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   281408篇
  免费   15646篇
  国内免费   656篇
林业   24317篇
农学   14200篇
基础科学   2978篇
  45608篇
综合类   27772篇
农作物   17617篇
水产渔业   17740篇
畜牧兽医   116276篇
园艺   6407篇
植物保护   24795篇
  2021年   2557篇
  2020年   2934篇
  2019年   3731篇
  2018年   4348篇
  2017年   4730篇
  2016年   5008篇
  2015年   4455篇
  2014年   5869篇
  2013年   16439篇
  2012年   7559篇
  2011年   9678篇
  2010年   7945篇
  2009年   8425篇
  2008年   9003篇
  2007年   8215篇
  2006年   8520篇
  2005年   7725篇
  2004年   7540篇
  2003年   7391篇
  2002年   6602篇
  2001年   7512篇
  2000年   7210篇
  1999年   6459篇
  1998年   4248篇
  1997年   4295篇
  1996年   4034篇
  1995年   4598篇
  1994年   4007篇
  1993年   3687篇
  1992年   4992篇
  1991年   5221篇
  1990年   5023篇
  1989年   5025篇
  1988年   4445篇
  1987年   4482篇
  1986年   4340篇
  1985年   4522篇
  1984年   4108篇
  1983年   3820篇
  1982年   3058篇
  1981年   2912篇
  1980年   2860篇
  1979年   3488篇
  1978年   3042篇
  1977年   2812篇
  1976年   2628篇
  1975年   2502篇
  1974年   2671篇
  1973年   2754篇
  1972年   2447篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Six cats with an advanced stage squamous cell carcinoma (SCC) of the nasal planum were treated with a combination of superficial radiotherapy and intralesional carboplatin therapy. This multimodality protocol was well tolerated by the majority of cats and resulted in complete responses in all cats (100%). Median follow‐up for all cats is 268 days, and the median time‐to‐recurrence, time‐to‐progression and overall survival have not yet been reached. Our study, although limited in number of animals and with a relatively short median follow‐up compared to other studies for this disease, suggests that a combination of radiotherapy and intralesional carboplatin is a useful treatment option for an advanced stage SCC of the nasal planum in cats and warrants further application of the multimodality approach presented here.  相似文献   
992.
Introduction: Palliative therapy is essential to improve the quality of life of dogs with osteosarcoma (OSA), when definitive therapy is not considered a valid option. Bisphosphonates, a novel class of antiosteoclastic drugs, are widely used in humans for several painful osteolytic conditions. Dual energy x‐ray absorptiometry (DEXA) is recognized as a reliable tool to measure bone mineral density (BMD), and to monitor treatment response to bisphosphonates in humans. A prospective evaluation of pamidronate, an injectable aminobisphosphonate, is ongoing in dogs with appendicular OSA. The potential value of DEXA for objective evaluation of BMD variations with palliative therapies is concurrently being assessed. Materials and Methods: Dogs with naturally occurring appendicular OSA treated with pamidronate constitute the patient population. A DEXA scan (QDR‐4500 W, Hologic, Bedford, MA) is performed on day 0 (baseline) and on every treatment day with pamidronate thereafter (every 28 days). For each dog, a whole body scan is performed, followed by a scan of the tumor, and contralateral normal bone. Three regions of interest are subsequently analyzed for BMD changes in tumor and normal bone. Statistical analysis was performed using Student t‐test and paired t‐tests, with significance being set at p < 0.05. Results: Nineteen dogs have been enrolled to date. Seven responders and 6 non‐responders have suitable data for analysis. A significant difference is observed (p = 0.04) between tumor BMD variations of responders and non‐responders at day 28 (mean variations +18.0% and ?4.6% respectively). The changes at day 28 are significant only in the responders (p = 0.038 vs p = 0.05 in non‐responders). When BMD of tumor and normal bone at day 84 is compared to day 0 in six responders, only tumor had a significant increase (p = 0.017 vs p = 0.279, respectively). Conclusions: Objective measurements of response to therapy are essential in pain palliation studies. Increased tumor bone BMD, as obtained by DEXA analysis, may correlate with subjective clinical improvement in pamidronate‐treated dogs with appendicular OSA.  相似文献   
993.
