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   1537篇
  免费   133篇
林业   183篇
农学   46篇
基础科学   2篇
  371篇
综合类   7篇
农作物   102篇
水产渔业   117篇
畜牧兽医   695篇
园艺   27篇
植物保护   120篇
  2023年   11篇
  2022年   19篇
  2021年   41篇
  2020年   41篇
  2019年   42篇
  2018年   107篇
  2017年   99篇
  2016年   106篇
  2015年   64篇
  2014年   74篇
  2013年   95篇
  2012年   111篇
  2011年   130篇
  2010年   82篇
  2009年   30篇
  2008年   57篇
  2007年   71篇
  2006年   46篇
  2005年   53篇
  2004年   53篇
  2003年   49篇
  2002年   50篇
  2001年   24篇
  2000年   18篇
  1999年   26篇
  1998年   8篇
  1997年   7篇
  1996年   8篇
  1995年   11篇
  1994年   5篇
  1993年   8篇
  1992年   6篇
  1991年   8篇
  1990年   9篇
  1989年   6篇
  1988年   4篇
  1987年   4篇
  1986年   9篇
  1985年   6篇
  1984年   9篇
  1983年   4篇
  1982年   10篇
  1981年   8篇
  1977年   7篇
  1976年   14篇
  1975年   2篇
  1972年   2篇
  1971年   2篇
  1968年   2篇
  1966年   2篇
排序方式: 共有1670条查询结果,搜索用时 0 毫秒
1.
Papillomaviruses are non-enveloped, DNA viruses that infect skin and mucosa of a wide variety of vertebrates, causing neoplasias or simply persisting asymptomatically. Avian papillomaviruses, with six fully sequenced genomes, are the second most studied group after mammalian papillomaviruses. In this study, we describe the first oral avian papillomavirus, detected in the tongue of a dead Yorkshire canary (Serinus canaria) and in oral swabs of the same bird and other two live canaries from an aviary in Madrid, Spain. Its genome is 8,071 bp and presents the canonical papillomavirus architecture with six early (E6, E7, E1, E9, E2, E4) and two late open reading frames (L1 and L2) and a long control region between L1 and E6. This new avian papillomavirus L1 gene shares a 64% pairwise identity with FcPV1 L1, so it has been classified as a new species (ScPV1) within the Ethapapillomavirus genus. Although the canary died after showing breathing problems, there is no evidence that the papillomavirus caused those symptoms so it could be part of the oral microbiota of the birds. Hence, future investigations are needed to evaluate the clinical relevance of the virus.  相似文献   
2.
Birds obtained by embryo engineering are used to study embryo development and to produce transgenic birds. As this method of producing birds still generate strong emotions of the public opinion head ornaments, testes and semen characteristics of sex chimera roosters were examined to check whether they differ from chickens obtained by non‐manipulated methods. Measurements of head ornaments, testes and semen were correlated with each other. Semen quality factor (SQF) was calculated, as well as the level of fluctuating asymmetry (FA) of bilateral traits (wattles and testes). Positive correlation was found for comb width and wattle length and comb thickness and sperm concentration. Semen characteristics and FA did not exceed the level encounter in other chicken lines. Results obtained indicate that germline chimeras are similar in appearance of secondary sexual traits, and semen and testes characteristics to chickens produced in non‐manipulated way.  相似文献   
3.
The aim of the present study was to investigate the effects of crossbreeding on collagen content and solubility, shear force (WBSF) and the eating quality of Infraspinatus (INF) and Semimembranosus (SM) muscles of young bulls and the relationships between collagen content and solubility, shear force and the eating quality of beef. The experimental material comprised muscles of crossbred young bulls (about 600 days old) of Polish Holstein‐Friesian (PHF) × Limousine (LM) (n = 10), PHF × Charolaise (CH) (n = 9), PHF × Hereford (HER) (n = 9) breeds. The crossbreeding influenced WBSF, aroma and taste, total, water‐soluble, acid‐soluble, total soluble and insoluble collagen content, as well as the acid‐soluble, total soluble and insoluble collagen proportions. WBSF was significantly negatively correlated with sensorial tenderness and water‐soluble collagen content. The eating quality of beef obtained from different crossbreds was similar; however, the meat from PHF × LM and PHF × HER bulls had lower WBSF values than PHF × CH bulls. © 2016 Japanese Society of Animal Science  相似文献   
4.
1. The aim of this study was to evaluate the occurrence of Campylobacter spp. in domestic and free-living pigeons and to evaluate the antibiotic resistance profiles.

