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   9054篇
  免费   573篇
  国内免费   516篇
林业   586篇
农学   592篇
基础科学   222篇
  1245篇
综合类   2472篇
农作物   611篇
水产渔业   536篇
畜牧兽医   2879篇
园艺   361篇
植物保护   639篇
  2024年   25篇
  2023年   88篇
  2022年   182篇
  2021年   255篇
  2020年   230篇
  2019年   246篇
  2018年   231篇
  2017年   302篇
  2016年   249篇
  2015年   252篇
  2014年   331篇
  2013年   454篇
  2012年   564篇
  2011年   640篇
  2010年   549篇
  2009年   503篇
  2008年   541篇
  2007年   544篇
  2006年   469篇
  2005年   403篇
  2004年   308篇
  2003年   339篇
  2002年   399篇
  2001年   424篇
  2000年   300篇
  1999年   173篇
  1998年   43篇
  1997年   46篇
  1996年   35篇
  1995年   47篇
  1994年   46篇
  1993年   38篇
  1992年   48篇
  1991年   41篇
  1990年   54篇
  1989年   51篇
  1988年   34篇
  1987年   40篇
  1986年   31篇
  1985年   34篇
  1984年   51篇
  1983年   27篇
  1982年   26篇
  1979年   28篇
  1978年   28篇
  1977年   27篇
  1975年   25篇
  1974年   37篇
  1972年   30篇
  1971年   37篇
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
991.
OBJECTIVE: To evaluate the use of subdermal plexus skin flaps for closing defects after excision of cutaneous and subcutaneous tumors in dogs and to compare outcome of flaps secured with sutures and those secured with butyl-cyanoacrylate and intermittent sutures. STUDY DESIGN: Clinical study. ANIMALS: Fifteen dogs. METHODS: After excision of cutaneous or subcutaneous tumors the skin defect was reconstructed by random flaps based on the subdermal plexus. Flap skin edges were apposed with simple interrupted 4-0 monofilament nylon sutures (group 1; 5 dogs) or nylon sutures alternated with butyl-cyanoacrylate adhesive (group 2; 10 dogs). Flaps were evaluated every 48 hours when bandages were changed, until complete healing. RESULTS: Random flaps based on the subdermal plexus were effectively used to close wound defects; mean flap survival was 89%. Partial flap necrosis occurred in 4 dogs. Wound margins apposed with butyl-cyanoacrylate had thinner and more esthetic scars than sutured margins. CONCLUSION: Random flaps based on the subdermal plexus proved to be versatile for covering limb wounds after excision of cutaneous or subcutaneous tumors. Mean survival rate was comparable to that reported for axial pattern flaps. Butyl-cyanoacrylate adhesive was easy to apply, allowed accurate margin apposition with good cosmetic outcome and reduced sutures needed. CLINICAL RELEVANCE: Cyanoacrylate adhesive should be considered in lieu of suture closure to secure random skin flaps based on the subdermal plexus in dogs.  相似文献   
992.
Faecal samples from 222 healthy dairy goats on 12 farms in Spain, as well as bulk tank milk samples of these farms, were screened for the presence of verotoxin-producing Escherichia coli (VTEC) and enteropathogenic E. coli (EPEC). VTEC and EPEC were isolated in 47.7 and 7.7% of the animals, respectively. VTEC were isolated more frequently from adults and replacement animals than from goat kids. In contrast, EPEC were detected more frequently from goat kids than from replacement animals and adults. VTEC or EPEC strains were not detected in the bulk tank milk samples. Although a selective enrichment protocol was used, the serotype O157:H7 was not detected. The most frequent serotypes among the 106 VTEC strains isolated from goats were O5:H-, O76:H19, O126:H8, O146:H21, ONT:H- and ONT:H21. None VTEC strain was eae-positive. The absence of the eae gene in the VTEC strains could indicate that these strains are less virulent for humans that the classical eae-positive enterohaemorrhagic E. coli types. However, 16% of VTEC strains isolated from healthy goats belonged to serotypes associated with haemolytic uraemic syndrome in humans. The ehxA gene was detected in 84.9 and 52.9% of the VTEC and EPEC from goats, respectively. The beta1, theta/gamma2 and zeta were the most frequent intimin types among the 17 EPEC strains studied and the most prevalent serotypes of these strains were O156:H25 and O177:H11. Our data show that in Spain healthy goats are an important reservoir of VTEC and EPEC, and a potential source of infection for humans.  相似文献   
993.
