoflurane, regardless of sensor positioning, there was an increase in suppression ratio coincident with BIS < 40 in some dogs, whereas paradoxic increases in BIS (> 60) were recorded in others. Furthermore, at 3.0% isoflurane, the SQI was significantly lower for the bifrontal sensor position (compared with values for the other positions), but low SQI values prevented recording of BIS values from the frontal-occipital sensor position in 2 dogs. Overall, BIS values derived from the 3 sensor positions did not differ. CONCLUSIONS AND CLINICAL RELEVANCE: In dogs, BIS values may not reflect changes in depth of isoflurane anesthesia in the absence of noxious stimulation. Of the 3 sensor positions, frontal-temporal positioning provided better correlation with changes in depth of anesthesia induced via changes in isoflurane concentrations. However, the sensor placements yielded similar results at SQI values > 50.  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