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   3252篇
  免费   316篇
  国内免费   12篇
林业   259篇
农学   135篇
基础科学   16篇
  549篇
综合类   165篇
农作物   214篇
水产渔业   453篇
畜牧兽医   1413篇
园艺   68篇
植物保护   308篇
  2024年   4篇
  2023年   39篇
  2022年   99篇
  2021年   165篇
  2020年   190篇
  2019年   215篇
  2018年   204篇
  2017年   212篇
  2016年   176篇
  2015年   123篇
  2014年   164篇
  2013年   219篇
  2012年   236篇
  2011年   259篇
  2010年   122篇
  2009年   129篇
  2008年   152篇
  2007年   147篇
  2006年   105篇
  2005年   74篇
  2004年   68篇
  2003年   78篇
  2002年   81篇
  2001年   63篇
  2000年   54篇
  1999年   31篇
  1998年   17篇
  1997年   8篇
  1996年   15篇
  1995年   11篇
  1994年   9篇
  1993年   4篇
  1992年   10篇
  1991年   6篇
  1990年   6篇
  1989年   10篇
  1988年   7篇
  1986年   6篇
  1985年   4篇
  1984年   5篇
  1983年   6篇
  1981年   5篇
  1980年   6篇
  1979年   6篇
  1976年   4篇
  1975年   2篇
  1973年   4篇
  1970年   3篇
  1969年   3篇
  1948年   2篇
排序方式: 共有3580条查询结果,搜索用时 15 毫秒
981.
For the neonatal patient, precocity of diagnosis is crucial for effectiveness of medical approach. However, the newborn has its own physiological peculiarities due to ongoing adaptive mechanism for extrauterine life and deserves special attention in order to underline a specific management or clinical approach. The objective of this work was to verify clinical adaptations and biochemical balance of neonates during immediate period, with special reference to haematological, renal and metabolic functions. Neonatal puppies (n = 51) were physically examined for vitality and rectal temperature at birth, 5 and 60 min post‐birth. Blood was collected at birth and 60 min post‐birth for analysis of glucose, sodium, potassium, chlorine, blood urea nitrogen (BUN), haematocrit and haemoglobin. Neonatal vitality was lower at birth compared with 5 min and 60 min post‐birth. Progressive decline in rectal temperature (36.5 ± 0.3°C, 34.2 ± 0.2°C, 32.3 ± 0.5°C) was observed at birth, 5 min and 60 min post‐birth, respectively. Puppies presented slight hyponatremia (140.7 ± 0.5 mmol/L) at birth and hypopotassemia (3.5 ± 0.1 mmol/L) and blood urea nitrogen (13.1 ± 0.7 mg/dl) during the first hour, and high haematocrit (45.1 ± 1.0%) and haemoglobin (15.3 ± 0.3 g/dl) concentration. In conclusion, puppies had rapid evolution of vitality. Marked decrease in rectal temperature occurred at 5 min post‐birth. Haematological values of neonates immediately after birth reflected mainly the dam's blood status, not being useful for a blood panel at this time point. The peculiar pattern of BUN, sodium and potassium observed during transition period, suggested that specific reference range should be considered for neonatal puppies.  相似文献   
982.
A total of 1,936 pigs were transported through 8 trips (8.4 ± 0.5 hr) from 2 grow-to-finish farms to a commercial slaughter plant, all located in Southern Brazil. On each trip, a sub-sample of each load (36 barrows/load, weighing 118.9 ± 9.8 kg) was randomly allocated into one of the following loading densities during transport: 200 kg/m2 (D200), 235 kg/m2 (D235), and 270 kg/m2 (D270). Behavioral recordings of postures and activities were made during transportation and lairage using video-cameras. At slaughter, blood samples were collected to assess the concentrations of creatine kinase (CK) and lactate. Carcass weights and skin lesion scores were assessed on-line, and meat quality was evaluated in the longissimus thoracis (LT) muscle by assessing pH, color, and drip loss. During transportation, the proportion of animals lying down was higher (P < 0.05) in D200 and D235 groups compared with D270. The proportion of sitting animals during transportation was higher (P < 0.01) in D270 compared with D200. In lairage, D200 and D235 pigs stood more compared with D270 (P = 0.01), while the proportion of lying pigs was higher (P = 0.02) for D270 pigs compared with D200 and D235. The frequency of drinking bouts in lairage was higher (P < 0.05) for D200 group compared with D235 and D270. The levels of CK were lower (P < 0.05) in D200 pigs transported compared with D270. Lesion scores tended to be higher (P = 0.06) in D270 carcasses compared with D200 and D235. A tendency for lower (P = 0.10) pH1 values in the LT muscle of D270 pigs compared with D200 pigs was also found. Based on the results of this study, the application of lower loading densities (≤235 kg/m2) in the truck allows pigs to have sufficient space to rest, travel more comfortably and arrive less fatigued at the slaughter plant.  相似文献   
983.
984.
