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   20520篇
  免费   235篇
  国内免费   2篇
林业   3905篇
农学   1428篇
基础科学   151篇
  3817篇
综合类   942篇
农作物   2428篇
水产渔业   2239篇
畜牧兽医   2500篇
园艺   1191篇
植物保护   2156篇
  2023年   47篇
  2022年   93篇
  2021年   188篇
  2020年   179篇
  2019年   220篇
  2018年   2852篇
  2017年   2815篇
  2016年   1339篇
  2015年   206篇
  2014年   217篇
  2013年   307篇
  2012年   1122篇
  2011年   2428篇
  2010年   2278篇
  2009年   1416篇
  2008年   1581篇
  2007年   1859篇
  2006年   243篇
  2005年   277篇
  2004年   249篇
  2003年   304篇
  2002年   205篇
  2001年   25篇
  2000年   61篇
  1999年   24篇
  1998年   15篇
  1997年   15篇
  1996年   10篇
  1995年   12篇
  1994年   11篇
  1993年   20篇
  1992年   13篇
  1991年   4篇
  1990年   10篇
  1989年   15篇
  1988年   17篇
  1987年   9篇
  1986年   6篇
  1985年   6篇
  1984年   10篇
  1983年   4篇
  1982年   3篇
  1980年   3篇
  1977年   7篇
  1973年   3篇
  1972年   3篇
  1969年   4篇
  1968年   5篇
  1966年   4篇
  1955年   3篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
ObjectiveTo assess the brachial plexus block in chickens by an axillary approach and using a peripheral nerve stimulator.Study designProspective, randomized, double-blinded study.AnimalsSix, 84-week old, female chickens.MethodsMidazolam (1 mg kg−1) and butorphanol (1 mg kg−1) were administered into the pectoralis muscle. Fifteen minutes later, the birds were positioned in lateral recumbency and following palpation of the anatomic landmarks, a catheter was inserted using an axillary approach to the brachial plexus. Lidocaine or bupivacaine (1 mL kg−1) was injected after plexus localization by the nerve stimulator. Sensory function was tested before and after blockade (carpus, radius/ulna, humerus and pectoralis muscle) in the blocked and unblocked wings. The latency to onset of motor and sensory block and the duration of sensory block were recorded. A Friedman nonparametric one-way repeated-measures anova was used to compare scores from baseline values over time and to compare the differences between wings at each time point.ResultsA total of 18 blocks were performed with a success rate of 66.6% (12/18). The latency for motor block was 2.8 ± 1.1 and 3.2 ± 0.4 minutes for lidocaine and bupivacaine, respectively. The latencies for and durations of the sensory block were 6.0 ± 2.5 and 64.0 ± 18.0 and 7.8 ± 5.8 and 91.6 ± 61.7 minutes for lidocaine and bupivacaine, respectively. There was no statistical difference between these times for lidocaine or bupivacaine. Sensory function was not abolished in nonblocked wings.Conclusions and clinical relevanceThe brachial plexus block was an easy technique to perform but had a high failure rate. It might be useful for providing anesthesia or postoperative analgesia of the wing in chickens and exotic avian species that have similar wing anatomy.  相似文献   
62.
The amplification by degenerate primers FAP59/FAP64 and sequencing allowed the detection of 15 putative new BPV types in cutaneous warts as well as in healthy skin. Four of these isolates were recently recognized as new BPV types (BPV-7, -8, -9, and -10) after determination of their complete genome sequences. In Brazil, investigations involving the definition of BPV types present in skin warts are still rare. The aim of the current study was to identify the BPV types associated with cutaneous papillomatosis observed in Brazilian cattle herds. Twenty-two cutaneous papilloma specimens were submitted to PCR assay employing the FAP primer pair. All PCR products with approximately 480 bp were submitted to direct sequencing. Cloning was performed for the amplicons which prior analysis revealed as putative new BPV types. From 16 cutaneous lesions, BPV-1, -2, and -6 were identified in two, six, and eight papilloma specimens, respectively. In addition, four putative new BPV types were identified in other six skin warts, and then designated as BPV/BR-UEL2 to -5. The detection of the BPV-1, -2, and -6 types in skin wart specimens supports the existence of these BPV types throughout the Brazilian cattle herd. In addition, the identification of four putative new BPV types is the first report of the presence of different BPV types in the American continent.  相似文献   
63.