Primary hyperoxaluria (L-glyceric aciduria) in a cat   总被引:1,自引:0,他引:1  
A 7-month-old, male European cat was examined because of weakness and inappetence. The cat was dehydrated, polypnoeic and severely weak. Severe, generalised muscle atrophy was present. Spinal reflexes were all decreased to absent. Blood analysis and urinalysis showed several abnormalities, including intermittent hyperoxaluria. The L-gliceric acid concentration was remarkably increased. Electrodiagnostic tests of the peripheral nervous system were abnormal. At necropsy, generalised muscle atrophy was observed. Microscopically, both kidneys showed intraluminal birefringent oxalate crystals. Motor neuron degeneration and accumulation of neurofilaments were observed in the axons of the spinal motor neurons.  相似文献   
994.
995.
996.
The influence of soil drench applications of ancymidol (0.5 mg), GA3 (25 mg), and Ga4+7 (25 mg) was determined on the growth and development of the tulip under greenhouse conditions. Ancymidol applied on greenhouse day 1 or 6 significantly reduced the total length of the scape. Maximum reduction in growth occurred in the first internode, with a declining effect on internodes 2, 3 and 4. GA4+7 applied simultaneously with ancymidol completely reversed the ancymidol effects. GA3 was relatively ineffective. Compared to control plants, ancymidol reduced the number of cell divisions in the first internode, but not in the fourth internode. Cells of ancymidol treated plants were reduced in length and exhibited greater radial expansion. Ancymidol reduced the fresh weight of the stem and tended to conserve the fresh weight of the mother scales. The effect on the leaves and roots was variable. Ancymidol tended to increase the fresh weight of the daughter bulblets. There was no significant effect of ancymidol or the GA's on floral morphology or the number of days to flower in the greenhouse.  相似文献   
997.
Systematic investigations on the forcing of tulips, hyacinths, daffodils, Easter lilies and Dutch iris have produced a fairly complete set of scientific principles. In this review, these principles have been classified into a 3-phase concept of forcing. These are: production, programming, and greenhouse. The production phase is defined as all processes which occur during bulb production and it terminates with the harvesting of the bulbs. The programming phase comprises all handling of the bulbs from harvesting until they are placed under greenhouse conditions. The greenhouse phase is the accelerated development of the bulbs until anthesis or marketing of the plants. These phases have been discussed relative to floral and root development and the basic environmental requirements of the bulb species.  相似文献   
998.
999.
Early in autumn, at the end of September or at the beginning of October, strawberry plants of the cultivars ‘Glasa’ and ‘Tioga’ were transferred from outdoors to separate phytotron glasshouses at constant temperatures of 10° and 14°C. In November a number of these plants were chilled at 3°C for 0 to 4 weeks and subsequently forced; the rest remained at 10° and 14°C until June.The plants kept at 10°C and subsequently chilled and forced, grew faster and more vigorously than those pretreated at 14°C. The 14° plants showed more pronounced growth differences resulting from the length of the chilling treatments than did the 10° plants. Those remaining continuously at 10° developed vigorously from March onwards, while those at 14°C retained their flat appearance into June. These results showed that a continuous temperature as high as 10°C was still able to break dormancy in the strawberry plants, while 14°C was ineffective.  相似文献   
1000.
Porcine reproductive and respiratory syndrome virus (PRRSV) mutates continuously, and it is increasingly difficult to control it. To monitor the genetic evolution characteristics of PRRSV timely under the condition of natural infection, a novel PRRSV variant named SHpd1/2018 was isolated from PRRSV positive clinical samples. The results showed that the SHpd1/2018, with a total genome length of 15 018 bp (excluding poly A), showed similar proliferation characteristics to HP-PRRSV strain HuN4. However, it could not be recognized by the monoclonal antibody against HuN4-Nsp2. The sequence analysis indicated that SHpd1/2018 had the greatest homology with HP-PRRSV-like strains, reaching 94.3% with HuN4 strain. The results of recombination analysis showed that SHpd1/2018 was recombined from HP-PRRSV-like strain (main parent strain) and NADC30 strain (secondary parent strain), and both the two recombination breakpoints nt2002 and nt3205 are located in the hypervariable regions of the Nsp2 gene. In short, we confirmed that the isolated strain SHpd1/2018 is a recombinant PRRSV, which may be the main cause of the disease in the pig farm in Shanghai.  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