2. The material consisted of cloacal swabs obtained from 108 homing pigeons and fresh faeces from 72 wild birds from Lublin and its vicinity. The identification of strains isolated on differential/selective media for Campylobacter spp. was carried out by MALDI-TOF and PCR. The susceptibility to antibiotics was evaluated by minimum inhibitory concentration (MIC) in Mueller-Hinton broth.

3. A total of 35 strains of Campylobacter spp. were isolated; 27 were identified as Campylobacter jejuni and 8 as Campylobacter coli. Over half of the isolates were resistant to erythromycin and streptomycin, 40% of strains were resistant to tetracycline and ampicillin and 37% isolates were resistant to amoxicillin. Resistance to two or more antibiotics was observed in all strains tested.

4. The results indicate that both domestic and free-living pigeons are reservoirs for bacteria of the genus Campylobacter, which are characterised by varied and growing resistance to commonly used antibiotics.  相似文献   

5.
REASONS FOR PERFORMING STUDY: Connexin 43 (Cx43) is a ubiquitously distributed gap junction protein in testes and other reproductive tissues. Adjacent cells share ions and small metabolites through intercellular channels, which are present in gap junctions. Previously, Cx43 has not been reported in testes, epididymides and prostates either in healthy stallions or cryptorchid horses. OBJECTIVES: To demonstrate the expression pattern of Cx43 in the reproductive tissues of stallions and examine whether naturally occurring bilateral cryptorchidism has any influence on distribution and expression of Cx43. METHODS: The expression and the presence of Cx43 protein were detected by means of immunohistochemistry and Western blot analysis using a polyclonal rabbit anti-Cx43 antibody. RESULTS: In stallions, gap junctions appeared as structures localised to cell-cell contacts between adjacent cells. In testes, Cx43 expression was detected in the interstitial tissue and seminiferous tubules, between Leydig and Sertoli, as well as Sertoli and germ cells. In epididymides, Cx43 was localised between epithelial cells, whereas in prostates, between secretory cells of the glandular epithelium. In the cryptorchid, a clear reduction of Cx43 signal was observed in all reproductive tissues. CONCLUSIONS: Coupling of Leydig cells via gap junctions may suggest that steroidogenic function of the testis is under the influence of these intercellular channels. Within seminiferous tubules, the expression was found to be stage-specific, pointing to its role in coordinating spermatogenesis. Differential distribution of Cx43 protein in the reproductive tract of normal and cryptorchid stallions indicates that expression is clearly dependent on the physiological status of the horse. POTENTIAL RELEVANCE: Detection of Cx43 expression in equine testicular, epididymal, and prostatic cells is important for a better understanding of the role of intercellular membrane channels in direct cell communication within the reproductive tract of stallions.  相似文献   
6.
The lack of protective action of oestrogens which appears during menopausal period may be the reason of serious metabolic disturbances including oxidative stress. The hypothesis was stated that ovariectomy may induce the variations of antioxidant/oxidant status which can be detected in rat liver. A total of 102 healthy Wistar female rats were included in the experiment and divided into control (CON; n = 6), sham-operated (SHO; n = 48) and ovariectomized (OVX; n = 48) groups. Animals from SHO (n = 6) and OVX (n = 6) groups were killed every week during 8 weeks of experiment to detect dynamic changes in examined parameters. Anti-oxidative enzyme activities [glutathione peroxidase (GSH-Px); superoxide dismutase (SOD)] as well as total antioxidant capacity (TAC) and the intensity of lipid peroxidation, measured by the concentration of N,N,diethyl-p-phenylene diamine (DEPPD) radical, were determined in liver homogenates by the use of spectrophotometric methods. Wave-like patterns of examined parameters within 8 weeks of experiment were detected. GSH-Px activity tended to be higher in OVX animals and was significantly lower at 8th week when compared with 1st week of experiment. SOD activity was higher in SHO animals and showed significant differences between 3rd, 4th, 7th and 1st week. TAC values were significantly higher in OVX when compared with SHO groups in 2nd, 4th, 5th week and significantly lower in 3rd, 6th and 7th week of the experiment. The concentration of DEPPD radicals tended to increase in OVX group. In conclusion, ovariectomy which leads to oestrogen insufficiency is reflected as well in variation of anti-oxidative/oxidative parameters in rat liver homogenates.  相似文献   
7.
8.
Theonella swinhoei is a fairly common inhabitant of reefs throughout the Indian and Pacific Oceans. Metabolomic analyses of samples of T. swinhoei collected in different depths in the Gulf of Aqaba revealed two chemotypes differing in the profiles of the theonellamides they produce, some of which seem to be unknown. Driven by this finding, we examined a sample of T. swinhoei collected more than 40 years ago in the southern part of the Gulf of Aqaba. Large-scale extract of this sample yielded four theonellamides, the known theopalauamide (4), as the major component, and three new metabolites, theonellamide J (1), 5-cis-Apoa-theopalauamide (2), and theonellamide K (3), as the minor components. The planar structure of these complex cyclic glycopeptides was elucidated by combination of 1D and 2D NMR techniques and HRESIMS. The absolute configuration of the amino acids was established by Marfey’s and advanced Marfey’s methods, and the absolute configuration of its galactose unit using “Tanaka’s method” for monosaccharides. The biological activity of the pure compounds was tested for antibacterial activity and for cytotoxicity to HTC-116 cell line. The compounds presented significant cytotoxicity against the HTC-116 cell line, illuminating the importance of the Apoa subunit for the activity.  相似文献   
9.
The aim of this article was to analyse the process of pikeperch, Sander lucioperca, egg swelling and to apply tannic acid to eliminate egg stickiness at different moments of the swelling process on artificially obtained eggs. The first experiment involved observation of egg swelling process and the second determined the effect of temperature (12, 14 and 16°C) on the egg swelling rate. The third experiment involved elimination of egg stickiness in a tannin solution (0.75 g L?1) where eggs were submerged in a solution for 0.5, 1, 2 and 5 min – 5, 10, 15, 20, 25 and 30 min following gamete activation. The results indicate that the pikeperch egg swelling process lasts 30 min. It was found that the temperature did not affect the process duration. The results of the third experiment showed that the effectiveness of tannic acid application in egg stickiness elimination increases with time. The best result was obtained in groups of eggs submerged for 1 and 2 min (86.5% and 80.5% of larvae were obtained respectively) 30 min following the gamete activation. The results presented in this study for the first time indicate the possibility of highly effective procedure of egg stickiness elimination with tannic acid in pikeperch aquaculture.  相似文献   
10.
ABSTRACT