Codiostomum struthionis is a nematode parasite of the ostrich caecum. Little is known about its pathology, being considered by many authors as a non-pathogenic parasite. Infections by C. struthionis are sometimes overlooked because its eggs are indistinguishable from another ostrich nematode, Libyostrongylus spp. Fecal cultures and infective larvae identification are necessary for proper identification. The aim of this study is to provide improved morphological characterization of adults and infective larvae of C. struthionis. Ten caeca of adult ostriches were collected and washed in 0.09% saline solution. Male and female nematodes were collected and quantified separately. Nematodes were fixed in A.F.A. for optical microscopy or fixed in Karnovsky solution for scanning electron microscopy. To obtain infective larvae, fecal samples were collected at sites of high concentration of parasites in the caeca and fecal cultured. The resultant larvae were identified and measured with light microscope at 400x. Nine of the 10 slaughtered ostriches were parasitized by C. struthionis. All nematodes were found in the distal third of the caeca. A total of 566 parasites were recovered (234 males and 332 females). All the cultured larvae had characteristics of C. struthionis (rounded cephalic region with a flat extremity, an acute larvae tail termination and a long and filamentous sheath tail). All the adult parasites were characterized as C. struthionis. Through the analysis of the infective larvae it was determined that the morphology of the larvae tail was the best trait to use in the distinction of this species (live bird diagnosis).  相似文献   
64.
The objective of the present study was to describe the prevalence and risk factors associated with cryptosporidiosis in buffalo calves in Middle Egypt. During one year, 458 fecal samples were collected from buffalo calves less than 3 month age in 55 small scale herds and examined for the presence of Cryptosporidium oocysts. Data describing age, gender, season, and herd management practices were gathered to assess potential risk factors. Fecal examination showed that 14.19% of the examined calves were positive for Cryptosporidium spp. Calves at 1-15 days were at the highest risk (P < 0.001), and a significant relationship between season and infection (P < 0.05) was recorded. A significant association between infection and hygiene (P < 0.001), type of floor (P < 0.01) and source of water (P < 0.01) was also recorded. Statistical analysis concerning the clinical signs and fecal characteristics revealed a significant association with fecal consistency (P < 0.001), presence of blood (P < 0.01) and mucous (P < 0.01). Moreover, a significant association was found between infection and the desire for suckling (P < 0.05) and tenesmus (P < 0.05). The results of the present study demonstrated the strong relation between infections by Cryptosporidium spp. and diarrhea in buffalo calves.  相似文献   
65.
This study describes a duplex real-time polymerase chain reaction (PCR) assay for the detection and differentiation between Dirofilaria immitis and Dirofilaria repens in dog blood and mosquitoes. Regions of a cytochrome oxidase 1 (cox1) mitochondrial DNA fragment and the second internal transcribed spacer (ITS-2) of nuclear ribosomal DNA were amplified from microfilariae and adult worm samples, using a sensitive SsoFast? EvaGreen(?) based real-time PCR method coupled with melting-curve analysis. The limit of the real-time PCR in detecting microfilaria and adult worm DNA was also tested both in dog blood and in artificially infected microfilarial. Two peaks at different melting temperatures (T(m)) for D. immitis (mean ± SD=75.7 ± 0.3°C) and D. repens (mean ± SD=70 ± 0.7°C), respectively, were obtained for microfilarial and adult positive controls of both species when examined separately and together. The real-time PCR protocol was also efficient in detecting microfilarial and adult DNA of both species when tested in samples spiked with DNA from Aedes albopictus, in Aedes aegypti experimentally infected by D. repens and in Culex pipiens naturally infected by D. repens and D. immitis. The high sensitivity of real-time PCR confirmed its reliability in detecting small amounts of genomic DNA either in dog blood or mosquitoes (2.5 pg/μl and 3 × 10(-1)pg/μl for D. immitis and D. repens, respectively). This assay is proposed as a tool for the epidemiological surveillance of the two most important Dirofilaria species in areas where they are endemic and sympatric.  相似文献   
66.