The cumulative cardiotoxicity that occurs as a result of doxorubicin chemotherapy is irreversible and can affect both quality and quantity of life for the cancer patient. Cardiac troponin I (cTnI) is a sensitive and specific marker of cardiomyocyte death. The purpose of this retrospective study was to evaluate serum concentrations of cTnI in dogs with lymphoma or osteosarcoma given doxorubicin chemotherapy, and with known cardiac outcome, based on a minimum assessment by physical examination and thoracic radiography. Serum samples were also available for cTnI measurement from seven healthy dogs given intracoronary doxorubicin. Serial serum samples obtained before, during and after doxorubicin chemotherapy showed increased cTnI concentrations in some clinical patients following chemotherapy (P = 0.0083 compared to baseline), but this did not correlate with clinical signs of cardiomyopathy. In dogs that subsequently developed cardiomyopathy however, serum cTnI concentrations were elevated before clinical signs became evident (confirmed with echocardiography).  相似文献   
994.
Objective: To determine plasma β‐d ‐glucuronidase (βG) activity in the first 4 hours following injury in dogs struck by a motor vehicle, and to evaluate whether the degree of enzyme activity is correlated with the severity of injury. Design: A prospective clinical study. Setting: Veterinary Medical Teaching Hospital. Animals: Thirteen client‐owned dogs that were presented to the Veterinary Hospital of the University of Pennsylvania between June and August 1999 for blunt vehicular trauma. Ten healthy student and staff‐owned dogs served as controls. Interventions: None. Measurements: Plasma was analyzed for βG enzyme activity at the time of presentation (n=13), and 1 and 4 hours (n=7) following presentation to the Emergency Service for blunt vehicular trauma. The results were compared with enzyme activity from healthy controls evaluated serially over 4 hours. Fluorometric analysis using 96‐well microtiter plates was used to perform the enzyme assays. The relationships between presentation (n=13) and 4 hours (n=7) of enzyme activity and 3 indices of metabolic and physical disturbance (serum pH, serum lactate and Animal Trauma Triage (ATT) score) at the time of presentation were also investigated. Main results: Of the 13 dogs, 7 fulfilled the inclusion criteria for comparison of enzyme activity of the trauma over time. A statistically significant difference in βG activity was found in the trauma group (mean 75.6±10.4 U) at 4 hours following presentation compared with controls (mean 48.0±6.4 U). This difference was suggested by 1 hour following presentation (trauma group, mean 70.4±10.9 U; control group, mean 49.8±5.5 U), although it did not reach statistical significance. Thirteen dogs fulfilled the inclusion criteria for comparison of only presentation enzyme activity with trauma severity score, serum lactate, and serum pH. No statistically significant relationship was found between the βd ‐glucuronidase activity and the presenting ATT score, serum lactate concentration, or serum pH at either presentation or 4 hours, although the power of these analyses was low. Conclusions: These results demonstrate that the activity of βG, a lysosomal enzyme, increases significantly in the systemic circulation in dogs 4 hours following blunt trauma. Additional research to include more severely injured dogs, a larger number of dogs, and to follow the course of injury for a longer period of time would be beneficial to further characterize βG activity following blunt trauma.  相似文献   
995.
996.
997.
Keck  G.  Berny  P.  Buronfosse  F.  Pineau  X.  Vermorel  E.  Rebelle  B.  Buronfosse  T. 《Veterinary research communications》2004,28(1):75-82
Veterinary Research Communications -  相似文献   
998.
