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   6527篇
  免费   531篇
  国内免费   33篇
林业   353篇
农学   447篇
基础科学   54篇
  1027篇
综合类   703篇
农作物   286篇
水产渔业   405篇
畜牧兽医   3057篇
园艺   97篇
植物保护   662篇
  2020年   67篇
  2019年   127篇
  2018年   223篇
  2017年   227篇
  2016年   182篇
  2015年   199篇
  2014年   201篇
  2013年   374篇
  2012年   264篇
  2011年   320篇
  2010年   254篇
  2009年   212篇
  2008年   305篇
  2007年   272篇
  2006年   235篇
  2005年   201篇
  2004年   197篇
  2003年   200篇
  2002年   144篇
  2001年   238篇
  2000年   187篇
  1999年   172篇
  1998年   71篇
  1997年   75篇
  1996年   54篇
  1995年   59篇
  1994年   45篇
  1993年   51篇
  1992年   104篇
  1991年   105篇
  1990年   108篇
  1989年   107篇
  1988年   85篇
  1987年   80篇
  1986年   76篇
  1985年   58篇
  1984年   64篇
  1983年   53篇
  1981年   44篇
  1980年   49篇
  1979年   73篇
  1978年   53篇
  1977年   52篇
  1976年   59篇
  1975年   52篇
  1974年   61篇
  1973年   75篇
  1972年   44篇
  1971年   45篇
  1969年   43篇
排序方式: 共有7091条查询结果,搜索用时 15 毫秒
61.
62.
The present study was carried out to investigate genetic diversity in Nile-Delta and Southern-Egypt buffalo populations in comparison with the Italian buffalo utilizing two microsatellite multiplexes. A total of 104 animals classified into three groups were used, 28, 38 and 38 representing the Nile-Delta, Southern-Egypt and Italian buffalo, respectively. The 15 studied microsatellites were CSSM38, CSSM70, CYP21, CSSM42, CSSM60, MAF65, BM0922, CSSM19, INRA006, ETH02, BM1706, BMC1013, CSSM47, INRA026 and CA004. All studied microsatellites showed allelic polymorphism. Number of polymorphic alleles ranged between 4 alleles (CSSM38, CSSM70 and CYP21) and 11 alleles (CA004). Pairwise Chi-square test for Nile Delta and Southern Egypt showed significant differences in allelic distribution at five loci, CSSM70, CSSM38, BM0922, ETH02 and BM1706. Italian buffalo showed the lowest percentage of observed heterozygotes (65%), while the Southern Egypt showed the highest (71%). Both the Italian and the Delta populations deviated significantly (P < 0.05) from HW equilibrium. Italian buffalo is relatively the most inbred population while the Southern-Egypt buffalo is the only outbred population. High level of genetic differentiation (FST estimates) between the Italian group and each of the Delta and Southern-Egypt group (0.083 and 0.076, respectively) was observed while Southern-Egypt group showed a lower level of genetic differentiation with the Delta group (0.014). Italian buffalo had the greatest genetic distance values with the two Egyptian groups (0.25 and 0.23) while much lower values between the Southern-Egypt and the Delta groups (0.06) was observed. Genetic variation between the Italian buffalo and the Egyptian buffalo was detected in 14 (out of 15) microsatellite loci. While a lower level (than that between Egyptian and Italian) of genetic variation between Southern-Egypt and Delta buffalo populations was expressed by 5 loci. It was concluded that the Southern-Egypt buffalo could be considered as distinct population from the Delta buffalo. In addition, Southern-Egypt group, being the only group with non-significant global deviation from HW equilibrium, the most heterozygous, and the only outbred population as well, is expected to respond more favorably to selection.  相似文献   
63.
64.
Anorexigenic substances released during infection may hinder the therapeutic efficacy of in-feed antibiotics. Paracetamol (acetaminophen; PARA) inhibits the anorexia of infection and seems to improve the clinical efficacy of doxycycline (DOX) against bacterial respiratory disease in swine herds. In order to verify whether PARA selectively stimulates intake of DOX-medicated feed in diseased pigs, we documented the pharmacokinetics (PK) of DOX when coadministered with PARA and examined the effect of in-feed PARA on the interindividual variability in plasma concentrations after systemic exposure to in-feed DOX in swine herds with respiratory disease. Systemic exposure to DOX was measured with the area under the curve (AUC) of its plasma concentrations over time. First, a rich-sampling PK study of in-feed and i.v. DOX (10 mg/kg of BW) and PARA (30 and 10 mg/kg of BW, respectively) was performed on 5 pigs. The PK profiles of in-feed DOX were used in mathematical simulations to determine 5 optimal sampling times for the farm-based population PK study. A randomized, blind, parallel PK study was performed in 2 herds with bacterial respiratory disease, where liquid feed was fortified with DOX alone (5 mg x kg of BW(-1) x meal(-1)) or combined with PARA (15 mg x kg of BW(-1) x meal(-1)). Medicated meals were given twice, 12 h apart, to group-housed growing pigs (n > 50 pigs x treatment(-1) x herd(-1), totaling 215 pigs). Plasma concentrations of DOX and PARA were measured with HPLC. At variance with our expectations, PARA decreased (P = 0.069) mean AUC of in-feed DOX and did not decrease its variability (P > 0.34). Mean AUC of DOX increased with feed intake and with initial exposure to DOX, and was greater in sick animals. Therefore, symptomatic PARA-induced improvement in bacterial respiratory disease control with DOX is more likely caused by its analgesic/antipyretic effects than by its orexigenic effect. Interindividual variation in the AUC of DOX was large in pigs given group medication, even when sufficient feeding space was allowed and the amount of feed offered was greater than their requirements. Therefore, future studies to improve the efficacy of group antibiotic therapy should focus on feeding behavior characteristics as well as biopharmaceutical properties of medicated feeds.  相似文献   
65.