67.
68.
The ovicidal effect of the nematophagous fungus Pochonia chlamydosporia on eggs of Ascaris suum was tested under laboratory conditions. A. suum eggs were plated on 2% water–agar with seven fungal isolates (Isol. 5, Isol. 31, Isol. 1, VC1, Isol. 12, Isol. 22 and VC4) and control without fungus. After 5, 7, 10, 14, 15 and 21 days of incubation, approximately 100 eggs were removed from the plates and classified according to the following parameters: type 1, biochemical and physiological effect without morphological damage to the eggshell, type 2, lytic effect with morphological alteration of the eggshell and embryo and type 3, lytic effect with morphological alteration of eggshell and embryo showing hyphal penetration and internal egg colonization. The isolates effectively destroyed A. suum eggs and all types of effects were observed during the experiment. There was no variation in ovicidal capacity (type 3 effect) among the isolates (p > 0.05) throughout the experiment. After 21 days, isolate 5 showed the highest percentages of type 3 effect (58.33%). The results indicated that P. chlamydosporia (Isol. 5, Isol. 31, Isol. 1, VC1, Isol. 12, Isol. 22 and VC4) can destroy A. suum eggs and is, therefore, a potential biological control agent of nematodes.  相似文献   
69.
Oxidative stress is an imbalance between radical-generating and radical-scavenging activity, resulting in oxidation products and tissue damage. This study was aimed to evaluate the status of oxidative stress indices in blood of camels naturally infested with S. scabiei. Forty-seven male camels (Camelus dromedaries) were divided according to the extent of the infested area with Sarcoptes scabiei into four groups, mild (MID, n = 12), moderate (MOD, n = 10), severely infested (SEV, n = 10) and healthy control group (n = 15). Blood was used for determination of red cell count (RBC), hemoglobin (Hb), packed cell volume (PCV), serum nitric oxide (NO, a free radical), ascorbate and albumin concentrations, and erythrocytic values of malondialdehyde (MDA, a marker of lipid peroxidation), protein carbonyls (PC, an indicator of protein oxidation), glutathione (GSH) superoxide dismutase (SOD) and catalase (CAT). Decreased levels (P < 0.05) of RBC, Hb, PCV, albumin and ascorbate were noticed in MOD and SEV compared to controls with the lowest values (P < 0.05) in SEV except for ascorbate, where MOD did not differ from SEV. Compared to controls, NO gradually increased (P < 0.05) in MID followed by MOD and SEV, whereas MDA and PC were higher (P < 0.05) in MOD and SEV. PC was higher (P < 0.05) in MOD than SEV. In addition, the antioxidants GSH, SOD and CAT were higher (P < 0.05) in MID and lower (P < 0.05) in MOD and SEV compared to controls. GSH was lower (P < 0.05) in SEV compared to MOD. Besides, Hb was negatively correlated with NO (r = −0.68, P < 0.001), MDA (r = −0.53, P < 0.001) and PC (r = −0.73, P < 0.001). In conclusion, dromedary sarcoptosis is accompanied by a state of oxidative stress process, which increased by increasing the area of infestation, and may contribute to the pathogenesis of the disease.  相似文献   
70.
OBJECTIVE: This experiment evaluated the perinatal hypoxic effect on the retina of offspring of the ovoviviparous fish. ANIMAL STUDIED: The ovoviviparous fish Xiphophorous maculates was used for the experiment. PROCEDURE: The mothers were kept in a hypoxic environment of 3.5% oxygen for 6 h, starting 30 h before hatching. Subsequently, the retinae of the offspring were fixed, sectioned at 6 microm and evaluated microscopically from the age of 1 to 35 days. RESULTS: Degeneration of the outer nuclear layer of the retina was noted on the 3rd day and severe retinal degeneration was observed on the 35th day. Immunocytochemistry confirmed apoptosis by TUNEL reaction. There was no difference in neovascularization, as revealed by vascular endothelial growth factor, between controls (group 1) and hypoxic fish (group 2). CONCLUSIONS: Perinatal hypoxia could have long-lasting effects on the central nervous system in some species.  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