The isolation and identification of Yersinia enterocolitica from minced meat on CIN agar medium is still one of the major problems in food microbiology because of the low selectivity of cefsulodin–irgasan–novobiocin (CIN) agar. A total of 198 minced meat samples were collected from commercial establishments (butcher shops and supermarkets) in seven German cities in order to investigate the sensitivity and specificity of three identification techniques suitable for the differentiation of Y. enterocolitica within the rich background flora on CIN agar plates. As expected isolation of Y. enterocolitica from minced meat on CIN agar medium after 72 h enrichment in peptone, sorbitol and bile salts (PSB) broth was difficult because all plates were abundantly covered with numerous ‘typical’Yersinia‐like colonies of bull's eye appearance as well as with atypical colonies. Based on the phenotype of the colonies it was possible to detect colonies showing Yersinia‐like growth on CIN agar in 52 samples (26%). For identification of Y. enterocolitica the API 20E system (bioMerieux, Nürtingen, Germany), the Yersinia identification kit (Merlin, Bornheim‐Hersel, Germany) and a 16S rRNA based PCR assay were compared. Only in one sample (0.5%) a Y. enterocolitica strain was detected by all methods. Of the three identification systems tested for routine laboratory diagnostics the API 20E system was found to be the most suitable tool to identify Y. enterocolitica colonies within the rich background flora from minced meat samples on CIN agar plates.  相似文献   
999.
The purpose of this retrospective study was to evaluate six cases of equine sarcoidosis for initial presenting symptoms, response to therapy and actual outcome. Dermatologists and dermatopathologists from Europe, the United States, Australia and Canada were contacted to obtain these six cases, as this is a rare disease. Signalment, clinical signs, histological findings, clinical management and outcome were determined via a questionnaire and compared to former reports. There was no age or breed predilection, and four of six horses were geldings. Age of onset ranged from 3 months to 17 years. Onset of the disease was insidious or rapid. Interestingly, in five of six cases, scaling began on the trunk (girth and shoulder). Scaling, crusting and alopecia were seen in all six horses. In one horse, clinical signs of systemic disease were reported and included intermittent fever, prescapular lymphadenopathy, depression, poor body condition and nasal discharge. Treatment included phenylbutazone, deworming agents, antibiotics, short‐term low‐dose corticosteroids, and 1–1.5 mg/kg of prednisolone. One horse showed a partial response to trimethoprim and sulfonamide, and five of six went into clinical remission with corticosteroid treatment. Five of six horses were still alive 1 year after diagnosis; one horse was diagnosed <12 months ago. Two horses are in complete remission 4 and 8 years after diagnosis. In both horses, clinical signs recurred after cessation of therapy and went into remission again with reintroduction of treatment. Both of these horses have been in remission for several years without therapy. Funding: Self‐funded.  相似文献   
1000.
The aim of these experiments was to investigate the potential antiviral effect of Saccharomyces cerevisiaeβ‐glucan on the pneumonia induced by swine influenza virus (SIV). Forty colostrum‐deprived 5‐day‐old piglets were randomly divided into four groups of 10. The 20 pigs in groups 1 and 2 were administered Saccharomyces cerevisiaeβ‐glucan orally (50 mg/day/pig; En‐Bio Technology Co., Ltd) for 3 days before SIV infection and those in groups 3 and 4 were given culture medium/diluent alone. Groups 1 and 3 were inoculated intranasally with 3 ml of tissue culture fluid containing 2 × 106 tissue culture infective doses 50% (TCID50)/ml of SIV and those in groups 2 and 4 were exposed in the same manner to uninfected cell culture supernatant. The microscopic lung lesions induced by SIV infection (group 1 pigs) were significantly more severe than those induced by infection in animals pre‐administered β‐glucan (group 3) (P < 0.05). Significantly more SIV nucleic acid was detected in the lungs of pigs experimentally infected with SIV only (group 1) at 5, 7 and 10 days post‐inoculation (dpi) compared with lungs from pigs pre‐administered β‐glucan and infected with SIV (group 3) (P < 0.05). The concentrations of interferon‐γ (IFN‐γ) and nitric oxide (NO) in bronchoalveolar lavage fluid from pigs pre‐administered β‐glucan and infected with SIV (group 3) were significantly higher than for any other group at 7 and 10 dpi for IFN‐γ, and at 5, 7 and 10 dpi for NO (P < 0.05). Saccharomyces cerevisiaeβ‐glucan reduced the pulmonary lesion score and viral replication rate in SIV‐infected pigs. These findings support the potential application of β‐glucan as prophylactic/treatment agent in influenza virus infection.  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