Antipyrine disposition in the dehydrated camel   总被引:1,自引:0,他引:1  
In the present study the effects of water deprivation in the camel ( Camelus dromedarius ) on the pharmacokinetic profile of antipyrine were assessed. A crossover design was used. The pharmacokinetics of antipyrine in adult and young camels were compared. Antipyrine was administered intravenously to young and adult female camels when water was available ad libitum and to the adult camels after 14 days of dehydration. The elimination half-life of antipyrine in watered adult camels was 136.5 ± 16.7 min. The half-life of elimination and the mean residence time of antipyrine were significantly prolonged following dehydration. The observed effects of water deprivation were not a function of age, as the pharmacokinetic profile of antipyrine in young camels was similar to that of the adults, but more likely due to the changes in oxidative metabolic capacity of the liver as a result of a reduced general metabolism. The results of the present study also show that the intrinsic clearance of antipyrine is proportional to the camel's body weight, as previously shown for other mammalian species.  相似文献   
66.
The morphologic and morphometric features of the lower respiratory system in mole rats were examined. It was seen that the low respiratory system of this species leading a special life under highly hypoxic/hypercapnic conditions underground is structurally similar to other mammals living on land in terms of the parts examined; trachea was formed by 29.5 ± 4 oval‐formed cartilaginous tracheals arranged backwards and became gradually more stenotic diameter from cranial to the caudal of the neck. The trachea was separated in two principal bronchus at the fourth thoracal intercostal spatium level. The angle between the two main principal bronchi was 60.5 ± 2.35°. The lung constituted 1.29 ± 0.03% of the body weight and the right lung was heavier than the left lung. Fissura inter‐lobaris was deep and separated the lung lobes wholly, and the right lung was separated in four lobes, whereas the left lung was not separated into the lobes. Also, the medial lobe of the left lung was the lightest lobe.  相似文献   
67.
This study was conducted to analyze the prevalence and quantitative loads of Salmonella spp. on pig farms in Chiang Mai, Lamphun, Thailand to assess loading levels before slaughtering. The serotype diversity, antimicrobial-resistance pattern and pulse-field type of Salmonella spp. were also characterized to assess the dynamic propagation of the pathogen. The Salmonella-positive prevalence was 246/805 (30.56%), and the quantitative loads varied from 1.48~4.04 Log10MPN/g, with a mean ± standard deviation of 2.11 ± 0.57. AMP/S/TE (ampicillin/streptomycin/tetracycline) was the highest frequency antimicrobial resistance pattern found in this study. In addition, Salmonella Rissen was the primary serotype in this region. PFGE results indicated the occurrence of infection by cross contamination among pig farms. Our study showed that pork is easily contaminated with this pathogen. Farm control programs must be based on strict biosecurity and hygienic measures, which could further reduce the contamination pressure at slaughterhouses or retail shops.  相似文献   
68.
69.
1. The objectives of the study were to find polymorphic sites and elucidate the association between SNPs in the nuclear receptor coactivator 1 (NCOA1) gene and reproductive traits. 2. SNPs were detected by PCR-SSCP and DNA sequencing. Four SNPs were detected, including T10155007A, T10125838C, G10118492A and G10109315T. Three polymorphisms were associated with total egg production at the age of 300 d and the G10109315T polymorphism was associated with age at first egg. 3. In conclusion, the NCOA1 gene can be used as a molecular marker for reproductive traits in hens.  相似文献   
70.
Genetic parameters of traits related to hepatic lipid metabolism, carcass composition, and product quality of overfed mule ducks were estimated on both parental lines of this hybrid: the common duck line for the maternal side and the Muscovy line for the paternal side. The originality of the statistical model was to include simultaneously the additive genetic effect of the common ducks and that of the Muscovy ducks, revealing a greater genetic determinism in common than in Muscovy. Plasma metabolic indicators (glucose, triglyceride, and cholesterol contents) were heritable, in particular at the end of the overfeeding period, and heritabilities increased with the overfeeding stage. Carcass composition traits were highly heritable in the common line, with values ranging from 0.15 for liver weight, 0.21 for carcass weight, and 0.25 for abdominal fat weight to 0.32 for breast muscle weight. Heritabilities of technological outputs were greater for the fatty liver (0.19 and 0.08, respectively, on common and Muscovy sides for liver melting rate) than for the pectoralis major muscle (between 0.02 and 0.05 on both parental sides for cooking losses). Fortunately, the processing industry is mainly facing problems in liver quality, such as too high of a melting rate, than in meat quality. The meat quality appraisal criteria (such as texture and cooking losses), usually dependent on pH and the rate of decline of pH, were also very lowly heritable. This study demonstrated that genetic determinism of meat quality and ability of overfeeding is not similar in the common population and in the Muscovy population; traits related to fattening, muscle development, and BW have heritability values from 2 to 4 times greater on the common line than on the Muscovy line, which is relevant for considering different selection strategies.  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