The on-farm trials of rotational rice-prawn farming in a semi-deep water area in the Mekong Delta of Vietnam was carried out in six rice fields (0.7–1.0 ha) to evaluate the production and economic efficiency of using low and high cost feed on prawn culture in paddies at different densities. Two stocking densities of 4 and 5 PL/m2 were investigated. Two treatments of feed types (pellets only or a combination of pellets, trash fish, and snail meat) were applied at stocking 4 PL/m2. At the treatment of 5 PL/m2, prawns were fed a combination of pellets, trash fish, and snail meat. Prawns were stocked in the mid-April and harvested in mid‐November before the next dry season rice crop. Rice farming was started 3 to 5 days after prawn harvesting. By cull harvesting during the culture period, final mean weights of prawn ranged from 47.2 to 57.2 g/prawn and the male:female ratio at harvesting was 2.5:1.0. The prawn yield of treatment 5 PL/m2 was highest (630 ± 22 kg/ha). Net profits in treatments using the combination of pellets, trash fish, and snail meat were 861 ± 193 US$/ha to 1,019 ± 25 US$/ha for the prawn crop and 1,393 ± 71 US$/ha to 1,576 ± 180 US$/ha for the whole system (prawn crop + dry rice crop) and significantly higher than in treatment using pellet only (P < 0.05). Prawns fed on pellets or a combination of pellets and snail meat both offer similar results in terms of production and economics. The dry rice crop offered high cost benefit ratio (2.29–2.33) with low operating cost (414–434 USD/ha) and it made a better use in sustainable rice fields through the rotational rice-prawn system.  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