ObjectiveThe present study describes the isolation of linalool from the essential oil of Lippia alba (Mill.) N. E. Brown, and its anesthetic effect in silver catfish (Rhamdia quelen) in comparison with essential oil. The potentiation of depressant effects of linalool with a benzodiazepine (BDZ) and the involvement of GABAergic system in its antagonism by flumazenil were also evaluated.Study designProspective experimental study.AnimalsJuvenile silver catfish unknown sex weighing mean 9.24 ± 2.83 g (n = 6 for each experimental group per experiment).MethodsColumn chromatography was used for the isolation of S-(+)-linalool. Fish (n = 6 for each concentration) were transferred to aquaria with linalool (30, 60, and 180 μL L?1) or EO of L. alba (50, 100, and 300 μL L?1) to determine the induction time for anesthesia. After induction, the animals were transferred to anesthetic-free aquaria to assess their recovery time. To observe the potentiation, fish were exposed to linalool (30, 60, and 180 μL L?1) in the presence or absence of BDZ (diazepam 150 μm). In another experiment, fish exposed to linalool (30 and 180 μL L?1) or BDZ were transferred to an anesthetic-free aquaria containing flumazenil (5 μm) or water to assess recovery time.ResultsLinalool had a similar sedation profile to the essential oil at a proportional concentration in silver catfish. However, the anesthesia profile was different. Potentiation of linalool effect occurred only when tested at low concentration. Fish exposed to BDZ showed faster anesthesia recovery in water with flumazenil, but the same did not occur with linalool.Conclusions and clinical relevanceThe use of linalool as a sedative and anesthetic for silver catfish was effective at 30 and 180 μL L?1, respectively. The mechanism of action seems not to involve the benzodiazepine site of the GABAergic system.  相似文献   
985.
For over a decade, molecular short standardised DNA fragments, termed DNA barcodes, have been developed for species discrimination around the world. As of 2010, the vast majority of barcoding research was biased toward particular taxonomic groups and geographic regions largely because researchers in developed countries were the ones with the resources and capacity to carry out such work. To rectify this, the International Barcode of Life Project was launched with the intent to extend the geographic and taxonomic coverage of the barcode reference library. South Africa committed to this mission in an attempt to catalogue all of its known biodiversity and, possibly, help identify new species. To date, approximately 48 000 South African faunal barcodes are housed in the Barcode of Life Data System (BOLD), which represent only 2.3% of all known South African animal species. Although insects are the best represented in absolute terms, with over 37 000 samples recorded, they are still grossly lacking with just over 1% representation. Much like the global trend, there is a general taxonomic bias, with fish, birds and mammals showing the greatest representation. Moreover, geographic bias is also present, with the Free State province particularly under-represented on BOLD, likely owing to limited human capacity. Although few studies have been published with respect to barcoding, the majority reveal that the cytochrome c oxidase 1 (CO1) gene, used in isolation or in conjunction with other molecular markers, can greatly benefit South African biodiversity research. Several limitations of DNA barcoding are discussed and recommendations specific to South Africa provided.  相似文献   
986.
987.
Toxocara (Neoascaris) vitulorum is a gastrointestinal nematode parasite of young ruminants, responsible for high mortality rates in parasitized cattle and buffalo calves. The objective of this work was to compare the predatory capacity under laboratory conditions of four fungal isolates of the nematophagous fungus Pochonia chlamydosporia (VC1, VC4, VC5 and VC12) on T. vitulorum eggs in 2% water-agar (2% WA). T. vitulorum eggs were plated on 2% WA Petri dishes which contained cultured fungal isolates and control plates without fungi. After 10 and 15 days one hundred eggs were removed 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 in addition to hyphal penetration and internal egg colonization. The fungal isolates were effective in the destruction of T. vitulorum eggs presenting the type 3 effect at 10 and 15 days after contact with the fungus. No nematophagous fungi were observed in the control group during the experiment. There was no variation in the predatory capacity of the fungal isolates (P?>?0.01) at the intervals of 10 and 15 days. These results indicate that P. chlamydosporia (VC1, VC4, VC5 and VC12) negatively influenced the development of T. vitulorum eggs and can be considered a potential candidate for the biological control of nematodes.  相似文献   
988.
The multidrug efflux system in bacteria can reduce antibiotic concentration inside the cell, leading to failure in the treatment of bacterial diseases. This study evaluated the influence of two efflux pump inhibitors (EPIs), phenylalanine arginyl ß-naphthylamide (PAßN) and 1-(1-naphthylmethyl)-piperazine (NMP), on the gene expression of three multidrug efflux systems, AcrAB, AcrEF and EmrAB in Escherichia coli bovine mastitis isolates resistant to ampicillin and sulfamethoxazole/trimethoprim simultaneously. Each isolate had at least three multidrug efflux system genes. The acrA and acrB had the lowest expression levels in all treatments, while the emrA or emrB showed the highest expression levels in the presence of ampicillin, sulfamethoxazole/trimethoprim, PAβN and NMP. EPIs also contributed to the decrease in arcF expression when used in combination with ampicillin treatment. Since PAßN showed stronger effects than NMP, it may serve as an alternative to assist in the antimicrobial therapy of mastitis.  相似文献   
989.
In Brazil, mycoplasmas were isolated from the sinuses of Japanese quails (Coturnix coturnix japonica) from two commercial flocks affected with sinusitis. The major respiratory signs and gross lesions are described. Based on serological and biochemical results, the mycoplasmas isolated were identified as Mycoplasma gallisepticum. One of the isolates was pathogenic for chickens.  相似文献   
990.
The aim of this study was to identify candidate genes and genomic regions associated with ultrasound‐derived measurements of the rib‐eye area (REA), backfat thickness (BFT) and rumpfat thickness (RFT) in Nellore cattle. Data from 640 Nellore steers and young bulls with genotypes for 290 863 single nucleotide polymorphisms (SNPs) were used for genomewide association mapping. Significant SNP associations were explored to find possible candidate genes related to physiological processes. Several of the significant markers detected were mapped onto functional candidate genes including ARFGAP3, CLSTN2 and DPYD for REA; OSBPL3 and SUDS3 for BFT; and RARRES1 and VEPH1 for RFT. The physiological pathway related to lipid metabolism (CLSTN2, OSBPL3, RARRES1 and VEPH1) was identified. The significant markers within previously reported QTLs reinforce the importance of the genomic regions, and the other loci offer candidate genes that have not been related to carcass traits in previous investigations.  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